This PDF file contains the front matter associated with SPIE Proceedings Volume 7581, including the Title Page, Copyright information, Table of Contents, and the Conference Committee listing.

Experiments and modeling have led to continued enhancements in the Electric Oxygen-Iodine Laser (ElectricOIL) system. This continuous wave (cw) laser operating on the 1315 nm transition of atomic iodine is pumped by the production of O₂(a) in a radio-frequency (RF) discharge in an O₂/He/NO gas mixture. New discharge geometries have led to improvements in O₂(a) production and efficiency. A 95% enhancement in cw laser power was achieved via a 50% increase in gain length, flow rates, and discharge power. A further 87% increase in extracted laser power was obtained using a larger mode volume resonator. The gain has improved by more than 100-fold from the initial demonstration of 0.002% cm^-1 to 0.26% cm^-1, and similarly the outcoupled laser power has improved more than 500-fold from 0.16 W to 102 W.

Results of experimental and theoretical study of singlet delta oxygen (SDO) production in transverse gas flow RF slab discharge for an electric discharge oxygen-iodine laser are presented. The electric discharge facility operating in both pulse-periodic and CW mode was manufactured: gas flow duct including multi-path cryogenic heat exchanger, dielectric slab channel, and slab electrode system incorporated in the channel for RF discharge ignition. Experiments on SDO production in transverse gas flow RF discharge were carried out. SDO production depending on gas mixture content and pressure, gas flow velocity, and RF discharge power was experimentally studied. It was shown that SDO yield increased with gas pressure decrease, gas flow deceleration and helium dilution of oxygen at the same input power. CW RF discharge was demonstrated to be the most efficient for SDO production as compared to pulse-periodic RF discharge with the same averaged input power. SDO yield was demonstrated to be not less than 10 percent. The model developed was further modified to do simulations of CW and pulse periodic RF discharges. A reasonable agreement between experimental and theoretical data on SDO production in CW and pulse-periodic RF discharges in oxygen is observed.

Scaling of Electric Oxygen-Iodine Laser (EOIL) systems to higher powers requires extension of electric discharge powers into the kW range and beyond, with high efficiency and singlet oxygen yield. This paper describes the implementation of a moderate-power (1 to 5 kW) microwave discharge at 30 to 70 Torr pressure 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 is confined near the flow axis by a swirl flow. The discharge effluent, containing active species including O₂(a1▵), 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 monitors the absolute concentrations of O2(a), 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. The experimental results include numerous observations of positive gain and lasing in supersonic flow, and the scaling of gain with a variety of flow and reaction rate conditions. The results are compared with kinetics modeling predictions to highlight key discrepancies as well as areas of agreement. The observed gains are generally lower than the predicted values, due in part to chemical kinetics effects and also due to mixing limitations specific to the reagent injection design. We discuss in detail the observed effects related to O-atom chemistry, and their import for scaling the gain to higher levels. We also will present initial beam quality measurements.

A new kinetic scheme for the dissociation of I₂ by O₂(a) has been proposed by Azyazov et al. (J. Chem. Phys. 130, 104306/9 (2009)). In principle, the reactions initiated by UV photolysis of N₂O/I₂ mixtures can be used to probe the chain propagation stage of this dissociation model, and provide additional validation. In the present study, 193 nm laser photolysis of N₂O/I₂ mixtures was used to initiate secondary chemical reactions and to produce iodine atoms. Singlet oxygen was generated in this system by the fast reaction O(¹D)+N₂O→ O₂(a)+N₂. Emission spectroscopy and laser induced fluorescence techniques were used to follow the time evolutions of I* and I₂. The photolysis of N₂O/I₂ mixtures creates all of the species needed to sustain the chain propagation stage of I₂ dissociation process. However, it was found that the high pressures of N₂O needed to generate sufficient concentrations of O₂(a) suppressed the I₂ dissociation process. Computational modeling indicated that suppression of the chain propagation reactions under the conditions examined was consistent with the revised dissociation model.

Theoretical and experimental studies of the amine-based all gas-phase iodine laser (AGIL) are conducted. The numerical simulation code is a detailed one-dimensional, multiple-leaky-stream-tubes kinetics code combined with all the known rate equations to date. Using this code, we find that the key reactions to achieve positive gain are the deactivation reaction of excited iodine atoms by chlorine atoms and the self annihilation reactions of NCl(¹Δ). The order of the injection nozzles is crucial to suppress these reactions. Following the calculations, we fabricate a flow reactor apparatus and demonstrate laser action for the ²P_1/2-²P_3/2 transition of iodine atom pumped by energy transfer from NCl(¹Δ) produced by a set of amine-based, all gas-phase chemical reactions. Continuous-wave laser output of 50 mW with 40% duty factor is obtained from a stable optical resonator consisting of two 99.99% reflective mirrors. The observed laser characteristics are reasonably explained by numerical calculations. To our knowledge, this is the first achievement of amine-based AGIL oscillation.

We are investigating catalytically enhanced production of singlet oxygen, O₂(a1▵_g), observed by reaction of O₂/He discharge effluents on an iodine oxide film surface in a microwave discharge-flow reactor at 320 K. We have previously reported a two-fold increase in the O₂(a) yields by this process, and corresponding enhancement of I(²P_1/2) excitation and small-signal gain upon injection of I₂. In this paper we report further observations of the effects of elevated temperature up to 410 K, and correlations of the catalytically generated O₂(a) with atomic oxygen over a large range of discharge-flow conditions. We have applied a diffusion-limited reaction rate model to extrapolate the catalytic reaction rates to the highpressure, fast-flow conditions of the subsonic plenum of a supersonic EOIL test reactor. Using the model and the flow reactor results, we have designed and implemented a first-generation catalytic module for the PSI supersonic MIDJet/EOIL reactor. We describe preliminary tests with this module for catalyst coating deposition and enhancement of the small-signal gain observed in the supersonic flow. The observed catalytic effect could significantly benefit the development of high-power electrically driven oxygen-iodine laser systems.

The development of discharge singlet oxygen generators (DSOG's) that can operate at high pressures is required for the power scaling of the discharge oxygen iodine laser. In order to achieve efficient high-pressure DSOG operation it is important to understand the mechanisms by which singlet oxygen (O₂(a¹Δ)) is quenched in these devices. It has been proposed that three-body deactivation processes of the type O₂(a¹Δ))+O+M→2O₂+M provide significant energy loss channels. To further explore these reactions the physical and reactive quenching of O₂(a¹Δ)) in O(³P)/O₂/O₃/CO₂/He/Ar mixtures has been investigated. Oxygen atoms and singlet oxygen molecules were produced by the 248 nm laser photolysis of ozone. The kinetics of O₂(a¹Δ)) quenching were followed by observing the 1268 nm fluorescence of the O₂ a1Δ-X³Ε transition. Fast quenching of O₂(a¹Δ)) in the presence of oxygen atoms and molecules was observed. The mechanism of the process has been examined using kinetic models, which indicate that quenching by vibrationally excited ozone is the dominant reaction.

We report on our latest results in the development of high-energy, long-cavity Chirped Pulse Oscillators (CPOs). Our concept allows the generation of ultrashort laser pulses at MHz repetition rates with a pulse duration of less then 50fs and an energy approaching the μJ-level directly out of an oscillator. Thus, our unique approach completely avoids the need for any additional amplification stages. This paper is, to the best of our knowledge, the first demonstration that laser pulses with a peak power exceeding 18MW can be generated directly out of a femtosecond oscillator.

We report the optical amplification characteristics of an optical-field-induced-ionization (OFI) Ar₂ ^* excimer vacuum ultraviolet (VUV) amplifier at 126 nm by using two experimental approaches. We have observed the amplification of OFI Ar₂ ^* excimer emission and evaluated the gain length product of 1.0 by using an optical cavity. We also achieved the gain length product of 5.0 by measuring the one pass amplification inside a hollow fiber with the length of 5 cm. The use of a hollow fiber was effective to guide the VUV emission and to extend a gain length. A small signal gain coefficient of 1.0 cm^-1 was evaluated in both experimental approaches.

Super-hard functional coatings are obtained by high power excimer laser based PLD. Diamond-like, tetrahedral amorphous carbon (ta-C) is grown on substrates moderately heated to below 90°C inside a vacuum chamber upon ablating a graphite target by means of a high pulse energy excimer laser at a wavelength of 248 nm. The fast evaporation of the target material induced by the high photon energy of 5 eV, the short temporal width of 30 ns and the high fluence of the excimer laser pulses generates plume species with a high degree of ionisation and high kinetic energies. As a consequence, the kinetic energies resulting from excimer based PLD are significantly higher than those associated with the thermal evaporation and the ion sputtering deposition methods. In fact, the mean kinetic energy of the atoms and ions in the plume are in the range of 30 eV to 80 eV for fluencies of 5 J/cm² to 20 J/cm². Such large ontarget UV fluences are easily provided by high energy excimer lasers such as the Coherent LPXpro and by LSX laser models which can operate at output energies up to 1 J and average output powers up to 540 W.

Optical components within high energy laser systems are susceptible to laser-induced material modification when the breakdown threshold is exceeded or damage is initiated by pre-existing impurities or defects. These modifications are the result of exposure to extreme conditions involving the generation of high temperatures and pressures and occur on a volumetric scale of the order of a few cubic microns. The response of the material following localized energy deposition, including the timeline of events and the individual processes involved during this timeline, is still largely unknown. In this work, we investigate the events taking place during the entire timeline in both bulk and surface damage in fused silica using a set of time-resolved microscopy systems. These microscope systems offer up to 1 micron spatial resolution when imaging static or dynamic effects, allowing for imaging of the entire process with adequate temporal and spatial resolution. These systems incorporate various pump-probe geometries designed to optimize the sensitivity for detecting individual aspects of the process such as the propagation of shock waves, near-surface material motion, the speed of ejecta, and material transformations. The experimental results indicate that the material response can be separated into distinct phases, some terminating within a few tens of nanoseconds but some extending up to about 100 microseconds. Overall the results demonstrate that the final characteristics of the modified region depend on the material response to the energy deposition and not on the laser parameters.

We have developed a novel method to correct the spatial distortion resulting from temporally stretching/compressing optical pulses with a chirped volume holographic grating (CVHG) in glass. We show that the inherent spatial beam distortion can be corrected to produce a distortion-free round beam output. We fabricated a 30 mm long CVHG with 9 nm bandwidth, 300 ps delay at 1031nm exhibiting a smooth round spatial Gaussian profile after compression. Coupling efficiencies for the compressed pulse exceeds 75% into a single mode fiber. The spatial profile is maintained over a wide temperature range from 10 to 60 degrees Celsius. We believe that the spatial beam profile improvements of CVHG demonstrate herein enables the practical realization of ultra-compact and efficient chirped pulse amplification laser systems.

There has been recent interest in Diode Pumped Alkali Lasers (DPALs) and their scaling to higher powers. Scaling of DPALs to high powers requires using multiple pump sources such as laser diode arrays or stacks of arrays. Coupling of multiple pump beams into the laser gain medium can be realized using a transverse pumping scheme that is most efficient for the laser operating with large mode volume. We have demonstrated Cs laser with unstable resonator transversely pumped by 15 narrowband diode laser arrays. This laser operates on lowest transverse mode with a diameter of 7 mm with an optical-to-optical efficiency higher than 30%. An alternative power scaling approach: Master Oscillator and power Amplifier (MOPA) system with transversely pumped by multiple diode lasers Cs amplifier was studied experimentally and demonstrated high optical efficiency.

We report on the results from several of our alkali laser systems. We show highly efficient performance from an alexandrite-pumped rubidium laser. Using a laser diode stack as a pump source, we demonstrate up to 145 W of average power from a CW system. We present a design for a transversely pumped demonstration system that will show all of the required laser physics for a high power system.

Diode pumped alkali lasers (DPAL) offer the potential for high power and efficient operation. The extremely low quantum defect of the alkali system minimizes thermal management requirements. At the same time DPALs keep advantages of gas lasers (no thermal stresses, high intrinsic beam quality). Side pumped geometry simplifies system design, separating laser and pump light and providing physical space for a large number of diode stacks needed for power scaling. The three-level nature of these lasers complicates modeling, making numerical simulation the most viable option for system studies in this geometry. We have built a simplified numerical code for simulation of CW laser performance in different side pumped geometries and studied performance of a rubidium DPAL with helium and methane buffer gases at high pump power. We observed dramatic differences in pump absorption with the laser turned off compared to an operating laser. Cell temperature is a key parameter that controls effective absorption length. If pump density is sufficiently high, we can find an operating point with optical to optical efficiency above 60% with reasonably homogenous spatial laser output profile even for a single side pumped laser cell.

Optically Pumped Alkali Lasers (OPAL) involve interactions of alkali atoms with a buffer gas typically consisting of a noble gas together with C₂H₄. Line broadening mechanisms are of particular interest because they can be used to match a broad optical pumping source with relatively narrow alkali absorption spectra. To better understand the line broadening processes at work in OPAL systems we focus on the noble gas collisional partners. A matrix of potential energy surfaces (PES) has been generated at the multi-configurational self consistent field (MCSCF) level for M + Ng, where M=Li, Na, K, Rb, Cs and Ng=He, Ne, Ar. The PES include the X²Σ ground state surface and the A²II, B²Σ excited state surfaces. In addition to the MCSCF surfaces, PES for Li+He have been calculated at the multi-reference singles and doubles configuration interaction (MRSDCI) level with spin-orbit splitting effects included. These surfaces provide a way to check the qualitative applicability of the MCSCF calculations. They also exhibit the avoided crossing between the B2Σ and A²II_1/2 surfaces that is partially responsible for collision induced relaxation from the ²P_3/2 to the ²P_1/2 atomic levels.

An analytic model for the cw diode pumped alkali laser is developed by considering the longitudinally averaged number densities of the ground ²S_1/2 and first excited ²P_3/2, and ²P_1/2 states. The pump intensity to reach threshold requires fully bleaching the pump transition and exceeding optical losses, typically about 200 Watts/cm². Slope efficiency depends critically on the fraction of incident photons absorbed and the overlap of pump and resonator modes, approaching the quantum efficiency of 0.95 - 0.98. For marginal cavity transmission losses, peak performance is achieved for low output coupling. For efficient operation, the collisional relaxation between the two upper levels should be fast to prevent bottlenecking. By assuming a statistical distribution between the upper two levels, the limiting analytic solution for the quasitwo level system is achieved. For properly designed gain conditions, the quasi two level solution is usually achievable and represents ideal performance.

Excimer-pumped alkali vapor lasers (XPALs) are a new class of photoassociation lasers which take advantage of the spectrally broad absorption profiles of alkali-rare gas collision pairs. In these systems, transient alkali-rare gas molecules are photopumped from the thermal continuum to a dissociative X²Σ⁺ _1/2 interaction potential, subsequently populating the n²P_3/2 state of the alkali. The absorption profiles ≥5 nm and quantum efficiencies >98% have been observed in oscillator experiments, indicating XPAL compatibility with conventional high power laser diode arrays. An alternative technique for populating the n²P_3/2 state is direct photoexcitation on the n²P_3/2←n²S_1/2 atomic transition. However, because the XPAL scheme employs an off-resonant optical pump, the strengths of resonantly-enhanced nonlinear processes are minimized. Additionally, the absorption coefficient may be adjusted by altering the number densities of the lasing species and/or perturbers, a valuable asset in the design of large volume, high power lasers. We present an overview of XPAL lasers and their operation, including the characteristics of recently demonstrated systems photopumped with a pulsed dye laser. Lasing has been observed in Cs at both 894 nm and 852 nm by pumping CsAr or CsKr pairs as well as in Rb at 795 nm by pumping RbKr. These results highlight the important role of the perturbing species in determining the strength and position of the excimer absorption profile. It is expected that similar results may be obtained in other gas mixtures as similar collision pair characteristics have historically been observed in a wide variety of transient diatomic species.

The exciplex pumped alkali laser (XPAL) system was recently demonstrated in mixtures of Cs vapor, Ar, and ethane, by pumping Cs-Ar atomic collision pairs and subsequent dissociation of diatomic, electronically-excited CsAr molecules (exciplexes or excimers). Because of the addition of atomic collision pairs and exciplex states, modeling of the XPAL system is far more complicated than classic diode pumped alkali laser (DPAL) modeling. In this paper we discuss BLAZE-V multi-dimensional modeling of this new laser system and compare with experiments.

We describe a series of measurements of absorption and laser induced fluorescence on cells that contained cesium and rubidium and a rare gas: He, Ar, Kr, or Xe. These studies showed strong blue wing absorption to the short wavelength side of the alkali atom D2 lines due to collisionally formed Cs- or Rb-rare gas excimers. We also have observed an efficient two photon excitation of higher lying states in Cs and Rb that produces both intense blue emission and IR atomic emission in the 1.3 to 3.8 μm spectral region.

Cornell University is developing a high brightness, high average current electron source for the injector of an Energy Recovery Linac (ERL) based synchrotron radiation source. Master oscillator-power amplifier (MOPA) laser systems have been developed to satisfy the requirements of the Cornell ERL high brightness electron photoinjector. One system operates at 50-MHz and low average power, and the second system operates at 1.3 GHz and high average power. The GHz system is comprised of a commercial harmonically mode-locked Yb-fiber oscillator, a SMF pre-amplifier, and a double-clad, large-mode area Yb-doped fiber amplifier. Currently, the system provides 45 watts infrared power in a train of 3-ps-long pulses at 1.3 GHz in a near diffraction-limited beam. A BBO Pockels cell is used to generate macropulse trains at various repetition rates. The infrared pulses are frequency-doubled to produce green beam average power of 15 watts. The green pulses (Gaussian shape, FWHM 2.5 ps) are efficiently shaped to flat-top pulses with sharp rise and fall times through differential delay in a set of birefringent crystals (YVO₄). The transverse shaping is implemented with commercial refractive beam shaper (Newport). The laser systems design and characterization will be presented. Future work will address achieving of even larger average powers.

A fiber-optic RF distribution system has been developed for synchronizing lasers and RF plants in short pulse FELs. Typical requirements are 50-100fs rms over time periods from 1ms to several hours. Our system amplitude modulates a CW laser signal, senses fiber length using an interferometer, and feed-forward corrects the RF phase digitally at the receiver. We demonstrate less than 15fs rms error over 12 hours, between two independent channels with a fiber path length difference of 200m and transmitting S-band RF. The system is constructed using standard telecommunications components, and uses regular telecom fiber.

The Space Elevator Games with $2 Million in prize money is one of the most exciting challenges in the NASA Centennial Challenges program. We had an 8kW TRUMPF laser beaming power straight up 1 kilometer to a moving vehicle. This paper is the team captain's analysis of the state of the art in power beaming, and the excitement and challenge of the games themselves. Predictions are made of what new technology we will see in the next round of the games coming spring 2010.