This PDF file contains the front matter associated with SPIE Proceedings Volume 10082, including the Title Page, Copyright information, Table of Contents, Introduction (if any), and Conference Committee listing.

A vortex Raman laser pumped by the second-order optical vortex mode was demonstrated. The first- and the second- Stokes waves that lased at the first-order optical vortex mode were generated. Considering the spatial intensity overlap between the pump and the first-Stokes beam, and between the first- and second-Stokes beams, the generation of a topological charge of 1 in the Stokes fields could be theoretically predicted.

Radially-polarised beams are attracting growing interest owing to their unique properties and numerous applications. Power-scaling whilst preserving the polarisation-purity of radially-polarised beams is challenging, with efforts predominantly focused on cylindrically-symmetric systems. We explore an alternative strategy for power-scaling radially-polarised beams using a thin-slab amplifier geometry, which, to the best of our knowledge, has not been previously investigated. We show that very high radial polarisation-purity can be maintained in an architecture that can be operated at high powers. A radially-polarised seed-source was constructed using an Yb:YAG rod in a plane-parallel configuration, pumped by a capillary delivery-fiber which provided effective overlap with the LG01 mode. By tuning the cavity length and utilising thermally-induced birefringence, a robust multi-Watt LG01 mode was generated with an excellent radial polarisation-purity of 15dB and good beam quality M2=2.2. The Yb:YAG slab was pumped by a diode-bar producing a highly-elongated inversion region. The seed was amplified in a double-pass configuration, using a cylindrical lens to spatially-match the inversion. The output beam was re-collimated by the cylindrical lens, and compensation for the Gouy phase-shift was made using a half-waveplate. At 50W of incident pump power we obtained a small-signal gain of 7.5dB and a power gain of 4.5dB for 1.45W seed power. At maximum pump power the radial polarisation-purity was maintained at 15dB, and the beam quality only degraded slightly to M2=2.3. Further optimisation of slab design and pump geometry will be discussed in addition to power-scaling the system to higher output powers necessary for a range of applications.

In this effort, we report on the preservation of the spatial mode quality as composite vortex beams propagate through a flashlamp pumped amplifier system. Because of the spatially asymmetric nature of the transient thermal lensing, a laser beam propagating through this type of amplifier will be distorted. This makes an ideal environment to assess the mode integrity of propagating composite vortex beams. We demonstrate that a 3-lobe composite vortex beam can propagate under extreme transient thermal lensing and maintain the mode structure through the amplification process. Even though the actual amplification wasn’t the main thrust of this effort, we demonstrate gain greater than a factor of 4 for two different seed energy levels. Since the flashlamp pumped system is an extreme case, this result shows the potential for using concentric vortex beams in high power amplifiers and could open up new applications in propagation and sensing.

Retina-safe operation in open-air is of high interest to the next generation of lasers that are being utilized for many industrial, defense and medical applications. Those wavelengths that are considered to be the best for retina safe operations (also called eye-safe) fall in the range between 1400nm and1800nm. This wavelength region also coincides with the low loss window of fused silica fibers used for optical fiber communications [1], where the S and C bands near 1500nm are heavily utilized for long range communications due to the lowest attenuation losses possible in the fiber. The trivalent Er ion can produce direct emission into the 1540 nm wavelength, thus, it is the rare-earth emitter of choice for many eye-safe applications. In recent years, the need for high beam quality under passive operation in open air applications have renewed interest in Er-doped bulk glasses as the gain material of choice for solid-state eye-safe lasers. The need for performance stability under a broad operating range from -400C to 1000C without active cooling is a challenge for amorphous gain materials. Moreover, there is very little known about how temperature may affect performance. In this study, we describe our first attempts to understand material behavior by systematically analyzing temperature driven variations exhibited in absorption and emission from the commercially available gain materials. As part of these investigations, we will also present our method for assessing quantum efficiency through measurements for critical evaluation from laser community at large.

Q-Peak has demonstrated a novel, compact, pulsed eyesafe laser architecture operating with <10 mJ pulse energies at repetition rates as high as 160 Hz. The design leverages an end-pumped solid-state laser geometry to produce adequate eyesafe beam quality (M² ~4), while also providing a path towards higher-density laser architectures for pulsed eyesafe applications. The baseline discussed in this paper has shown a unique capability for high pulse repetition rates in a compact package, and offers additional potential for power scaling based on birefringence compensation. The laser consists of an actively Q-switched oscillator cavity producing pulse-widths <30 ns, and utilizing an end-pumped Nd: YAG gain medium with a Rubidium Titanyl Phosphate (RTP) electro-optical crystal. The oscillator provides an effective front-end-seed for an optical parametric oscillator (OPO), which utilizes Potassium Titanyl Arsenate (KTA) in a linear OPO geometry. This laser efficiently operates in the eyesafe band, and has been designed to fit within a volume of 3760 cm³. We will discuss details of the optical system design, modeled thermal effects and stress-induced birefringence, as well as experimental advantages of the end-pumped laser geometry, along with proposed paths to higher eyesafe pulse energies.

Er:YGG planar waveguide amplifiers (PWAs) are promising candidates to meet the needs of greenhouse-gas differentialabsorption LIDAR applications. We report pulsed–laser-deposition growth of this doped crystal and net-gain performance (internal gain ~2 dB/cm for 0.7-at.% Er-doping) in a 0.9-cm-long uncoated single-pass PWA. Rapid fabrication is also demonstrated with optimized parameters, where crystal growth rates approaching 20 microns/hour have been realized. We compare Er-doping concentrations ranging from 0.5 at.% - 4 at.%, and report on their spectroscopic properties. Furthermore, we show the ability to tailor the deposited crystal properties, controlling the waveguide and gain characteristics. Finally, we discuss the spectroscopy and potential performance of this relatively unstudied material for PWAs in the eye-safe regime.

We describe compact and efficient Q-switched diode-pumped, Tm:YAP lasers operating at 1.94μm. Laser CW and Q-switched performance is compared, using both compact mechanical as well as passive Q-switching. For passive Q-switching using a Cr:ZnS saturable absorber (unsaturated transmission of 95%), the laser produced 0.5mJ pulses with an average power of 4.4W and 6.5kW peak power, and had an optical efficiency of 30%. A resonant mirror mechanical Q-switch resulted in a 4 kHz PRF pulse train, with an optical slope efficiency of 52% and an optical-to-optical conversion efficiency of 41%. The laser generated 1.5 mJ, 45 ns FWHM, 33kW peak power pulses, and 6.2W of average output. A second mechanically Q-switched laser operating at 10 kHz PRF produced 1mJ, 35kW peak power pulses, generating 11W average power with an optical efficiency of 46%, and a beam quality of 1.4x diffraction limit.

Tm:Lu₂O₃ has a multi–featured absorption spectrum in the usual pump band around 796 nm with peaks and valleys narrower than the bandwidth of conventional pump diodes in this range. As a result, accurate prediction of the spatial deposition of absorbed pump power is rather challenging. This is of particular importance for the edge-pumped disk laser where the spatial gain profile is adjusted by temperature tuning of the laser pump diodes to optimize performance for amplification of pulses with spatial top hat or with spatial Gaussian profiles. The frequently used "lumped-line" pump model was found inadequate for Tm:Lu₂O₃. This work reports on the development of a spectral absorption model for a more accurate prediction of pump power deposition and its correlation with the gain uniformity and amplifier output pulse energy.

We describe a variety of technological advances in the development of efficient, powerful, and continuously tunable Cr:ZnSe lasers operating in the 2.3-2.7 μm spectral region. This includes the development of compact "single chip" waveguide Cr:ZnSe lasers, waveguide mode-locked Cr:ZnSe lasers, and the creation of homogeneously broadened laser material.

Fe²⁺:Cd_1-xMn_xTe solid solution spectroscopic and lasing properties depending on temperature and Mn concentration x were investigated. A set of Fe²⁺:Cd_1-xMn_xTe crystals with different concentration of Mn (x = 0.1, 0.52, 0.68, and 0.78) was synthesized using Bridgeman technique with the Fe²⁺ ions doping (c ~ 10¹⁷ cm^-3) during the synthesis process. The absorption spectra are broad covering the range from 2700 to 6000 nm with the maximum around 3500 nm. The fluorescence spectra are also broad ranging from 3500 nm to 7000 nm. The Fe²⁺:Cd_1-xMn_xTe laser oscillations at 77 K under short pulse (~200 ns) Fe:ZnSe cryogenically-cooled 4080 nm laser pumping and under long pulse (~150 us) Dy³⁺:PbGa₂S₄ 4330 nm pumping were achieved successfully. The output energy of ~3 μJ was achieved in both cases. The oscillation spectrum maxima at 77 K were ~4950 nm for x = 0.1; ~5130 nm for x= 0.52; and ~5300 nm for x=0.78.

We report on CW, acousto-optically tuned Cr:ZnS mid-IR laser operating over 1890 - 2785 nm spectral range with 40% slope efficiency with respect to the pump power in the maximum of tuning curve. The tuning range over 1890 - 2785 nm was demonstrated by tuning the radio frequency (RF) applied to a TeO₂ acousto-optical filter between 30.3 MHz and 20.12 MHz. A maximum output power of 2.8 W was achieved at 2.23 μm under 10.7 W of pump power. The linewidth of the Cr:ZnS laser measured at central wavelength was < 0.8 nm.

Large Yb:YAG crystals were grown using of new improved technology enabling to produce YAG crystals without central growth defect. The crystals diameter reached 115-120mm and their central part was used for manufacturing of discs with the diameter larger than 55 mm. Both sides of this discs were polished and coated. Doping concentration of Yb³⁺ ions in Yb:YAG crystals was measured using of X-ray fluorescence spectrometry. Absorption coefficient of Yb:YAG was measured for different doping concentration of Yb³⁺ ions. Fluorescence decay time of Yb:YAG was measured at temperatures of 300K and 80 K. We found the fluorescence decay time of the values of 0.95-1 ms at both temperatures stable and independent on the Yb³⁺ doping concentration in the range of 1-10 at.% Yb/Y demonstrating high chemical purity of grown crystals. Optical homogeneity as measured using of Fizeau double pass interferometer at 633nm resulted with PV values lower than 0.15 λ on clear aperture of 35 mm. Polished surfaces were ideally parallel with the wedge lower than 2 arcsec. Uniformity of laser properties of Yb:YAG was verified by scanning of the disc as active media in plan-convex pulsed laser resonator pumped by semiconductor diode (wavelength 969 nm, pumping beam diameter 100 μm). It was confirmed, that newly developed technology allows to manufacture very large high quality Yb:YAG discs suitable for high power lasers and amplifiers.

The main challenge in thin disk laser design is the realization of efficient heat removal from the pumped area by optimizing the heat spreading and the water impingement cooling. This generally requires calculating of the temperature distribution in the disk by numerically solving the heat conduction equation using finite element algorithms.

We have developed a simple method to calculate disk temperature profiles that is based on analytically solving the heat conduction equation in Hankel Transform Space. This method can be applied to disks that are mounted on multi-layered, water-cooled heat spreaders, which may include glue or solder layers and dielectric coating layers. This allows parametric optimization of the heat removal process in pumped solid state and semiconductor disks without having to use finite-element programs.

We present a novel multi-pass resonator architecture paving the way for pulse energy scaling of mode-locked thin-disk lasers. It consists of a concatenation of nearly identical optical segments, each segment corresponding to a round-trip in an optically stable cavity containing an active medium exhibiting soft aperture effects. Contrarily to state-of-the-art multi-pass oscillators based on imaging schemes, the stability region (for variations of the active medium thermal lens) of the here disclosed resonator architecture does not shrink with the number of passes. As a result, the proposed architecture enables the realization of an arbitrarily large number of passes at the thin-disk at a given pump power without the reduction of output power seen in the imaging-based state-of-the-art multi-pass oscillators.

Today thin-disk lasers routinely provide high pulse energies at picosecond pulse durations and kHz repetition rates. Systems with more than 200mJ per pulse are commercially available. After the introduction of the Dira 200-1, providing 200mJ at 1kHz, TRUMPF Scientific Lasers complements its thin-disk regenerative amplifier product portfolio by systems with a few hundred Watts of average output power. Still based on a single disk a flexible laser system with more than 500W was realized. Originally, it was designed for a 50kHz operation, delivering 10mJ pulses, but it also can be set-up for different repetition rates like 10kHz or 100kHz. TRUMPF Scientific Lasers regenerative amplifiers show an excellent long-term performance. The 500W system has a power stability of 0.5%.

Scientific applications often require higher average output powers, even with high pulse energies. Based on the extensive experience with highest average power continuous wave laser systems by TRUMPF a more powerful regenerative amplifier system is currently under development by TRUMPF Scientific Lasers. This laser uses two disk laser heads inside the same cavity to provide more than 1kW average output power. First results show an average power of more than 1kW at repetition rates of 10kHz and higher. A pulse duration below 1ps could be reached.

A compact passively Q-switched Nd:YAG laser was end-pumped by a water-cooled 808 nm vertical-cavity surface-emitting laser (VCSEL) pump module comprising four high power, high brightness VCSEL chips with a combined 10 mm diameter circular emitting area and 2.3 kW total peak power, resulting in 47 mJ laser pulse energy at 1064 nm with 16% optical efficiency at 15 Hz repetition frequency. A laser package comprising an air-cooled 1.6 kW VCSEL pump module produced 37 mJ laser pulse energy, while more than 13 mJ laser pulse energy was demonstrated in a bench-top experiment with a very compact laser set-up using a single 5 mm x 5 mm VCSEL chip.

In this paper, we review the development, at the STFC’s Central Laser Facility (CLF), of high energy, high repetition rate diode-pumped solid-state laser (DPSSL) systems based on cryogenically-cooled multi-slab ceramic Yb:YAG. Up to date, two systems have been completed, namely the DiPOLE prototype and the DiPOLE100 system. The DiPOLE prototype has demonstrated amplification of nanosecond pulses in excess of 10 J at 10 Hz repetition rate with an opticalto- optical efficiency of 22%. The larger scale DiPOLE100 system, designed to deliver 100J temporally-shaped nanosecond pulses at 10 Hz repetition rate, has been developed at the CLF for the HiLASE project in the Czech Republic. Recent experiments conducted on the DiPOLE100 system demonstrated the energy scalability of the DiPOLE concept to the 100 J pulse energy level. Furthermore, second harmonic generation experiments carried out on the DiPOLE prototype confirmed the suitability of DiPOLE-based systems for pumping high repetition rate PW-class laser systems based on Ti:sapphire or optical parametric chirped pulse amplification (OPCPA) technology.

The development of coherent light sources with emission in the mid-IR is currently undergoing a remarkable revolution. The mid-IR spectral range has always been of tremendous interest, mainly to spectroscopists, due to the ability of mid-IR light to access rotational and vibrational resonances of molecules which give rise to superb sensitivity upon optical probing [1-3]. Previously, high energy resolution was achieved with narrowband lasers or parametric sources, but the advent of frequency comb sources has revolutionized spectroscopy by providing high energy resolution within the frequency comb structure of the spectrum and at the same time broadband coverage and short pulse duration [4-6]. Such carrier to envelope phase (CEP) controlled light waveforms, when achieved at ultrahigh intensity, give rise to extreme effects such as the generation of isolated attosecond pulses in the vacuum to extreme ultraviolet range (XUV) [7]. Motivated largely by the vast potential of attosecond science, the development of ultraintense few-cycle and CEP stable sources has intensified [8], and it was recognized that coherent soft X-ray radiation could be generated when driving high harmonic generation (HHG) with long wavelength sources [9-11]. Recently, based on this concept, the highest waveform controlled soft X-ray flux [12] and isolated attosecond pulse emission at 300 eV [13] was demonstrated via HHG from a 1850 nm, sub-2-cycle source [14]. Within strong field physics, long wavelength scaling may lead to further interesting physics such as the direct reshaping of the carrier field [15], scaling of quantum path dynamics [16], the breakdown of the dipole approximation [17] or direct laser acceleration [18]. The experimental development of long wavelength light sources therefore holds great promise in many fields of science and will lead to numerous applications beyond strong field physics and attosecond science.

In this paper, we present results about a high energy picosecond Holmium YLF laser developed in order to be used as the puming laser for the first mid-IR optical parametric chirped pulse amplifier (OPCPA) operating at a center wavelength of 7 μm with output parameters suitable already for strong-field experiments. It is also the first demonstration of an Optical Parametric Chirped Pulse Amplifier (OPCPA) using a 2 μm laser pump source which enables the use of nonoxide nonlinear crystals with typically limited transparency at 1 mm wavelength. This new OPCPA system is alloptically synchronized and generates 0.2 mJ energy, CEP stable optical pulses. The pulses are currently compressed to sub-8 optical cycles but support a sub-4 cycle pulse duration. The discrepancy in compression is due to uncompensated higher order phase from the grating compressor which will be addressed in the future.

Based on established short pulse lasers with an output wavelength around 1 μm optical parametric frequency converters open up the spectral range between 1.4 and 4.0 μm for the first time in a power range of interest to laser material processing. The systems can be flexibly adapted as regards wavelength, pulse parameters and spectral properties to the requirements of various applications.

We will discuss technical implementation and characterization of different optical parametric generators (OPG) based on periodically poled Lithium Niobate (PPLN) to show the parameter flexibility of this approach as well as current technical limits. Actual design examples will address output wavelengths between 1.6 μm and 3.4 μm with output powers ranging from several watts to tens of watts. The pulse parameters of these lasers range from a pulse duration of 9 ps with a repetition rate of 86 MHz to 1.5 ns and 100 kHz.

The spectral bandwidth of the OPG examined can be very large. In particular, spectral bandwidths of about 100 nm are measured at the degenerated point, where the output wavelength is equal to twice the pump wavelength. Even beyond this point, a spectrum of typically a few tens of nanometers width generally accompanies a large conversion efficiency (>50 %). For applications that require a narrower spectrum, the OPG can be operated in a seeded mode, where only a few milliwatts of power from a continuously emitting laser diode are sufficient to seed a pulsed high power OPG efficiently and reduce the bandwidth to few nanometers.

First pulse effect, commonly seen in nanosecond cavity-dumped lasers and picosecond regenerative amplifiers, not only leads to degradation of processing quality, but also acts as potential threat to optical switching elements. Several methods have been developed to suppress that effect, including electronic controls, polarization controls, and diffraction controls. We present a new way for first pulse self-suppression without any additional components. By carefully arranging the cavity mirror of a regenerative amplifier, we realized ‘parasitic lasing like’ radiation. When the regenerative amplifier works in ‘operation ready’ status, the parasitic lasing occurs and prevents the gain crystal from saturation. When the regenerative amplifier starts working and amplifying pulses, the first pulse in a pulse train will not get much more gain and energy than pulses following it. As parasitic lasing disappears at the same time, the average output power of the amplifier does not significantly reduce. This cost effective method does not require any additional component. In addition, as it is not polarization dependent, this method is widely suitable for different kinds of regenerative amplifiers. It’s the easiest and cheapest way to suppress first pulse effect, to the best of our knowledge.

Subnanosecond Nd: YAG laser with output energy at 1064 nm up to 1.1 J and pulse repetition rate 10 Hz was developed for applications, related to medical skin treatment. Available pulse durations are 400 – 750 ps. Laser includes master oscillator with pulse duration 5.5 ns, stimulated Brillouin scattering (SBS) pulse compressor, and amplifier system. Original multi-pass scheme provide compression using liquid cell with small overall length ~15 - 20 cm.

Overlapping of pump beams during multiple passes along cell leads to several effects, which can produce negative influence on output pulse performance. We develop schemes, where overlapping is eliminated or reduced, and obtain reliable generation of compressed pulses with the same duration and stability, as can be obtained for long (with total length ≥ 70 cm) single-pass SBS compressors.

We studied the cw LD and rectangular pulsed LD pumped saturable output coupler (SOC) passively Q-switched Nd:YVO₄ transmission microchip laser experimentally. We demonstrated that the SOC passively Q-switched Nd:YVO₄ transmission microchip laser pumped by a highly stabilized narrow bandwidth pulsed LD has a much lower timing jitter than pumped by a continuous wave (CW) LD, especially at low output frequency regime. By changing the pump beam size in the rectangular shape pulsed pump scheme, the output frequency can be achieved from 333.3 kHz to 71.4 kHz, while the relative timing jitter decreased from 0.09865% to 0.03115% accordingly. Additionally, the microchip laser has a good stability of output power, the power fluctuation below 2%.

A trigonal 5.6 at.% Yb:YAl₃(BO₃)₄ (Yb:YAB) crystal is employed in continuous-wave (CW) and passively Q-switched microchip lasers pumped by a diode at 978 nm. Using a 3 mm-thick, c-cut Yb:YAB crystal, which has a higher pump absorption efficiency, efficient CW microchip laser operation is demonstrated. This laser generated a maximum output power of 7.18 W at 1041–1044 nm with a slope efficiency η of 67% (with respect to the absorbed pump power) and an almost diffraction-limited beam, M² _x,y < 1.1. Inserting a Cr:YAG saturable absorber, stable passive Q-switching of the Yb:YAB microchip laser was obtained. The maximum average output power from the Yb:YAB/Cr:YAG laser reached 2.82 W at 1042 nm with η = 53% and a conversion efficiency with respect to the CW mode of 65% (when using a 0.7 mm-thick Cr:YAG). The latter corresponded to a pulse duration and energy of 7.1 ns / 47 μJ at a pulse repetition rate (PRR) of 60 kHz. Using a 1.3 mm-thick Cr:YAG, 2.02 W were achieved at 1041 nm corresponding to η = 38%. The pulse characteristics were 4.9 ns / 83 μJ at PRR = 24.3 kHz and the maximum peak power reached 17 kW. Yb:YAB crystals are very promising for compact sub-ns power-scalable microchip lasers.

A high gain cryogenic Yb:YAG ceramics laser amplifier for a high energy laser amplification system has been developed. The laser system consists of a fiber oscillator and two stage LD pumped cryogenic Yb:YAG ceramic amplifiers. The preamplifier stage has a 5-pass laser amplifier head and the main amplifier stage has a 2-pass laser amplifier head, respectively. The preamplifier obtained an average stored energy density of 0.836 J/cc and small-signal gain (SSG) of 60 with 33 J of stored energy. Then about 1 μJ of input energy from the oscillator was amplified to 3.6 J. The main amplifier head had four pumping LD modules which irradiated the Yb:YAG ceramics directly. This original angular pumping scheme ideally increases irradiation intensity and homogenizes irradiation pattern on the Yb:YAG ceramics due to superposition effect of all of the LD modules. A maximum peak power of over 100 kW was generated by one LD module. When the output energy of the LD modules was 450 J, a 20 of SSG at single pass was obtained. Stored energy density was evaluated to 0.429 J/cc when 148 J energy was stored in 346 cc of Yb:YAG ceramics. As a result, a 55-J output energy with 10 ns pulse duration was demonstrated at a pumping energy of 450 J. The optical-tooptical conversion efficiency which includes transmissivity of the LD modules was 12 %. The extraction efficiency was estimated to 37%.

Many scientific endeavors are benefitted by the development of increasingly high energy laser sources for lidar applications. Space-based applications for lidar require compact, efficient and high energy sources, and we have designed a novel gain head that is compatible with these requirements. The gain medium for the novel design consists of a composite Nd:YAG/Sm:YAG slab, wherein the Sm:YAG portion absorbs any parasitic 1064 nm oscillations that might occur in the main pump axis. A pump cavity is built around the slab, consisting of angled gold-coated reflectors which allow for five pump passes from each of the four pumping locations around the slab. Pumping is performed with off-axis diode bars, allowing for highly compact conductively cooled design. Optical and thermal modeling of this design was done to verify and predict its performance. In order to ultimately achieve 50 W average power at a repetition rate of 500 Hz, three heads of this design will be used in a MOPA configuration with two stages of amplification. To demonstrate the pump head we built it into a 1064 nm laser cavity and performed initial amplification experiments. Modeling and design of the system is presented along with the initial oscillator and amplifier results. The greatest pulse energy produced from the seeded q-switched linear oscillator was an output of 25 mJ at 500 Hz. With an input of 25 mJ and two planned stages of amplification, we expect to readily reach 100 mJ or more per pulse.

For achieving highest peak powers in a solid state laser (SSL) system, significant energy output and short pulses are necessary. For mode-locked lasers, it is well-known from the Fourier theorem that the largest gain bandwidths produce the narrowest pulse-widths; thus are transform limited. For an inhomogeneously broadened line width of a laser medium, if the intensity of pulses follow a Gaussian function, then the resulting mode-locked pulse will have a Gaussian shape with the emission bandwidth/pulse duration relationship of pulse ≥ 0.4402/c. Thus, for high peak power SSL systems, laser designers incorporate gain materials capable of broad emission bandwidths. Available energy outputs from a phosphate glass host doped with rare-earth ions are unparalleled. Unfortunately, the emission bandwidths achievable from glass based gain materials are typically many factors smaller when compared to the Ti:Sapphire crystal. In order to overcome this limitation, a hybrid “mixed” laser glass amplifier – OPCPA approach was developed. The Texas petawatt laser that is currently in operation at the University of Texas-Austin and producing high peak powers uses this hybrid architecture. In this mixed-glass laser design, a phosphate and a silicate glass is used in series to achieve a broader bandwidth required before compression. Though proven, this technology is still insufficient for the future compact petawatt and exawatt systems capable of producing high energies and shorter pulse durations. New glasses with bandwidths that are two and three times larger than what is now available from glass hosts is needed if there is to be an alternative to Ti:Sapphire for laser designers. In this paper, we present new materials that may meet the necessary characteristics and demonstrate the laser and emission characteristics these through the internal and external studies.

An orthogonally polarized self-mode-locked Nd:YAG laser is demonstrated in a short linear cavity. Under an incident pump power of 8.2 W, the average output power can be measured to be 3.8 W. The beat frequency Δfc between two orthogonally polarized mode-locked components is observed and increases linearly with an increase in the incident pump power. The origin of the beat frequency is utterly confirmed to be caused by the thermal-stress-induced birefringence in the Nd:YAG crystal and is theoretically simulated. The present result provides a promising method to achieve orthogonally polarized mode-locked lasers with tunable beat frequency.

In this work, we have compared the Q-switched performance of single rod crystal to a newly developed distributed face cooling structure. This structure was made by surface activated bonding technology and allowed to combine transparent heatsink to a gain crystal at room temperature. The Sapphire and Nd³⁺:YAG crystal plates were combined in this fashion to produce eight crystal chip which was further used to obtain Q-switch pulses with Cr⁴⁺:YAG crystal as saturable absorber. Energy of 9 mJ and pulse duration of 815 ps were achieved. Although the energy obtained with single rod system was 10 mJ, the degradation of the beam prevents such crystal to be used in further applications. This is the first demonstration of distributed face cooling system outperformed conventionally single rod system.

The generation of tunable narrowband terahertz (THz) radiation has shown much interest in recent years. THz systems are used for rotational-vibrational spectroscopy, nondestructive inspection, security screening and others. Monochromatic THz emission has been generated by means of THz parametric oscillation, nonlinear difference frequency generation, and quantum cascade lasers. Intracavity difference frequency generation (DFG) in the nonlinear crystal gallium arsenide (GaAs) is known as an efficient way to generate a continuous wave THz radiation. A novel high power solid state resonator is presented with the use of volume Bragg grating (VBG) technology to create a dual channel system by spectral beam combination. The system consists of two separate Tm:YLF crystals and two VBGs for narrowband wavelength selection. At the end of the resonator both channels share common spherical mirrors, which provide feedback and focuses the beam for nonlinear purposes. This allows each channel to be independent in power and wavelength, eliminating gain competition and allowing individual wavelength tunability. The VBGs are recorded in photo-thermo-refractive glass, which has a high laser induced damage threshold and can withstand the high intracavity power present in the resonator. Tunability of the system has shown spectral spacing from 5 to 20 nm, 0.4 - 1.7 THz, and intracavity continuous wave power levels from 80 to 100 W. By placing the GaAs crystal near the waist, THz radiation can be extracted from the cavity.

Microwave plasma chemical vapour deposition (CVD) of diamond has enabled a multitude of optical applications due to its range of extreme properties. Transparency from the ultra-violet to the infra-red is complemented by the highest thermal conductivity of any bulk material, high laser damage threshold, low thermal expansion and chemical inertness. Element Six will review and summarize key progress made in state of the art diamond for a number of case studies, including high power laser optics, cooling in high power disk lasers, diamond Raman lasers and photonics applications.

In this contribution we detail the full characterization of the anisotropy of the absorption properties of two different Yb-doped monoclinic borate compounds under polarized light. The studied crystals are Li₆(Gd)_0.75Yb_0.25(BO₃)₃ and Li₆Y_0.75Yb_0.25(BO₃)₃, respectively, grown by the Czochralski method. We focused on the study of their absorption at the zero line transition as a function of the polarization direction of the incident light for two different crystal cuts of each compound. We discuss the different Eigen frames that must be considered in these materials due to their monoclinic character, as well as the optimal crystal orientation for the considered absorption and the potential influences when used as laser materials.

Many organic molecules have strong and narrow absorption features in the middle Infrared (mid-IR) spectral range. The ability to directly probe absorption features of molecules enables numerous mid-IR applications in non-invasive medical diagnosis, industrial processing and process control, environmental monitoring, etc. Thus, there is a strong demand for lasers operating in mid-IR spectral range. Transition metal (TM) doped II-VI semiconductors such as Fe/Cr:ZnSe/S are the material of choice for fabrication of mid-IR gain media due to favorable combination of properties: a four level energy structure, absence of excited state absorption , broad mid-IR vibronic absorption and emission bands. Despite the significant progress in post-growth thermal diffusion technology of TM:II-VI fabrication there are still some difficulties associated with diffusion of certain TM’s in these materials. In this work we address the issue of poor diffusion of Fe in ZnSe/S polycrystals. It is well known that with the temperature increase the diffusion rate of impurity also increases. However, simple application of high temperatures during the diffusion process is problematic for ZnSe/S crystals due to their strong sublimation. The sublimation processes can be suppressed by application of high pressures. Hot isostatic pressing was utilized as the means for simultaneous application of high temperatures (1300°C) and high pressures (1000atm, 3000atm). It was determined that diffusion coefficient of Fe was improved 13 and 14 fold in ZnSe and ZnS, respectively, as compared to the standard diffusion at 950°C. The difference in diffusion coefficients can be due to strong increase in the grain size of polycrystals.

We report on the growth, spectroscopic and laser characterization of a novel monoclinic laser crystal, 3.5 at.% Yb, 5.5 at.% In:KLu(WO₄)₂ (Yb,In:KLuW). Single-crystals of high optical quality are grown by the TSSG method. The absorption, stimulated-emission and gain cross-sections are determined for this material at room temperature with polarized light. The maximum σ_abs is 9.9×10^-20 cm² at 980.8 nm for light polarization E || N_m. The radiative lifetime of Yb³⁺ in Yb,In:KLuW is 237±5 μs. The stimulated-emission cross-sections are σ_SE(m) = 2.4×10^-20 cm² at 1022.4 nm and σ_SE(p) = 1.3×10^-20 cm² at 1039.1 nm corresponding to an emission bandwidth of >30 nm and >35 nm, respectively. A diode-pumped N_g-cut Yb,In:KLuW microchip laser generates 4.11 W at 1047-1052 nm with a slope efficiency of 78%. Passive Q-switching of a Yb,In:KLuW laser is also demonstrated. The Yb,In:KLuW crystal seems very promising for sub-100 fs mode-locked lasers.

Tetragonal rare-earth calcium aluminates, CaLnAlO₄ where Ln = Gd or Y (CALGO and CALYO, respectively), are attractive laser crystal hosts due to their locally disordered structure and high thermal conductivity. In the present work, we report on highly-efficient power-scalable microchip lasers based on 8 at.% Yb:CALGO and 3 at.% Yb:CALYO crystals grown by the Czochralski method. Pumped by an InGaAs laser diode at 978 nm, the 6 mm-long Yb:CALGO microchip laser generated 7.79 W at 1057–1065 nm with a slope efficiency of η = 84% (with respect to the absorbed pump power) and an optical-to-optical efficiency of η_opt = 49%. The 3 mm-long Yb:CALYO microchip laser generated 5.06 W at 1048–1056 nm corresponding to η = 91% and ηopt = 32%. Both lasers produced linearly polarized output (σ- polarization) with an almost circular beam profile and beam quality factors M² _x,y <1.1. The output performance of the developed lasers was modeled yielding a loss coefficient as low as 0.004-0.007 cm^-1. The results indicate that the Yb³⁺- doped calcium aluminates are very promising candidates for high-peak-power passively Q-switched microchip lasers.

We demonstrate a volumetric random laser with an optical efficiency of 15%. We use a 1.33 mol% Nd:YVO₄ crystal, grind it and mix the particles into ten different size distributions with mean particle sizes ranging from approximately 10 micrometers to 100 micrometers. After pressing into pellets, each of the ten groups has its transport mean free path calculated from the distribution spectra and experimentally measured by means of its backscattering cone. We then calculate the fill fractions of each sample. The pellets are diode-pumped at 806.5 nm. Linewidth narrowing and output power are measured as a function of absorbed pump power. We demonstrate that the smaller particles, trapped between large particles, serve as gain centers whereas the large particles control the light diffusion into the sample. By optimizing diffusion and gain we achieve high slope efficiency.

We present a novel, robust and efficient scheme for nonlinear pulse compression at highest average powers, which is based on self-phase modulation in a bulk nonlinear medium placed inside a multi-pass-cell (MPC). The scheme is suitable for the compression of sub-ps pulses with peak powers exceeding the threshold for catastrophic self-focusing of the nonlinear medium. Experimentally, we compress the output pulses from an Yb:YAG-Innoslab amplifier from 850 fs to <170 fs at 375 W of output power, 37.5 μJ pulse energy and almost diffraction-limited beam quality using fused silica as the nonlinear medium. The efficiency of the compression unit exceeds 90%.

This presentation will describe the design and construction status of a new mobile high-energy femtosecond laser systems producing 500 mJ, 100 fs pulses at 10 Hz. This facility is built into a shipping container and includes a cleanroom housing the laser system, a separate section for the beam director optics with a retractable roof, and the environmental control equipment necessary to maintain stable operation. The laser system includes several innovations to improve the utility of the system for “in field” experiments. For example, this system utilizes a fiber laser oscillator and a monolithic chirped Bragg grating stretcher to improve system robustness/size and employs software to enable remote monitoring and system control. Uniquely, this facility incorporates a precision motion-controlled gimbal altitude-azimuth mount with a coudé path to enable aiming of the beam over a wide field of view. In addition to providing the ability to precisely aim at multiple targets, it is also possible to coordinate the beam with separate tracking/diagnostic sensing equipment as well as other laser systems. This mobile platform will be deployed at the Townes Institute Science and Technology Experimental Facility (TISTEF) located at the Kennedy Space Center in Florida, to utilize the 1-km secured laser propagation range and the wide array of meteorological instrumentation for atmospheric and turbulence characterization. This will provide significant new data on the propagation of high peak power ultrashort laser pulses and detailed information on the atmospheric conditions in a coastal semi-tropical environment.

We report the demonstration of a chirped pulse amplification laser system that produces 1.5 J pulses at 0.5 kHz repetition rate and 0.75 kW average power. These pulses are subsequently compressed resulting 1 J, ~5 ps duration pulses at 500 Hz repetition rate. The 8-pass main amplifier consists of two diode-pumped, cryogenic-temperature Yb:YAG active mirrors cooled by a thermally efficient, high capacity cryogenic-cooling system. This amplifier operates with an opticalto- optical efficiency of 37%. The amplified pulses have excellent beam quality with a measured M² factor of ~ 1.3. Over 30 minutes of continuous operation, we measured a shot-to-shot pulse energy fluctuation of only 0.75% RMS over the nearly 1 million shots fired. This laser was employed to make the first demonstration of a compact, plasma-based EUV/soft x-ray laser operating at a repletion rate of 400 Hz. In this proof-of-principle demonstration, shaped 1 J pulses of picosecond duration were focused onto a rotating molybdenum target at grazing incidence. The resulting plasma is collisionally ionized to the Ni-like ionic stage where a large, transient population inversion results in production of bright λ = 18.9 nm laser pulses.

Passively mode-locked sub 200 fs pulses are generated from Er-Yb co-doped ZBLAN waveguide laser using a semiconductor saturable absorber mirror repetition rates of up to 533 MHz. At 156 MHz and 1556 nm central wavelength, the chip laser operates with a broad 25 nm bandwidth. The waveguides were written in the Er-Yb co-doped ZBLAN glass by using ultrafast laser inscription.

We report output characteristics from the FC/APC connectorized photonics crystal hollow core fiber when is subjected to coiling down to 50 mm radius, bending, torsion etc. We achieved coupling efficiency up to 75%, output average power 2 W and 24 nJ pulse energy. With proper coupling the depolarization could be as low as 7%. Torsion of the photonic crystal patchcord destroys the polarization and other pulse properties.

High power OPCPAs above 10 W at short-wave IR wavelengths (SWIR: 1.4 - 3 μm) may be limited because of thermal heat dissipation in the nonlinear crystals. In this work we provide up-to-date measurements of the absorption coefficients of the nonlinear crystals used at these wavelengths and simulations of the thermal effects on critical parameters. In particular, power scaling limits will be discussed.

A high-power diode-pumped pure Kerr-lens mode-locked Yb:KGW laser was demonstrated. The developed laser delivered 240 fs pulses with 2.3 W of average output power at a repetition rate of 86.8 MHz. Shorter pulses of around 120 fs with 1.2 W of average output power were also generated. The self-starting operation of the oscillator was demonstrated. The limiting factor to the laser operation was the appearance of a strong continuous wave component in the mode-locked laser spectrum.

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, 3.5 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 (750x500x150 cm), 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 3.5 ps.

We present a high-power, single-crystal based, Yb:CALGO regenerative amplifier. The system delivers more than 50 W output power in continuous-wave regime, with diffraction limited beam quality. In Q-switching regime the spectrum is centered at 1043 nm and is 11 nm wide. In regenerative amplification experiments we achieved 34 W at 500 kHz with 12.7 nm FWHM wide spectra centered at 1044 nm seeding with a broadly tunable, single-prism SESAM mode-locked Yb:CALGO laser providing 9 nm wide spectra at 1049 nm. Pulse duration after compression was 140 fs, with excellent beam quality (M² < 1.25).

High repetition rate mode-locked lasers (in the GHz range), are desired for frequency comb spectroscopy. A major obstacle that currently impedes high repetition mode-locking is the inevitable subsequent reduction of the single pulse energy, which reduces the efficiency of the nonlinear Kerr effect in the cavity, eventually precluding mode-locking. The standard methods to overcome this restriction is to try to maintain the intra-cavity peak intensity in spite of the reduction of the single pulse energy, by tightening the focus of the intra-cavity beam on the crystal, or by enhancing the output coupler reflectivity and increasing the pump power. This standard approach is however limited since these actions also provide better conditions for CW operation, which reduces the ML robustness, and eventually spurs the laser to operate in CW. We demonstrate a fresh attack on this problem: instead of aiming to preserve the peak intensity by tightening the focus and lowering the OC loss, we enhance the nonlinearity inside the cavity to compensate for the reduction in intra-cavity peak intensity. We harness the enhanced nonlinearity to specifically target the intra-cavity peak intensity and explore its limits and effects. With an additional nonlinear window in the cavity we enhanced the Kerr nonlinearity by an order on magnitude compared to the standard Ti:S, allowing to maintain mode-locking with an output coupler reflectivity as low as R=55% and record-low intra-cavity peak intensity (10GW/cm², 50 times less than without enhanced non-linearity). Our results provide an important new knob for high-repetition rate mode-locking.

Spaceborne atmospheric LIDAR instruments enable the global measurement of aerosols, wind and greenhouse gases like CO₂, Methane and Water.

These LIDAR instruments require a pulsed single frequency laser source with emission at a specific wavelength. Pulse energies in the 10 mJ or 100 mJ range are required at bandwidth limited pulse durations in the multi-10 ns range. Pulse repetition rate requirements are typically around 100 Hz but may range from 10 Hz to some kHz. High efficiency is mandatory.

Building complex laser sources providing the performance, reliability and lifetime necessary to operate such instruments in space has been recognized to be still very challenging.

To overcome this, in the frame of the FULAS technology development project - funded by ESA and supported by the German Aerospace Center DLR - a versatile platform for LIDAR sources has been developed. For demonstration the requirements of the laser source in the ATLID instrument have been chosen.

The design is based on a single frequency seeded, actively Q-switched, diode pumped Nd:YAG laser oscillator and an InnoSlab power amplifier with frequency tripling. The laser architecture pays special attention on Laser Induced Contamination by avoiding critical organic and outgassing materials. Soldering technologies for mounting and alignment of optics provide high mechanical stability and superior reliability.

The FULAS infrared section has been assembled and integrated into a pressurized housing. The optical performance at 1064 nm has been demonstrated and thermal vacuum tests have been carried out successfully providing relevant data for the French-German climate mission MERLIN.

Growing interest in precise measurements of methane concentration and distribution in the Earth’s atmosphere is stimulating efforts to develop LIDAR systems in the spectral region of 1.65 μm utilizing Path Differential Absorption techniques. The key element of such systems is a tunable high energy transmitter operating in the vicinity of a methane absorption line. We developed a novel laser source meeting these system needs using in-band pumping Q-switched solid state lasers (SSLs) based on Er-doped active media. We demonstrated a feasibility to measure methane line at 1651nm.

The spectral stability of a previously reported Ho:YLF single frequency pulsed laser oscillator emitting at 2051 nm is drastically improved by utilizing a narrow linewidth Optically Pumped Semiconductor Laser (OPSL) as a seed for the oscillator. The oscillator is pumped by a dedicated gain-switched Tm:YLF laser at 1890 nm. The ramp-and-fire method is employed for generating single frequency emission. The heterodyne technique is used to analyze the spectral properties. The laser is designed to meet a part of the specifications for future airborne or space borne LIDAR detection of CO₂. Seeding with a DFB diode and with an OPSL are compared. With OPSL seeding an Allan deviation of the centroid of the spectral distribution of 38 kHz and 517 kHz over 10 seconds and 60 milliseconds of sampling time for single pulses is achieved. The spectral width is approximately 30 MHz. The oscillator emits 2 mJ pulse energy with 50 Hz pulse repetition frequency (PRF) and 20 ns pulse duration. The optical to optical efficiency of the Ho:YLF oscillator is 10 % and the beam quality is diffraction limited. To our knowledge this is the best spectral stability demonstrated to date for a Ho:YLF laser with millijoule pulse energy and nanosecond pulse duration.

In the field of atmospheric research, LIDAR is a powerful technology that can measure gas or aerosol concentrations, wind speed or temperature profiles remotely. To conduct such measurements globally, spaceborne systems are advantageous. Pulse energies in the 100 mJ range are required to achieve highly accurate, longitudinal resolved measurements. Measuring concentrations of specific gases, such as CH₄ or CO₂, requires output wavelengths in the IRB, which can be addressed by optical parametric frequency conversion.

An OPO/OPA frequency conversion setup was designed and built as a demonstration module to address the 1.6 μm range. The pump laser is an Nd:YAG-MOPA system, consisting of a stable oscillator and two subsequent Innoslab-based amplifier stages that deliver up to 500 mJ of output pulse energy at 100 Hz repetition frequency. The OPO is inherited from the OPO design for the CH₄ lidar instrument on the French-German climate satellite MERLIN. In order to address the 100 mJ regime, the OPO output beam is amplified in a subsequent multistage OPA. With KTP as nonlinear medium, the OPO/OPA delivered more than 100 mJ of output energy at 1645 nm from 450 mJ of the pump energy and a pump pulse duration of 30 ns. This corresponds to a quantum conversion efficiency of about 25 %.

Besides demonstrating optical performance for future lidar systems, this laser will be part of a LIDT test facility, which will be used to qualify optical components especially for the MERLIN mission.

Coherent Diode-Pumped Solid-State Orlando (CDO), formerly known as Lee Laser, headquartered in Orlando Florida produces CW and pulsed solid state lasers. Primary wavelengths include 1064 nm, 532 nm, and 355 nm. Other wavelengths produced include 1320 nm, 15xx nm, and 16xx nm. Pulse widths are in the range of singles to hundreds of nanoseconds. Average powers are in the range of a few watts to 1000 watts. Pulse repetition rates are typically in the range of 100 Hz to 100 KHz.

Laser performance parameters are often modified according to customer requests. Laser parameters that can be adjusted include average power, pulse repetition rate, pulse length, beam quality, and wavelength. Laser parameters are typically cross-coupled such that adjusting one may change some or all of the others. Customers often request one or more parameters be changed without changing any of the remaining parameters. CDO has learned how to accomplish this successfully with rapid turn-around times and minimal cost impact.

The experience gained by accommodating customer requests has produced a textbook of cause and effect combinations of laser components to accomplish almost any parameter change request. Understanding the relationships between component combinations provides valuable insight into lasing effects allowing designers to extend laser performance beyond what is currently available. This has led to several break through products, i.e. >150W average power 355 nm, >60W average power 6 ps 1064 nm, pulse lengths longer than 400 ns at 532 nm with average power >100W, >400W 532 nm with pulse lengths in the 100 ns range.

We describe and compare the performance of two types of compact, passively Q-switched Yb:YAG 1030nm lasers and their use for 257nm fourth harmonic generation (FHG). In the first implementation, an end-pumped Yb:YAG laser produced a 250μJ pulse train with an average power at 1030nm of 3.6W. Using a 10mm LBO crystal (70% doubling efficiency), followed by a 7mm BBO crystal (45% conversion efficiency), 1.1W at 257nm was generated (overall FHG efficiency of 30%). The second implementation was a side-pumped Q-switched Yb:YAG laser pumped by a 200W diode bar. A 10mm KTP crystal followed by a 6mm BBO crystal resulted a 15% FHG conversion efficiency. The UV emission was in a form of 1-5 Hz PRF, 2ms long burst of 0.2mJ pulses with a 30kHz intra-burst PRF. Within a 1.65ms emission window, an 11.5mJ burst at 257 nm was generated that had a maximum intra-burst power of 7W. This paper will address the merits of each approach for realizing a man-portable laser suitable for ultraviolet Raman explosives detection.

A frequency tripled, Nd:Glass laser has been constructed and installed at the Dynamic Compression Sector located at the Advanced Photon Source. This 100-J laser will be used to drive shocks in condensed matter which will then be interrogated by the facility x-ray beam. The laser is designed for reliable operation, utilizing proven designs for all major subsystems. A fiber front-end provides arbitrarily shaped pulses to the amplifier chain. A diode-pumped Nd:glass regenerative amplifier is followed by a four-pass, flashlamp- pumped rod amplifier. The regenerative amplifier produces up to 20 mJ with better than 1% RMS stability. The passively multiplexed four-pass amplifier produces up to 2 J. The final amplifier uses a 15-cm Nd:glass disk amplifier in a six-pass configuration. Over 200 J of infrared energy is produced by the disk amplifier. A KDP Type-II/Type-II frequency tripler configuration, utilizing a dual tripler, converts the 1053-nm laser output to a wavelength of 351 nm and the ultraviolet beam is image relayed to the target chamber. Output energy stability is better than 3%. Smoothing by Spectral Dispersion and polarization smoothing have been optimized to produce a highly uniform focal spot. A distributed phase plate and aspheric lens produce a farfield spot with a measured uniformity of 8.2% RMS. Custom control software collects all data and provides the operator an intuitive interface to operate and maintain the laser.

Nd:SYSO and Nd:CALYO lasers were demonstrated with hot band pumping at 914 nm for the first time. The output power achieved was 201 mW centered at 1078.0 nm with slope efficiency of 18.6% for Nd:SYSO and 154 mW output centered at 1074.9 nm with 8.6% slope efficiency for Nd:CALYO. This pumping approach could offer further power scaling possibility due to the strongly reduced quantum defect and consequently lower thermal lensing.

The main goal of this work was to investigate the influence of the temperature of the Er:YAG active medium on laser properties in eye-safe spectral region for three various pump wavelengths. The tested Er:YAG sample doped by 0.5% of Er³⁺ ions had a cylindrical shape with 25mm in length and 5mm in diameter. The absorption spectrum of the Er:YAG active medium in the range from 1400nm up to 1700nm for temperatures 80K and 300K was measured. The crystal was placed inside the vacuum chamber of a liquid nitrogen cooled cryostat. The temperature was controlled within the 80 - 340K temperature range. Three pump sources generating at 1535, 1452, and 1467nm were applied. The first one was flash lamp pumped Er:glass laser (repetition rate 0.5 Hz, pulse duration 1 ms, pulse energy 148 mJ). The further two sources were fiber coupled laser diodes (repetition rate 10 Hz, pulse duration 10 ms, maximum pulse energies 106mJ and 195 mJ). The semi-hemispherical laser resonator consisted of a pump curved mirror and output plan coupler with a reflectivity of 90% @ 1645 nm. The laser output characteristics were investigated in dependence on temperature of active medium for three laser pumping systems. The output energy has an optimum in dependence on active medium temperature and pump wavelengths. The maximal generated laser energies were 16.2mJ (90 K), 28.7mJ (120 K), and 33.2mJ (220 K), for pump wavelengths 1452 nm, 1467 nm, and 1535 nm, respectively.

We model output characteristics of the 1645 nm 8 mJ 10 ns 100 Hz Q-switched Er:YAG DPSSL. The laser is end pumped at a wavelength of 1532 nm. Fiber-coupled diode laser module was 10 nm FWHM, 12 W CW, 200 μm, NA 0.22. Various tapering of the active rod has been considered for 1 mm diameter, 20 mm long and 0.5% Er doping. We discuss the heat deposition process, the energy storage efficiency and the average power limitations for Q-switched regime of generation and amplification, and find the system scalable for the high power operation.

We demonstrate the high-gain of two double-pass Ho:YLF amplifiers with high-energy seed pulses injection via a modified population inversion Frantz-Nodvik model by numerical simulation. From the numerical simulation results, 26.2 mJ/1 kHz amplified pulses can be obtained by two double-pass amplifiers with 20 μJ/1 kHz, 40 nm (FWHM) bandwidth seed pulses injection. Due to ~1300 gain, the bandwidth of the amplified pulse decreases to about 3.5 nm (FWHM), corresponding to 466 fs pulse duration near 2 μm wavelength. Therefore, the spectrum shaping of seed pulses is induced to suppress the gain narrowing effect. Then, the pulses can be amplified to 22.8 mJ with a spectrum of 16 nm (FWHM), which supports 368 fs pulse duration near 2 μm by simulation.

We control the optical comb in Nd:YVO₄ mode-locked lasers with intracavity frequency doubling based on KTP crystals via changing the cavity length and its dispersion properties and achieve high-purity radiofrequency (RF) signals. The laser output wavelength (532 nm) is in the range of the molecular iodine absorption spectrum with narrow (1.5 kHz) homogeneously broadened lines. We propose to stabilize the two longitudinal modes on two narrow iodine absorption lines. The third derivative of the absorption line could be obtained by heterodyning the absorption signal with the third harmonic of the modulation signal. The resulting RF error signal could be used to stabilize two locked longitudinal modes separated by 1.37 GHz which results in stabilized beat note signal.

We report on Pr:SrF₂ single crystal laser operation at 639nm wavelength under blue laser diode pumping. The laser system was operated in the pulsed regime at 100 Hz repetition rate and 2 ms pulse duration. Using 3.5W InGaN laser diode as a pump source, 6mW of the mean output power at 639nm was extracted from the Pr:SrF₂ sample. The corresponding slope efficiency related to the absorbed mean power was 16.4 %.

The goal of this work was an investigation of the temperature influence (in range 77 - 300 K) on laser properties of Tm:SrF₂-CaF₂ solid-solution, which is suitable as a gain medium for generation of radiation at 1.8-2 μm. The tested Tm:SrF₂-CaF₂ sample (60 mol% CaF₂, 38 mol% SrF₂) was doped with 2 mol% of TmF₃. The diameter of the grown boule was 10 mm. The sample was cut and optically polished parallel to growing axis. The polished sample thickness was 8.5 mm. It was fixed in temperature controlled cupreous holder, placed inside vacuum chamber of the liquid nitrogen cryostat. A fiber coupled laser diode, operating in pulsed regime (10 ms pulse length, 10 Hz repetition rate) at wavelength 764 nm, was used for longitudinal sample pumping. The 142mm long semi-hemispherical laser cavity consisted of at pumping mirror (HR @ 1:8 - 2:0 μm, HT @ 0.77 μm) and curved (r = 150mm) output coupler with a reflectivity of ~ 92% @ 1:8 - 2:0 μm. From the results it follows that the temperature of the active medium has a strong infkuence on laser slope efficiency. The highest slope efficiency (42% in respect to absorbed power), obtained for temperature 77 K, was more than five times higher than slope efficiency for 300 K. The threshold decreased twice with the temperature lowering from 300 to 77 K. Laser output power amplitude 5.5W at wavelength 1856nm was reached for absorbed power 15.8W at 77 K.

The goal of this work was an investigation of the temperature influence (in range from 80 up to 320 K) on the laser properties of Yb:YAG/Cr:YAG Q-switched diode-pumped microchip laser. This laser was based on monolith crystal (diameter 3mm) which combines in one piece an active laser part (Yb:YAG crystal, 10 at.% Yb/Y, 3mm long) and saturable absorber (Cr:YAG crystal, 1.36mm long, initial transmission 90% @ 1031 nm). The laser resonator pump mirror (HT for pump radiation, HR for generated radiation) was directly deposited on the Yb:YAG monolith part. The output coupler with reflection 55% for the generated wavelength was placed on the Cr:YAG part. The microchip laser was placed in the temperature controlled cupreous holder inside vacuum chamber of the liquid nitrogen cryostat. For Yb:YAG part longitudinal pulsed pumping (pumping pulse length 2.5 ms, rep-rate 20 Hz, power amplitude 21W) a fibre coupled (core diameter 400 μm, NA= 0:22) laser diode, operating at wavelength 933 nm, was used. The microchip laser mean output power, pulse duration, repetition rate, emission wavelength, and laser beam profile were measured in dependence on temperature. The generated pulse length was in range from 2.2 ns to 1.1 ns (FWHM) with the minimum at 230 K. The single pulse energy was peaking (0.4 mJ) at 180 K. The highest peak power (325 kW) was obtained at 220 K. The highest pulse repetition rate (38 kHz) and output mean power (370mW) was reached for temperature 80 K.

We report on a diode pumped ultrafast amplifier based on Yb:CaF₂ delivering 32 mJ, at a repetition rate of up to 200 Hz, with a central wavelength of 1030nm. The pulses have spectral bandwidth of 5.5 nm, supporting a theoretical pulse duration of 250 fs, are compressed to 300 fs in a compressor based on reflection gratings with a transmission efficiency up to 89%. This laser source constitutes an ideal source for pumping nonlinear crystals through Optical Parametric Amplification or Optical rectification. It is also well adapted for seeding ultrafast high energy amplifiers based on Yb:YAG crystals

We demonstrate a pulse-bursting phenomenon in Yb:Er glass laser operating at 1.54 μm. Glass-ceramic material with a low value of saturation threshold based on Co²⁺:β-ZnSiO₄ nanocrystals was used as a passive gate for pulse-burst operation. The bursts of pulses were 1.5 ms long, each burst consisted of 40-55 pulses with 9-30 μJ energy per pulse and 0.2-3 μs pulse width. Bursting outputs arise via a coupling between slow switching arising via a slow pump modulation and fast pulsations resulting from Q-switch mechanism. We show that absorption cross-section strongly affects the mode of laser operation ranging from relaxation oscillations corresponding to low cross-section values to bursting and conventional Q-switch operation in the case of their higher values.

This work reports on a compact single-mode diode laser emitting at 633 nm based on an AlGaAs/AlGaInP structure with an integrated DBR surface grating. The micro-fabricated diode laser package includes optics for beam shaping, optical isolation and single-mode fiber coupling. The miniaturized optical isolator is based on cadmium manganese telluride, which provides a large Verdet constant and thus enables the realization of a compact Faraday rotator in the visible spectral range. We discuss the performance and the technological challenges for this approach. Furthermore, we present prospects towards the integration of atomic reference cells into compact laser systems. This would enable the realization of absolute frequency-stabilized diode lasers that could be used in quantum technology devices.

Temperature influence on spectroscopic characteristics is crucial for many aspects of laser engineering including output noise, single frequency oscillation, and thermal bistability. We report on the spectroscopic characterization of chromium and iron doped ZnSe gain element media at temperatures ranging from 77K to 389K. Heating of Cr:ZnSe resulted in the absorption peak shifting to a shorter wavelength from 1.806 μm at 77K to 1.753 μm at 389K. It also resulted in broadening of the absorption band from Δλ=260 cm^-1nm to Δλ=373 cm^-1nm and decreasing of the absorption cross section by 69%. Similar characterization was done for Fe:ZnSe laser material. The cooling of the Fe:ZnSe crystal from room temperature to 77K resulted in a 32% increase of the absorption coefficient at 2.94 μm which is usually used as a pump source. We also studied the absorption of the electrical free-carriers in n-type Al:ZnSe crystals in visible and mid- IR absorption spectral ranges. Diffusion of Al into ZnSe samples was achieved by annealing at 1000°C during 4 days in Al vapors. It was demonstrated that free-carriers absorption of Al:ZnSe samples with resistivity σ=100-150 Ω×cm resulted in an increase of the absorption coefficient at 2.4 μm up to 2.5 cm^-1.

We report on the passive Q-switching of a compact diode-side-pumped Er,Yb:glass laser by a novel saturable absorber (SA) based on transparent glass-ceramics (GC) containing Co²⁺Mg(Al,Ga)₂O₄ nanocrystals. To prepare the GC, an initial magnesium aluminosilicate glass doped with Ga₂O₃ containing 0.1 mol% CoO was synthesized by a conventional melt-quenching technique and heat-treated at 850–950 °C. The X-ray diffraction analysis of the GC confirmed the precipitation of Co²⁺Mg(Al,Ga)₂O₄ crystals with spinel structure (6-7 nm in size). Depending on the heat-treatment temperature, the saturation intensity for the GC measured at 1540 nm was in the 0.5...0.7 J/cm² range and the recovery time was in the 240...335 ns range. Using the SA based on GC prepared by the heat-treatment at 950 °C with an initial transmission of 84.7%, we generated stable Q-switched pulses 1.14 mJ in energy and 7.2 ns in duration. The peak power reached 160 kW, the repetition rate was 1 Hz and the laser wavelength was 1535 nm. The developed GCs are promising for Q-switching of erbium lasers emitting at 1.5-1.7 μm.

Absorption, stimulated-emission and gain cross-sections are determined for 3 at.% Tm:CaGdAlO₄. This crystal is employed in a microchip laser diode-pumped at 802 nm. In the continuous-wave (CW) regime, this laser generates 1.16 W at 1883-1893 nm with a slope efficiency of 32% with respect to the absorbed pump power. Using a special "bandpass" output coupler, vibronic CW laser operation up to 2043 nm is achieved. For passive Q-switching of the Tm:CaGdAlO₄ laser-saturable absorbers (SAs) based on CVD-grown graphene and randomly-oriented arc-discharge single-walled carbon nanotubes (SWCNTs) in a PMMA film. The SWCNT-SA demonstrates superior performance. The laser produced a maximum average output power of 245 mW at 1844 nm with a slope efficiency of 8%. The latter corresponds to a pulse energy and duration of 6 μJ and 138 ns, respectively, at a repetition rate of 41 kHz. Using the graphene-SA, 2.8 μJ, 490 ns pulses are obtained at a repetition rate of 86 kHz.