This PDF file contains the front matter associated with SPIE Proceedings Volume 8898, including the Title Page, Copyright Information, Table of Contents, and the Conference Committee listing.

Quantum cascade laser (QCL) systems are mature and at the vanguard of a new generation of products that support military applications such as Infrared Countermeasures (IRCM) and targeting. The demanding product requirements for aircraft platforms that include reduced size, weight, power consumption and cost (SWaP-C) extends to portable, battery powered handheld products. QCL technology operates throughout the mid-wave (MWIR) and long-wave (LWIR) infrared to provide new capabilities that leverage existing thermal imaging cameras. In addition to their suitability for aircraft platforms, QCL products are a natural fit to meet operator demands for small, lightweight pointer and beacon capabilities. Field-testing of high power, lightweight, battery operated devices has demonstrated their utility across a range of air and ground applications. This talk will present an overview of QCL technology and the Defense and Security products and capabilities that are enabled by it. This talk will also provide an overview of the extensive environmental and performance testing associated with products based on QCL technology.

The quantum-cascade lasers (QCL), first demonstrated in 1994, has since been developed into a mature laser emitting within nearly the entire spectrum from 2.6 to 250 μm, particular within the mid-infrared part of the spectrum from 3 to 12 μm for applications in gas sensing for security, environmental and medical uses, as well as for defense-related IR countermeasures. The QCL heterostructure is generally based on the InGaAs/InAlAs system lattice-matched to InP or on its strain-compensated extension to maximize the conduction band discontinuity between well and barrier material. A refinement is the use of mixed-height barriers to engineer the interface scattering of the different levels involved in the lasing process. This design strategy appears to be universally applicable, across the entire range of QCL emission wavelengths. By using low barriers where the upper laser state has its maximum probability and high barriers where the lower laser state has its maximal probability in strain-compensated designs for short wavelength emission, the lifetime of the upper laser state can be increased, while decreasing the lifetime of the lower laser state. First realizations of this design result in J_th = 1.7kA/cm² at 300 K, slope efficiency η = 1.4 W/A, T₀ = 175 K, and T₁ = 550 K. Further increases in efficiency can be achieved through designs in which parasitic states near the upper laser level are separated from it, either energetically or oscillator strength. These states may be associated with other k values, or with higher-lying subbands.

High-power diode lasers are highly efficient sources of optical energy for industrial and defense applications, either directly or as pump sources for solid state or fiber lasers. We review here how advances in diode laser design and device technology have enabled the performance to be continuously improved. An overview is presented of recent progress at JENOPTIK in the development of commercial diode lasers optimized for peak performance, robust high-yield manufacture and long lifetimes. These diode lasers are tailored to simultaneously operate with reduced vertical carrier leakage, low thermal and electrical resistance and low optical losses. In this way, the highest electro-optical efficiencies are sustained to high currents. For example, 940-nm bars with high fill factor are shown to deliver continuous wave (CW) output powers of 280 W with conversion efficiency of < 60%. These bars have a vertical far field angle with 95% power content of just 40°. In addition, 955-nm single emitters with 90μm stripe width deliver 12 W CW output with power conversion efficiency at the operating point of 69%. In parallel, the Ferdinand-Braun-Institut (FBH) is working to enable the next generation of high power diode lasers, by determining the key limitations to performance and by pioneering new technologies to address these limits. An overview of recent studies at the FBH will therefore also be presented. Examples will include structures with further reduced far field angles, higher lateral beam quality and increased peak power and efficiency. Prospects for further performance improvement will be discussed.

Mid-infrared sources are a key enabling technology for various applications such as remote chemical sensing, defense communications and countermeasures, and bio-photonic diagnostics and therapeutics. Conventional mid-IR sources include optical parametric amplifiers, quantum cascade lasers, synchrotron and free electron lasers. An all-fiber approach to generate a high power, single mode beam with extremely wide (1μm-5μm) and simultaneous wavelength coverage has significant advantages in terms of reliability (no moving parts or alignment), room temperature operation, size, weight, and power efficiency. Here, we report single mode, high power extended wavelength coverage (1μm to 5μm) supercontinuum generation using a tellurite-based dispersion managed nonlinear fiber and an all-fiber based short pulse (20 ps), single mode pump source. We have developed this mid IR supercontinuum source based on highly purified solid-core tellurite glass fibers that are waveguide engineered for dispersion-zero matching with Tm-doped pulsed fiber laser pumps. The conversion efficiency from 1922nm pump to mid IR (2μm-5μm) supercontinuum is greater than 30%, and approaching 60% for the full spectrum. We have achieved > 1.2W covering from 1μm to 5μm with 2W of pump. In particular, the wavelength region above 4μm has been difficult to cover with supercontinuum sources based on ZBLAN or chalcogenide fibers. In contrast to that, our nonlinear tellurite fibers have a wider transparency window free of unwanted absorption, and are highly suited for extending the long wavelength emission above 4μm. We achieve spectral power density at 4.1μm already exceeding 0.2mW/nm and with potential for higher by scaling of pump power.

The paper describes two laser prototypes devoted to the jamming or the damaging of heat-seeking missiles for use in field trials. The semi-ruggedized compact jamming prototype is based either on an OP-GaAs or a ZnGeP₂ (ZGP) OPO directly pumped by a 2.09 μm Q-switched Ho³⁺:YAG laser with up to 20 W of average power around 2.1 μm and an M² of less than 1.1. For jamming in band II, up to 3.5 W of average power were obtained and repetition rates from 20 kHz to 100 kHz were achieved. For 3.5 W of averaged output power, the M² of the signal and idler beams were estimated to be less than 1.2. The destruction laser consists of a Ho³⁺:LLF MOPA laser system which is used to pump a ZGP OPO. The maximum pulse energy of the Ho³⁺:LLF MOPA was 82 mJ at a repetition rate of 100 Hz. The pump beam quality was measured to M²x = 1.01 and M²y = 1.03 at a wavelength of 2053 nm. The total 3-5 μm energy obtained for destruction was 23.4 mJ, corresponding to an optical-to-optical conversion efficiency of 51 %. The M² values of the signal were M²x = 1.81 and M²y = 1.98. The M² values of the corresponding idler beam were M²x = 1.91 and M²y = 1.94, respectively. ISL is also currently working on new laser sources and non linear conversion setups for proposing new versions that should be more compact, more efficient and more integrable.

Pulsed erbium lasers operating in the eye-safe spectral band around 1.6 μm can find numerous defense and civil applications that often require high pulse energy, reasonable pulse repetition frequency (100 Hz), specific wavelength and last not least very good beam quality. Even though resonant pumping shifts a significant part of thermal load from gain medium to pumping diodes, fulfillment of all these requirements is still rather difficult, what can be attributed to spectroscopic limitations of erbium doped crystalline gain media as well as to low spatial brightness of available InP pumping diodes. In the paper we report recent breakthroughs in the field of pulsed erbium lasers. Main difficulties towards multi-ten-mJ output from systems based on the TIR (total- internal-reflection) pump scheme arrangement will be defined and solutions proposed. We also demonstrate for the first time to the best of our knowledge a Q-switched Er³⁺:YAG laser operating at the repetition rate of 100 Hz with truly diffraction limited beam quality (M² =1) and pulse energy of up to 24mJ (damage free).

Recent computational work to optimize the output spectrum of As₂Se₃ and As₂S₃ chalcogenide photonic crystal fibers is summarized. Design procedures for both maximizing the output bandwidth and maximizing the power spectral density in the 3-5 μm range are described. With a 2.5μm pulsed pump source, it is possible to obtain a bandwidth of 4 μm in As₂Se₃ fibers, and, with a 2.0 μm pulsed pump source, it is possible to shift 25% of the input power to the 3-5 μm range in As₂S₃. With a source at 2.8 μm, it is possible to obtain an output power spectral density in As₂S₃ that extends between 2.5 μm and 6.5 μm. The single-shot output power spectral density exhibits rapid 10-20 dB fluctuations as the wavelength varies. Moreover, when the pump pulse duration and peak power vary, there are substantial shot-to-shot fluctuations in both the output bandwidth and spectral power density. With 10% variations of the pump pulse duration and peak power, the output spectrum averaged over 5000 shots exhibits less than 5 dB of variation in the intermediate wavelength range of 2.8-4.6 μm and has a reproducible bandwidth of slightly less than 3 μm. The average over 5000 shots yields the same output spectrum with 10⁶ shots, indicating that the spectrum has converged.

Mid Infrared (MIR) fiber optics has gained a great deal of interest over the past several decades. Applications range from passive transport to fiber lasers and nonlinear applications. These fibers have found use in a wide array of fields such as sensing, military countermeasures, scientific instrumentation, medical instrumentation, and in research laboratories. As with all fiber development there is a continual urge to seek better performance characteristics including transparency over a wide wavelength range, corrosion resistance, high power handling and low loss. We report on development of tellurite glass fibers displaying exceptionally high performance for various applications including wide band, low loss passive transport for mid IR, high efficiency, wide wavelength range and high power supercontinuum generation from visible to MIR wavelengths >4.5um, and active doping in fibers for use in laser cooling. High performance in each of these areas of interest has been brought about by development of a stable glass formulation and advanced processing techniques to remove impurities ions, entrapped hydroxyl, and scatter centers which allow fibers to be made with exceptionally low losses ~0.2dB/m.

We have investigated the possibilities of using Computational Fluid Dynamics (CFD) simulations to characterize the impact of refractive index fluctuations in a jet engine plume on Directed InfraRed CounterMeasure (DIRCM) system performance. The jet plume was modelled using both Reynolds-Averaged Navier-Stokes (RANS) and Large Eddy Simulation (LES) formulations of Navier-Stokes equations. The RANS calculations provided a time-averaged description of the refractive index and the turbulence strength. The more computationally intense LES model provided time resolved data on large scale turbulent eddies within the engine plume. The smaller structures are assumed to be isotropic and are modelled implicitly to reduce the computational demands to levels feasible for current computational hardware. The refractive index data from the CFD calculations was integrated along the optical propagation path to produce phase screens. For RANS data this approach provided time averaged aberrations, whereas for LES data the temporal variation of low spatial frequency aberrations were available for a short time sequence. Modal descriptions of the phase screens were investigated to allow study of temporal variation at longer time scales. Alternatively the structure parameter (C_n²) can be estimated and used to provide order of magnitude approximations for the optical effects. The generated phase screens were used to calculate laser beam system level quality parameters including beam wander, fidelity ratio and power-in-bucket. The paper focuses on method development, but examples of a jet plume simulation showing that the engine plume turbulence has a significant impact on DIRCM system functionality are presented.

The ultraviolet (UV) band of the electromagnetic spectrum has potential as a host medium for the operation of guided weapons. Unlike in the infrared (IR), a target which is propelled by an air breathing jet engine generates no detectable radiation in the UV band, and is opaque to the background UV produced by the Sun. In theory the blocking of UV radiation from the sun causes a detectable ‘negative contrast’ between the target and the background. In order to determine the outcome of engagement scenarios between airborne platforms and guided weapon systems that utilise a guard channel operating in the UV, it is necessary to accurately model background UV levels. This paper presents a comparison between the atmospheric modelling code moderate resolution atmospheric transmission (MODTRAN®5) and measured data. The spectral irradiance levels generated by the MODTRAN®5 code are compared to those of the World Ozone and Ultraviolet Data Centre (WOUDC ) database, for various global positions and times of year. Radiance data collected at the Defence Academy of the United Kingdom (Shrivenham, England) for various observer geometries is also compared to that generated by the MODTRAN®5 code.

Optical distraction is likely one of the original and simpler optical countermeasure concepts with a technology history dating back to the 1800’s. The objective is to distract or suppress either equipment or personnel with optical radiation from a safe distance. This paper is intended to review and expand on the concepts presented at the 2012 SPIE Security and Defense meeting; “Non-Lethal Optical Interruption (Dazzling): Technology, Devices, and Scenarios”. The information that follows will focus primarily on the technology and techniques associated with the safe laser dazzling of personnel. Key product design guidelines will be highlighted and reviewed. Recent advances in laser technology and their associated impact on hand-held devices will also be discussed. Finally, the author will offer his opinion on the growth rate of military and non-military markets for laser dazzlers.

A growing problem for the Police and Security Forces has been to prevent potentially hostile individuals to pass a checkpoint, without using lethatl violence. Therefore the question has been if there is a laser or any other strong light source that could be used as a warning and dazzling device, without lethal or long term effects. To investigate the possibilities a field trial has been performed at a motor-racing track. A green CW laser with an irradiance on the eye of maximum 0.5 MPE, as defined by ICNIRP [1] and the ANZI standard [2], was used as a dazzle source. Ten drivers have been driving with dipped headlights through a course of three lines with orange cones. In every line there has been only one gate wide enough to pass without hitting the cones. The time through the course, the choice of gates and the number of cones hit have been measured. For every second trial drive through the track, the driver was exposed to the laser dazzler. The background illuminances ranged from a thousand lux in daylight to about ten millilux in darkness. The protective effect of the sun-visor of the car was investigated. The drives visual system was carefully examined before and after experimental driving and a few weeks after the experimental driving to verify that no pathological effects, that could potentially be induced by the laser exposure, pre-existed or occurred after the laser exposure. An analysis of variance for a within subjects design has been used for evaluation. It was found that green laser light can have an obvious warning effect in daylight. Dazzling does reduce the drivers ability to make judgments and manouver the car in twilight and darkness. A sun-visor can reduce the glare and give the driver an improved control, but that perception can be unjustified. No damage to the visual system was observed.

In this study we investigated the effectiveness of high power illuminators that are intended to be used as warning devices or non-lethal weapons to deny car drivers their view on the outside world through windscreens. The test is based on a measurement of the amount of veiling glare resulting when a high intensity light source hits a windscreen. We measured the veiling glare for new, used and colored windscreens that were either clean or dirty. We found no significant difference between the scatter function for new, used and colored windows. The scatter function for dirty windscreens is a factor 14 larger than for clean windscreens. We also derived a method to assess the impact of the illumination of a windscreen by a high intensity light source on driving behavior. The method is based on the assumption that drivers reduce their speed when veiling glare reduces the detection distance of objects on the road. Estimates of respectively the detection distance for objects on the road and the maximum safe driving speed are directly related to operational requirements, and can therefore be used to assess the operational effectiveness of high intensity light sources as powerful warning devices or non-lethal weapons.

The proliferation of a wide variety of weapons including Anti-Aircraft Artillery (AAA), rockets, and small arms presents a substantial threat to both military and civilian aircraft. To address this ever-present threat, Northrop Grumman has assessed unguided threat phenomenology to understand the underlying physical principles for detection. These principles, based upon threat transit through the atmosphere, exploit a simple phenomenon universal to all objects moving through an atmosphere comprised of gaseous media to detect and track the threat in the presence of background and clutter. Threat detection has rapidly become a crucial component of aircraft survivability systems that provide situational awareness to the crew. It is particularly important to platforms which may spend a majority of their time at low altitudes and within the effective range of a large variety of weapons. Detection of these threats presents a unique challenge as this class of threat typically has a dim signature coupled with a short duration. Correct identification of each of the threat components (muzzle flash and projectile) is important to determine trajectory and intent while minimizing false alarms and maintaining a high detection probability in all environments.

Detection and localisation of optical assemblies used for weapon guidance or sniper rifle scopes has attracted interest for security and military applications. Typically a laser system is used to interrogate a scene of interest and the retro-reflected radiation is detected. Different system approaches for area coverage can be realised ranging from flood illumination to step-and-stare or continuous scanning schemes. Independently of the chosen approach target discrimination is a crucial issue, particularly if a complex scene such as in an urban environment and autonomous operation is considered. In this work target discrimination strategies in optics detection are discussed. Typical parameters affecting the reflected laser radiation from the target are the wavelength, polarisation properties, temporal effects and the range resolution. Knowledge about the target characteristics is important to predict the target discrimination capability. Two different systems were used to investigate polarisation properties and range resolution information from targets including e.g. road signs, optical reflexes, rifle sights and optical references. The experimental results and implications on target discrimination will be discussed. If autonomous operation is required target discrimination becomes critical in order to reduce the number of false alarms.

There are many weapon systems in which a human operator acquires a target, tracks it and designates it. Optical countermeasures against this type of systems deny the operator the possibility to fulfill this visual task. We describe the different effects that result from stimulation of the human visual system with high intensity (visible) light, and the associated potential operational impact. Of practical use are flash blindness, where an intense flash of light produces a temporary “blind-spot” in (part of) the visual field, flicker distraction, where strong intensity and/or color changes at a discomfortable frequency are produced, and disability glare where a source of light leads to contrast reduction. Hence there are three possibilities to disrupt the visual task of an operator with optical countermeasures such as flares or lasers or a combination of these; namely, by an intense flash of light, by an annoying light flicker or by a glare source. A variety of flares for this purpose is now available or under development: high intensity flash flares, continuous burning flares or strobe flares which have an oscillating intensity. The use of flare arrays seems particularly promising as an optical countermeasure. Lasers are particularly suited to interfere with human vision, because they can easily be varied in intensity, color and size, but they have to be directed at the (human) target, and issues like pointing and eye-safety have to be taken into account. Here we discuss the design issues and the operational impact of optical countermeasures against human operators.

We will present the setup of a 50 kW Laser Weapon Demonstrator (LWD) and results achieved with this system. The LWD is a ground based Air Defence system consisting of a Skyguard sensor unit for target acquisition and two laser equipped weapon turrets. The weapon turrets used are standard air defence turrets of Rheinmetall Air Defence which were equipped with several 10 kW Laser Weapon Modules (LWM). Each LWM consists of one 10 kW fiber laser and a beam forming unit (BFU). Commercial of the shelf fiber laser were modified for our defence applications. The BFU providing diffraction limited beam focusing, target imaging and fine tracking of the target was developed. The LWD was tested in a firing campaign at Rheinmetall test ground in Switzerland. All laser beams of both weapon turrets were superimposed on stationary and dynamic targets. Test results of the LWD for the scenarios Air Defence and C-RAMM (counter rockets, artillery, mortar and missiles) will be presented. An outlook for the next development stage towards a 100 kW class laser weapon on RWM will be given.

In this paper, we illustrate the latest advancement on the eye-safe Solid State Heat-Capacity Laser (SSHCL) investigated for the development of medium and high energy laser sources. Nearly all the solid-state lasers considered for defence applications in the range of 10 kW up to over 100 kW emit at a wavelength of 1.03 μm– 1.06 μm. Therefore, we perform research on an alternative emitting around 1.6 μm, which unites many advantages in use (robustness, a simple technology, flexibility in volume and weight). The heat-capacity principle, in which the laser material is cooled only after the laser action has ended, results in low temperature gradients in the laser medium, leading to a good beam quality and a high performance. Previous investigations on Er³⁺:YAG SSHCL demonstrated the scalability of the heat-capacity laser principle and up to 4.65 kW and 440 J in less than 800 ms have been achieved, representing the current world record in eye-safe diode-pumped solid-state laser technology. Optical-to-optical efficiencies of over 41% and slope efficiencies of over 51% are obtained with respect to the incident pump power. In this report we further investigate the possibility of compensating any parasitic residual heating. Indeed, it has been shown that the optimal laser operation is directly coupled with the intensity distribution of the laser mode inside the laser medium. The ideal resonator configurations are those which allow an extraction of the laser energy as homogeneous as possible. Using an intra-cavity adaptive optics system beams with phase fronts as flat as possible, on the order of less that 1/10 of the wavelength for each of the considered Zernike polynomials have been generated, and the shot duration has been lengthened by 50%. The influence of the crystal geometry on the pump distribution homogeneity and the possible ways for maximizing the extraction efficiency are investigated.

This paper highlights the latest advances of disk laser technology at TRUMPF. The disk laser combines unique properties, especially high output brilliance (at the lowest pump brilliance requirements of any high power platform), power scalability and insensitivity to back reflections. In the latest generation of CW disk lasers, 6kW are extracted from one disk in an industrial product at beam qualities suitable for cutting and welding. Laboratory results with up to 4 kW laser power at nearly diffraction limited beam quality (M²=1.38) and 8 kW with a beam quality of 3 mm mrad from a single disk and even higher output power levels with lower beam quality will be presented. Finally, results of a frequency doubled CW disk laser will be shown.

In this paper, we propose and demonstrate a single-element beam shaper for transforming a fiber laser beam into a near-diffraction-limited dark hollow beam. The single-element beam shaper contains two aspheric surfaces. One aspheric surface redistributes the intensity distribution of the incident beam and the other re-collimates the output beam. The distributions of these surfaces are derived by the energy conservation condition and constant optical path length condition. The comparisons between the single-element beam shapers based on different working principles are analyzed in detail. Based on the Fourier optics and Geometrical optics, the near field, far field intensity distribution and wavefront distribution of the output beam are studied in detail. The influences of deviations of the beam shape from the assumed value, distance between dual aspheric surfaces and optical alignment errors are studied in detail. Results show that the shaping errors of the single-element Keplerian beam shaping system are much smaller than that of the single-element Galilean beam shaping system. The wavefront distribution of the output beam is maintained. The dark hollow intensity distribution of the output beam can be maintained for a certain distance in the near field and the far filed intensity distribution exhibits airy disk pattern.

Over the last years high-power diode lasers in the wavelength window between 1.8μm and 3.0μm have demonstrated impressive characteristics in terms of output power, beam quality and efficiency. This facilitates the realization of compact and efficient light sources for use in the field of infrared countermeasures (IRCM), optically pumped semiconductor lasers emitting in the 2-4μm regime, low probability of intercept communication links, and trace gas analysis. The small size of a diode laser chip of typically less than a square millimeter allows for the fabrication of compact scalable laser modules with output powers of up to 140W. We will present results on MBE grown (AlGaIn)(AsSb) quantum-well diode laser single emitters and bars emitting between 1.8μm and 3.0μm. Different epitaxial and resonator designs have been investigated in cw and pulsed mode in order to meet industrial needs of high wall-plug and fiber-coupling efficiencies. More than 30% maximum wall-plug efficiency in cw operation for single emitters and laser bars has been reached together with output powers for single emitters of 2W (cw) and 9W (pulsed). The single emitters and bars are all suitable for fiber coupling. For a 1-bar module typical coupling efficiencies between 70% and 80% have been established for 400μm core fibers. In terms of output power, an AuSn soldered laser stack built of 10x 20% fill factor bars emitting at 1908nm, results in a record value of 140W at 58A in cw condition.

Alkali vapor lasers are under extensive research and development during the past decade because of their potential for scaling to high powers while maintaining a good beam quality. Also, a possibility of using efficient diode lasers for pumping alkali vapor promises high total wall plug efficiency for a Diode Pumped Alkali Laser (DPAL). Since the first DPAL demonstration with output power of 130 mW in 2005¹, a significant progress in this field was achieved. The output power of about 1 kW in continuous wave (CW) operation with optical efficiency close to 50% was recently demonstrated for a Cs DPAL². Also, the DPALs based on other alkali metals (Rubidium and Potassium) were demonstrated^3,4 . In spite of these significant achievements, there are still several problems in DPAL power scaling exist that must be addressed. Among them are the thermal⁵ and photoionization⁶ issues that become important even at power level about several tens of watts. In this paper we present a historical review of the alkali laser research and development, discuss the most important achievements and future perspectives in this field of research.

Kinetic and fluid dynamic processes in diode pumped alkali lasers (DPALs) are analyzed in detail using a semianalytical model, applicable to both static and flowing-gas devices. The model takes into account effects of temperature rise, excitation of neutral alkali atoms to high lying electronic states and their losses due to ionization and chemical reactions, resulting in a decrease of the pump absorption, slope efficiency and lasing power. Effects of natural convection in static DPALs are also taken into account. The model is applied to Cs DPALs and the results are in good agreement with measurements in a static [B.V. Zhdanov, J. Sell and R.J. Knize, Electron. Lett. 44, 582 (2008)] and 1-kW flowing-gas [A.V. Bogachev et al., Quantum Electron. 42, 95 (2012)] DPALs. It predicts the dependence of power on the flow velocity in flowing-gas DPALs and on the buffer gas composition. The maximum values of the laser power can be substantially increased by optimization of the flowing-gas DPAL parameters. In particular for the aforementioned 1 kW DPAL, 6 kW maximum power is achievable just by increasing the pump power and the temperature of the wall and the gas at the flow inlet (resulting in increase of the alkali saturated vapor density). Dependence of the lasing power on the pump power is non-monotonic: the power first increases, achieves its maximum and then decreases. The decrease of the lasing power with increasing pump power at large values of the latter is due to the rise of the aforementioned losses of the alkali atoms as a result of ionization. Work in progress applying two-dimensional computational fluid dynamics modeling of flowing-gas DPALs is also reported.

We explore the feasibility of supersonic operation of diode pumped alkali lasers (DPALs) applying model calculations. The power and efficiency of Cs and K atoms DPALs are estimated based on a semi-analytical model previously used for studying static and subsonic flow DPALs. The operation of supersonic lasers is compared with that measured and modeled in subsonic lasers. The maximum power of supersonic Cs and K lasers is found to be higher than that of subsonic lasers with the same resonator and alkali density at the laser inlet by 25% and 70%, respectively. These results indicate that for scaling-up the power of DPALs, supersonic expansion should be considered. Work in progress applying three-dimensional computational fluid dynamics modeling of supersonic DPALs is also reported.

A review of studies fulfilled at the Lebedev Institute in collaboration with the Moscow State University and Institute of Atmospheric Optics in Tomsk (Siberia) on influence of various characteristics of ultrashort laser pulse on plasma channels formed under its filamentation is presented. Filamentation of high-power laser pulses with wavefront controlled by a deformable mirror, with cross-sections spatially formed by various diaphragms and with different wavelengths was experimentally and numerically studied. An application of plasma channels formed due to filamentation of ultrashort laser pulse including a train of such pulses for triggering and guiding electric discharge is discussed.