This PDF file contains the front matter associated with SPIE Proceedings Volume 9251, including the Title Page, Copyright information, Table of Contents, Invited Panel Discussion, and Conference Committee listing.

Conventional anti-aircraft infrared seekers all operate on the principle of detecting the position of a IR source by modulating the FOV to encode the track of the target. This is a fundamental susceptibility of this class of seeker that renders them vulnerable to laser jamming. There are several DIRCM systems available that meet these requirements and provide a high degree of protection against reticle seekers. The latest generation of IR seekers use imaging technology that discriminates the target position in an essentially different manner. This class of seeker is not susceptible to DIRCM jamming. This paper examines the effectiveness of laser jamming against imaging seekers to derive requirements for laser countermeasures. Imaging seekers processing techniques that can be used to track the target and reject countermeasures are entirely defined by the on-board software of the seeker. Imaging seekers may be vulnerable to higher power laser jamming. The effect of laser dazzle appears to degrade the image quality. However, actual scatter levels can be modelled and it can be shown that usable information is still available to the seeker under dazzle. If neither decoy expendables nor dazzle lasers are expected to be effective against imaging seekers then the logical next step is to increase the laser power to produce damage. Estimates are provided to indicate the laser power levels that would be required against an imaging seeker focal plane. Although it is possible to design seekers that are hardened against laser damage, it is not clear that such designs are practical.

This paper discusses the advanced and novel technologies and underlying systems capabilities that Selex ES has applied during the development, test and evaluation of the twin head Miysis DIRCM System in order to ensure that it provides the requisite levels of protection against the latest, sophisticated all-aspect IR MANPADS. The importance of key performance parameters, including the fundamental need for “spherical” coverage, rapid time to energy-on-target, laser tracking performance and radiant intensity on seeker dome is covered. It also addresses the approach necessary to ensure that the equipment is suited to all air platforms from the smallest helicopters to large transports, while also ensuring that it achieves an inherent high reliability and an ease of manufacture and repair such that a step change in through-life cost in comparison to previous generation systems can be achieved. The benefits and issues associated with open architecture design are also considered. Finally, the need for extensive test and evaluation at every stage, including simulation, laboratory testing, platform and target dynamic testing in a System Integration Laboratory (SIL), flight trial, missile live-fire, environmental testing and reliability testing is also described.

The use of lasers for Electronic Warfare applications will be discussed and reviewed. Specific examples of deployed EW systems which include lasers will be presented along with a discussion of their most salient features.

Quantum cascade lasers can be designed to emit at any desired wavelength in the mid-infrared. When the optical output power of a single quantum cascade laser is too low, the beams of different lasers can be combined, e.g. by incoherent aperture beam combining. For incoherent aperture beam combining the laser beams are arranged side by side on the aperture of the (multi-) laser system and combine in the far field. The technique is neither limited to any number of lasers nor to any laser characteristics. We investigated incoherent aperture beam combining of quantum cascade laser beams in experiment and simulations at different distances from the laser aperture. We present results of combining laser sources of different wavelengths and demonstrate advantages of various beam arrangements.

3~5μm mid-infrared laser has many important applications, such as gas detection, spectral analysis, remote sensing, medical treatment, and also in the military laser radar, infrared countermine, and so on. Optical parametric oscillator (OPO) is an efficient way to generate laser in this wavelength range, which has attracted the eyes of many people. In this paper, the recent development of mid-infrared OPO is overviewed. Meanwhile, detailed introduction on our recent work is given. Maximum idler output power of 34.2W at center wavelength of 3.35μm was obtained, to our knowledge, which is the new power record of the international public reporting for the continue-wave (CW) mid-infrared OPO. It is worth mentioning that the pump source, the quasi single-frequency (SF) narrow line width fiber laser, was also developed by our groups. According to the current status of research, some solutions is proposed in order to achieve higher power, narrower line width, and compact volume mid-infrared OPO in a wide tunable range.

This paper describes new laser sources and non linear conversion setups for 2 μm and mid-IR generation based on fiber technologies developed at ISL. Especially for jamming heat-seeking missiles, these novel designs allow to propose future compact, efficient and integrable laser systems. The specialty of the ISL technology lies in the use of single 2 μm fiber laser oscillators, which deliver the full output peak power to pump optical parametric oscillators or nonlinear fibers. No multi-stage amplifiers at 2 μm or 1.55 μm are necessary to efficiently pump non linear converters to obtained useful energies in the mid-infrared spectral range. This technology leads to efficient, simple and promising setups to be implemented in flying platforms. The best results achieved in continuous-wave (CW), Q-switched (QS) and mode-locked (ML) regimes with fiber lasers based on Tm³⁺-doped and Tm3+,Ho³⁺-codoped fibers are presented. Up to 70 W of average power was achieved around 2 μm with a Tm³⁺-doped fiber in CW regime. In ML regimes, at a repetition rate of 66 MHz, 50 W of average power was reached. In QS regime, up to 32 W of average power was generated around 2 μm with a polarization maintaining Tm³⁺-doped fiber at a repetition rate of 40 kHz. With a Tm³⁺,Ho³⁺-codoped fiber, up to 25 W of average power was obtained around 2070 nm in Q-switched regime. For example at 50 kHz, the pulse duration was around 50 ns at the maximum output power. The M² was estimated to be less than 1.2. The emission from QS fiber lasers was used to directly pump OP-GaAs and ZGP OPOs. For example, in band II, up to 6.5 W of averaged power was recently obtained from a ZGP OPO pumped by a Tm³⁺-doped fiber laser. At 40 kHz repetition rate, the pulse duration was around 65 ns at the maximum output power. For 3 W of averaged output power, the M² of the signal beam was estimated to be less than 2.1 and less than 2.4 for the idler beam. Using a mode-locked Tm³⁺-doped fiber laser to pump a ZBLAN fiber at an injection efficiency of ~60%, an overall supercontinuum power of up to 2.2 W from a pump power of 5.4 W was achieved. The power above 2650 nm was 0.7 W.

We present a high energy infrared laser source where a Tm:fiber laser is used to pump a high-energy 2-μm cryogenically cooled Ho:YLF laser. We have achieved 550 mJ of output energy at 2.05 μm, and through non-linear conversion in ZnGeP2 generated 200 mJ in the 3-5-μm range. Using a numerical simulation tool we have also investigated a setup which should generate more than 70 mJ in the 8-12-μm range. The conversion stage uses a master-oscillator-power-amplifier architecture to enable high conversion efficiency and good beam quality.

In this paper, we model the performance of a device with a simple architecture for high-power mid-wave infrared beam generation at a wavelength of 3.8 microns. We believe that this device can be used as an efficient frequency converter for an infrared countermeasure source. The device is a seeded idler efficiency-enhanced optical parametric generator (IEE-OPG) based on an aperiodically poled MgO-doped LiNbO3 (APMgLN) grating pumped by a high-repetition rate nanosecond-pulsed 1064-nm laser and seeded by a low-power 1478-nm distributed feedback diode laser. In the IEE-OPG, two optical parametric amplification (OPA) processes, OPA-1 and OPA-2, are simultaneously phase matched in a single APMgLN grating. The signal at 1478 nm is amplified and the idler at 3800 nm is generated as a result of OPA-1, the signal acts as the pump for OPA-2 and the conversion efficiency of the idler is enhanced as a result of OPA-2. Also, a difference-frequency beam at 2418 nm is generated. We characterized the device performance using a realistic model that takes the diffraction of the beams into account. We designed multiple aperiodic gratings with varying relative strengths of OPA-1 and OPA-2. For various crystal lengths, optimum relative strengths of the two processes and input pump power levels for achieving the maximum mid-wave infrared conversion efficiency and output power are determined. Efficiency-enhanced mid-wave infrared beam generating optical parametric oscillators (OPOs) based on AP- MgLN gratings were reported before. However, no attempt was made for the optimization of the relative strengths of the simultaneously phase-matched processes in these devices. Our model calculations show that it is possible to reach and exceed the mid-wave infrared conversion efficiencies of these OPOs by correctly choosing the design parameters of the seeded OPGs based on relatively long APMgLN gratings.

Lithium niobate (LN) is commonly used as an electro optic (EO) Q-switch material in infrared targeting lasers because of its relatively low voltage requirements and low cost compared to other crystals. A common challenge is maintaining good performance at the sub-freezing temperatures often experienced during flight. Dropping to low temperature causes a pyro-electric charge buildup on the optical faces that leads to birefringence non-uniformity and depolarization resulting in poor hold-off and premature lasing. The most common solution has been to use radioactive americium to ionize the air around the crystal and bleed off the charge, but the radioactive material requires handling and disposal procedures that can be problematic. We have developed a superior solution that is now being implemented by multiple defense system suppliers. By applying a low level thermo-chemical reduction to the LN crystal optical faces we induce a small conductivity that allows pyro-charges to dissipate. As the material gets more heavily treated, the capacity to dissipate charges improves, but the corresponding optical absorption also increases, causing insertion loss. Even though typical high gain targeting laser systems can tolerate a few percent of added loss, the thermo-chemical processing needs to be carefully optimized. We describe the results of our process optimization to minimize the insertion loss while still giving effective charge dissipation. Treatment is performed at temperatures below 500°C and a conductivity layer less than 0.5mm in depth is created that is uniform across the optical aperture. Because the conductivity is thermally activated, the charge dissipation is less effective at low temperature, and characterization needs to be performed at cold temperatures. The trade-off between optical insertion loss and potential depolarization due to low temperature operation is discussed and experimental results on the temperature dependence of the dissipation time and the optical loss are reported.

Despite the advent of remotely operated and autonomous targeting systems, human (direct) vision is still critical for the successful performance of many tasks on the battlefield. Since high intensity light sources have the potential to generate a variety of disturbing visual effects, ranging from short-term disruption to lasting eye damage, they may offer a simple and cost-effective method to deny operators the possibility to successfully fulfill their tasks. Here we describe the full range of different effects that result from stimulation of the human visual system with high intensity (visible) light, and their associated potential operational impact. To systematically investigate the capability of high intensity light sources to disturb human vision and degrade human task performance we designed test protocols involving a range of military relevant tasks. The effectiveness of optical countermeasures is quantified both through their impact on task performance and through subjective reports on the experienced level of discomfort. We also derived a model that predicts normal driving behavior during exposure to a high intensity light source. These predictions can be directly related to operational requirements and can thus be used to assess the operational effectiveness of optical countermeasures. Unexpectedly, the results from our tests indicate that severe light insults have only very limited effect on human performance, even when the associated levels of visual discomfort are extremely high. Together with the limited window of operation (only during darkness) and other operational limitations (e.g., the difficulty of pointing a beam straight at the adversary) these findings question the effectivity of high intensity light sources as robust countermeasures against human operators. Further research should focus on the stimulus characteristics and methods of delivery to optimize the effectiveness of these countermeasures.

A simple model has been developed and implemented in Matlab code, predicting the over-exposed pixel area of cameras caused by laser dazzling. Inputs of this model are the laser irradiance on the front optics of the camera, the Point Spread Function (PSF) of the used optics, the integration time of the camera, and camera sensor specifications like pixel size, quantum efficiency and full well capacity. Effects of the read-out circuit of the camera are not incorporated. The model was evaluated with laser dazzle experiments on CCD cameras using a 532 nm CW laser dazzler and shows good agreement. For relatively low laser irradiance the model predicts the over-exposed laser spot area quite accurately and shows the cube root dependency of spot diameter on laser irradiance, caused by the PSF as demonstrated before for IR cameras. For higher laser power levels the laser induced spot diameter increases more rapidly than predicted, which probably can be attributed to scatter effects in the camera. Some first attempts to model scatter contributions, using a simple scatter power function f(θ), show good resemblance with experiments. Using this model, a tool is available which can assess the performance of observation sensor systems while being subjected to laser countermeasures.

The deliberate use of biological warfare agents (BWA) and other pathogens can jeopardize the safety of population, fauna and flora, and represents a concrete concern from the military and civil perspective. At present, the only commercially available tools for fast warning of a biological attack can perform point detection and require active or passive sampling collection. The development of a stand-off detection system would be extremely valuable to minimize the risk and the possible consequences of the release of biological aerosols in the atmosphere. Biological samples can be analyzed by means of several optical techniques, covering a broad region of the electromagnetic spectrum. Strong evidence proved that the informative content of fluorescence spectra could provide good preliminary discrimination among those agents and it can also be obtained through stand-off measurements. Such a system necessitates a database and a mathematical method for the discrimination of the spectral signatures. In this work, we collected fluorescence emission spectra of the main BWA simulants, to implement a spectral signature database and apply the Universal Multi Event Locator (UMEL) statistical method. Our preliminary analysis, conducted in laboratory conditions with a standard UV lamp source, considers the main experimental setups influencing the fluorescence signature of some of the most commonly used BWA simulants. Our work represents a first step towards the implementation of a spectral database and a laser-based biological stand-off detection and identification technique.

The ability to accurately model background radiation from the sun is important in understanding the operation of missile systems with ultraviolet (UV) guard channels. In theory a missile system’s UV channel detects a target’s silhouette, caused by its ‘negative contrast’ with respect to background UV radiation. The variation in background levels of UV will therefore have an effect on the operability of a missile system that utilises a UV channel. In this paper an update on the measurement and comparison of background UV-A radiation to data produced by Moderate Resolution Atmospheric Transmission 5 (MODTRAN®5) is given. In the past surface flux and radiance data calculated using MODTRAN®5 has been compared to data from the World Ozone and Ultraviolet Data Centre (WOUDC) archive, and measurements taken by the author at the Defence Academy of the UK. With the aid of spectral measurement equipment, new measurements have been made and compared with the radiance profiles produced by MODTRAN®5, including measurements made throughout both winter and summer months. Also discussed are the effects of scattering and absorption by different cloud types on the amount of radiation observed at the Earth’s surface.

In this paper authors provide a description of the currently deployed Man Portable Air Defense System (ManPADS) heat-seeking missiles. Principles of IR seeking and Aircraft signatures are shortly described. Basic information are listed on currently designed Infra-Red Counter Measure Systems, intended to protect Aircrafts against ManPADS. Authors provide an overview on ELT-572(v)2 DIRCM Program, funded by Italian Air Force, currently in low rate production phase. Description of the Design and Development phase, completed in Elettronica SpA in 2013, is reported. Development Test and Evaluation (DTE) Activities on ELT-572(v)2 DIRCM, jointly performed by Elettronica Spa and Italian Air Force Flight Test Centre, are shortly described. A summary of tests and some results are also discussed. Platform Installation Programs, using the low rate production units from ELT-572(v)2 DIRCM Program, are finally listed.

The Ultraviolet (UV) band of the electromagnetic (EM) spectrum has the potential to be used as the host medium for the operation of guided weapons. Unlike in the Infrared (IR), a target propelled by an air breathing jet engine produces no detectable radiation in the UV band, and is opaque to the background UV produced by the Sun. Successful engineering of spectral airborne IR countermeasures (CM) against existing two colour IR seekers has encouraged missile counter-countermeasure (CCM) designers to utilise the silhouette signature of an aircraft in the UV as a means of distinguishing between a true target and a flare CM. In this paper we describe the modelling process of a dual band IR and UV rosette scan seeker using CounterSim, a missile engagement and countermeasure simulation software package developed by Chemring Countermeasures Ltd. Results are shown from various simulated engagements of the dual band MANPAD with a C-130 Hercules modelled by Chemring Countermeasures. These results have been used to estimate the aircrafts’ vulnerability to this MANPAD threat. A discussion on possible future optical countermeasures against dual band IR-UV seekers is given in conclusion to the simulation results.

Infrared missiles pose a significant threat to civilian and military aviation. ManPADS missiles are especially dangerous in the hands of rogue and undisciplined forces. Yet, not all the launched missiles hit their targets; the miss being either attributable to misuse of the weapon or to missile performance restrictions. This paper analyses some of the factors affecting aircraft vulnerability and demonstrates a structured analysis of the risk and aircraft vulnerability problem. The aircraft-missile engagement is a complex series of events, many of which are only partially understood. Aircraft and missile designers focus on the optimal design and performance of their respective systems, often testing only in a limited set of scenarios. Most missiles react to the contrast intensity, but the variability of the background is rarely considered. Finally, the vulnerability of the aircraft depends jointly on the missile’s performance and the doctrine governing the missile’s launch. These factors are considered in a holistic investigation. The view direction, altitude, time of day, sun position, latitude/longitude and terrain determine the background against which the aircraft is observed. Especially high gradients in sky radiance occur around the sun and on the horizon. This paper considers uncluttered background scenes (uniform terrain and clear sky) and presents examples of background radiance at all view angles across a sphere around the sensor. A detailed geometrical and spatially distributed radiometric model is used to model the aircraft. This model provides the signature at all possible view angles across the sphere around the aircraft. The signature is determined in absolute terms (no background) and in contrast terms (with background). It is shown that the background significantly affects the contrast signature as observed by the missile sensor. A simplified missile model is constructed by defining the thrust and mass profiles, maximum seeker tracking rate, maximum guidance acceleration and seeker sensitivity. For the purpose of this investigation the aircraft is equipped with conventional pyrotechnic decoy flares and the missile has no counter-countermeasure means (security restrictions on open publication). This complete simulation is used to calculate the missile miss distance, when the missile is launched from different locations around the aircraft. The miss distance data is then graphically presented showing miss distance (aircraft vulnerability) as a function of launch direction and range. The aircraft vulnerability graph accounts for aircraft and missile characteristics, but does not account for missile deployment doctrine. A Bayesian network is constructed to fuse the doctrinal rules with the aircraft vulnerability data. The Bayesian network now provides the capability to evaluate the combined risk of missile launch and aircraft vulnerability. It is shown in this paper that it is indeed possible to predict the aircraft vulnerability to missile attack in a comprehensive modelling and a holistic process. By using the appropriate real-world models, this approach is used to evaluate the effectiveness of specific countermeasure techniques against specific missile threats. The use of a Bayesian network provides the means to fuse simulated performance data with more abstract doctrinal rules to provide a realistic assessment of the aircraft vulnerability.

For some years Rheinmetall Waffe Munition has successfully developed, realised and tested a variety of versatile high energy laser (HEL) weapon systems for air- and ground-defence scenarios like C-RAM, UXO clearing. By employing beam superimposition technology and a modular laser weapon concept, the total optical power has been successively increased. Stationary weapon platforms and now military mobile vehicles were equipped with high energy laser effectors. Our contribution summarises the most recent development stages of Rheinmetalls high energy laser weapon program. We present three different vehicle based HEL demonstrators: the 5 kW class Mobile HEL Effector Track V integrated in an M113 tank, the 20 kW class Mobile HEL Effector Wheel XX integrated in a multirole armoured vehicle GTK Boxer 8x8 and the 50 kW class Mobile HEL Effector Container L integrated in a reinforced container carried by an 8x8 truck. As a highlight, a stationary 30 kW Laser Weapon Demonstrator shows the capability to defeat saturated attacks of RAM targets and unmanned aerial vehicles. 2013 all HEL demonstrators were tested in a firing campaign at the Rheinmetall testing centre in Switzerland. Major results of these tests are presented.

The Department of Navy has been pursuing a technology development program for advanced, all-fiber, Ultra Short Pulsed Laser (USPL) systems via Small Business Innovative Research (SBIR) programs. Multiple topics have been published to promote and fund research that encompasses every critical component of a standard USPL system and enable the demonstration of mJ/pulse class systems with an all fiber architecture. This presentation will summarize published topics and funded programs.

Laser system emitting within IR wavelength range from 2.5 to 16.57 micron is discussed. The hybrid laser system consists of molecular gas lasers with a frequency conversion in a nonlinear crystal. One gas laser is a carbon monoxide laser operating in multi-line or single-line mode. Another one is a carbon dioxide laser operating in multi-line mode. These lasers operate in a Q-switched mode. The laser emission is mixed in various nonlinear crystals producing sum and difference frequency conversion into above mentioned broadband IR spectral range.

In this Report, we present a record-high-peak-power single-frequency master oscillator power amplifier (MOPA) system based on a newly developed double-clad large-mode-area Yb-free Er-doped fiber (DC-LMA-EDF). A fiber Bragg grating wavelength-stabilized fiber-coupled diode laser at λ=1551 nm with ~2 MHz spectral width was used as the master oscillator. Its radiation was externally modulated with a 5 kHz repetition rate and 92 ns pulse duration and then amplified in a core-pumped Er-doped fiber amplifier up to an average power of 4 mW. The amplified spontaneous emission (ASE) generated at the last preamplifier stage was suppressed by a narrow-band (0.7 nm) DWDM filter. The last MOPA stage was based on the recently developed single-mode DC-LMA-EDF with a mode field diameter of 25 microns and pump clad-absorption of 3 dB/m at λ=980 nm. The pump and the signal were launched into this fiber through a commercial pump combiner in a co-propagating amplifier scheme. At first, we used a 3-m long DC-LMAEDF. In such configuration, a peak power of 800 W was achieved at the output of the amplifier together with a ~ 12 % pump conversion slope efficiency. Further power scaling was limited by SBS. After that we shortened the fiber length to 1 m. As a result, owing to large unabsorbed pump power, the efficiency decreased to ~5 %. However, a peak power of more than 3.5 kW was obtained before the SBS threshold. In this case, the pulse shape changed and its duration decreased to ~60 ns owing to inversion depletion after propagation of the forward front of the pulse. To the best of our knowledge, the peak power of more than 3.5 kW reported here is the highest value ever published for a single-frequency single-mode silica-based fiber laser system operating near λ=1550 nm.

Alkali laser has been one of the most promising paths to high energy laser during past dozen years. As the first group realized DPAL and XPAL lasing in China, we had done lots of theoretical and experimental works to further clarify the mechanism of alkali lasers, such as exploring scaling parameters design balance and MOPA configuration amplified spontaneous emission suppression in DPAL based on our self-developed fast converging algorithm, XPAL’s continuous wave operation threshold, performance degradation of VBG narrowed diode laser array and stacks due to conductive thermal flow, heat deposition induced gas dynamic parameters variation estimation, local atomic number density change measurement with single frequency tunable diode laser, ionization and other higher level nonlinear effects with opto-galvanometer method. Based on above research works, preliminary considerations and conclusions for alkali laser scaling are given.

Comprehensive analysis of kinetic and fluid dynamic processes in flowing-gas diode pumped alkali lasers (DPALs) using two- and three-dimensional computational fluid dynamics (2D and 3D CFD) models is reported for Cs DPALs. The models take into account effects of temperature rise and losses of alkali atoms due to ionization. Various gas flow regimes and transverse and parallel flow-optics directions configurations are studied. Optimization of the Cs DPAL parameters, using 3D CFD modeling, shows that applying high flow velocity and narrowband pumping, maximum lasing power as high as 40 kW can be obtained at pump power of 80 kW for transverse flow configuration in a pumped volume of ~ 0.7 cm³. At high pump power the calculated laser power is higher for the transverse scheme than for the parallel scheme because of a more efficient heat convection from the beam volume in the transverse configuration. The CFD models are applied to experimental devices and the calculated results are in good agreement with the measurements.

Comparison between a semi-analytical and two- and-three dimensional computational fluid dynamics (2D and 3D CFD) models is reported. The models take into account effects of temperature rise and losses of alkali atoms due to ionization and chemical reactions, resulting in a decrease of the slope efficiency and lasing power. Effects of natural convection in static DPALs are also taken into account. Both models are 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 flowinggas [A.V. Bogachev et al., Quantum Electron. 42, 95 (2012)] DPALs. Comparison of the models applied to the flowinggas DPAL shows that for low pump power both models predict very close values of the laser power; however, at higher pump power, corresponding to saturation of the absorption of the pump transition, the values of the laser power calculated using the 2D CFD model are much higher than those obtained using the semi-analytical model.

Results of recent semi-analytical and three dimensional computational fluid dynamics (3D CFD) modeling of supersonic diode pumped alkali lasers (DPALs), as well as summary of work in progress, are reported. DPALs have been extensively studied in the past few years and static and flowing-gas devices have been investigated. Modeling of these devices has been conducted as well and fluid dynamics and kinetic processes have been taken into account, but until recently only flowing-gas DPALs with subsonic velocity of the gas were considered. Following our previous work on supersonic DPALs we further explore in the present study the feasibility of operating DPALs with supersonic expansion of the gaseous laser mixture, consisting of alkali atoms, He atoms and (frequently) hydrocarbon molecules. The motivation for this exploration stems from the possibility of fast and efficient cooling of the mixture by the supersonic expansion. In a recent paper (S. Rosenwaks et al, Proc. SPIE 8962, 896209 (2014)) we have reported on semi-analytical modeling for a supersonic Cs DPAL with parameters similar to those of the 1-kW flowing-gas subsonic Cs DPAL (A.V. Bogachev et al, Quantum Electron. 42, 95 (2012)); the maximum power, P_lase, for the former was found to be higher than for the latter by 25%. Optimization of the He/CH₄ buffer gas composition and flow parameters using 3D CFD modeling shows that for Bogachev et al resonator parameters, extremely high lasing power and optical-to-optical efficiency, 33 kW and 82%, respectively, are achievable in the Cs supersonic device. Comparison between the semi-analytical and the 3D CFD models for Cs shows that the latter predicts much higher maximum achievable laser power than the former. For a supersonic K DPAL the semi-analytical model predicts P_lase = 43 kW, 70% higher than for subsonic with the same resonator and K density at the inlet, the maximum optical-to-optical efficiency being 82%. The paper also includes estimates for closed cycle supersonic systems.

New concepts are presented to realize a chemical oxygen laser (COL) based on the transition from O₂(¹Δ_g) to O₂ (³Σ_g). The chemical oxygen iodine laser (COIL) utilizes the energy transfer from the chemically generated O₂(¹Δ_g) to iodine I (²P_3/2) because the stimulated emission cross section of O₂(¹Δ_g) is too small to give a direct oscillation. But since extractable laser energy has no relation to the stimulated emission cross section, a COL has a potential to produce a high energy laser output if it has a long enough active medium to give a positive gain. The intrinsically long upper-state life time enables the storage of large energy, which has a potential give a giant pulsed laser. Since the previous report elucidated the problems 1), the proposed concepts are based on the consideration of them. Also a Q switched COL oscillator is simulated with a rate equation. The simulation results show that a giant pulse of ~0.05ms width can be obtained with the extraction efficiency of 10-20%.

This paper presents the results of our experiments on development of the efficient hydrocarbon free Diode Pumped Alkali Laser based on potassium vapor buffered by He gas at 600 Torr. We studied the performance of this laser operating in pulsed mode with pulses up to 5 ms long at different pulse energies and cell temperatures. A slope efficiency of more than 50% was demonstrated with total optical efficiency about 30% for the pump pulses with duration about 30 μs. For the longer pump pulses the DPAL efficiency degraded in time with a characteristic time in the range from 0.5 ms to 4.5 ms depending on the pump pulse energy and cell temperature. The recorded spectrum of the side fluorescence indicates that multi-photon excitation, energy pooling collisions and ionization may be strong candidates for explaining the observed performance degradation.