The electric oxygen iodine laser (EOIL) offers a vastly more practical, implementable, and safer alternative to its predecessor, the chemical oxygen iodine laser (COIL), particularly for airborne or other mobile military applications. Despite its promise and after 25 years effort, numerous laboratories around the world have not succeeded in providing the known basic physical requirements needed to electrically convert O₂ into O₂(a¹Δ)with the fractional yields and efficiencies needed to make a practical laser. Hence, as of this date, the world record power generated from an EOIL device is only 6.5 watts. In this paper, a 30% conversion from O₂ into O₂(a¹Δ) operating at substantial oxygen mass flow rates (0.090 moles O₂/sec at 50 torr) and 40% electrical efficiency is reported. The O₂(a¹Δ) flow stream being produced carries 2400 watts. Gain measurements are currently in progress, to be followed shortly by power extraction. Current conditions imply that initial power extraction could push beyond 1 KW. Efforts to date have failed to generate substantial laser power because critical criteria have not been met. In order to achieve good O₂(a¹Δ) fractional yield, it is normally mandatory to impart on the order of 100 KJ/mole O₂ while efficiently removing the waste heat energy from the generator so that less than a few hundred degrees Kelvin rise occurs due to gas heating. The generator must be excited by an electric field on the order of 10 Td. This is far below glow potential; hence, a fully externally sustained plasma generation technique is required. Ionization is supplied by means of applying short (tens of nanosecond) pulses to the O₂(a¹Δ) generator at 50,000 PPS, which are on the order of ten times breakdown potential. This enables a quasi-steady adjustable DC current to flow through the generator, being conducted by application of a DC, 10 to 14 Td pump E-field. This field is also independently tunable. The result is that up to 180 KJ/mole O₂ gets imparted to the gas by means of the ~6 KW sub-breakdown pump field, while another 2700 watts is applied to the controlled avalanche field. The generator consists of 24 each, 1 cm diameter tubes that are submerged in rapidly circulating cold fluorinert. Heat is efficiently removed so that that the gas temperature, initially 273°K, raises only by 125°K, as evidenced by spectrographic analysis of the fine structure of O₂(b¹Σ) at lower pressure. Since all necessary conditions have been met, a 30% conversion rate of O₂ to O₂(a¹Δ) has been achieved. Fortuitously, neither excited O atom production nor O₂(b¹Σ) production is visible in the spectra of the higher pressure, best yield runs. Essentially all other spectral lines are dwarfed in comparison the O₂(a¹Δ) line. Energy normally partitioned to O₂(b¹Σ) and apparently O atoms now feeds into O₂(a¹Δ) directly, enabling electrical efficiency to exceed 40%. As a continuation of this work, an I₂ disassociating mixing section - then subsequently a 20 cm transverse M = 2.5 laser channel - has been coupled to the O₂(a¹Δ) generator. The effects of titrating NO, NO₂, etc. to scavenge O atoms and O₃ atoms is under current investigation. Laser power extraction will commence after having optimized all parameters to achieve maximum gain.

Predictive modeling of the performance of EOIL laser systems must address the kinetics of the active oxygen flow, including the production of O₃ from recombination of O and O₂, and the effects of NO as an additive to remove O and promote O₂(a) formation. This paper describes experimental measurements of the reaction kinetics for active-oxygen flows generated by microwave discharge of O₂/He mixtures at 3 to 10 torr. The concentrations of O₂(a¹Δ), O, and O₃ were directly measured as functions of reaction time in a discharge-flow reactor. Both the O removal rate and the O₃ production rate were observed to be significantly lower than expected from the widely accepted three-body recombination mechanism for O₃ production, indicating the existence of a previously unknown O₃ dissociation reaction. Addition of NO to the flow well downstream of the discharge resulted in readily detectable production of O₂(a) in addition to that generated by the discharge. The observed O2(a) production rates were remarkably insensitive to variations in total pressure, O₂ concentration, and NO concentration over the ranges investigated. The mechanism for this O₂(a) production remains to be identified, however it appears to involve a hitherto undetected, metastable, energetic species produced in the active-oxygen flow.

Experimental investigations of radio-frequency discharges in O₂/He/NO mixtures in the pressure range of 1-100 Torr and power range of 0.1-1.2 kW have indicated that O₂(a¹Δ) production is a strong function of geometry, excitation frequency, pressure and diluent ratio. The goal of these investigations was maximization of both the yield and flow rate (power flux) of O₂(a¹Δ) in order to produce favorable conditions for application to an electric oxygen-iodine laser (EOIL). At lower pressures, improvements in yield are observed when excitation frequency is increased from 13.56 MHz. As pressure is increased, increasing excitation frequency in the baseline configuration becomes detrimental, and yield performance is improved by reducing the discharge gap and increasing the diluent ratio. Numerous measurements of O₂(a¹Δ), oxygen atoms, and discharge excited states are made in order to describe the discharge performance dependent on various parameters.

Scaling of EOIL systems to higher powers requires extension of electric discharge powers into the kW range and beyond with high efficiency and singlet oxygen yield. We have previously demonstrated a high-power microwave discharge approach capable of generating singlet oxygen yields of ~25% at ~50 torr pressure and 1 kW power. This paper describes the implementation of this method in a supersonic flow reactor designed for systematic investigations of the scaling of gain and lasing with power and flow conditions. The 2450 MHz microwave discharge, 1 to 5 kW, is confined near the flow axis by a swirl flow. The discharge effluent, containing active species including O₂(a¹Δ_g, b¹Σ_g⁺), O(³P), and O₃, passes through a 2-D flow duct equipped with a supersonic nozzle and cavity. I2 is injected upstream of the supersonic nozzle. The apparatus is water-cooled, and is modular to permit a variety of inlet, nozzle, and optical configurations. A comprehensive suite of optical emission and absorption diagnostics is used to monitor the absolute concentrations of O₂(a), O₂(b), O(³P), O₃, I₂, I(²P_3/2), I(²P_1/2), small-signal gain, and temperature in both the subsonic and supersonic flow streams. We discuss initial measurements of singlet oxygen and I* excitation kinetics at 1 kW power.

An optical resonance transition rubidium laser (5²P_1/2 → 5²S_1/2) is demonstrated with a hydrocarbon-free buffer gas. Prior demonstrations of alkali resonance transition lasers have used ethane as either the buffer gas or a buffer gas component to promote rapid fine-structure mixing. However, our experience suggests that the alkali vapor reacts with the ethane producing carbon as one of the reaction products. This degrades long term laser reliability. Our recent experimental results with a "clean" helium-only buffer gas system pumped by a Ti:sapphire laser demonstrate all the advantages of the original alkali laser system, but without the reliability issues associated with the use of ethane.

Diode pumped alkali vapor lasers developed during the last several years have the potential to achieve high power. Efficient operation of Rubidium, Cesium and Potassium lasers has been demonstrated. Laser slope efficiencies higher than 80% have been achieved. A diode laser pumping can provide high overall efficiency of these devices. A diode pumped continuous wave 10 W Cs laser and continuous wave 17 W Rb laser were demonstrated. In this paper we review the main results and recent achievements in high power alkali lasers development, discuss some problems existing in this field and ways to solve them.

General Atomics has been engaged in the development of diode pumped alkali vapor lasers. We have been examining the design space looking for designs that are both efficient and easily scalable to high powers. Computationally, we have looked at the effect of pump bandwidth on laser performance. We have also looked at different lasing species. We have used an alexandrite laser to study the relative merits of different designs. We report on the results of our experimental and computational studies.

The beam combination method using stimulated Brillouin scattering phase conjugate mirrors is a promising technique for solid state lasers of high power/energy operating with high repetition rate. The key technology of this method is the phase control of the SBS waves. In the previous works, the principle of this phase control technique was demonstrated experimentally. As a next step, in this work, amplifiers have been added to the beam combination system. Inserting the amplifiers, a stabilized phase difference has been obtained with a fluctuation less than λ/50 at 44 mJ total output energy and 10 Hz repetition rate.

Electra is a repetitively pulsed, electron beam pumped Krypton Fluoride (KrF) laser at the Naval Research Laboratory that is developing the technologies that can meet the Inertial Fusion Energy (IFE) requirements for durability, efficiency, and cost. The technologies developed on Electra should be directly scalable to a full size fusion power plant beam line. As in a full size fusion power plant beam line, Electra is a multistage laser amplifier system which, consists of a commercial discharge laser (LPX 305i, Lambda Physik), 175 keV electron beam pumped (40 ns flat-top) preamplifier, and 530 keV (100 ns flat-top) main amplifier. Angular multiplexing is used in the optical layout to provide pulse length control and to maximize laser extraction from the amplifiers. Single shot yield of 452 J has been extracted from the initial shots of the Electra laser system using a relatively low energy preamplifier laser beam. In rep-rate burst of 5 Hz for durations of one second a total energy of 1.585 kJ (average 317 J/pulse) has been attained. Total energy of 2.5 kJ has been attained over a two second period. For comparison, the main amplifier of Electra in oscillator mode has demonstrated at 2.5 Hz rep-rate average laser yield of 270 J over a 2 hour period.

Stable, high energy excimer lasers providing pulsed output energies ranging from 100 mJ up to over 1000 mJ in the ultraviolet region with photon energies as high as 5 eV (248 nm), 6.3 eV (193 nm) or 7.9 eV (157 nm) lend maximum flexibility to laser microprocessing, since virtually every material is amenable to accurate, high resolution material ablation without subsequent cleaning. Due to the UV photons provided with no up-conversion required as direct output by excimer lasers, output powers of many hundred watts are easily achievable and are key to high throughput, and up-scaling capability of manufacturing processes. Most important for reproducible production results is a temporally and spatially stable behavior of consecutive laser pulses as well as utmost lateral homogeneity of the on-sample energy density (fluence). These requirements constitute the superiority of excimer lasers over other pulsed UV laser sources such as lamp-pumped Nd:YAG lasers. Pulse-to-pulse stabilities of less than 1 %, rms as easily provided by excimer laser systems which cannot be achieved with frequency converted Nd:YAG. Laser systems. In particular, the large flat-top excimer laser profile is well-suited for most efficient parallel processing of two and three dimensional microstructures. Spectral properties, temporal pulse and laser beam parameters of state of the art UV excimer lasers and beam delivery systems will be compared with frequency converted, flash-lamp pumped Nd:YAG lasers.

We have been developing an ultrashort-pulse high-intensity vacuum ultraviolet (VUV) laser. Ultrashort VUV pulses at 126 nm have been produced in rare-gases by nonlinear wavelength conversion of an infrared Ti:sapphire laser at 882 nm. This pulse will be amplified inside an Ar₂* amplifier excited by optical-field-induced ionization electrons. The amplification characteristics of the Ar₂* amplifier has been improved by plasma channeling induced by a high-intensity plasma-initiating laser.

High intensity ultra-short pulse UV laser system found many applications in atomic researches, picosecond phenomena and bio researches. We present a high intensity ultra-short pulse UV laser system that not only can generate single amplified high intensity ultra-short pulse UV laser system, but also can be operated in repetitive mode up to tenths pulses per second. Our complete laser system could also be extract as femtosecond ultra-short pulses sub-system, three amplifiers four passes single amplified medium to high intensity ultra-short pulse laser sub-system, and ultimately, high intensity ultra-short pulse UV laser system. Techniques of single amplified high intensity ultra-short pulse of this laser system are presented and characterized.