This PDF file contains the front matter associated with SPIE Proceedings Volume 10511, including the Title Page, Copyright information, Table of Contents, Introduction (if any), and Conference Committee listing.

Highly efficient, diode pumped Tm:YAP lasers generating emission in the 1.85-1.94 μm range are demonstrated and characterized. Laser optical efficiencies of 51% and 45%, and electrical efficiencies of 31% and 25% are achieved under CW and Q-switched operation, respectively. Laser performance was characterized for maximum average powers up to 20W with various cavity configurations, all using an intra-cavity lens to compensate for thermal lensing in the Tm:YAP crystal. Q-switched lasers incorportating a Cr:ZnS saturable absorber (SA), resonant mechanical mirror scanner, or acousto-optic modulator were characterized. To enable higher average output powers, measurements of the thermal lens were conducted for the Tm:YAP crystal as a function of pump power and were compared to values predicted by a finiteelement- analysis (FEA) thermal-optical model of the Tm:YAP crystal. A resonator model is developed to incorporate this calculated thermal lens and its effect on laser performance. This paper will address approaches for improving the performance of Tm:YAP lasers, and means for achieving increased average output powers while maintaining high optical efficiency for both SA and mechanical Q-switching.

We report on initial lasing of Tm:Lu₂O₃ ceramic laser with tunable output in the vicinity of 2 μm. Tm:Lu₂O₃ ceramic gain materials offer a much lower saturation fluence than the traditionally used Tm:YLF and Tm:YAG materials. The gain element is pumped by 796 nm diodes via a "2-for-1" crossrelaxation energy transfer mechanism, which enables high efficiency. The high thermal conductivity of the Lu₂O₃ host (~18% higher than YAG) in combination with low quantum defect of ~20% supports operation at high-average power. Konoshima’s ceramic fabrication process overcomes the scalability limits of single crystal sesquioxides. Tm:Lu2O3 offers wide-bandwidth amplification of ultrashort pulses in a chirped-pulse amplification (CPA) system. A laser oscillator was continuously tuned over a 230 nm range from 1890 to 2120 nm while delivering up to 43W QCW output with up to 37% efficiency. This device is intended for initial testing and later seeding of a multi-pass edge-pumped disk amplifier now being developed by Aqwest which uses composite Tm:Lu2O3 disk gain elements.

A numerical model for solid-state regenerative amplifiers is presented, which is able to precisely simulate the quantitative energy buildup of stretched femtosecond pulses over passed roundtrips in the cavity. In detail, this model is experimentally validated with a Ti:Sapphire regenerative amplifier. Additionally, the simulation of a Ho:YAG based regenerative amplifier is conducted and compared to experimental data from literature. Furthermore, a bifurcation study of the investigated Ho:YAG system is performed, which leads to the identification of stable and instable operation regimes. The presented numerical model exhibits a well agreement to the experimental results from the Ti:Sapphire regenerative amplifier. Also, the gained pulse energy from the Ho:YAG system could be approximated closely, while the mismatch is explained with the monochromatic calculation of pulse amplification. Since the model is applicable to other solid-state gain media, it allows for the efficient design of future amplification systems based on regenerative amplification.

Flashlamp pumped Cth:YAG lasers are mainly used in medical applications (urology). The main laser transition is at 2.13μ and is called a quasi-three level having an emission cross-section of 7x10^-21 cm² and a ground state absorption of approximately 5%/cm. Because of the relatively low absorption, combined with a modest emission cross-section, the laser requires high reflectivity output coupling, and therefore high intra-cavity energy density which limits the output to approximately 4J/pulse for reliable operation.

This paper will describe a method of efficiently generating high output energy at low intra-cavity energy density by using an alternative 2.097μ transition having an emission cross-section of 5x10^-21 cm² and a ground level absorption of approximately 14%/cm.

Hi-tech industrial or biotechnological laser applications request for picosecond pulsed 2-um laser generating sub-1-J pulses in >kHz repetition range. At Hilase development of laser system with target to generate 1-J picosecond pulses with 1-kHz repetition rate has started. Design of the system based on Ho:YAG thin-disk generating at 2.1-um is divided into several phases. First phase includes demonstration of new mode-locked graphen-based saturable absorber Ho-doped fiber laser concept followed by preamplifier systems delivering 10-uJ pulses. Pulses are then amplified to >10-mJ level in Ho:YAG thin-disk regenerative amplifier operating at 10-kHz, and finally amplified in double stage cryogenically-cooled multi-pass amplifier to 1-J at 1-kHz so average output power reaches 1-kW in mid-IR. We present a concept of this laser system with emphasize on the front-end and the first regen. The holmium fiber front-end is pumped by a continuous wave 0.5-W thulium fiber laser generating at wavelength of 1950-nm. Mode-locking in the oscillator is reached by graphene multilayer optical element as a passive saturable absorber (GSA). The GSA provides broadband wavelength operation and is promising for MIR sources. In the laser setup, the GSA is placed in a free-space cavity as a part of ring laser configuration. This oscillator produces <10-ps-pulses with ~nJ energy and <40-MHz repetition rate. The repetition rate reduces acousto-optic modulator, pulses are pre-amplified in a chain containing Ho-doped fibers and a single crystal fiber to 10-uJ/10-to-100-kHz, and seeded to thin-disk regen. We expect demonstration of the front-end, detailed design of first regenerative amplifier and conceptual design of full system.

We present CPA-free linear amplification of 6:3 ps pulses in Ho:YLF crystals up to 100 μJ pulse energy at 10 kHz repetition rate. The seed pulses at a wavelength of 2:05 μm are provided by a Ho-based all-fiber system consisting of a soliton oscillator and a subsequent pre-amplifier followed by a free-space AOM as pulse-picker. Considering the achieved pulse peak power at MW-level, this system is a powerful tool for efficient pumping of parametric amplifiers addressing the highly demanded mid-IR spectral region. In detailed numerical simulations we verified our experimental results and discuss scaling options for pulse duration and energy.

A buried depressed-index channel waveguide with a circular cladding and a core diameter of 40 μm is fabricated in a bulk monoclinic 3 at.% Tm:KLu(WO₄)₂ crystal by femtosecond direct laser writing. In the continuous-wave regime, the Tm waveguide laser generates ∼210 mW at 1849.6 nm with a slope efficiency η of 40.8%. Passively Q-switched operation is achieved by inserting transmission-type 2D saturable absorbers (SAs) based on few-layer graphene and MoS₂. Using the graphene-SA, a maximum average output power of ∼25 mW is generated at 1844.8 nm. The pulse characteristics (duration/energy) are 88 ns/18 nJ at a repetition rate of 1.39 MHz.

We report on the first application of a topological insulator based on antimony telluride (Sb₂Te₃) as a saturable absorber (SA) in a bulk microchip laser. The transmission-type SA consisted of a thin film of Sb₂Te₃ (thickness: 3 nm) deposited on a glass substrate by pulsed magnetron sputtering. The saturable absorption of the Sb₂Te₃ film was confirmed for ns-long pulses. The microchip laser was based on a Tm:GdVO₄ crystal diode-pumped at ∼802 nm. In the continuous-wave regime, this laser generated 3.54 W at 1905-1921 nm with a slope efficiency η of 37%. The Q-switched laser generated a maximum average output power of 0.70 W at 1913 nm. The pulse energy and duration were 3.5 μJ and 223 ns, respectively, at a repetition rate of 200 kHz. The Sb₂Te₃ SAs are promising for passively Q-switched waveguide lasers at ∼2 μm.

Q-Peak has demonstrated a novel pulsed eyesafe laser architecture operating with >50 mJ pulse energies at Pulse Repetition Frequencies (PRFs) as high as 320 Hz. The design leverages an Optical Parametric Oscillator (OPO) and Optical Parametric Amplifier (OPA) geometry, which provides the unique capability for high power in a comparatively compact package, while also offering the potential for additional eyesafe power scaling. The laser consists of a Commercial Off-the-Shelf (COTS) Q-switched front-end seed laser to produce pulse-widths around 10 ns at 1.06-μm, which is then followed by a pair of Multi-Pass Amplifier (MPA) architectures (comprised of side-pumped, multi-pass Nd:YAG slabs with a compact diode-pump-array imaging system), and finally involving two sequential nonlinear optical conversion architectures for transfer into the eyesafe regime. The initial seed beam is first amplified through the MPA, and then split into parallel optical paths. An OPO provides effective nonlinear conversion on one optical path, while a second MPA further amplifies the 1.06-μm beam for use in pumping an OPA on the second optical path. These paths are then recombined prior to seeding the OPA. Each nonlinear conversion subsystem utilizes Potassium Titanyl Arsenate (KTA) for effective nonlinear conversion with lower risk to optical damage. This laser architecture efficiently produces pulse energies of >50 mJ in the eyesafe band at PRFs as high as 320 Hz, and has been designed to fit within a volume of 4,500 in³ (0.074 m³ ). We will discuss theoretical and experimental details of the nonlinear optical system for achieving higher eyesafe powers.

Tunable middle infrared generation is now affordable through optical parametric generation and amplification in a number of infrared nonlinear crystals. However, maintaining narrow bandwidth, while achieving high conversion efficiency, remains a challenge. In this report, we propose and experimentally demonstrate a relatively simple setup, which utilizes a single-wavelength diode laser as a seed laser for an optical parametric amplifier.

We present a laser source providing up to 18 W and 1.5 mJ at a wavelength of 3 μm. The output is generated by frequency conversion of randomly polarized multimode radiation at 1064 nm of an Nd:YAG laser in a two-stage conversion setup. The frequency converter comprises an optical parametric oscillator and a subsequent optical parametric amplifier using PPLN as nonlinear medium in both stages. To implement fiber-based beam delivery for materials processing, we coupled the output at 3 μm to a multimode ZrF₄-fiber. This source was then used to remove epoxy resin from the surface of CFRP samples.

We describe mid-IR sources utilizing ZGP and CSP Optical Parametric Oscillators (OPO) directly pumped by high efficiency 1.94 μm Tm:YAP Q-switched lasers. Compact Q-switched Tm:YAP lasers, implemented using Cr:ZnS saturable absorbers, generated 29 kW peak power pulses and an average power of 4W. The OPOs, constructed using the latest generation ZGP and CSP crystals with low 1.94 μm absorption, were operated at near-degeneracy with mid-IR output in the 3.6-4.2 μm range. Various doubly-resonant OPO configurations were evaluated, including single-pass pump pass and double-pass pumping. Maximum mid-IR powers of 2.3 W and 2.5 W and optical conversion efficiencies of 58% and 64% were measured for ZGP and CSP double-pass pump OPOs, respectively.

Fe:ZnSe and other transition metals have broad upper and lower energy manifolds which give rise to broad absorption and fluorescence bands in the mid-IR spectral region. Energy transfer between Fe²⁺ ions via re-absorption of fluorescence (due to the spectral overlap of these bands) and phonon-assisted energy transfer (due to the lattice dynamics of ZnSe) becomes more probable with increasing Fe²⁺ concentration. Here we treat these processes as additional terms in the rate equations which govern the spontaneous decay of the Fe²⁺ ion. This treatment gives insight into anomalous behavior seen in the thermal lifetime of the Fe:ZnSe system. We also apply the model to other transition metal doped II-VI materials.

We report on a newly developed high-energy diode side-pumped Er:YLF solid state laser emitting at at 2.81 μm. The pulsed laser generates 100 mJ pulses at 400 μs and 100 Hz, respectively 10W average laser power. The laser operates efficiently at room temperature and has a good beam quality of M² < 12. The long lifetime of the upper laser level and the inherently linearly polarized laser beam of Er:YLF enables efficient Q-switching for tissue ablation with nanosecond pulses and pumping of non-linear crystals for mid-IR generation.

TRUMPF Scientific Lasers provides ultrafast laser sources for the scientific community with high pulse energies and high average power. All systems are based on the industrialized TRUMPF thin-disk technology. Regenerative amplifiers systems with multi-millijoule pulses, kilohertz repetition rates and picosecond pulse durations are available. Record values of 220mJ at 1kHz could be demonstrated originally developed for pumping optical parametric amplifiers. The ultimate goal is to combine high energies, <100mJ per pulse, with average powers of several hundred watts to a kilowatt.

Based on a regenerative amplifier containing two Ytterbium doped thin-disks operated at ambient temperature pulses with picosecond duration and more than 100mJ could be generated at a repetition rate of 10kHz reaching 1kW of average output power. This system is designed to operate at different repetition rates from 100kHz down to 5kHz so that even higher pulse energies can be reached. This type of ultrafast sources uncover new application fields in science. Laser based lightning rods, X-ray lasers and Compton backscatter sources are among them.

New technological developments in high power disk lasers emitting at 1030 nm are presented. These include the latest generation of TRUMPF’s TruDisk product line offering high power disk lasers with up to 6 kW output power and beam qualities of up to 4 mm*mrad. With these compact devices a footprint reduction of 50% compared to the previous model could be achieved while at the same time improving robustness and increasing system efficiency. In the context of Industry 4.0, the new generation of TruDisk lasers features a synchronized data recording of all sensors, offering high-quality data for virtual analyses. The lasers therefore provide optimal hardware requirements for services like Condition Monitoring and Predictive Maintenance. We will also discuss its innovative and space-saving cooling architecture. It allows operation of the laser under very critical ambient conditions.

Furthermore, an outlook on extending the new disk laser platform to higher power levels will be given. We will present a disk laser with 8 kW laser power out of a single disk with a beam quality of 5 mm*mrad using a 125 μm fiber, which makes it ideally suited for cutting and welding applications.

The flexibility of the disk laser platform also enables the realization of a wide variety of beam guiding setups. As an example a new scheme called BrightLine Weld will be discussed. This technology allows for an almost spatter free laser welding process, even at high feed rates.

Based on the thin-disk laser architecture, TRUMPF has been developing and building high-power cw lasers for over two decades. The short pulse thin-disk lasers of the TruMicro 7000 series are employed in a wide range of industrial applications as well. With different wavelengths and pulse energies, the TruMicro 7000 series enables processes like cutting, structuring, and ablation of many materials. Recently, TRUMPF introduced short pulsed UV lasers based on a disk laser medium for applications requiring high average powers in combination with nanosecond pulse lengths. With 180 W of average output power the TruMicro 7370 combines the highest average power of a solid-state laser with UV output and pulse energies of 18 mJ. With the solid-state platform, the lifetime is significantly increased compared to excimer lasers typically used for high power UV nanosecond applications. Here, we present the latest development of this laser platform allowing for an increase of the laser power up to 400 W and the pulse energy to 40 mJ employing a cascading scheme for third-harmonic generation. By accessing TRUMPF’s elaborated disk-laser expertise, the new UV nanosecond laser TruMicro 7380 also provides enhanced pulse energy stability. All these benefits of these short-pulse solid-state UV laser are predestining this platform for large-area applications as e. g. laser-lift-off of flexible OLED displays where average power and pulse energy can be translated into productivity by means of line-beam optics. The possibility of synchronizing up to twelve of these laser devices allows for even higher productivities.

In many fields of modern physics and industrial applications high-average power pulsed diode-pumped solid-state lasers are essential. Scaling of these lasers towards higher pulse energies is often limited by the onset of thermal effects which are determined by the average power. In this paper we would like to propose a way of increasing the pulse energies by operating the PERLA B laser system in 100 Hz burst mode with 1 ms burst duration and intra-burst repetition rate of 10 kHz. The CPA-based system incorporates fiber front-end, regenerative amplifier and the multipass amplifier followed by the booster amplifier and <2ps compressor.

We report on testing of an edge-pumped ceramic Yb:YAG disk laser having a tailored spatial gain profile for preferential amplification of the TEM00 mode. The disk has a composite construction with a Yb-doped large-aperture central portion cosintered with an undoped perimetral edge. Light from multi-kW diodes is transported though the disk edge and absorbed in the Yb-doped center. This configuration makes it poss¬ible to conveniently arrange the diode light and produce a spatially flat gain profile, such as is desir¬able for the amplification of a spatial flat top beam or a tailored gain profile [1]. Amplified spontan¬eous emis¬sion (ASE) and parasitic lasing is mitigated by the geometry of the laser disk edge, which is designed to efficiently outcouple laser fluorescence [2]. This work experimentally investigated the tailored spatial gain profile and the lasing performance of TEM00 mode (Gaussian spatial profile) beam without the distorting effects of gain saturation. Compari¬son of the lasing performance of a flat spatial gain to that with tailored gain is presented. This work was supported in-part by the US Department of Energy grants DE-SC0013762 and DE-SC0015834. 1. Drew A. Copeland and John Vetrovec, “Gain Tailoring Model and Improved Optical Extraction in CW Edge–Pumped Disk Amplifiers,” SPIE Vol. 8235, 82350U (2012). 2. John Vetrovec, Drew A. Copeland, Amardeep S. Litt, Suraj J. Thiagarajan, and Eldridge Briscoe "Stored Energy and Gain in an Edge-Pumped Ceramic Yb:YAG Disk Laser under Intense Pumping," SPIE Vol. 10084, 1008407 (2017).

Inertial confinement fusion (ICF) cryogenic experiments on the 60-beam OMEGA laser have strict requirements for the laser energy delivered on target to be power balanced in order to maximize target-irradiation uniformity. For OMEGA, this quantity (power balance) is inferred from measurements of the time-integrated energy and time-resolved, spatially integrated temporal profile of each of the 60 beams at the output of the laser. The work presented here proposes a general definition of power balance as measured at the laser output and discusses the conditions that are fundamental to achieving laser power balance. Power balance necessitates equal gain across all stages of amplification, equal net losses across each amplifier stage, equal frequency conversion (from 1053 nm to 351 nm) of all 60 beams, and equal beam path lengths (beam timing). Typical OMEGA ICF laser pulse shapes consist of one or more short (100-ps) "pickets" followed by a shaped "drive" pulse of 1 to 2 ns. For these experiments, power balance is assessed for the pickets and the drive independently, with the ultimate goal of achieving root-mean-square (rms) imbalance across all 60 beams of less than 2% rms on both. This work presents a comprehensive summary of laser shot campaigns conducted to significantly improve laser power balance from typical rms values of 4.7% and 5.2%, respectively, to the 3% level for both features along with a discussion of future work required to further reduce the rms power imbalance of the laser system.

We report about the development of two new subnanosecond solid-state laser models for application in dermatology and cosmetics. One model uses subnanosecond Nd: YAG microchip laser as a master oscillator and includes Nd: YAG double- and single-pass amplifiers. At 10 Hz this laser produces more than 600 mJ pulse energy with duration 500 +/- 5 ps. Another model (under development) is gain-switched Ti: Sapphire laser with short cavity. This laser produces 200 mJ, 560 ps pulses at 790 nm and uses standard Q-Switched Nd: YAG laser with nanosecond pulse duration as a pumping sourse.

We report on the successful demonstration of the world’s first kW average power, 100 Joule-class, high-energy, nanosecond pulsed diode-pumped solid-state laser (DPSSL), DiPOLE100. Results from the first long-term test for amplification will be presented; the system was operated for 1 hour with 10 ns duration pulses at 10 Hz pulse repetition rate and an average output energy of 105 J and RMS energy stability of approximately 1%. The laser system is based on scalable cryogenic gas-cooled multi-slab ceramic Yb:YAG amplifier technology. The DiPOLE100 system comprises three major sub-systems, a spatially and temporally shaped front end, a 10 J cryo-amplifier and a 100 J cryo-amplifier. The 10 J cryo-amplifier contain four Yb:YAG ceramic gain media slabs, which are diode pumped from both sides, while a multi-pass architecture configured for seven passes enables 10 J of energy to be extracted at 10 Hz. This seeds the 100 J cryo-amplifier, which contains six Yb:YAG ceramic gain media slabs with the multi-pass configured for four passes. Our future development plans for this architecture will be introduced including closed-loop pulse shaping, increased energy, higher repetition rates and picosecond operation. This laser architecture unlocks the potential for practical applications including new sources for industrial materials processing and high intensity laser matter studies as envisioned for ELI [1], HiLASE [2], and the European XFEL [3]. Alternatively, it can be used as a pump source for higher repetition rate PW-class amplifiers, which can themselves generate high-brightness secondary radiation and ion sources leading to new remote imaging and medical applications.

A simplified flash-lamp pumped high-average-power Nd:YAG Q-switched laser system based on a master oscillator power amplifier platform was developed toward outside laser remote sensing. The performance of the laser system was demonstrated, obtaining 4.7 J output pulse energy with a 50 Hz operating frequency on the optical breadboard of 1.8 m x 0.7 m size. The pulse energy from master oscillator was approximately 250 mJ with 14 ns pulse duration that was amplified by first Nd:YAG rod crystals with double pass amplification. Then, output laser pulse from first YAG rod was amplified by second and third Nd:YAG rod crystals. The beam pattern was image relayed using lens pair between all Nd:YAG rods to maintain the good beam spatial profile in rod amplifiers to avoid the optical damages induced by non-uniform beam profile. The focal lengths of thermal lens effect in each Nd:YAG rod crystal was about 2 m that were compensated by an adjustment of lens pairs. The amplified pulse laser was focused using focusing lens pair on the concrete surface to generate panel vibrations by laser ablation and/or thermal stress, acting thus as a hammer. The focal length of lens pair was approximately 7 m that is assumed the typical a tunnel roof in Japan. The energy transfer efficiency from final amplifier to concrete surface was approximately 87%, its main reason of reduction of efficiency was beam quality of master oscillator. That efficiency was 89% with only oscillator beam.

Conventional laser drivers for Inertial Confinement Fusion used phosphate glass as laser medium. The main disadvantage of the glass host is its low thermal conductivity and only one laser shot every 5 minutes can be obtained in the joule range with Laser Megajoule Preamplifier system. Recently, the disordered Nd:CaF2 crystals with co-doping ions has been studied intensely because of wide emission and absorption spectrum, broadband laser operation around 1μm and very good thermal properties. We demonstrate that co-doping Nd:CaF2 single crystals with Lu3+ non-optically active ions significantly improves their absorption, emission, and fluorescence lifetime properties and their laser performance. Laser operation is obtained around 1.055 μm which make these suitable for laser diver for ICF application at 1053 nm. Over the past few years, broadband laser emission has been achieved with Nd-doped fluorite-type crystals, around 1053 nm (4F4I transition Nd3+) by co-doping the host with buffer ions, such as Y3+ and Lu3+. These configurations are very interesting because absorption and emission spectra as wide as with glasses can be obtained. They still being single crystals and having thus among other advantages a high thermal conductivity which makes these materials suitable for high-energy high repetition rate pulsed laser amplifiers applications. However, in the case of CaF2, the 1 μm Nd3+ emission is completely quenched because of clustering of Nd3+ ions. The quenching of the 4F3/2 emitting level starts at low dopant concentration (0.1 at%). To address this drawback, the co-doping of the crystal with non-optically-active ions to form clusters around single Nd3+ ion and then isolated them from each other. In this work, we present the distinct absorption and emission spectra, fluorescence and radiative lifetimes as well as the respective concentrations of the two main emitting centers in CaF2: Nd3+ :Lu3+.Absorption spectra around 800nm (4I9/26>F5/2 transition) for different co-doped samples. Measurements of the thermal conductivity of CaF2 have been realized with a thermal lens technique and a mean value of 4.3 W/m.K has been obtained for a 5%Lu concentration. This value is about ten times higher than the thermal conductivity of glasses, between 0.3 and 0.6 W/mK. For demonstration of lasing performance in our laser ICF driver system, crystals with concentration of 5% Lu have been chosen because it offers the best compromise between spectra wide and thermal conductivity.

The HiLASE “Bivoj” laser system developed at CLF Rutherford Appleton Laboratory in collaboration with HiLASE team as DiPOLE100 was relocated to Dolni Brezany near Prague, Czechia at the end of 2015 and fully re-commissioned at the end of 2016. In 2016, the system demonstrated average output power of 1kW generating pulses of 105 J at 10 Hz repetition rate for the first time in the world. Since then the system has been subjected to several testing campaigns in order to determine some of its key characteristics. Beam quality, wavefront quality, pointing stability, energy stability and experience with long term operation of 1 kW laser are presented. In addition, depolarization effects have been detected inside the main amplifier. Details on these results along with numerical simulations are presented.

The latest progress on high power laser facilities in NLHPLP was reported. Based on a high power laser prototype, damage behavior of 3ω optics was experimentally tested, and the key influencing factors contributed to laser-induced damage in optics were deeply analyzed. The latest experimental results of advanced precision measurement for optical quality applied in the high power laser facility were introduced. At last, based on the accumulated works of 3ω elements damage behavior status in our laboratory, beam expanding scheme was presented to increase the total maximum output 3ω energy properly and decrease the laser induced damage risking of ω optics simultaneously.

We demonstrate the bleaching characteristics of Cr²⁺: CdSe (Cr: CdSe) crystal around 2 μm and prove that Cr: CdSe crystal is an effective saturable absorber to obtain Q-switched pulsed output in Tm³⁺-doped fiber laser pumped Ho: YAG system. The saturable absorption property of Cr: CdSe is investigated with a pulsed source at 2090 nm. The laserinduced damage threshold of uncoated Cr: CdSe is estimated around 9.92 J/cm² at 2090 nm with the pulse duration of 30 ns. With the measured bleaching curve, the estimated pulse saturation fluence is around 1.06 J/cm², and the estimated ground-state absorption cross section is 8.97×10^-20 cm², which is very close to the experimental value. The preliminary laser experiments are all finished with an antireflection coated Cr: CdSe crystal to reduce the insertion loss. The maximum output pulse energy is about 1.8 mJ with repetition frequency of 685 Hz, pulse duration of 15.4 ns, and pulse peak power of 115 kW. The pulsed laser wavelength is measured to be 2090.2 nm.

The high average power from pulsed good quality mode laser emitting at fundamental wavelength of 1066.3 nm is needed for obtaining of high-fidelity pulsed radiation with wavelength centered at 589.15 nm for spaceborne Na Doppler resonance fluorescence LIDAR. The conversion of radiation from 1066.3 nm to 589.15 nm can be achieved through one stage of Raman lasing and subsequent frequency doubling using qualified nonlinear crystals. Although efficient scaling of average power at 1064 nm using a-cut Nd:YVO4 to multiple of 10W was demonstrated for more than a decade ago, the efficient demonstration of 1066 nm power scaling from single Watt level to 10W level of average power is yet to be done. Multiple publications with a-cut Nd:YVO4 laser host with fundamental emission wavelength at 1064 nm showed good conversion efficiencies to both 1176 nm and to 588 nm using intracavity Raman lasing and frequency doubling. We experimentally demonstrated efficient lasing at 1066 nm with output average power in excess of 15W using single c-cut Nd:YV04 crystal end-pumped with 888 nm diode pump laser. The achieved optical-to-optical efficiency of converting absorbed 888 nm pump to 1066 nm with short linear test cavity and output coupler of 84% was in excess of 32% while maximum reached optical-to-optical slope efficiency 50%. We discuss challenges of efficient 1066 nm generation and overall electro-optical efficiencies reachable for potential spaceborne LIDAR Sodium transmitter laser.

High beam quality visible laser emission can be directly generated using optically pumped rare-earth (RE) ion doped praseodymium (Pr3+) in a suitable low phonon energy host. Trivalent Pr3+ can generate laser emission in the red, orange, green and blue spectral domains [1]. Direct generation in a RE ion has the advantage of energy storage and broad gain-bandwidths thus allowing tunable, Q-switched, and mode-locked laser operation [2]. Previously we have reported waveguide-based ZBLAN chip lasers in the near IR to mid-IR spectral domain. These chip lasers are based on the ultra-fast laser inscription (ULI) of depressed cladding waveguides into bulk RE ion doped ZBLAN chips. We report here visible continuous wave laser emission at 636 nm from a praseodymium doped fluorozirconate glass guided-wave chip laser. This ultra-fast laser inscribed gain chip is demonstrated to be a compact and integrated laser module. The laser module, pumped by two polarisation-coupled 442 nm single-mode GaN laser diodes, generates >8 mW lasing output with a beam quality of M2xy~ 1.15 and 1.1 (±0.1). To the best of our knowledge, this is the first visible laser emission from a glass-based waveguide chip laser. Improved laser performance may also realize laser operation of the lower gain 527 nm green transition, thus allowing the chip laser to simultaneously emit blue (un-depleted pump), green and red laser emission from the same waveguide. 1. T. Sandrock, et al.," Applied Physics B 58, 149-151 (1994). 2. M. Gaponenko, et al., Opt Lett 39, 6939-6941 (2014).

We describe generation of near-infrared (944nm, 970nm), blue (472nm, 485nm), and UV (236 nm) light by frequency up-conversion of 2 μm output of a compact and efficient passively Q-switched Tm:YAP laser. The Tm:YAP laser source was near diffraction limited with maximum Q-switched pulse peak power of 190 kW. For second harmonic generation (SHG) of NIR, both periodically poled lithium niobate (PPLN) and lithium tri-borate (LBO) were evaluated, with 58% conversion efficiency and 3.1 W of 970 nm power achieved with PPLN. The PPLN 970nm emission was frequency doubled in 20mm long type I LBO, generating 1.1 W at 485nm with a conversion efficiency of 34%. With LBO used for frequency doubling of 2.3 W of 1888 nm Tm:YAP output to 944nm, 860mW was generated, with 37% conversion efficiency. Using a second LBO crystal to generate the 4th harmonic, 545mW of 472nm power was generated, corresponding to 64% conversion efficiency. To generate the 8th harmonic of Tm:YAP laser emission, the 472nm output of the second LBO was frequency doubled in a 7mm long BBO crystal, generating 110 mW at 236nm, corresponding to 21% conversion efficiency.

We present a 400 W Q-switched 532 nm laser using several techniques to control the pulse duration and shape. The laser consists of two separate intracavity frequency-doubled cavities, incoherently combined to give 50 mJ total pulse energy. By extending the cavity length the pulse duration can be increased from 66 ns to 140 ns at 8 kHz with no significant power reduction. Varying the repetition rate and the triggering delay for each cavity’s Q-switch allows further adjustment of the pulse duration. The pulse shape can be controlled by adjusting this delay and attenuating the individual cavities.

High-power femtosecond (fs) lasers in the visible wavelength regime have numerous applications in areas including micro-machining, medical eye surgery, communication, spectroscopy, etc. To generate this laser beam, frequency conversion, especially second-harmonic generation (SHG), of near-IR lasers using nonlinear optical crystals is known to be the most standard technique. However, the use of a long-length crystal, which is preferred to achieve high SHG conversion efficiency for long-pulse or cw lasers, cannot be applied to the fs laser with broad linewidth due to the tight phase matching condition and the exacerbated walk-off effect. Thus the conditions of the nonlinear optical crystal should be optimized to achieve efficient SHG generation and hence, the high power visible fs laser pulses. There are many reports for the efficient SHG of the fs lasers but not many reports about influence of the crystal length on the SHG process, such as the pulse width and the linewidth and the conversion efficiency. Here, we report efficient SHG of femtosecond Yb lasers at 1 um by optimizing the conditions of nonlinear optical crystals. The SHG pulse and the conversion efficiency were numerically calculated to find the optimized conditions of the nonlinear optical crystals for the high power fs laser pulses with different pulse widths. Preliminary experiments were conducted using a Type I LBO crystal and the femtosecond Yb laser at 1 um, which was in good agreement with the theoretical results. The theoretical and the experimental results for LBO and BBO crystals will be reported in detail.

A diode-pumped femtosecond Kerr-lens mode-locked Yb:CALGO laser with a low repetition rate of 10.2 MHz was developed. The oscillator produced 650 mW of average output power with pulse duration of 66 fs. This corresponds to the pulse energy of 64 nJ with a peak power of 0.97 MW. No external pulse compression was used. To the best of our knowledge, this is the first Yb:CALGO laser that generated sub-100 fs pulses directly out of the cavity at such a low repetition rate. The ∼98 ns time delay between the pulses can be useful for fluorescence lifetime imaging of biological samples.

A semiconductor saturable absorber mirror (SESAM) passively mode-locked Alexandrite laser was demonstrated. Using an InP/InGaP quantum-dot saturable absorber mirror, pulse duration of 420 fs at 774 nm was obtained. The laser was pumped at 532 nm and generated 325 mW of average output power in mode-locked regime with a pump power of 7.12 W. To the best of our knowledge, this is the first report of a passively mode-locked Alexandrite laser using SESAM in general and quantum-dot SESAM in particular.

Controlled few-cycle light waveforms find numerous applications in attosecond science, most notably the production of isolated attosecond pulses in the XUV spectral region for studying ultrafast electronic processes in matter. Scaling up the pulse energy of few-cycle pulses could extend the scope of applications to even higher intensity processes, such as the generation of attosecond pulses with extreme brightness from relativistic plasma mirrors. Hollow-fiber compressors are widely used to produce few-cycle pulses with excellent spatiotemporal quality, whereby octave-spanning broadened spectra can be temporally compressed to near-single-cycle duration. In order to scale up the peak power of hollow-fiber compressors, the effective length and area mode of the fiber has to be increased proportionally, thereby requiring the use of longer waveguides with larger apertures. Thanks to an innovative design utilizing stretched flexible capillaries, we show that a stretched hollow-fiber compressor can generate pulses of TW peak power, the duration of which can be continuously tuned from the input seed laser pulse duration down to almost a single cycle (3.5fs at 750nm central wavelength) simply by increasing the gas pressure at the fiber end. The pulses are characterized online using an integrated d-scan device directly under vacuum. While the pulse duration and chirp are tuned, all other pulse characteristics, such as energy, pointing stability and focal distribution remain the same on target. This unique device makes it possible to explore the generation of high-energy attosecond XUV pulses from plasma mirrors using controllable relativistic-intensity light waveforms at 1kHz.

A high intensity Gamma source is required for Nuclear Spectroscopy, it will be delivered by the interaction between accelerated electron and intense laser beams. Those two interactions lasers are based on a multi-stage amplification scheme that ended with a second harmonics generation to deliver 200 mJ, 5 ps pulses at 515 nm and 100 Hz.

A t-Pulse oscillator with slow and fast feedback loop implemented inside the oscillator cavity allows the possibility of synchronization to an optical reference. A temporal jitter of 120 fs rms is achieved, integrated from 10 Hz to 10 MHz.

Then a regenerative amplifier, based on Yb:YAG technology, pumped by fiber-coupled QCW laser diodes, delivers pulses up to 30 mJ. The 1 nm bandwidth was compressed to 1.5 ps with a good spatial quality: M2 of 1.1. This amplifier is integrated in a compact sealed housing (750 x 500 x 150 mm), which allows a pulse-pulse stability of 0.1 % rms, and a long-term stability of 1,9 % over 100 hours (with +/-1°C environment).

The main amplification stage uses a cryocooled Yb:YAG crystal in an active mirror configuration. The crystal is cooled at 130 K via a compact and low-vibration cryocooler, avoiding any additional phase noise contribution, 340 mJ in a six pass scheme was achieved, with 0.9 of Strehl ratio. The trade off to the gain of a cryogenic amplifier is the bandwidth reduction, however the 1030 nm pulse was compressed to 4.4 ps. As for the regenerative amplifier a long-term stability of 1.9 % over 30 hours was achieved in an environment with +/-1°C temperature fluctuations

The compression and Second Harmonics Generation Stages have allowed the conversion of 150 mJ of uncompressed infrared beam into 60 mJ at 515 nm.

Residual timing noise from two synchronized diode pumped solid-state ytterbium-doped ultrafast laser oscillators is investigated. The lasers are passively mode-locked with a SESAM, which allows self-starting and stable laser operation coupled to a robust and cost-efficient design. A balanced optical cross-correlator is used to synchronize the laser repetition rates and to characterize their residual timing noise. The timing jitter measurement resolution is 8as and is limited by the cross-correlator photocurrent shot-noise. The integrated residual timing jitter is estimated to 73 as from 10 kHz to 31 MHz offset frequency. The timing jitter performance is limited by intracavity amplitude-noise-to-timing-noise conversion, mostly attributed to the SESAM. The timing jitter amounts to 4:5 fs when integrated from 10 Hz to 31 MHz because of excess technical noise contribution. This performance already makes the tested laser oscillator suitable for challenging time-resolved experiments setups.

A highly stable and robust laser system is a key component of the space-based Laser Interferometer Space Antenna (LISA) mission, which is designed to detect gravitational waves from various astronomical sources. The baseline architecture for the LISA laser consists of a low-power, low-noise Nd:YAG non-planar ring oscillator (NPRO) followed by a diode-pumped Yb-fiber amplifier with ∼2 W output. We are developing such laser system at the NASA Goddard Space Flight Center (GSFC), as well as investigating other laser options. In this paper, we will describe our progress to date and plans to demonstrate a technology readiness level (TRL) 6 LISA laser system.

We propose a nadir-pointing space-based Na Doppler resonance fluorescence LIDAR on board of the International Space Station (ISS). The science instrument goal is temperature and vertical wind measurements of the Earth Mesosphere Lower Thermosphere (MLT) 75-115 km region using atomic sodium as a tracer. Our instrument concept uses a high-energy laser transmitter at 589 nm and highly sensitive photon counting detectors that permit range-resolved atmospheric-sodium-temperature profiles. The atmospheric temperature is deduced from the linewidth of the resonant fluorescence from the atomic sodium vapor D2 line as measured by our tunable laser. We are pursuing high power laser architectures that permit limited day time sodium lidar observations with the help of a narrow bandpass etalon filter. We discuss technology, prototypes, risks and trades for two 589 nm wavelength laser architectures: 1) Raman laser 2) Sum Frequency Generation. Laser-induced saturation of atomic sodium in the MLT region affects both sodium density and temperature measurements. We discuss the saturation impact on the laser parameters, laser architecture and instrument trades. Off-nadir pointing from the ISS causes Doppler shifts that effect the sodium spectroscopy. We discuss laser wavelength locking, tuning and spectroscopic-line sampling strategy.

Northrop Grumman Cutting Edge Optronics (NGCEO) has developed a robust line of diode-pumped solid-state (DPSS) lasers for LIDAR applications. These lasers utilize a variety of design and manufacturing approaches depending on the platform, payload, and performance requirements of the system in which they will be utilized. This work contains an analysis of the design and manufacturing trade space based on a number of system requirements – location (land, sea, airborne, space), SWaP, energy level, repetition rate (10s of Hz to 10s of kHz), beam quality, desired mode structure, etc. For airborne applications, data is presented for systems on helicopters, turbo-prop aircraft, and large jets. Data is also presented from systems with multiple injection seeding approaches for single longitudinal mode (SLM) operation. Special attention is paid to utilizing NGCEO’s in-house diode array and gain module manufacturing capabilities to tailor all components of the laser to the application. For example, life test data from dozens of epitaxial wafers can be analyzed to pick the diode bar lot with the best performance for mission-critical systems.

We are developing a Q-switched narrow linewidth intra-cavity Raman laser for a space based sodium lidar application. A novel Raman laser injection seeding scheme is proposed and is experimentally verified. A Q-switched, diode pumped, c-cut Nd:YVO4 laser has been designed to emit a fundamental wavelength at 1066.6 nm. This fundamental wavelength is used as the pump in an intra-cavity Raman conversion in a Gd_0.2Y_0.8VO₄ composite material. By tuning the temperature of the crystal, we tuned the Raman shifting to the desired sodium absorption line.

A diode end pumped, T-shaped laser cavity has been built for experimental investigation. The fundamental pump laser cavity is a twisted mode cavity to eliminate the spatial hole burning for effective injection seeding. The Raman laser cavity is a linear standing wave cavity because Raman gain medium does not suffer spatial hole burning as traditional laser gain medium. The linewidth and temporal profile of the Raman laser is experimentally investigated with narrow and broadband fundamental pump emission. We have, for the first time, demonstrated an injection seeded, high peak power, narrow linewidth intra-cavity Raman laser for potential use in a sodium resonance fluorescence lidar.

Fiber and bulk lasers form two distinct classes of solid-state laser, both of which have achieved tremendous success in various arenas, but they are not without their limitations. In this paper, we investigate an alternative laser geometry occupying a domain that lies between traditional fiber and bulk laser systems. This geometry comprises a fiber-based thin-rod structure, with a diameter on the order of several hundred microns, and with length on the order of several centimetres. The motivation is to combine the advantages of the fiber geometry for excellent thermal management and the bulk geometry for greater immunity to non-linear effects and optical damage, whilst elegantly controlling the laser mode profile using thermally-induced waveguiding. Rare earth ion-doped silica is an excellent candidate to demonstrate the thermally-guided fiber-rod laser (TGFRL) due to its high fracture limit, positive thermo-optic coefficient and well-established fabrication which can produce high purity material with exceptionally low loss. A 300μm core diameter, triple-clad Yb-doped fiber is used to demonstrate the TGFRL. Thermally-induced waveguides can be tailored to have significantly larger transverse dimensions than conventional ‘engineered’ waveguides yielding potential performance benefits, especially in pulsed mode. We will present results covering thermally-induced waveguiding, amplification performance and cw laser performance at 976nm and 1030nm, with >10W achieved at 1030nm with excellent beam quality, M2 < 1.1, and slope efficiencies approaching 50% with respect to absorbed pump power. We will also present preliminary results for amplification of radially-polarised beams, highlighting the potential of these devices in a range of applications.

In this paper, we report the first LED-pumped transition-metal-doped laser oscillator and amplifier based on an alexandrite crystal (Cr³⁺:BeAl₂O₄). A Ce:YAG luminescent concentrator illuminated by blue LEDs is used to reach higher pump powers than with LEDs alone. The luminescent 200-mm-long-composit luminescent concentrator involving 2240 LEDs can delivers up to 268 mJ for a peak irradiance of 8.5 kW/cm². In oscillator configuration, an LED-pumped alexandrite laser delivering an energy of 2.9 mJ at 748 nm in free running operation is demonstrated. In the cavity, we measured a double pass small signal gain of 1.28, in good agreement with numerical simulations. As amplifier, the system demonstrated to boost a CW Ti:sapphire laser by a factor of 4 at 750 nm in 8 passes with a large tuning range from 710 nm to 800 nm.

We present our recent advances on power scaling of a high-power single-pass pumped CVD-diamond Raman oscillator at 1.2 μm. The single pass scheme reduced feedback to the high gain fiber amplifier, which pumps the oscillator. The Yb-doped multi-stage fiber amplifier itself enables up to 1 kW output power at a narrow linewidth of 0.16 nm. We operate this laser in quasi-cw mode at 10% duty cycle and on-time (pulse) duration of 10 ms. With a maximum conversion efficiency of 39%, a maximum steady-state output power of 380 W and diffraction limited beam quality was achieved.

Vector beams that carrying orbital angular momentum (OAM) have become ubiquitous and topical in a variety of research fields. The quality of such beams usually degrades while propagating in space. Here, we report a noval technique to improve the quality of vector beams by amplifying these beams through birefringent amplifier. We demonstrated this experimentally over the different orientation of the amplifier to reach enhancement in the quality of maximum 20% of that for the incident beam.

Solar Pumped Solid State Lasers (SPSSL) is a kind of solid state lasers that can transform solar light into laser directly, with the advantages of least energy transform procedure, higher energy transform efficiency, simpler structure, higher reliability, and longer lifetime, which is suitable for use in unmanned space system, for solar light is the only form of energy source in space.

In order to increase the output power and improve the efficiency of SPSSL, we conducted intensive studies on the suitable laser material selection for solar pump, high efficiency/large aperture focusing optical system, the optimization of concave cavity as the second focusing system, laser material bonding and surface processing. Using bonded and grooved Nd:YAG rod as laser material, large aperture Fresnel lens as the first stage focusing element, concave cavity as the second stage focusing element, we finally got 32.1W/m² collection efficiency, which is the highest collection efficiency in the world up to now.

Spectroscopic investigation of Co²⁺:CdTe was performed to evaluate it’s potential as a lasing medium. The sample had a targeted doping concentration of 2% and measurements were performed from 10 - 120K. Cross-sections for Co:CdTe were calculated using Füchtbauer-Ladenburg and reciprocity methods. Calculations suggest the potential for efficient lasing at ~3.7μm when pumped by a 3μm laser source on the ⁴A₂ ↔ ⁴T₂ transition. The fluorescence lifetime was measured to quantify the temperature dependence of the non-radiative relaxation rate. This work aims to characterize Co:CdTe as a novel gain medium for compact, tunable mid-infrared lasers operating within the atmospheric transmission window.

Rare-earth doped single crystal (SC) yttrium aluminum garnet (YAG) fibers have great potential as high-power laser gain media. SC fibers combine the superior material properties of crystals with the advantages of a fiber geometry. Improving processing techniques, growth of low-loss YAG SC fibers have been reported. A low-cost technique that allows for the growth of optical quality Ho:YAG single crystal (SC) fibers with different dopant concentrations have been developed and discussed. This technique is a low-cost sol-gel based method which offers greater flexibility in terms of dopant concentration. Self-segregation of Nd ions in YAG SC fibers have been observed. Such a phenomenon can be utilized to fabricate monolithic SC fibers with graded index.

We report on laser performance of ceramic Yb:YAG and single crystal Tm:YAG double-clad crystalline fiber waveguide (CFW) lasers towards the goal of demonstrating the design and manufacturing strategy of scaling to high output power. The laser component is a double-clad CFW, with RE³⁺:YAG (RE = Yb, Tm respectively) core, un-doped YAG inner cladding, and ceramic spinel or sapphire outer cladding. Laser performance of the CFW has been demonstrated with 53.6% slope efficiency and 27.5-W stable output power at 1030-nm for Yb:YAG CFW, and 31.6% slope efficiency and 46.7-W stable output power at 2019-nm for Tm:YAG CFW, respectively. Adhesive-Free Bond (AFB®) technology enables a designable refractive index difference between core and inner cladding, and designable core and inner cladding sizes, which are essential for single transverse mode CFW propagation.

To guide further development of CFW designs, we present thermal modeling, power scaling and design of single transverse mode operation of double-clad CFWs and redefine the single-mode operation criterion for the double-clad structure design. The power scaling modeling of double-clad CFW shows that in order to achieve the maximum possible output power limited by the physical properties, including diode brightness, thermal lens effect, and simulated Brillion scattering, the length of waveguide is in the range of 0.5~2 meters. The length of an individual CFW is limited by single crystal growth and doping uniformity to about 100 to 200 mm lengths, and also by availability of starting crystals and manufacturing complexity. To overcome the limitation of CFW lengths, end-to-end proximity-coupling of CFWs is introduced.

Middle-infrared (mid-IR) lasers enabling a wide range of scientific, medical, technological, and defense related applications continue to enjoy a strong demand. Transition metal (TM) doped II-VI chalcogenides are appealing mid-IR gain medial providing direct access to 1.8-6 μm spectral range. . II-VI chalcogenides are available in single crystal and in polycrystalline forms. With respect to single crystals, polycrystalline gain elements fabricated by postgrowth thermal diffusion of TM impurities in II-VI hosts feature better optical quality and enable superior laser characteristics. Despite significant progress in post-growth thermal diffusion technology, there are still some difficulties associated with the diffusion of certain TM ions in certain II-VI hosts. Specifically, the diffusion length Fe in ZnS during ~1 month annealing at 950°C is of the order of 0.1 mm. In this work, enhancement of diffusion coefficient under Hot Isostatic Pressing, at temperature and pressure of 1350°C and 2000 atm, and effect of these extreme conditions on the overall optical quality of the crystal were studied. The high temperature was applied to increase the diffusion rate, and the high pressure was needed to suppress strong sublimation and sphalerite - wurtzite phase transition at elevated temperatures. Under these conditions, the diffusion coefficient Fe in ZnS was enhanced by 5500 times as compared to standard diffusion processes carried out at 950°C. It was also demonstrated that the grain size had grown from ~30μm to ~5.5mm, which is believed to be another reason for efficient diffusion besides the elevation of temperature. The XRD patterns were measured such that the X-ray beam falls on a single grain. The XRD patterns showed only peaks characteristic to single crystals with zinc blende structure. Lasing characterization was performed to investigate the optical quality of the crystal. Slope efficiencies of 23.2% and 15.4% were obtained for TM₁₁ and TM₀₀ modes of operation, respectively. The emission of the laser was demonstrated to be in the 3840-3920 nm.

Nd:YLiF4 is the gain material of choice whenever outstanding beam quality or a birefringent gain material is necessary such as in certain applications for terahertz radiation or dual-frequency mode-locking. However, for high power CW applications the material is hampered by a low thermal fracture threshold. This problem can be mitigated by special 2D pump set-ups or by keeping the quantum defect to a minimum. Direct pumping into the upper laser level of Nd:YLiF4 is usually performed at 880 nm. For quasi-three level laser emission at 908 nm, direct pumping at this wavelength provides a high quantum defect of 0.97, which allows for very high CW pump powers. Although the direct pumping transition to the upper laser state at 872 nm has a slightly smaller quantum defect of 0.96, its pump absorption cross section along the c-axis is 50% higher than at 880 nm, leading to a higher absorption efficiency. In this work we explore, for the first time to our knowledge, 908 nm lasing under 872 nm diode pumping and compare the results with 880 nm pumping for quasicw and cw operation. By inserting a KGW crystal in the cavity, Raman lines at 990 nm and 972 nm were obtained for the first time from a directly pumped 908 nm Nd:YLF fundamental laser for both quasi-cw and cw conditions.

Laser facility such as the Megajoule Laser dedicated to laser-matter interaction including inertial fusion need pre-amplifier modules (PAM) which must respect a high beam quality. The current PAM use Nd:Phosphate material to work at 1053 nm with a repetition rate of 1shot/5min limited by a low thermal diffusion. However, it would be interesting to increase the shot rate for alignment or diagnostic purposes. Therefore, we propose to change this amplification material by crystal Nd:Lu:CaF2 with a thermal diffusion ten times higher in a new amplification architecture scheme in view of achieving a repetition rate of 10Hz. However, this material must fulfill the beam specifications to be integrated in the actual amplification chain. We report here a characterization of the thermal induced effects under a diode pump energy density of 13J/cm2. We begin by studying the spatially resolved induced birefringence with a cross polarizer-analyzer setup and then we measure the wave-front variations along two perpendicular polarizations. As the thermal elevation implies stress and then birefringence, we use an IR camera to study the surface thermal diffusion of the samples. Finally we reconstruct the stress pattern of our samples by simulating the global setup with COMSOL software which includes the thermal and mechanic Multiphysics interaction. This model allows us first to compare with experimental results and then to entirely simulate the mechanical behavior of this new material. These results obtained for the regenerative amplifier would enable us to study a new architecture scheme like disks multi-pass amplifier.

Alexandrite is a well-known material for broadly tunable and power-scalable near-IR lasers. We measured the thermal coefficients of the optical path (TCOP) and thermo-optic coefficients (TOCs) of Alexandrite at 632.8 nm for three principal light polarizations, E || a, E || b and E || c. All TOCs are positive and show a notable polarization-anisotropy, dn_a/dT = 5.5, dn_b/dT = 7.0 and dn_c/dT = 14.9×10^-6 K^-1. We also characterized thermal lensing in a continuous-wave Alexandrite laser which used a Brewster-oriented c-cut 0.16 at.% Cr³⁺ doped BeAl₂O₄ crystal pumped at 532 nm and emitted at 750.9 nm (E || b). The measured thermal lens was positive and astigmatic. The sensitivity factors of the thermal lens (M_x,y = dD_x,y/dP_abs) were found to be M_x = 1.74 and M_y = 2.38 [m^-1/W].

Tetragonal calcium rare-earth aluminates, CaLnAlO₄, are attractive laser host crystals. The emission of Nd³⁺ ions at 1.3- 1.4 μm due to the ⁴F_3/2 → ⁴I_13/2 transition is of interest for medicine, fiber optics, and light conversion. We report on compact Nd:CaLnAlO₄ lasers using a plane-plane cavity. With an a-cut 0.8 at.% Nd:CaYAlO₄ crystal diode-pumped at 802 nm, a maximum continuous-wave output power of 365 mW was achieved at 1.365 & 1.390 μm corresponding to the σ-polarization. The ⁴F_3/2 → ⁴I_13/2 laser performance of the Nd:CaLnAlO₄ crystals was compared to that from a monoclinic Nd:KGd(WO₄)₂. At the ⁴F_3/2→ ⁴I_11/2 transition (1.08 μm), a Nd:CaYAlO₄ micro-laser generated multi-watt output (>4 W) with a slope efficiency of 39%.

A continuous-wave dual-wavelength operation of an Alexandrite laser was demonstrated. The oscillator produced 870 mW of average output power for 5W of incident pump power. This corresponded to a slope efficiency of 21% and an optical-to-optical efficiency of 17.4%. A single 4-mm-thick intracavity birefringent filter plate placed at Brewster’s angle resulted in dual-wavelength radiation at 744.2 nm and 757.2 nm wavelengths (6.9 THz of frequency difference). To the best of our knowledge, this is the first report of a dual-wavelength operation of an Alexandrite laser.

A passively mode-locked Nd:YVO₄ laser operating at 1073 nm and 1085 nm was demonstrated with an intracavity birefringent filter as the wavelength selecting element. The average output powers achieved were 2.17 W and 2.18 W with optical-to-optical efficiency of 19.6% and 19.7%, respectively. The slope efficiencies were more than 31% at both output wavelengths. The pulse durations at the highest average output power were 10.3 ps and 8.4 ps, respectively. We believe that this is the first report of mode locking of a Nd:YVO₄ laser operating at 1073 nm or 1085 nm lines.

Multi-watt dual-wavelength operation of a diode-pumped Yb:CALGO laser was achieved by introducing a thin birefringent filter (BRF) plate into a standard laser cavity. A BRF plate with a thickness of 0.5 mm was capable of generating a dual-wavelength output with a frequency offset of 1.31 THz (equivalent to a wavelength separation of 4.8 nm). The output power of the dual-wavelength laser at 1044.7 nm and 1049.5 nm was 2.6 W. The developed dual-wavelength Yb:CALGO laser with multi-watt output power is an attractive and cost-effective candidate for generation of THz radiation and dual-wavelength mode-locked lasers.

Coherent modulation imaging providing fast convergence speed and high resolution with single diffraction pattern is a promising technique to satisfy the urgent demands for on-line multiple parameter diagnostics with single setup in high power laser facilities (HPLF). However, the influence of noise on the final calculated parameters concerned has not been investigated yet. According to a series of simulations with twenty different sampling beams generated based on the practical parameters and performance of HPLF, the quantitative analysis based on statistical results was first investigated after considering five different error sources. We found the background noise of detector and high quantization error will seriously affect the final accuracy and different parameters have different sensitivity to different noise sources. The simulation results and the corresponding analysis provide the potential directions to further improve the final accuracy of parameter diagnostics which is critically important to its formal applications in the daily routines of HPLF.

The spectroscopic and laser properties of Er:YAP crystal, that is appropriate for generation at 2.7 μm, in temperature range 78 - 400 K are presented. The sample of Er:YAP (1 at. % of Er³⁺) had face-polished plan-parallel faces without anti-reflection coatings (thickness 4.47 mm). During experiments the Er:YAP was attached to temperature controlled copper holder and it was placed in vacuum chamber. The transmission and emission spectra together with the fluorescence decay time were measured depending on temperature. The Er:YAP crystal was longitudinally pumped by radiation from laser diode that works in pulse regime (repetition rate 66.6 Hz, pulse duration 1.5 ms, pump wavelength 972.5 nm) or in CW regime. Laser resonator was hemispherical, 145 mm in length with flat pumping mirror (HR @ 2.7 μm) and spherical output coupler (r = 150 mm, R = 95 % @ 2.5 - 2.8 μm). The fluorescence decay time of manifold ⁴I_11/2 (upper laser level) became shorter and intensity of up-conversion radiation was increasing with decreasing temperature. In pulsed regime, the highest slope efficiency with respect to absorbed mean power was 1.27 % at 78 K. The maximum output of mean power was 3.5 mW at 78 K, i.e. 8.7 times higher than measured this value at 300 K. The maximal output power 27 mW with slope efficiency up to 3.5 % was achieved in CW. The radiation generated by Er:YAP laser (2.73 μm) is close to absorption peak of water (3 μm) thus this wavelength can be use in medicine and spectroscopy.

We report on influence of temperature on spectroscopic and lasing properties of Alexandrite (^Cr3+:BeAl₂O₄) crystal. Fluorescence lifetime, polarization-resolved absorption and emission spectra, and laser characteristics at ∼750 nm are described in detail within the 78-400K temperature range. As a pumping source, 3.5W InGaN blue laser-diode operating at 444nm wavelength was used. The best results achieved were at ∼353K crystal temperature — 326mW of continuous output power at 750nm wavelength with the slope efficiency near 20% (related to absorbed pump power). At cryogenic temperatures, the Alexandrite laser generation at the so-called R-line, i.e not in the vibronic mode, has been observed.

Solid-state eye-safe lasers are interesting sources for various applications, such as lidar, remote sensing, and ranging. A resonantly diode-pumped Er:YAG laser could be one of them allowing to reach a tunable laser emission in 1.6 μm spectral region. To overcome low pump absorption and poor pumping beam quality generated by commercially available laser diode, an active medium could be formed to long and thin laser rod guiding pumping radiation. Such an effective cooling during a high power pumping, which is a "crystal-fiber" benefit, may be useful for “standard“ crystal active medium. The main goal of this work was to investigate the laser characteristics of new developed Er:YAG crystal with a special shape for diode-pumping.

Er:YAG fiber-shape crystal with square cross-section (1x1mm) and 40mm in length was doped by 0.1% Er³⁺ ions. All sides of this crystal were polished and in addition the end-faces of it were antireflection coatings for the wavelength 1470 and 1645 nm.

As a pump system, a fiber coupled laser diode (f = 10 Hz, t = 10 ms) emitting radiation at 1465 nm wavelength was used. Er:YAG fiber-shape crystal was placed onto a copper holder in the 85 mm long plan-concave resonator consisting of a pump flat mirror and output curved (r = 150 mm) coupler with a reflectivity of 96 % @ 1645 nm. The dependence of the output peak power on absorbed pump power was investigated and the maximum 0.8 W was obtained. The corresponding slope efficiency was 14.5 %. The emitting wavelength was equaled to 1645 nm (4 nm linewidth, FWHM). The spatial beam structure was close to the Gaussian mode.

The spectroscopy properties and lasing of diode pumped Tm-doped strontium molybdate SrMoO₄ single crystal were investigated at room temperature. The Tm:SrMoO₄ crystal was grown by modified Stepanov method (2 wt.% of TmNbO₄ in the melt). The tested Tm:SrMoO₄ sample was cut from the grown crystal boule perpendicularly to growth direction 100. For spectroscopy and laser experiments 4.2mm thick plane-parallel face-polished plate (without AR coatings) was used. A fiber-coupled laser diode operating at wavelength 793nm was used for longitudinal Tm:SrMoO₄ pumping which corresponds to ³H₄ level excitation. Fluorescence spectra measurement showed strong emission in vicinity of 1.8 μm (³F₄ → ³H₆ transition), and also significant emission close to wavelengths 1.45 μm (³H₄ → ³F₄ transition) and 2.3 μm (³H₄ → ³H₅ transition). The lasing was successfully reached for all these three transitions and output characteristics were measured. The pumping laser diode was operating in the pulsed regime with a low duty cycle. The 145mm long semi-hemispherical laser resonator consisted of flat pumping mirror (HT @ 0.79 μm) and curved (r = 150mm) output coupler. For each lasing transition the particular set of resonator mirrors was used to reach high reflexivity of pumping mirror and output coupler transmission 0.5% at laser operation wavelength. The obtained laser emission wavelengths were 1.95 μm, 1.45 & 1.49 μm, and 2.30 μm. In spite of low laser slope efficiency in respect to absorbed pumping power (0.45% for ³H₄ → ³F₄ transition, 0.50% for ³F₄ → ³H₆ transition and 0.83% for ³H₄ → ³H₅ transition), results obtained are promising for further development of diode-pumped laser at 2.3 μm spectral region.

Two side-pumping schemes suitable for the development of an ultraviolet femtosecond amplifier system using a Ce³⁺:LiCaAlF₆ crystal are reported. Firstly, a Bethune-type prismatic cell configuration that uniformly illuminates the four sides of a micro-pulling down method-grown crystal is used to amplify 290 nm, femtosecond pulses with no significant increase in pulse duration and B-integral. The second pumping scheme uses a two-side-pumped large crystal. These two side-pumping schemes can pave new possibilities for achieving high-energy ultraviolet femtosecond pulses.

The goal of this study was the investigation of temperature-dependent spectroscopic and laser properties of novel Fe:ZnMnSe crystal with high manganese (Mn) content of 0.4. The fluorescence spectrum at 78 K is broad covering the region from 4000 to 5500 nm. In comparison with a Fe:ZnSe crystal, the fluorescence maximum shift of ~600 nm towards the mid-IR region can be observed. With the increasing temperature, the fluorescence spectrum is getting generally broader together with the maximum shift towards the mid-IR spectral region. The central laser oscillation wavelengths were increasing with temperature from 5450 nm at 78 K up to 5800 nm at 300 K. The output energies were decreasing from 2 mJ at 78 K to 0.1 mJ at 300 K. To our best knowledge, these are the longest oscillation wavelengths generated using a ZnSe-based crystal under Er:YAG laser excitation.

Erbium-ytterbium-codoped titanium in-diffused ridge waveguides optical amplifiers in x-cut congruent LiNbO₃ substrates pumped at 980.5 nm and 1486 nm are reported for the first time. An internal gain of 2.8 dB/cm has been measured in 2.3 cm long Yb:Er:Ti:LiNbO₃ ridge waveguides for the coupled pump power of 145 mW at 980.5 nm, which is the highest gain ever reported, to the best of our knowledge, for erbium-based LiNbO₃ waveguide amplifiers under 980 nm excitation. Furthermore, we realized an internal gain of 3.2 dB/cm for the coupled pump power of 200 mW at 1486 nm, which also exceeds the best literature values for Er:Ti:LiNbO₃ waveguide amplifiers pumped at this wavelength. In addition, we report on a method for local periodic poling (periods of 30 μm and 18.4 μm) of ridge waveguides in LiNbO₃, which allows for future integration of waveguide lasers and nonlinear frequency converters on the same substrate.

We present a novel industrial-grade prototype version of a continuous-wave 193 nm laser system entirely based on solid state pump laser technology. Deep-ultraviolet emission is realized by frequency-quadrupling an amplified diode laser and up to 20 mW of optical power were generated using the nonlinear crystal KBBF. We demonstrate the lifetime of the laser system for different output power levels and environmental conditions. The high stability of our setup was proven in > 500 h measurements on a single spot, a crystal shifter multiplies the lifetime to match industrial requirements. This laser improves the relative intensity noise, brilliance, wall-plug efficiency and maintenance cost significantly. We discuss first lithographic experiments making use of this improvement in photon efficiency.

In this paper, prospects of using diamond with NV− centers as a gain medium have been studied. Spectroscopic characterization of NV− centers in diamond as well as absorption saturation and pump-probe experiments have been carried out. Absorption and emission cross-sections were estimated to be 2.8 × 10^-17 cm² and 4.3 × 10^-17 cm² at the maximum of absorption and emission bands, respectively. It was observed from emission spectra under pulse excitation that some NV− are photoionized to NV⁰ centers with ZPL at 575 nm. Room temperature luminescence lifetime of NV− centers was measured to be 12ns, which is close to the previously reported lifetime in bulk diamond (~13ns). Saturated transmission was only about 11% of calculated values even at energy fluence much higher than the saturation flux. Two excited state absorptions (ESAs) with different relaxation times (“fast-decay” and “slow-decay with relaxation times of ~500 ns and several tens of microseconds, respectively) were revealed in transmission decay kinetics at 632 nm. Kinetics of transmission at 670 nm was dominated by “slow-decay” ESA process. Kinetics of dk/k₀ in shorter wavelength were strongly dominated by “fast-decay” ESA process. These results definitively indicate that stimulated emission of NV− centers is suppressed by photoionization and ESAs and the possibility of diamond lasers based on NV− centers is low.

Diode side-pumped solid-state lasers have the potential to yield high quality laser beams with high efficiency and reliability. This paper summarizes the results of simulation of the most predominant active media that are used in high power diode pumped solid-state (DPSS) laser systems. Nd:YAG, Nd:glass, and Nd:YLF rods laser systems were simulated using the special finite element analysis software program LASCAD. A performance trade off analysis for Nd:YAG, Nd:glass, and Nd:YLF rods was performed in order to predict the system optimized parameters and to investigate thermally induced thermal fracture that may occur due to heat load and mechanical stress. The simulation results showed that at the optimized values Nd:YAG rod achieved the highest output power of 175W with 43% efficiency and heat load of 1.873W/mm³. A negligible changes in laser output power, heat load, stress, and temperature distributions were observed when the Nd:YAG rod length was increased from 72 to 80mm. Simulation of Nd:glass at different rod diameters at the same pumping conditions showed better results for mechanical stress and thermal load than that of Nd:YAG and Nd:YLF which makes it very suitable for high power laser applications especially for large rod diameters. For large rod diameters Nd:YLF is mechanically weaker and softer crystal compared to Nd:YAG and Nd:glass due to its poor thermomechanical properties which limits its usage to only low to medium power systems.

In this paper, we present an enhanced model to predict the effect of thermal blooming and atmospheric turbulence, on high energy laser beams free space propagation. We introduce an implementation technique for the proposed mathematical models describing the effect of thermal blooming and atmospheric turbulence including wind blowing, and how it effect high power laser beam power, far field pattern, phase change effect and beam quality

. An investigated model of adaptive optics was introduced to study how to improve the wave front and phase distortion caused by thermal blooming and atmospheric turbulence, the adaptive optics model with Actuator influence spacing 3 cm the that shows observed improvement in the Strehl ratio and in wave front and phase of the beam. These models was implemented using cooperative agents relying on GLAD software package. Without taking in consideration the effect of thermal blooming It was deduced that the beam at the source takes the Gaussian shape with uniform intensity distribution, we found that the beam converge on the required distance 4 km using converging optics, comparing to the laser beam under the effect of thermal blooming the far field pattern shows characteristic secondary blip and “sugar scoop" effect which is characteristic of thermal blooming. It was found that the thermal blooming causes the beam to steer many centimeters and to diverge beyond about 1.8 km than come to a focus at 4 km where the beam assumed to be focused on the required target. We assume that this target is moving at v = (4,-4) m/sec at distance 4 km and the wind is moving at v = (-10,-10) m/sec, it was found that the effect will be strongest when wind and target movement are at the same velocity.

GLAD software is used to calculate the attenuation effects of the atmosphere as well as the phase perturbations due to temperature change in the air and effects caused as the beam crosses through the air due to wind and beam steering.

Sr-laser with high pulse repetition rate and high peak radiation power is a unique tool for studying rapidly occurring processes in time (plasma diagnostics, photoablation, etc.). In addition, the study of the frequency characteristics of the active medium of the laser helps to reveal the physics of the formation of an inverse medium in metal vapor lasers. In this paper, an experimental study of an Sr-laser with an active volume of 5.8 cm3 in the pulse repetition frequency range from 25 to 200 kHz is carried out, and a comparison with the frequency characteristics of media with large active volumes is given.

We considered the frequency characteristics of the active medium in two modes: at a constant energy in the excitation pulse CU2 / 2 and at a constant average power consumed by the rectifier. In the presented work with a small-volume GRT using the TASITR-5/12 TASITRON switch, a laser was generated for Pairs of strontium at a CSF of 200 kHz. The behavior of the characteristics of the generation lines of 6.456 μm, ~ 1 μm, and ~ 3 μm at increased repetition frequencies is considered. Using the example of large-volume GRT, it is shown that tubes with a large active volume increase their energy characteristics with the growth of the CSF. The possibility of laser operation at pulse repetition rates above 200 kHz is shown.

A high-speed asynchronous optical sampling system (ASOPS) based on Yb:KYW oscillators with 1-GHz repetition rate is reported. Two frequency-offset-stabilized diode-pumped Yb:KYW oscillators are employed as pump and probe source, respectively. The temporal resolution of this system within 1-ns time window is limited to 500 fs and the noise floor around 10^-6 (ΔR/R) close to the shot-noise level is obtained within an acquisition time of a few seconds. Coherent acoustic phonons are investigated by measuring multilayer semiconductor structures with multiple quantum wells and aluminum/silicon membranes in this ASOPS system. A wavepacket-like phonon sequence at 360 GHz range is detected in the semiconductor structures and a decaying sequence of acoustic oscillations up to 200 GHz is obtained in the aluminum/silicon membranes. Coherent acoustic phonons generated from semiconductor structures are further manipulated by a double pump scheme through pump time delay control.

The spontaneous emission in a cw rubidium diode dumped alkali laser (DPAL) system was analyzed. The fluorescence from higher lying states decreases with additional buffer gas. The intermediate states (7S, 6P, 5D) decay more slowly with buffer gas and scale super-linearly with alkali density. A detailed kinetic model has been constructed, where the dominant mechanisms are energy pooling and single photon ionization. It also includes pumping into the non-Lorentzian wings of absorption profiles, fine structure mixing, collisional de-excitation, and Penning ionization. Effects of ionization in a high powered CW rubidium DPAL were assessed.

The diode-pumped rare gas laser (DPRGL) has been suggested as a potential high-gain, high-energy laser which requires densities on the order of 10¹³ cm⁻³ at pressures around 1 atmosphere for efficient operation. Argon 1s₅ number densities have been measured in micro-hollow cathode discharges with electrode gaps of 127 and 254 μm and hole diameters from 100-400 μm. The dependency of the metastable argon (1s₅) density on total gas pressure, electrode gap distance and hole diameter were explored. The measured densities were all in the range of 0.5 − 2 × 10¹³ cm⁻³ with the 400 μm hole diameters being the lowest.

Due to complex kinetics of formation and loss mechanisms, such as ion-ion recombination reaction, neutral species harpoon reaction, excited state quenching and photon absorption, as well as their interactions, the performance behavior of different laser gas medium parameters for excimer laser varies greatly. Therefore, the effects of gas composition and total gas pressure on excimer laser performance attract continual research studies. In this work, orthogonal experimental design (OED) is used to investigate quantitative and qualitative correlations between output laser energy characteristics and gas medium parameters for an ArF excimer laser with plano-plano optical resonator operation. Optimized output laser energy with good pulse to pulse stability can be obtained effectively by proper selection of the gas medium parameters, which makes the most of the ArF excimer laser device. Simple and efficient method for gas medium optimization is proposed and demonstrated experimentally, which provides a global and systematic solution. By detailed statistical analysis, the significance sequence of relevant parameter factors and the optimized composition for gas medium parameters are obtained. Compared with conventional route of varying single gas parameter factor sequentially, this paper presents a more comprehensive way of considering multivariables simultaneously, which seems promising in striking an appropriate balance among various complicated parameters for power scaling study of an excimer laser.

We report the first CW lasing from two-photon pumping via a virtual state. Pulsed and the CW lasing of the 3096 nm 7² P_1/2 to 7² S_1/2 line are observed from degenerate two-photon pumping of the cesium 7² S_1/2 to 6² D_3/2 transition. High intensity pulses excite over 17 lasing wavelengths. Under lower intensity CW excitation, 3 μm lasing is still observed with efficiencies of 0.7%. CW experiments utilized a Cs heat pipe at 150 °C to 270 °C, and a highly-focused, single pass, Ti-Sapphire pump with no aid of a cavity. Unlike normal DPALS, this architecture does not require buffer gas, and heat is released optically so a flowing system is not required. Both suggest a very simple device with excellent beam quality is possible. This proof of concept can be greatly enhanced with more optimal conditions such as non-degenerate pumping to further increase the two-photon pump cross section and the addition of a cavity to improve mode volume overlap. These improvements may lead to an increase in efficiencies to a theoretical maximum of 14%. Results suggest two-photon pumping with diodes is feasible.