This PDF file contains the front matter associated with SPIE Proceedings Volume 11259, including the title page, copyright information, table of contents, and author and conference committee lists.

Nd:YVO₄ has a high gain transition at 1.34 μm. It can be q-switched by the saturable absorber Vanadium:YAG, which has quick recovery, enabling repetition rates above 1 MHz. I demonstrated a 1.34 μm laser for LIDAR with 1.08 nsec pulse duration, 24 kHz repetition rate and 1.75 kW peak power, and in another configuration, 4.8 nsec pulse duration, 1.82 MHz repetition rate and 68 W peak power. Several intermediate cases are described as well. These lasers have part-for-part correspondence with green pointer lasers sold for under $5 which are the size of a penlight. The eye-safe class 1 power at 1.34 μm is 1.9 times that allowable in the 1.4-1.6 μm range.

We report on experimental evaluation of laser gain and q-switched output pulse energy in vicinity of 2-microns in Tm:Lu2O3 ceramic rod end-pumped by 796-nm diodes. Also included is Comparative test evaluation of upconversion effects in Tm:Lu2O3, Tm:YLF, and Tm:YAG materials. Wide-band tunable 2 µm Tm:Lu2O3 laser is sought for remote sensing, eye–safe lasers, laser processing of transparent plastics, medical therapy, ultra¬fast lasers (UFL), accelera¬tion of nuclear particles, and generation of visible output via harmonic conversion.

The lasing of Tm or Tm,Ho-doped mixed gadolinium-gallium-aluminum-garnet (Tm:GGAG and Tm,Ho:GGAG) under 1.7 μm pumping was investigated for the first time. Three Tm:GGAG samples with Tm³⁺ concentrations 1.4 at.%, 2.5 at.% and 5.1 at.% (Tm/Gd) and one Tm, Ho:GGAG sample with concentration 0.4 at.% (Ho/Gd) and 4 at.% (Tm/Gd) in a form of face-polished plane-parallel plates were available. The original crystal boules were grown by Czochralski method in a slightly oxidative atmosphere. A fiber (core diameter 400 μm, NA= 0.22) coupled laser diode (Bright Lase Ultra - 100) was used to longitudinally pump each crystal placed in a water cooled (16 °C) heatsink. The laser diode was operated in a pulsed regime (up to 20 ms pulse duration, 10 Hz repetition rate, 1684 nm wavelength, output power amplitude up to 24 W) and CW regime (1690 nm wavelength, power up to 30 W). A hemispherical resonator (30 mm length for CW regime, 100 mm for pulsed regime) was assembled using a at pumping mirror (HR @ 1.9-2.25 μm, HT @ 1.7 μm) and concave output couplers: r = 150 mm, reflectivity _ 97.5 % @1.85-2.05 μm for Tm:GGAG; r = 100 mm, reflectivity _ 99 % @ 1.8 - 2.11 μm for Tm, Ho:GGAG. The 1.4 at.%, 2.5 at.% and 5.1 at.% (Tm/Gd) Tm:GGAG laser efficiencies with respect to the absorbed power were 57 %, 37 % and 33 % respectively with maximum achieved output power amplitude of 750 mW, 1.9 W and 3.0 W. The 1.4 at.% and 2.5 at.% sample lasers operated also in CW regime with output powers of 0.6 W and 1.8 W and efficiencies 54 % and 38 % respectively. Tm, Ho:GGAG laser had a slope efficiency of 35 % and output power amplitude of 2.1 W in pulsed regime and efficiency of 19 % and output power of 180 mW in CW regime. Considering these results, the 1.7 μm diode pumping appears to be a viable alternative for Tm and Tm, Ho-doped solid-state lasers, especially for lower concentration of the active ions.

A diode-end-pumped Tm:YLF laser, passively Q-switched (PQS) with a Cr:ZnS saturable absorber, generated 10 mJ, 29 ns-long pulses at 1.9 μm, corresponding to a peak power of 350kW. A PQS laser operated at a maximum pulse repetition frequency (PRF) of 1 kHz, generating an average power of 10 W. The demonstrated pulse energy and average power represent significant increases over previous results with PQS Tm-doped lasers, and the 10 mJ pulse energy is comparable to that of much more complex actively Q-switched versions of such lasers. Using a cadmium silicon phosphide (CSP) optical parametric oscillator (OPO), the laser output was converted to 3.5-4.2 μm mid-IR emission. The OPO exhibited an optical efficiency of 64%, and generated 6W of mid-IR power.

We describe a compact mid-IR source utilizing an intracavity, non-critically phase matched potassium titanyle arsenate (KTA) optical parametric oscillator (OPO) placed inside a passively Q-switched (PQS), 1.06μm Nd:YAG laser resonator. The 20mm long KTA intracavity OPO was singly resonant, with the output coupler coated for partial reflectivity of 60% at the 1.5μm signal emission and for high transmission at the 3.5μm idler wavelength. With the Nd:YAG pumped by a 3-λ 12-bar diode stack at 5Hz PRF, the OPO generated a maximum 20mJ signal pulse at 1.5μm and 8.8mJ idler pulse at 3.5μm. A cadmium silicon phosphide optical parametric amplifier (OPA), phase matched for 1.5μm-pumped amplification of the 3.5μm OPO idler, was placed in the near field of the intracavity OPO to further increase the mid-IR pulse energy. A maximum 3.5μm pulse energy of 12.1mJ was measured after the OPA, with an additional 4.0mJ measured at 2.8μm. The 3.5μm pulses had a temporal duration of 20ns, corresponding to a peak-power of 605kW. This paper will detail the Nd:YAG pumped intracavity KTA OPO/CSP OPA and optimization of its performance for maximizing the mid-IR pulse energy.

We show that efficiency, average power and thermal loading of Er-doped 3 μm Q-switched lasers can be significantly improved by enabling free-running upper- and lower cascade lasing at the ⁴S_3/2 → ⁴I_9/2 and the ⁴I_13/2 → ⁴I_15/2 transitions. Using Er:YLF as an example, we numerically and experimentally demonstrate, how overall performance of the cascade laser depends on Er concentration and pumping regimes. The best results were obtained with 1% of Er-doping of YLF. While the influence of the lower cascade (1.62 μm) vanishes after ~ 2% of Er³⁺, the upper cascade (1.73 μm) continues to provide some thermal relief even at very high Er-doping level The experimental results with 1% and 2% of Er-doped YLF, based in a split-channel cavity supporting cascade-assisted Q-switching, are in a good agreement with conclusions of theoretical modeling.

Flashlamp pumping of heavily doped Er:YAG is an economical method of obtaining relatively high pulse energy and average power for medical and other applications. We will present results from our investigation into the effects of gain media configurations, resonator geometries, and operating parameters on energy per pulse, slope efficiency, thermal lensing, and beam divergence.

Much progress has been made in power scaling mid-infrared lasers based on transition metal ions such as Cr²⁺, Co²⁺, and Fe²⁺ in zinc and cadmium chalcogenides. Still, the exploration of the physics of the devices is incomplete. In this work, we analyze absorption spectra from Fe²⁺ in several binary and ternary hosts at low temperatures. We examine the effect of host ion size and mass on the zero-phonon energy of these spectra and further develop our previous model for the upper state lifetime of Fe²⁺ in these materials. The effect of the relative disorder in the crystalline environment on the lasing characteristics of Cr:ZnS, Cr:ZnSe, Fe:ZnSe, and Fe:CdMnTe laser devices is explored. We show that increasing disorder of the crystal host is easily observed in broadening of the absorption spectra and the spectral linewidth of the laser output, and the reduction in the portion of the emission spectrum accessible for mode locking. Practical design guidelines for laser devices are developed.

We present a laser beam source with average output powers of up to 15 W and pulse energies of up to 50 μJ at a wavelength of 3.4 μm based on a frequency converted ultrashort pulse laser. The laser beam source consists of a commercially available ultrashort pulse laser with a pulse duration of 10 ps and a downstream multi-stage optical parametric frequency converter based on large-aperture PPLN crystals. Different output powers, pulse energies, conversion efficiencies and beam qualities are achieved depending on the design of the multi-stage setup. In addition, we present some results of processing experiments on different polymer films obtained with the laser beam source presented here.

Vortex lasers are an attractive prospect for efficient generation of high-quality beams in compact, environmentally robust, and turnkey systems. We demonstrate conversion of a Q-switched, diode-pumped Nd:YVO₄, TEM₀₀ Gaussian laser into a vortex laser source by replacing the output coupling mirror by a vortex output coupler (VOC) based on an imbalanced Sagnac interferometer. The Q-switched VOC laser generated a vortex output with 5.1 W average power, slope efficiency of 46% at 150 kHz pulse repetition rate, only marginally lower than the 5.4 W and 49% slope efficiency of the plane mirror laser. Vortex handedness was switchable with a single VOC control without loss of vortex power. In both handedness cases the vortex mode quality was assessed to be excellent by detailed analysis of vortex phase profile and propagation characteristics and comparison to an ideal vortex. The power scaling potential of the VOC was demonstrated in a higher power cavity, achieving a vortex output power of 14.3 W and a slope efficiency of 55%. Further investigation verified the ability for the VOC laser to self-mode-filter the intracavity mode, showing maintenance of high TEM₀₀ quality even after introducing deliberate mode to pump size mismatch, when the equivalent plane mirror laser becomes multimode. This work highlights the potential of the VOC as a simple route to high powered structured light sources using just standard high-power handling mirror components and its self-mode-filtering property to compensate intra-cavity spatial mode degradation when power-scaling.

The automated selection and stabilization of the transverse mode of a radially polarized Ho:YAG laser is reported. A convolutional neural network (CNN) was developed to analyze the modal composition of the laser output in real-time. Calculated error signals from the CNN are compared to the desired mode, allowing a PID control algorithm to dynamically optimize the position of an intracavity lens and therefore maintain desired modal content over pump power changes. This CNN based diagnostic system provides a fast method for selection and stabilization of transverse modes in order to advance radially polarized sources for applications such as laser processing.

A high power conical refraction (CR) laser was demonstrated based on Yb:CALGO laser crystal with a separate intracavity CR element. The CR laser delivered the maximum output power of 6.25 W at 25 W of incident pump power which is the highest output power for the CR lasers to date. The separation of the CR element from the laser gain medium reduced the complexity of laser pumping. The generated CR laser beam exhibited excellent quality with well-resolved concentric rings and the Poggendorff dark ring.

Twisted light carrying orbital angular momentum (OAM) has given rise to many developments ranging from optical manipulation to optical communications. Generating twisted light from solid-state lasers was initially achieved by amplitude and dynamic phase control, and more recently by manipulating the geometric phase of light. These lasers have been limited to generate superposition of OAM modes as well as scalar modes with OAM ℓ = 10. Here we incorporate a metasurface device into a visible solid-state laser to control the angular momentum of light by arbitrary spin-to-orbit coupling. We demonstrate the generation of pure Laguerre Gaussian modes with OAM up to ℓ = 100. Modal decomposition measurements of the output beams reveal the higher purity of the generated modes can reach up to 96% for ℓ = 1 and 88% for ℓ = 100. our approach offers a new route for high brightness OAM states at the source.

We report on the realization of a narrow-linewidth diode-pumped solution-processed solid-sate vertically emitting surface organic laser (VECSOL) using a Volume Bragg Grating as an output coupler. The diode pumped VECSOL used a commercial dye molecule (DCM) embedded in a polymer matrix leading to a laser emission at 610 nm. The ultimate linewidth achievable under that configuration as well as the broadening mechanisms have been investigated under different pumping conditions. An optimal laser linewidth of 40 MHz has been achieved for pump pulse duration of 50 ns.

In this work we present a novel compact Alexandrite laser with continuous wavelength tuning and dual wavelength operation. Wavelength tuning is achieved by tilting a Brewster-cut Alexandrite crystal to change the path length and birefringence in a plane-plane cavity. Fiber-coupled diode pumping provides a small footprint stable system with <1W of output power in TEM₀₀ mode. Results are shown for two laser crystals with the broadest tuning of 746-768nm demonstrated with 15 GHz linewidth. Wavelength tuning at a rate of −0.07nmK⁻¹ is also demonstrated by varying the crystal temperature. Stable dual wavelength operation with 12-13nm peak-to- peak separation is shown in addition. A theoretical model for wavelength tuning based on the change in geometrical path length and refractive index is found to be in excellent agreement with the experimental results. Power scaling of the system is also investigated with a second compact cavity design. A total tuning range of 754-769nm and dual wavelength operation is demonstrated with a maximum power of 3.2W and beam quality M² = 1.8.

An Nd:YLF/KGW intracavity Raman laser in DBMC (double-beam-mode-controlling) configuration has been investigated in this work. The fundamental wavelength laser was generated using a Nd:YLF crystal pumped in DBMC configuration generating an emission wavelength of 1053 nm in σ-polarization. A VBG (volume-Bragg-grating) equipped diode emitting at 797 nm was used as pump source. The KGW crystal has two strong Raman lines, 768 cm^-1 and 901 cm^-1, generating two Raman wavelengths at 1147 nm and 1163 nm, respectively. The DBMC technique allows to produce TEM₀₀ stable output in a side-pumped configuration with no requirement to introduce any additional mode selection technique, thus achieving high efficiency for fundamental TEM₀₀ operation. The high power density of the fundamental laser combined with intracavity Stokes conversion produces an efficient Raman laser. Allying both techniques, the Nd:YLF in DBMC configuration and the intracavity Raman generation, it was possible to generate an output power at 1163 nm of 3.2 W corresponding to a diode-to-Raman conversion efficiency of 8% with slope efficiency of 8.8 %. For the emission at 1147 nm, 3.5 W of output power was achieved with a diode-to-Raman conversion efficiency of 11% and slope efficiency of 9%. The beam quality was M² =1.9 and 1.1 in the horizontal and vertical direction, respectively. This is, to our knowledge, the first report of a side-pumped Nd:YLF/KGW intracavity Raman laser in DBMC configuration.

Based on our study of a high stability ultra-narrow linewidth fiber amplifier for the gravitational wave detector LISA, we have set up a hybrid fiber and Innoslab amplifier for further power scaling into <100 Watt regime. The fiber amplifier can provide a seed power of up to 8 W at 1064 nm and a linewidth <10 kHz. The booster stage consists of an in-band pumped Innoslab amplifier, which is pumped by stabilized laser diodes at 880 nm. An output power of 437 W has already been demonstrated with almost diffraction-limited beam quality. Further investigations of power stability and modal properties are currently ongoing.

We demonstrate an innovative design dedicated to scalable amplification at 1030 nm, which enables the combination of very high gains at room temperature with output pulse energies of several tens milliJoules (mJ). The optical architecture involves an edge-pumped, thick slab of Yb³⁺: YAG, which is operated in a fairly compact and scalable, non-resonant multi-pass cavity. The laser performance is experimentally benchmarked by means of a 12- pass multiplexing scheme. Thanks to seeding 3ns-long seed pulses with an energy of 300 μJ at 1 Hz, as permitted by usual fibered sources, we experience straightforward linear amplification up to 20-50 mJ with net gains in the range of 15-20 dB. The optical performance needs to be optimized by controlling the operating conditions in a convenient way, in terms of the pump-beam spatial overlap and of alignment. This takes advantage of ultimately high Gain x Energy products, in excess of 10dB.J, in a single-stage unit.

A laser amplifier can shape the sub-ns pulses of a microchip laser (Opt. Express 26(07), 8609 (2018) and 27(14), 19555 (2019)). In this work, by numerical calculations based on the rate equation for population inversion and photon density taking into account temporal pulse shape, we simulated propagation in the highly excited Nd:YAG-rod amplifier of sub-ns Micro-MOPA and proved amplification conditions to compress the pulse length toward under 100 ps operation.

A diode-pumped passively Q-switched Nd:YVO₄ laser operating at 914nm is demonstrated. The solid-state laser is quasi-continuously pumped at 808nm using a 35W fiber-coupled diode laser. Several Cr⁴⁺:YAG saturable absorbers with different outcoupling coefficients are utilized to optimize the overall system performance. The simple two component cavity design reduces the system complexity and enables efficient pump power conversion along with long-term stability concerning power and wavelength. Furthermore, temperature dependent stimulated-emission cross-section in the Q-switched regime is investigated by observing the evolution of the single pulse energy over a temperature range of 70 K.

We report <100 kHz continuous wave diode pumping of Alexandrite lasers in self-Q-switched (SQS) operation using an ultra-compact system. The laser had up to 1:46W of average power with slope efficiency of 49% and M² ≤ 1.2. A pulse duration of 657 ns at 138 kHz is obtained, with a corresponding pulse energy and peak power of 9.6 μJ and 14.6 W, respectively. Detailed results related to the laser power, spectrum and temporal profile are provided. A description of the pulse stability with respect to pump power and crystal temperature is also shown. The SQS mechanism is attributed to a time-dependent variation in the refractive index of the population inversion density giving rise to a time-dependent population lens. In a separate study we obtain the value for the variation in polarizability of the excited and ground state that gives rise to the refractive index variation. It is found to be in good agreement with a prior measurement for Alexandrite and in the range measured for other Chromium-doped gain media for which SQS has also been observed.

Nanosecond laser pulses can be controlled using fast electronics and fast EOM modulators. Its usefulness has been proven in high density plasma physics, avoidance of Brillouin scattering, laser peening, laser amplification in OPCPA among others. We present an active feedback loops between the end of a regenerative amplifier and the arbitrary waveform generator that modulates its seed. We explore several algorithms and several pulse shapes, exploring the difference between them and the optimal parameters for each, finding a robust solution. The method applied here can be used to obtain any pulse shape.

We have developed a kind of compact diode-pumped solid-state (DPSS) lasers targeting laser cleaning applications in railway, automobile and aeroplane industries. Based on a master oscillate power amplifier (MOPA) configuration, the laser output is coupled to optical fibers with core diameters of 0.2-0.4 mm depending on the output power. The master oscillator is an actively Q-switched Nd:YAG laser in a thermal insensitive cavity for good beam quality at high average power. The laser repetition rate is adjustable in 1-10 kHz. At a typical 8 kHz, we obtained pulse energy ~50 mJ, pulse width ~50 ns, peak power ~0.8 MW and M²~22, which can satisfy the requirements of most industrial laser cleaning and take advantage over commercial fiber lasers with similar output powers in terms of processing efficiency and machineable materials. The increase of either pump power or repetition rate can elevate average laser output power up to 1 kW.

We have developed a fiber/solid-state hybrid laser system operated in a burst mode with a high flexibility of pulse structure. The laser beam is used to neutralize high-energy hydrogen ion beam in the accelerator at the Spallation Neutron Source (SNS). The developed laser system will be applied to non-intrusive beam diagnostics and extraction of proton beam in the SNS particle accelerator.

Recent progress in the development of dual-wavelength passively Q-switched lasers has allowed for the generation of high-average-power, narrow-band THz waves based upon the frequency down-conversion in nonlinear crystals. Here we demonstrate a compact, multi-wavelength, passively Q-switched Nd3+:YAG laser utilizing volume Bragg gratings (VBG) for the spectral selectivity and combination of multiple modes oscillating in a single linear cavity. The cavity is capable of supporting more than two lasing modes, each having sub-30-ns pulse duration at 10s of KHz repetition rate. The presence of more than two wavelengths in the output beam further allows for the generation of multiple THz frequencies.

We demonstrate operation of a compact, passively Q-switched Yb:YAG laser producing 10W average power at 1030nm in an 8.5kHz train of 1.2mJ, 1.6ns pulses. The laser is cw end-pumped with a fiber-coupled wavelength-stabilized 940nm diode. The pump light from the 105m diameter (0.1 NA) pigtail is collimated using a short focal length lens and directed into a 3mm long, 1mm thick 10 at.% Yb:YAG crystal. The saturable absorber is a Cr⁴⁺:YAG crystal with 76% unsaturated transmission. The laser’s slope efficiency is 52% and the optical-to-optical conversion efficiency is 33% at a pump power of 30W.

Electro-optic active Q-switching in a Tm:YLF laser operating at 1.88 μm is demonstrated using a potassium lithium tantalate niobate (KLTN) crystal as the electro-optic medium. Upon approaching the ferroelectric phase transition temperature, KLTN manifests an exceptionally strong quadratic electro-optic effect. Operation with low driving voltages of 550V on a 3 mm wide and 2mm long crystal were demonstrated. Pulse energy of 1.4 mJ with 17 ns pulse duration was obtained at 1 kHz repetition rate with 9.5W incident pump power. A special trapezoidal configuration of the KLTN crystal was used in order to suppress the acousto-optic oscillations that are generated due to the strong electrostriction manifested in KLTN close to the phase transition temperature which lead to strong instabilities in the laser performance. New EO Q switching mechanism was implemented, in which the resonator gain rather than the loss was shifted between two levels by exploiting the different gain of the Tm:YLF crystal in the  and  polarizations. This obviated the need for inserting a polarizer in the laser cavity, and allowed the shortening of the laser cavity.

Underwater vision among existing surveillance systems plays an important role. With it, you can solve many problems in places such as emergency rescue operations, work at great depths, the study of the seabed and minerals. The development of such systems and methods of their use should be based on a fairly universal theory of visual and instrumental vision, which allows predicting the potential capabilities of optical systems of various types depending on the characteristics of the object of observation, the location of the vision system (underwater, surface), the nature of lighting (natural, artificial), optical parameters of water and atmosphere, severity of excitement, etc. The development of this theory was initiated by research on the problem of visual visibility in water under natural light. Subsequently, the issues of instrumental observation came to the fore. Their solution required, on the one hand, the development of a rather complicated section of the theory of radiation transfer), and on the other hand, the development of a qualitatively new approach to the analysis of the image formation process (based on the results of the theory of signals and noise). The usual method used to detect an underwater target is to send and receive some form of acoustic energy. But speakers have limitations in resolution and range accuracy; while the potential benefits of laser detection of underwater targets include high directivity, high sensitivity and high range accuracy. Lasers operating in the blue-green region of the light spectrum (420: 570 nm) have several applications in the field of detection and determination of the range of immersed targets due to the minimum attenuation in water (less than 0.1 m-1) and the maximum laser reflection from the calculated targets (e.g. mines or submarines) to provide early warning. The laser response from various targets (metal, plastic, wood and rubber) is detected using a high resolution CCD camera. The position of the detection camera is adjusted to provide laser radiation with high reflection from the target and noise with low backscattering from the aquatic environment, digital image processing methods are also used to detect and distinguish echo signals from a metal target and subtract echo signals from other objects. The image of the target is extracted from the scattering noise using the methods of background subtraction and edge detection. Thus, it is possible to obtain high image quality and distinguish objects in troubled waters, which systems using acoustic waves cannot allow.

In this research we focused on experimental measurement and modeling of the thermal lens in the active medium of diode pumped solid-state lasers at low temperature. The numerical model included the temperature and stress distribution leading to change of the index of refraction distribution and bulging of the faces of active medium. Evaluation of the influence of the main thermomechanical and thermo-optical properties of the active medium is presented. The important dependence of these parameters on the temperature and the doping concentration which leads to nonlinear equations is emphasized. The numerical model is compared with commonly used simple analytical solution. The results of the simulations are confronted with the experimental results of the measurement of refractive power of thermal lens formed in diode pumped Yb:LuAG and Yb:YAG lasers. In the experiments the crystals with different doping concentration were longitudinally pumped by fiber coupled CW laser diode at 0.930 μm with the focal point 0.2 mm in diameter. The 38 mm long semi-hemispherical laser resonator was used. The output laser oscillation wavelength was 1.03 μm. The refractive power of thermal lens was estimated indirectly by measuring of change in the position of focused laser beam focal point. The measurement was performed for constant absorbed power of 10 W in temperature range from 80 up to 240 K. The experiments showed strong dependence of refractive power on doping concentration at higher temperatures and importance of temperature and doping concentration dependence of material parameters for simulation which is often neglected.

Ytterbium-doped transparent ceramics based on cubic garnets are promising for thin-disk lasers. 3.6 at.% Yb:Lu₃Al₅O₁₂ transparent ceramics were fabricated by a solid-state reaction at 1800 °C in vacuum using Yb:Lu₂O₃ and Al₂O₃ nanopowders produced by laser ablation and their spectroscopic properties were studied. The stimulated-emission crosssection is 2.46×10^-20 cm² at 1030.2 nm. The Stark splitting of the Yb³⁺ multiplets was also determined. A compact CW Yb:Lu₃Al₅O₁₂ ceramic laser pumped by a fiber-coupled 968 nm InGaAs laser diode generated 5.65 W at ~1031 nm with a slope efficiency of 67.2%. Using quasi-CW pumping, the peak power reached 8.83 W.

Rare-earth-doped calcium niobium gallium garnets (Ca₃Nb_1.5Ga_3.5O₁₂, shortly CNGG) are disordered laser materials attractive for ultrashort pulse generation. We report on the crystal growth by the Czochralski method, spectroscopy and efficient laser operation of Yb³⁺,Na⁺ and Yb³⁺,Na⁺,Li⁺-codoped CNGG-type crystals. Their cubic structure is confirmed by X-ray diffraction and Raman spectroscopy. The absorption / stimulated-emission cross-sections and lifetime of Yb³⁺ are determined. Continuous-wave (CW) laser experiments are performed in a compact cavity using a 968-nm InGaAs pump laser diode. A 11.9 at.% Yb,Na:CNGG crystal generated 3.74 W at 1069.9 nm with a slope efficiency of 56.5%. Yb,Na:CNGG is promising for sub-100-fs mode-locked lasers at ~1 μm.

We report laser operation of spinning mirror mechanically Q-switched (MQS), flashlamp pumped 2.94 μm Er:YAG laser depending on the angular speed of the mirror, repetition rate, size and temperature of the gain element, pulse duration and jitter of Q-switch pulses, as well as pump pulse energy. The highest output energy of 260 mJ with a pulse duration of 150 ns was realized with the use of 7×120 mm Er(50%):YAG at 5 Hz repetition rate and 4200 rad/s angular speed of the spinning mirror. The efficiency of Q-switched operation was ~50% with respect to free-running regime. Using optical triggering, the pulse jitter was measured to be smaller than 10 ns for 160 ns Q-switched pulses. Optical triggering could be used for synchronization with mode-locked laser in chirp-pulse and regenerative amplifiers. We also report on development of room temperature gain-switched Fe:ZnSe laser pumped by a radiation of MQS Er:YAG laser. The maximum output energy of 9 mJ from Fe:ZnSe laser was demonstrated using MQS Er:YAG laser as pump source.

The National Ignition Facility (NIF) laser produces 192 pulsed beams with transverse dimensions ∼40 cm × 40 cm and a diversity of temporal shapes with typical durations ranging from 1 to 30 ns and a total energy on target up to 2.1 MJ in the UV.¹ Standard diagnostics include near-field cameras that record the spatial dependence of the time-integrated pulse fluence, as well as sensors that record the spatially integrated pulse power versus time. While these diagnostics are indispensable, beamlines and the pulses they transport may be better characterized with a diagnostic that reveals more of the spatio-temporal pulse structure, i.e., the local irradiance, especially in the presence of nonlinear optical effects. Recently, the time-resolving capability of the Icarus camera has been leveraged in the Precision Diagnostic System (PDS) at the NIF. The Icarus is a gated CMOS sensor designed to capture X-ray images in various experimental settings.^{2, 3} However, its sensitivity in the near-IR is sufficient for capturing time-gated images of NIF beams, thus opening the door to better characterization than is possible with standard space- and/or time-integrated diagnostics. In this work, we present the first time-gated beam profiles measured in PDS at the NIF during high-energy and high-peak-power experiments, and discuss their implications in terms of past, present, and future laser performance.

Diamond Raman lasers are an emerging high-power laser technology offering kW-level beam powers with high brightness. Here we report experimental observation of a diamond thermal lens at output powers up to 1.1 kW in a quasi-steady-state regime. It is found that a thermal lens of up 16 diopters is induced, which causes the beam quality to evolve over the investigated power range. The results aid design at higher power and clarify conditions under which beam quality degradation is expected when scaling output power.

The National Ignition Facility (NIF), located at Lawrence Livermore National Laboratory, is the world’s largest and highest-energy laser system. NIF’s 192 intense laser beams can deliver more energy than any previous laser system with a design point of 1.8 MJ of UV and 500 TW peak power. Efforts are currently underway to better understand the NIF performance and its limitations. One goal of recent and future campaigns is to better understand the accumulation of Bintegral within the NIF laser using existing diagnostics, as well as the Precision Diagnostic System (PDS). Among these diagnostics, the Shack-Hartmann (SH) sensor in the Output Sensor Package (OSP), a standard NIF diagnostic, and the dedicated PDS Radial Shearing Interferometer (RSI) both measure the wavefront of the beam. Using these diagnostics in concert with the NIF Programmable Spatial Shaper (PSS), which is used to tailor arbitrary spatial beam profiles, we have performed integrated experiments to study the B-Integral induced wavefront through the entire NIF main laser. We propagated a probe beam with a slowly varying spatial intensity profile through the NIF laser to produce a spatially varying B-Integral induced wavefront at the laser output, from which we obtained the magnitude of the B-Integral of the system. We present these direct measurements of the spatially resolved B-Integral induced wavefront scaled for the first time from a table-top experiment to a fusion-class laser chain. These measurements are compared to results of current simulations using Virtual Beamline (VBL) software.

The Precision Diagnostic System (PDS) is an advanced set of laser diagnostic tools installed within the National Ignition Facility (NIF). It is capable of picking off a single, full aperture, 1053nm (1ω) beamline before the beam propagates to the target chamber and directing it to a suite of precision laser diagnostics. It was instrumental in validating the performance of the final optics 3Ω frequency conversion system design when NIF was built. The PDS has recently been recommissioned after more than a decade of non-use and enhanced to better understand laser performance limitations1 and to characterize underperforming beams. In addition to recommissioning existing diagnostics for calorimetry, power, wavefront, near-field and far-field imaging, new diagnostics have been added: two types of time-resolved near field imaging systems; higher resolution wavefront imaging; and a 1ω spectrometer. Additionally, the beam transport system was upgraded to allow PDS to select among four different 1ω beamlines to enable improved understanding of beam-to-beam variations. Two of these four beams are top-hemisphere beams, while two are bottom-hemisphere, with known performance variations. The results from NIF Shots with the new and recommissioned PDS diagnostic (spatial resolution, dynamic range, time gating, etc..) will be reviewed and data up to 14 kJ, 3.2 TW will be presented.

New laser applications as medicine treatment, air pollutants measurement, free-space communications, target illumination, and industrial technologies require laser radiation in the mid-infrared region of 4–6 μm where Fe²⁺-based lasers can generate. Pumping of Fe²⁺-doped active material is usually provided by sources generating near 3 μm (as YAG:Er, Er-fiber, or ZnSe:Cr) fitting the Fe²⁺ absorption maximum. Other promising pumping way is the energy transfer from Cr²⁺ to Fe²⁺ in co-doped materials. This energy transfer process in gain-switched operation under 200 ns, 1.73 μm pulse excitation was reported recently. In this paper we would like to present 1 ms, 10 Hz laser operation of the Zn_1-xMn_xSe:Fe²⁺,Cr²⁺ (x = 0.3) crystal within the 78–110 K temperature range under 1.94 μm commercial Tm:fiber laser pumping. The active crystal was placed in the cryostat and the cavity was formed by a curved dichroic pumping mirror and a curved output coupler. The slope efficiency of 1 % was achieved for 1.94 μm pumping at 78 K. The central laser output wavelength at 78 K was ~4.45 μm and the output spectrum temperature shift was about 2 nm/K. Furthermore, tunability range over 300 nm (4.35–4.67 μm) obtained at 78 K using intracavity tuning element. The results will be compared to an analogous Zn_1-xMn_xSe:Fe²⁺ (x = 0.3) crystal in a gain-switched mode under Q-switched YAG:Er³⁺ 2.94 μm laser pumping. Moreover, laser generation of crystals with different Mn concentration and CW generation will be also presented.

There is strong demand for effective gain materials for the 3.0-3.9 μm spectral range not nicely covered by Cr:ZnSe and Fe:ZnSe amplification bands. We characterized, Fe:ZnAl₂O₄ ceramic sample, Fe:MgAl₂O₄ and Fe:InP single crystals as promising laser materials for this mid-IR spectral range. In all crystals, the absorption bands corresponding to ⁵E↔⁵T₂ transition of Fe²⁺ ions in the tetrahedral sites were measured. In addition, absorption band of Fe²⁺ ions in the octahedral sites were observed in Fe:ZnAl₂O₄ sample with maximum absorption cross-section at ~1.0 μm. From the absorption measurements, the radiative lifetime of Fe:MgAl₂O₄ was calculated to be 60 μs. Saturation absorption of Fe²⁺ ions in Fe:ZnAl₂O₄ was studied using Ho:YAG@2.09 μm and Er:YAG@2.94 μm lasers. Saturation measurements were taken up to energy density of 2 J/cm² and showed no saturation of absorption. This can be explained by a fast non-radiative (<100 ps) relaxation time from the ⁵T₂ level of Fe²⁺ ions in the Fe:ZnAl₂O₄ sample at RT. A strong mid-IR photoluminescence (PL) signal in Fe:InP crystal was detected under the direct excitation of the ⁵E↔⁵T₂ transition of Fe²⁺ ions using Er:YAG@2.94 μm laser as well as excitation using photo-ionization process under radiation from Nd:YAG@1.064 μm laser. This indicates that Fe:InP crystals could become promising mid-IR laser media with optimization of fabrication technology.

Ultrafast thin-disk lasers are based on the mature thin-disk technology. This technique allows for highest pump powers due to very efficient cooling. Therefore, the thin-disk geometry offers exceptional scaling of laser performance in terms of average power. Over the last decade industrial lasers for cutting and welding applications were continuously improved. More than 12kW can be obtained by a single thin-disk in continuous wave mode. TRUMPF Scientific Lasers uses the same thin-disk components to develop and manufacture ultrafast amplifiers. The achieved output power is close to 2kW with record pulse energies >95 mJ.

Industrial ultrafast lasers such as TRUMPF’s TruMicro Series are indispensable tools in many precision machining processes. Large 24/7 applications range from machining of sapphire or glass to ceramics, polymers, and metals in industries from the automotive sector to consumer electronics. In typical installations such pico- and femtosecond lasers currently operate at average power levels up to 150 W, often with nonlinear frequency conversion to the visible or UV. Based on the advanced amplifier technology pioneered by AMPHOS we introduce our new hybrid fiber–InnoSlab amplifier generation TruMicro Series 6000, capable of producing the highest average power at utmost flexibility and reliability.

An ultrafast titanium sapphire (Ti:S) laser equipped with a compact and efficient pump laser is in high demand in many biomedical applications. Recently developed high power visible laser diodes are the cost-effective alternate option to commercial diode-pumped-solid-state lasers for pumping Ti:S. We used two spectrally combined direct laser diodes (LDs) to pump a Ti:S oscillator and demonstrated stable Kerr-lens mode-locking with an average output power of 190 mW. We have carefully studied and realized the beam shaping of both LDs to achieve the maximum pumping efficiency. Furthermore, we have analyzed the noise performance of the overall system.

The Vulcan laser has been a tool to preform high energy plasma physics, including among others laboratory astrophysics and particle acceleration. The Petawatt laser beamline/target area is now going to be updated with a new beamline. This new beamline is going to be entirely set upon OPCPA as an amplification technique, and will primarily be dedicated to betatron imaging. This laser will be used at the same time as a 600 J, PW beamline, a 250J ns beam and a kJ ns long pulse. Overall we present a PW class OPCPA system comparable with Ti:sapphire laser PW systems, 30J, sub-30fs pulses.

A review of current high power (100 W-level), femtosecond, optical parametric chirped-pulse amplifiers (OPCPA) at near IR (NIR) and short-wave IR (SWIR) wavelengths pumped by Yb-based solid-state lasers is presented. OPCPA technology together with white-light-generation (WLG) makes it possible to provide CEP-stable femtosecond broadband or tunable pulses (from 700nm to 2.1 μm), which are potentially scalable to much high power levels. An important feature of these new OPCPAs is their reliability and compact design, requiring no complex cooling systems.

Industrial applications increasingly demand femtosecond and picosecond pulse duration laser systems with a range of wavelengths from the near infrared to the ultraviolet. This paper reports a dual function thin slab femtosecond amplifier system operating at a range of wavelengths via frequency conversion. A Yb:YAG thin slab amplifier was demonstrated that incorporates both the pre-amplifier and power amplifier functions in a single crystal. To ensure efficient, homogenous pumping of the thin slab a novel diode bar imaging technique is used. The combination of the homogenous pumping and the unique amplifier architecture enables average output powers < 200 W to be maintained across a range of pulse repetition frequencies from 1 MHz to 40 MHz with a pulse duration of 50 ps at a wavelength of 1030 nm and M² ~ 1.2. The pulse was compressed to a duration of 900 ± 100 fs with a compressor efficiency of < 90 %. A modified LXR100 system which is based on this technology was used as the fundamental 1030 nm source, with output powers up to 130 W, from 1 MHz – 10 MHz and pulse durations in the 900 fs regime. Second harmonic generation of 515 nm was achieved by coupling the beam into a type-1 critically phase matched LBO crystal to enable efficient conversion whilst avoiding damage. Second harmonic generation of 515 nm to < 95 W at a conversion efficiency of ~74 % and pulse energy of < 96 μJ and M² < 1.3 was achieved. Further wavelength conversion was undertaken by coupling the 515 nm and unconverted 1030 nm output into a second LBO crystal for third harmonic generation. Type-1 and type-2 phasematching configurations for third harmonic generation were investigated, with an output power of < 20 W and pulse energy of < 20 μJ achieved at 343 nm with a conversion efficiency with respect to incident 1030 nm of < 21 % for both configurations.

An increasing number of scientific applications require highly energetic ultrafast laser system like OPA pumping, THz generation or filamentation. To address their requirements, a compact diode-pumped Terawatt-class laser was developed, this laser can deliver 220 mJ pulses at 50 Hz repetition rate and 415 fs pulse duration. The system is based on a CPA scheme starting with a synchronizable oscillator, a spectral shaper, then a regenerative amplifier and two multipass amplifiers. The laser’s modular structure allows for an upgrade with additional amplification stage. In order to maintain a large spectrum throughout the whole amplification, a spectrum modulator is used to shape the spectral amplitude of the seeded pulses. It allows the versatile shaping of the spectral bandwidth to efficiently compensate the spectral narrowing induced by the amplifiers. This spectrally shaped pulse is then seeded to a regenerative amplifier based on a Yb:CaF2 crystal. Thanks to its wide emission cross section and excellent storage efficiency, the pulse energy reached 30 mJ with a spectral bandwidth of 6nm centered at 1030 nm. This spectral shape is adapted to the two amplification stage which are based on Yb:YAG crystal. The first amplification multipass stage allows to increase the pulse energy to 90 mJ. The main amplification stage then increases the energy to 250 mJ. The energy is compressed by a pair of highly efficient gratings. The pulses are successfully compressed down to 415 fs with an output energy of 220 mJ. The beam after compression has an excellent spatial Gaussian shape, a remarkable pointing stability and a high Strehl ratio.

We report the generation of unprecedented 10 PetaWatt laser pulses obtained from each of the two beamlines of the High Power Laser System (HPLS) of ELI-NP (Extreme Light Infrastructure – Nuclear Physics) research infrastructure. The laser system is a hybrid system made of a double CPA based on amplification within Titanium Sapphire crystals combined with an OPCPA with a parametric amplification stage boosting the energy to 10 mJ at the entrance of the second CPA. A XPW filter is also inserted between the two CPA and in combination with the OPCPA improves the temporal contrast of the pulses by typically 7 orders of magnitude. The spectral effects occurring during amplification such as gain narrowing and wavelength shifting are compensated through the use of spectral filters. Final amplification stages are involving large aperture Ti:Sapphire crystals (up to 200 mm) which are pumped by high energy frequencydoubled Nd:Glass lasers delivering each 100 J of green light. Laser beams have been amplified respectively up to 332 J and to 342 J of pulse energy at 1 shot per minute without any occurrence of ASE and transverse lasing thanks to index matching fluid surrounding the crystal over is entire length and pump deposition management over the time before each beam pass within the Ti:Sapphire crystal. We have demonstrated full aperture compression by metric gratings of these amplified pulses down to 22.6 fs and therefore made the full demonstration for the first time ever of 10 PW capability from a laser system.

We report on a passively mode-locked, diode-pumped femtosecond laser that provides ~200fs, 1053nm optical solitonlike pulses with < 8 orders of magnitude (OM) temporal contrast. The average output power of the compact, air-cooled laser is ~450mW at 77MHz pulse repetition rate. The spectral bandwidth (FWHM) is around 5-6nm, corresponding to transform limited pulses. For synchronization purposes the pulse repetition rate can be fine tuned to and continuously kept at a desired value employing a controller circuit, a motorized translation stage and a piezo actuator. The center wavelength of the pulses is tunable and can be precisely set to 1053nm by adjusting the laser pump power. The selfstarting laser is mode-locked using a semiconductor saturable absorber mirror (SESAM). The SESAM parameters are optimized for producing fs pulses with high temporal contrast. The effects of an intra-cavity fused silica plate inserted near Brewster angle and used for fine wavelength tuning and for polarization selection on the temporal contrast of the emitted pulses are discussed. The high temporal contrast pulses from this laser oscillator are well suited for seeding very high gain, multiple Joule type, Nd:glass, chirped pulse amplification systems routinely used in high intensity laser interaction experiments. The automated high dynamic range autocorrelator (HDR-AC) capable of recording the autocorrelation trace over 8 OM is described. The HDR-AC is based on a BBO crystal for second harmonic generation and a PMT for high sensitivity detection. A lock-in amplifier increases the detectable signal range by ~2 OM.

High power and high repetition rate femtosecond lasers are crucial tools furthering the scientific development across many fields. So far, these systems have been realized by Ti:Sapphire lasers at 800 nm, being limited in power scaling. A novel optical parametric chirped-pulse amplifier (OPCPA), pumped by high-power Yb-doped solid state lasers, and combined with bulk crystal white-light-generation seeding (WLG) allows to circumvent the limitation in average power. The presented laser system features carrier-envelope phase (CEP) stable sub 20 fs pulses centered at 800nm with millijoule pulse energies and average power of 20W while remaining on a compact footprint. Such systems have recently become commercially available from Class 5 Photonics and allow for scalability beyond millijoule pulse energies at up to 100W average power.

We report on industrial high-power lasers in the green wavelength regime. By means of a thin disk oscillator and a resonator-internal nonlinear crystal for second harmonic generation we provide 2000 W continuous-wave laser radiation at a wavelength of 515 nm. Careful shaping and stabilization of the polarization and spectral properties leads to an excellent optical-to-optical efficiency (pump to green) above 55%. The beam parameter product is designed and measured to be below 7 mm∙mrad which allows the transport with a fiber of 150 μm core diameter and standard numerical aperture of 0.1. Fiber and beam guidance optics are adapted to the green wavelength, enabling low transmission losses and stable operation. The laser, beam guidance as well as a chiller and the common customer interfaces are packaged within a compact footprint of less than 1 m². The green laser is equipped with a wide range of sensors and interfaces, enabling the user to integrate the laser in a production network and to benefit from features such as condition monitoring and predictive maintenance. Application tests show that this laser is perfectly suited for copper welding due to the superior absorption of the green wavelength compared to IR, which allows the production of spatter-free weld spots and seams with an unprecedented reproducibility in diameter and welding depth. With the new green 2 kW laser, the welding performance for high quality welds can be increased compared to the already available 1 kW system.

A multi-wavelength green laser is presented based on a coaxial diode-end-pumping configuration by intracavity frequency doubling with a nonlinear crystal. The composite gain media (Nd:YVO₄ and Nd:GdVO₄) are placed coaxially and share one pump diode around 808 nm to generate two competition-free fundamental laser at 1064.4 nm and 1063.2 nm. The nonlinear crystal (KTP or LBO) are satisfactory for second-harmonic generation (SHG) and sum-frequency generation (SFG) with different fundamental wavelengths. Stable multi-watt green lasers at 532.2 nm, 531.6 nm and 531.9 nm are simultaneously obtained. Through gain controlling by tuning the pump focusing depth and pump absorption, the power ratio for those wavelengths and pulse interval can be manipulated actively. A rate-equation model is proposed and the experimental results coincide with the simulations. By replacing the gain media (Nd:YAG, Nd:GSGG, Nd:YAP, etc), various green lasers with multiple and selectable wavelengths are possible, which have great potential in practical applications.

The design and performance of a laser diode pumped ruby laser is reported. The laser consists of a 5 mm long 0.05% doped ruby crystal placed within a hemispherical laser resonator. A single mode gallium nitride laser diode, operating at 405 nm provided up to 320 mW of pump power. Beam shaping optics were used to circularize the pump beam and a 150 mm focal length lens produced a ~20 μm waist in the crystal. The laser produced up to 44 mW of output power with a slope efficiency of 17%.

The spectroscopic and laser properties of Er:GGAG active medium, in temperature range from 80 K to 300 K, are presented in this work. The sample of Er:GGAG (20 at. % of Er³⁺) crystal had face-polished plan-parallel faces without anti-reflection coatings (thickness 3.6 mm). During all experiments the Er:GGAG was attached to temperature controlled copper holder and it was placed in a vacuum chamber. The transmission and emission spectra together with the fluorescence decay time were measured depending on temperature. The excitation of Er:GGAG was carried out by a fibre-coupled laser diode radiation (pulse duration 2 ms, repetition rate 25 Hz, wavelength 964 nm). Laser resonator was hemispherical, 100 mm in length with flat pumping mirror (HR @ 2.95 μm) and a spherical output coupler (r = 100 mm, R = 97.5 % @ 2.65 - 2.95 μm). The tunability of laser at 300 K was tested using MgF₂ birefringent filter and several laser lines at several spectral bands 2800 – 2822 nm, 2829 – 2891 nm, and 2917 – 2942 nm were obtained. The fluorescence decay time of manifold ⁴I_11/2 (upper laser level) is slightly increasing with rising temperature from 482 μs (80 K) to 466 μs (300 K) on the other hand the intensity of up-conversion radiation was increasing with decreasing temperature. In the pulsed laser regime, the highest slope efficiency with respect to absorbed energy 9 % and the maximum output energy 2.6 mJ were reached at 5 % duty cycle. The laser radiation generated by Er:GGAG laser (2.94 μm) is close to the absorption peak of water (3 μm) thus this wavelength can be used in medicine or spectroscopy.

We have demonstrated a controllable dual-wavelength laser operation of a Nd:GdVO/Nd:YVO composite crystal at 1063 and 1064 nm with in-band diode pumping around 912 nm by simply varying the operational temperature of the laser diode. When compared with the traditional 808 nm pumping, this approach offers simpler laser system, more flexibility in dual-wavelength operation, higher efficiency and lower thermal lensing effect. The laser produced an output power of <4W with a slope efficiency of <45% and 1:1 spectral power ratio.

A continuous-wave dual-wavelength Yb:CALGO laser has been demonstrated using a 12-mm thick off-surface axis birefringent filter. The obtained wavelength spacing could be tuned from a few nm up to tens of nm. In the experiments ~7.5 W of output power was obtained for 25 W of the incident pump power.

High power performance of diode-pumped Yb:YAP lasers with different crystal orientation (cuts) was investigated. The crystal samples exhibited similar pump absorption properties. In continuous-wave (CW) regime, the maximum output power of <7 W could be generated using the b-cut and c-cut Yb:YAP crystals with slope efficiency up to 70%, while the laser with the a-cut crystal was limited to 5.6 W of output power most likely due to the thermal lensing effect. Owing to the high thermal conductivity and broad emission bandwidth of Yb:YAP, this crystal is a suitable laser host for high power laser operation in CW and pulsed regimes.

Dual-wavelength (DW) operation of Yb:KGW laser was demonstrated by using a 1 mm-thick birefringent filter (BRF). Based on gain balancing around a single transmission peak of the filter, DW pairs with wavelength separation far smaller than the free spectral range of the filter could be generated. A series of DW pairs with wavelength separation of around 0.5 nm (Δν≈0.14 THz) and 4 nm (Δν≈1.1 THz) within the available gain bandwidth were generated. This method can be also applied with the other lasers that have broad gain bandwidth.

A simplified design approach for a hard-aperture Kerr-lens mode-locked Ti:sapphire oscillator was proposed. The technique is based on a simple cavity design and the position of the laser crystal with respect to the cavity mode waist which ensures an enhanced Kerr sensitivity of the oscillator. Experimental results were demonstrated and compared to the numerical calculations. Such a technique can be used and for other laser hosts.

The thermal lensing effect in the Ng-cut Yb:KGW and a-cut Yb:CALGO laser crystals was evaluated and compared using a similar laser cavity and pumping scheme. The Yb:KGW crystal exhibited large anisotropy along the horizontal and vertical axes and the thermal lensing sensitivity factors of M_x=0.52 m^-1/W (||N_p) and M_y=0.18 m^-1/W (||N_m) were determined. The Yb:CALGO crystal exhibited negligible anisotropy in the thermal lensing power, and thermal lensing sensitivity factors of M_x=0.452 m^-1/W (⊥c) and M_y=0.458 m^-1/W (||c) were measured.

We present a programmable diode laser that can generate arbitrary optical pulse shapes and bursts with a timing resolution of 200 ps and 8 bit resolution for the amplitude level setting of each time bin. A PicoQuant developed ASIC is used as waveform generator. The use of a 5 GHz chip design and close arrangement of optimized electrical interfaces to the laser diode maintain the high frequency signal quality delivered into the laser diode. Fast current slopes result in picosecond gain switched operation while for nanosecond pulses undesired ringing effects at fast switch-on transients are reduced by defining specific current ramps.

The main goal of this work was to characterize the spectroscopic properties (absorption, fluorescence, and lifetime) of the samarium ion in the yttrium-aluminum-garnet matrix. The Sm:YAG crystals with various samarium concentrations (1, 3, 6.4, 10, and 20 at.% Sm/Y in the melt) were produced by the edge-defined, film-fed growth technique. Absorption characteristics were investigated in the spectral range of 185 - 3100 nm with detailed measurements in the near-infrared range of 1058 to 1125 nm, corresponding the energy level transition ⁶H_5/2 → ⁶F_9/2. The results indicate that the specific absorption properties of the Sm:YAG crystal could be advantageously used to an absorption of parasitic fluorescence around 1064 nm, generated by Nd:YAG laser. Concerning emission dependencies in a visible spectral region from 520 to 850 nm, a dominant peak was observed at 618 nm. In the infra-red spectral range from 850 to 1450 nm the dominant peak was found at the wavelength of 1231 nm. From the ⁴G_5/2 level lifetime measurements, the dependence of lifetime on the samarium ions concentration in the YAG matrix was proven. Lifetime values ranged from 0.2 (20 at.% Sm/Y) to 2.0 ms (1.0 at.% Sm/Y). From the spectroscopic results it follows that the Sm:YAG crystal is a suitable candidate for attenuation of an unwanted spontaneous radiation at 1064 nm wavelength of the Nd:YAG laser or for lightconversion from UV to yellow-red visible region.

Iron doped II-VI binary and ternary semiconductor materials are developed for mid-infrared (mid-IR) laser applications and some of them (ZnSe, ZnMnSe, ZnMgSe, CdMnTe) were already proven as laser active materials. In this article, the spectroscopic and laser properties of novel Fe²⁺ doped Zn_1-xMn_xTe (x ≈ 0.3) active material synthesized using Bridgman technique is presented. This active material was pumped by an Er:YAG laser at ~3 μm as well as Fe:ZnSe laser at 4.1 μm and has demonstrated various spectroscopic and laser output characteristics within the temperature range from 78 up to 300 K. At ~3 μm pumping, the central oscillation wavelength was ~4.8 μm at 78 K and shifted to 5.15 μm at 160 K. At 4.1 μm pumping, the central oscillation wavelength was red-shifted to ~4.9 μm at 78 K and shifted to 5.25 μm at 160 K. The output energy at 10 μJ level was achieved. These results present a great potential of the Fe²⁺:Zn_1-xMn_xTe (x ≈ 0.3) crystal for mid-IR laser radiation generation.

In this work we presented a compact femtosecond high average power (35 W), high energy (35 uJ) and high pulse repetition rate (1 MHz) laser system based on efficient room-temperature Yb:YAG crystal rod double-pass power amplifier and Yb doped fiber seed laser. High fidelity nearly transform-limited pulses (330 fs) were obtained by using matched dispersion pair of chirped fiber Bragg grating (CFBG) as a pulse stretcher and 4-pass diffraction grating based pulse compressor. Residual dispersion mismatch was compensated by applying linear thermal gradient along CFBG. Presented laser system is a compact and convenient solution for various industrial and scientific applications.

Tetragonal calcium rare-earth aluminates, CaLnAlO₄, combine a structural disorder with good thermo-mechanical properties. We report on efficient continuous-wave (CW) and passively Q-switched (PQS) ~2-μm laser operation of a 4 at.% Tm:CaYAlO₄ crystal using a compact (6-mm-long) plane-parallel cavity. The pump source was a 791 nm fibercoupled AlGaAs laser diode. The CW output power reached 5.78 W at ~1970 nm with a slope efficiency of 43.6% and a linear laser polarization. Stable PQS operation was achieved using a single-walled carbon nanotube (SWCNT) based transmission-type saturable absorber. The PQS laser generated 2.15 W at ~1945 nm, a record-high average output power for this type of lasers. The best pulse characteristics (energy/duration) were 9.1 μJ/165 ns at a repetition rate of 235 kHz.

The neutral vacancy (GR1) centers are the intrinsic lattice defects in diamond with interesting optical properties. In the present work, we performed optical characterization of the GR1 centers in CVD-grown bulk diamond to explore their laser feasibility. The non-linear optical measurements reveal efficient saturable absorption of ground level of the centers under ns-pulsed excitation at 632 nm. The transmission changes from 55% at small incident intensity to 84% at the saturated level. The experimentally measured data was fitted with equations representing two limiting cases and obtained the saturation parameters, namely saturation fluence (6.8 mJ/cm²) and saturation intensity (6.4 MW/cm²), at 633 nm for ground state absorption. The intensity of saturation 6.4 MW/cm² obtained after fitting the experimental data is two orders of magnitude smaller than that at 694 nm documented in the literature for GR1 centers in natural diamond. The calculation gives essentially the same value of absorption cross-section (⁓4.5 × 10^-17 cm²) at 633 nm for both approximations. We also estimated the radiative lifetime and quantum yield as about 8.5 ns and 13%, correspondingly. The cross-sections were estimated for transition ¹E ↔ ¹T₂. The emission cross-section was obtained to be ⁓9 × 10^-17 cm² near the maximum of emission band. Such a high absorption cross-section and fast recovery of ground state in combination with high concentration of the centers can provide high optical gain.

Tm,Ho co-doped disordered calcium niobium gallium garnet (CNGG) crystals are investigated as a novel gain medium for mode-locked lasers near 2 μm. With a GaSb-based semiconductor saturable absorber mirror (SESAM) and chirped mirrors for dispersion compensation such a laser is mode-locked at a repetition rate of 89.3 MHz. For a 5% output coupler, a maximum average output power of 157 mW is obtained with a pulse duration of 170 fs (28-nm broad spectrum centered at 2.075 μm, leading to a time-bandwidth product of 0.331). With a 0.5% output coupler, 73-fs pulses are generated at 2.061 μm with a spectral width of 62 nm (time-bandwidth product of 0.320) and an average output power of 36 mW.

With increasing demand for narrow-linewidth lasers for applications such as atom cooling, metrology and sensing, the research community has centered its focus around locking and referencing the lasing wavelength with the highest stability achievable. The two main platforms emerging to accommodate for such specific needs are diode pumped solid-state (DPSS) and external cavity diode lasers (ECDL). Being in the early stages of their product life cycles, both platforms are seeking ways to provide users with reasonably high and stable output powers. Our paper looks into the details of the performance differences between the two platforms. Primarily it shows that whilst similar output powers can be achieved using both platforms within Sub-GHz bandwidths, due to additional spontaneous emission noise terms, encountered in ECDLs, there exists a difference in the spectral density contrast. In fact, these noise terms, being detectable by power meters for output power specifications, compromise on the spectral density contrast within the linewidth of interest, which can be critical for narrow- linewidth applications. We have compared some of the most recently reported ECDL spectra to a standard Nd:YAG DPSS laser to show that in case of both platforms specified for the same output power, a DPSS laser can provide at least 3-times more useful output power, within the specified narrow spectral linewidth, than an ECDL, which puts the feasibility of these platforms into a new perspective.