This PDF file contains the front matter associated with SPIE Proceedings Volume 7196, including the Title Page, Copyright information, Table of Contents, Introduction (if any), and the Conference Committee listing

Generation of singlet oxygen and atomic iodine for operation of the chemical or discharge oxygen-iodine laser (COIL/DOIL) is described, employing novel methods and device configurations proposed in our laboratory. A centrifugal spray generator of singlet oxygen was developed, based on the conventional reaction between chlorine and basic hydrogen peroxide. Recent results of theoretical and experimental investigation of the generator parameters are presented. A new conception of the discharge generator of singlet oxygen was initiated, based on a combined DC arc jet and RF discharge techniques. Principle of the generator currently developed and constructed is described. A new device configuration was designed for the alternative method of atomic iodine generation using a radiofrequency discharge decomposition of iodine compounds like CH₃I or CF₃I. Some recent experimental results of this research are also presented.

Recent investigations of an Electric Oxygen-Iodine Laser system have shown that computational modeling over-predicts the laser power output measured in experiments for similar gain conditions. To help resolve this discrepancy, detailed 2-axis mapping of gain and gain recovery measurements downstream of an operating laser cavity were performed. Modeling and analyses of the gain recovery experiments indicate that when the pumping rate of I(²P_1/2) by O₂(a¹Δ) is reduced by an effective factor of approximately 4 as a result of an unknown competing reaction, the calculations are well matched to the experimental gain recovery measurements. The agreement between the measured and modeled laser power extraction also significantly improves when the reduced effective pumping rate is used. The results suggest that there may be a competing reaction that effectively reduces the forward pumping rate as compared to the classical chemical oxygen-iodine laser kinetics rates. Understanding of this kinetic process should enable us to accommodate or eliminate its impact on ElectricOIL performance.

Pulsed discharge is effective means to achieve high-peak lasing in COIL. Numerical model is developed for simulation of pulsed discharge in gas stream from the singlet oxygen generator mixed with CF₃I. The model comprises a system of kinetic equations for neutral and charged species, electric circuit equation, and gas thermal balance equation. Sources of iodine atoms under discharge and post-discharge conditions are analyzed. The dominant source in the discharge is electron-impact dissociation of CF₃I molecules. In post-discharge phase chemical reactions are identified giving notable input into I production. Deformation of laser pulse waveform observed experimentally is explained by influence of these reactions.

Enhanced production of singlet oxygen, O₂(a¹Δ_g), was observed by reaction of O₂/He discharge effluents on an iodine oxide film surface in a microwave discharge flow reactor at 320 K. We observed a two-fold increase in the O₂(a) yields in excess of discharge-generated amounts for non-catalytic conditions. The iodine oxide surface appears to catalyze the heterogeneous reaction to form O₂(a) with high collision efficiency. Injection of molecular iodine into the catalytically enriched active-oxygen flow resulted in excitation of the I(²P_1/2) state approaching optical transparency at 1315 nm. Addition of NO₂ resulted in positive small-signal gain in the 320 K subsonic flow. The observed catalytic effect could significantly benefit the development of electrically driven oxygen-iodine laser systems.

Herein the authors report on the demonstration of gain and a continuous-wave laser on the 1315 nm transition of atomic iodine using the energy transferred to I(²P_1/2) from O₂(a¹Δ) produced by both radio-frequency and microwave electric discharges sustained in a dry air-He-NO gas mixture. Active oxygen and nitrogen species were observed downstream of the discharge region. Downstream of the discharge, cold gas injection was employed to raise the gas density and lower the temperature of the continuous gas flow. Gain of 0.0062 %/cm was obtained and the laser output power was 32 mW in a supersonic flow cavity.

Electra is an electron beam pumped laser being developed at the Naval Research Laboratory as an inertial confinement fusion (ICF) driver. Two opposing 500 kV, 100 kA electron beams pump the main amplifier, which achieves energies of 730 J over a 100 ns pulse at 248 nm when run in an oscillator configuration. KrF lasers have been shown to have intrinsic efficiencies of greater than 12% and, based on that, wall plug efficiencies of >7% are projected for an IFE system based on our established improvements in laser physics and pulsed power technologies. The Electra main amp has run at rep-rates of 1 Hz, 2.5 Hz, and 5 Hz in runs exceeding 10,000 shots. This paper will present an overview of the Electra accomplishments and highlight recent research, including integrating Electra's amplifiers into a durable full laser system, interferometric measurements of the near field spatial distortions in the amplifiers and their effect on the far field profile, and spatially and temporally resolved temperature measurements of the electron beam transmission foil.

High energy excimer lasers lend maximum flexibility to laser microprocessing, since virtually every material is amenable to accurate, high resolution material ablation without subsequent post treatment. 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. In particular, the large flat-top excimer laser profile is well-suited for most efficient parallel processing of two and three dimensional microstructures. Compact micromachining concepts particularly suited for material ablation and surface activation will be introduced.

Parametric study of a slab first-overtone carbon monoxide laser was performed. The compact slab first-overtone CO laser with active volume 3x30x250 mm³ was excited by a repetitively pulsed capacitive RF discharge (81 MHz or 60 MHz) with pulse repetition rate 100-500 Hz. The laser electrodes were cooled down to 120 K. Gas mixtures CO:O₂:N₂:He with different component contents at gas pressures 15-22 Torr were used. Two laser resonator mirrors sets were used in the experiments on multiline lasing. More than 100 spectral lines within the spectral range ~2.5-4.0 μm with maximum single line average output power 12 mW were observed. Total output power of the slab firstovertone CO laser came up to 0.3 W, with maximum laser efficiency 0.5%. Special details of long time output laser power behavior are discussed.

When it comes to highest power laser applications CO₂-lasers are one of the most prominent choices. In most applications the raw laser beam which exhibits a Gaussian or Gaussian-like shape is employed. In contrast, homogeneous top hat profiles or customized beam shapes offer several application-specific advantages. Up to now the possibilities of beam shaping for CO₂-lasers were very limited based on traditional approaches only. To make the advantages of homogeneous beam profiles also accessible for CO₂ sources LIMO has expanded its range of production capabilities for the manufacturing of ZnSe micro-optics. LIMO's proprietary production technology is based on computer-aided design and no etching technique is involved at all. A Gaussian-to-top-hat converter made of ZnSe is demonstrated. The properties of the micro-lens surface, the generated beam profile with a CO₂-laser as well as first application results are shown.

Studies were performed using self-channeled femtosecond laser pulses (filaments) interacting with various materials at a distance of 30 meters. Using time resolved optical shadowgraphy, the filament interaction with the target is observed. Shockwaves in both the target and the surrounding atmosphere are observed and their velocities measured. Estimations of the shockwave energy are made from these observations. In transparent targets, optical coupling into the target material is observed. This coupling results in optical damage lines in the material. Results of the filament interactions will be discussed along with supporting modeling.

Lasing on the 6²P_1/2→6²S_1/2(D1) resonance transition of atomic Cs at 894.3 nm has been demonstrated in mixtures of Ar, ethane, and Cs vapor by the photoexcitation of ground state Cs-Ar collision pairs and subsequent dissociation of diatomic, electronically-excited CsAr molecules (exciplexes or excimers). The blue satellites of the alkali D₂ lines provide a pathway for optically pumping atomic alkali lasers on the principal series (resonance) transitions with broad linewidth (>2 nm) semiconductor diode lasers. In this paper we discuss different variations of this new laser system and the experiments of the initial demonstration.

We report on the results of our diode pumped alkali laser experiments. Using volume bragg gratings, we have produced a 1.28 kW diode stack with a 0.35 nm bandwidth and ~70% of the power contained in the peak. We use two of these stacks to pump a 23 mm rubidium cell. We achieve 29 W of average output power at a 14% duty factor.

Scaling of alkali lasers to higher powers requires combining beams of multiple diode laser pump sources. For longitudinal pumping this can be very complicated if more than four beams are to be combined. In this paper we report a first demonstration of a transversely pumped Cs laser with fifteen laser diode arrays. The LDA pump beams were individually collimated with a beam size of about 1 x 4 cm as measured at a 1 m distance from the diodes. All these beams were incident on a cylindrical lens to be focused and coupled through the side slit of a hollow, cylindrical diffuse reflector which contained the Cs vapor cell. We measured the output power and efficiency of the Cs laser for pump powers up to 200 W at different cell temperatures. Although the values of output power and slope efficiency obtained for this laser system were less than those for a longitudinally pumped alkali laser, these recent results can be significantly improved by using a more optimal laser cavity design. The demonstrated operation of Cs laser with transverse pumping opens new possibilities in power scaling of alkali lasers.

We describe a series of measurements of absorption and laser induced fluorescence using cells that contained cesium and rubidium and krypton as a bath gas. These studies showed strong blue wing absorption to the short wavelength side of the alkali atom D₂ lines due to collisionally formed Cs-Kr or Rb-Kr excimers. These studies indicate that these species may be appropriate candidates for optically excited Rb and Cs atomic lasers.

Alkali vapor lasers pumped by diode lasers are currently being investigated in several laboratories. One problem with this type of device is the poor matching of the broad linewidth of the pump source with the narrow absorption lines of the alkali atoms. A possible means for overcoming this difficulty is to use far-wing line broadening effects that are associated with alkali - metal rare gas interactions. This concept has recently been demonstrated for optical excitation of Cs-Ar dimers and collision pairs. Accurate data concerning the upper and lower state potential energy curves of M-Rg pairs are needed to evaluate the scaling possibilities for alkali metal rare gas dimer lasers. In addition to determining the details of the dimer absorption spectra, knowledge of the ground state potential also permits calculation of the number density of dimer pairs that will contribute to the absorption at a specific wavelength. In the present study we have used theoretical potential energy curves to predict equilibrium constants for the M + Rg ↔ MRg systems with M=Rb and Cs, and Rg=Ar, Kr and Xe. Excited state potential energy curves have been calculated for CsAr, and these data have been used to investigate the ability of first-principles calculations to predict the spectral properties of the Cs-Ar dimer.

We report on the first experimental demonstration of high order harmonic generation in rare gases directly from a high power Ytterbium doped fiber chirped pulse amplification system. The laser delivers 270 fs pulses in the 30-100 μJ energy range at repetition rate varying from 100 kHz to 1 MHz. A proper focalization allows reaching several 10¹³W/cm² in the gas jet. We have been able to produce and detect harmonics up to order 31 in Ar, Kr, and Xe at 100kHz repetition rate. Harmonic generation at 1 MHz is also demonstrated in Xe up to harmonic 15.

We have demonstrated an argon excimer vacuum ultraviolet (VUV) amplifier at 126 nm by using the optical-field induced ionization (OFI) of argon. The gain-length product of 5.6 was achieved as a result of the optical feedback inside the amplifier with a VUV mirror. Plasma self-channeling caused by the high-intensity pump laser was simultaneously observed when the maximum gain-length product was observed. We have also optimized the output power of a subpicosecond VUV seed beam at 126 nm produced in low-pressure rare-gases as a result of the seventh harmonic nonlinear wavelength conversion of a Ti:Sapphire laser at 882 nm.