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A design for generation of two ultra-high power laser beams, 130 TW and 1.4 PW, using a chain of optical parametric chirped pulse amplifiers, first pumped by a 10 Hz frequency doubled Nd:YAG laser, and later by the frequency tripled single-shot kilojoule level iodine laser Prague Asterix Laser System is presented. Expected enhancement of the parameters in the upgrade, besides the output power, are up to 1022 W/cm2 from 1016 W/cm2 in target intensity, and about 20 fs from 0.5 ns in pulse duration. Owing to the limited dimensions of the Prague Asterix Laser System building, the lay-out of the new equipment had to use only the left-over space in the laser hall. [ABSTRACT FROM PUBLISHER]

Abstract: The Asterix iodine laser of the PALS laboratory in Prague, operating at 1315nm fundamental frequency, 300ps pulse duration, 600J maximum pulse energy and 1016 W/cm2 intensity, is employed to irradiate thin hydrogenated targets placed in high vacuum. Different metallic and polymeric targets allow to generate multi-energetic and multi-specie ion beams showing peculiar properties. The plasma obtained by the laser irradiation is monitored, in terms of properties of the emitted charge particles, by using time-of-flight techniques and Thomson parabola spectrometer (TPS). A particular attention is given to the proton beam production in terms of the maximum energy, emission yield and angular distribution as a function of the laser energy, focal position (FP), target thickness and composition. [Copyright &y& Elsevier]

Abstract: Iodine radical reactions in single free-falling microdroplets of iodododecane, initiated using UV laser photolysis, are probed using Raman spectroscopy. Stimulated Raman spectra, with 532nm laser excitation, are recorded at varying time delays from the UV pulse. I atom recombination reactions lead to I2 that changes the optical properties of the microdroplet ultimately quenching the Raman signal. This quenching is observed over ∼10ns, which is about the time resolution of the two-laser experiment. Although the kinetics are too rapid to be measured in current laser configuration, it demonstrates that radical kinetics can be followed in single microdroplets. [Copyright &y& Elsevier]

A simple one-dimensional (1D) computational fluid dynamics (CFD) model of the chemical oxygen iodine laser (COIL) with supersonic mixing is compared with three-dimensional (3D) CFD models and with experimental measurements of the COIL parameters. Dependence of the gain, iodine dissociation fraction and temperature at the resonator optical axis and of the output lasing power on the iodine flow rate predicted by the 1D model is in good agreement with that found using 3D models and experimental results. Hence the 1D model can be used instead of much more complicated 3D models for estimates of the working parameters of supersonic COILs. [ABSTRACT FROM AUTHOR]

A two-stage optical parametric amplifier driven by a frequency-tripled beam from the high-energy iodine laser system SOFIA was built. This single-shot Optical Parametric Chirped Pulse-Amplification facility (OPCPA) and the system synchronizing the pump and signal pulses are described in detail. The chirped seed pulse of a Ti:sapphire oscillator running at the central wavelength of 800 nm is amplified in the two-stage (LBO and KDP) optical parametric amplifier over 10 times. The amplified spectral bandwidth of 68 nm corresponds to the pulse duration of 14 fs when a transform-limited pulse is assumed. This implies a compressed pulse of TW power. Systematic gain measurements reveal a good match with the theoretical predictions. Signal and idler beam fluence profiles are presented. The suitability of the iodine photo-dissociation laser as a pump source for the OPCPA technique is thus proved for the first time experimentally. A distinctive feature of the iodine laser is its very narrow gain bandwidth (<0.1 cm) and, therefore, the conventional chirped-pulse amplification technique does not lead to pulse durations at the femtosecond level. [ABSTRACT FROM AUTHOR]

The iodine laser at PALS Laboratory in Prague, operating at 1315 nm fundamental harmonics and at 300 ps FWHM pulse length, is employed to irradiate thin hydrogenated targets placed in vacuum at intensities on the order of 1016 W/cm2. The laser-generated plasma is investigated in terms of proton and ion emission in the forward and backward directions. The time-of-flight technique, using ion collectors and semiconductor detectors, is used to measure the ion currents and the corresponding velocities and energies. Thomson parabola spectrometer is employed to separate the contribution of the ion emission from single laser shots. A particular attention is given to the proton production in terms of the maximum energy, emission yield, and angular distribution as a function of the laser energy, focal position, target thickness, and composition. Metallic and polymeric targets allow to generate protons with large energy range and different yield, depending on the laser, target composition, and target geometry properties. [ABSTRACT FROM AUTHOR]

A photodissociation iodine laser with an intracavity spatio-temporal light modulator controlled by an external photodetector array is studied experimentally. The feasibility of lasing in different directions determined by a light signal is demonstrated. The laser radiation energy is 11 J per pulse, and the duration and divergence of the pulse are 180 μs and 1.2 × 10 rad, respectively. [ABSTRACT FROM AUTHOR]

Abstract: Radiative shock waves propagating in xenon at a low pressure have been produced using 60joules of iodine laser (λ =1.315μm) at PALS center. The shocks have been probed by XUV imaging using a Zn X-raylaser (λ =21nm) generated with a 20-ns delay after the shock creating pulse. Auxiliary high-speed silicon diodes allowed performing space- and time-resolved measurement of plasma self-emission in the visible and XUV. The results show the generation of a shock wave propagating at 60km/s preceded by a radiative precursor. This demonstrates the feasibility of radiative shock generation using high power infrared lasers and the use of XRL backlighting as a suitable diagnostic for shock imaging. [Copyright &y& Elsevier]

In this work, we studied the output power enhancement of an all gas-phase iodine laser (AGIL) by the addition of hydrocarbon gases. Enhancement is expected because hydrocarbon gases might scavenge Cl atoms, which are strong quenchers of the upper state of the laser medium, I( P). In AGILs, suppression of the Cl atom concentration is the key to improving the efficiency of the operation of the laser because Cl atoms are inherently generated by the self-annihilation of the energy donor, NCl(a Δ). We found that the addition of CH gave the best results, because of its high scavenging rate constant and inertness to I( P). An enhancement of 10% was observed in the output power when CH was added at a flow rate twice that of NCl. On the other hand, when CH or CH were added at the same flow rate as that of CH, the output power reduced despite their fast removal rate of Cl atoms. The reason for the reduced output power was that the unsaturated bonds scavenged not only the Cl atoms but also the H atoms, resulting in a low density of H atoms, and this decelerated the production of NCl(a Δ). The observed laser characteristics could reasonably be explained by numerical model calculations. To our knowledge, this is the first report of successful output power enhancement of an AGIL using a chemical agent. [ABSTRACT FROM AUTHOR]

We have investigated the interaction of regular and irregular structures - systems of shock waves, rarefaction waves, and turbulent layers - in a chemical oxygen-iodine laser. [ABSTRACT FROM AUTHOR]

The characteristics of an amine-based all-gas-phase iodine laser (AGIL) are studied. At constant flow rates of the chemical species, the small-signal gain and laser output power are measured at three different positions in the flow reactor. It is clarified that the positive gain exceeding the threshold (2.3×10%/cm) is maintained over a region more than 80 mm long along the flow. The highest small-signal gain of 7.8×10%/cm and laser output power of 50 mW are observed at 170 mm downstream from the mixing point of HI and H. Numerical simulations suggest that the long positive-gain region is attributable to the following characteristics of the present apparatus: inefficient mixing and inefficient H dissociation. It is confirmed experimentally and numerically that these limitations are beneficial for extending the positive-gain region to the downstream; however, the optimum HI flow rate is limited a small value and results in a much lower gain than the theoretical limit. In order to achieve a higher gain, fast mixing and efficient H dissociation must be simultaneously achieved so as to increase the optimum HI flow rate. Numerical simulation results suggest that a positive gain of 5.4×10%/cm, a 7-times higher gain than that indicated by the present experimental results, should be obtained with the same NCl flow rate. [ABSTRACT FROM AUTHOR]

Abstract: A chemical oxygen–iodine laser (COIL) is an electronic transition, low pressure, high throughput system. The field use of this laser demands the development of suitable pressure recovery systems. Ejector based pressure recovery systems form a potent alternative for open cycle COIL operation. The two possible configurations of motive gas injection in ejectors are peripheral and central. The present paper focuses on the investigation of a central injection low pressure ejector operated with a small scale supersonic COIL (SCOIL). The ejector handles a motive flow of nearly 120gs−1 and an entrained laser flow of nearly 3gs−1. The predicted geometry using integral methods has been validated numerically by employing Fluent 6.1 software in a 2-d axisymmetric viscous turbulent flow formulation. The numerical predictions have been experimentally validated, which indicate a pressure recovery of 63Torr at design conditions. The results also show that the recovered pressure improves to 75Torr for an off-design condition of higher motive flow rate. [Copyright &y& Elsevier]

spray type of singlet oxygen generator for driving the Chemical Oxygen-Iodine Laser was developed. Singlet oxygen, O(Δ), is generated by a fast reaction of chlorine with basic hydrogen peroxide solution in the form of a dense spray. A mathematical model of this reaction system showed that O(Δ) can be generated in this system with a high yield (0.70–0.80), high utilization of chlorine (0.75–0.95), and effective utilization of liquid (0.36–0.54) at very high generator pressures (35–75 kPa). Experimental studies of this reaction system without an efficient separation of liquid proved an efficient O(Δ) production characterized by a rather high product of chlorine utilization and O(Δ) yield (0.4–0.9) at very high generator pressures (30–80 kPa). This pressure is much higher than the operation pressure used in other generators, which should be beneficial for a pressure recovery system of the COIL. These results provided the basis for designing a centrifugal spray generator with an efficient separation of liquid from the gas flow, which is the subject of the following paper. [ABSTRACT FROM AUTHOR]

centrifugal spray generator of singlet oxygen, O(Δ), for driving a chemical oxygen-iodine laser was developed and its operation was experimentally studied. Modeling of the liquid separation from the gas flow showed that the separator designed could remove droplets larger than 0.5 μm from gas, which is very important for the laser operation. This result was confirmed by experiments. Experimental studies proved that O(Δ) could be produced with a high efficiency (chlorine utilization 0.68–0.87 and O(Δ) yield 0.35–0.7) even at very high generator pressures (25–70 kPa), which cannot be attained by other O(Δ) generators. [ABSTRACT FROM AUTHOR]

A chemical gas-phase reaction between CI2 and HI was used in the generation of molecular iodine for the chemical oxygen--iodine laser (COIL) operation. A yield of I2 in the generation reaction up to 85% was achieved in a reasonable volume of the reactor. A small-signal gain up to 0.75%/cm at a temperature of 150K in the center of supersonic cavity was measured. A comparison with the established evaporation way of I2 delivery confirmed that the chemical method has little or no impact on the COIL pumping kinetics. This chemical method is easily scalable and can simplify the COIL operation by providing better control of I2 flow rate. [ABSTRACT FROM AUTHOR]

We report on the investigation of strong radiative shocks generated with the high energy, sub-nanosecond iodine laser at PALS. These shock waves are characterized by a developed radiative precursor and their dynamics is analyzed over long time scales (∼50 ns), approaching a quasi-stationary limit. We present the first preliminary results on the rear side XUV spectroscopy. These studies are relevant to the understanding of the spectroscopic signatures of accretion shocks in Classical T Tauri Stars. [ABSTRACT FROM AUTHOR]

Abstract: Classical supersonic chemical oxygen iodine laser (SCOIL) systems operate under a low total pressure of nearly 18Torr (2400Pa) with cavity pressure being in the range 3Torr (400Pa) and Mach number of 1.7. These systems handle high flow rates and hence an efficient supersonic diffuser (SD) is a critical first step towards an open-cycle operation, which may be followed by a multi-stage ejector system. The present study discusses the various aspects in the design of a supersonic diffuser for a twin 10kW COIL module source which employs flow rates of 100gs−1 in each module. The results of computational studies based on 3-D, viscos compressible flow, k–ε turbulence formulation for the supersonic diffuser geometry have also been discussed. The experimental results from a single-module test of the supersonic diffuser show that a total recovered pressure of nearly 7Torr is achieved at the diffuser exit. [Copyright &y& Elsevier]

Abstract: Surface-assisted laser desorption/ionization (SALDI) is a matrix-free mass spectrometry (MS) approach that utilizes the unique properties of a nanostructured surface to promote desorption and ionization. However, there are still questions on what constitutes a suitable SALDI substrate for mass spectrometric application. A range of SALDI substrates prepared by anodization with an oxidizing electrolyte was investigated. The laser desorption/ionization (LDI) performance was examined on a reflectron time-of-flight (ToF) mass spectrometer. The physicochemical properties of the substrates were characterized by a number of surface analysis techniques including scanning electron microscopy (SEM), atomic force microscopy (AFM), secondary ion mass spectrometry (SIMS), X-ray photoelectron spectroscopy (XPS) and water contact angle measurement. Examination of surface cleaning technologies and methods for surface chemical modification were carried out. Correlation between the substrate physicochemical properties and the LDI performance was determined. It was found that only the substrate, which had a thick nanostructured layer, was effective for LDI-MS. SALDI substrate was found to have a high surface potential. However, this unique property offered no advantage for the application of LDI-MS. Surface chemistry is also an important factor in affecting the LDI performance. Plasma etching can effectively remove the surface contamination but it also increases the thickness of the oxide layer. Fluorine and hydroxyl termination is advantageous. Fluorine passivation increases the surface hydrophobicity, which confines the analyte solution droplet to a smaller area and also withdraws the electronic density from the surface, and acidifies the surface Si–OH moieties, which is believed a major proton source. The effect of laser etching was investigated by SIMS and XPS imaging and provided new insight of the SALDI ionization mechanism. [Copyright &y& Elsevier]

The hybrid iodine photodissociation laser SOFIA has been constructed. The pulse feeding the amplifier chain is the idler wave of an optical parametric oscillator (OPO) tuned to the atomic iodine transition at 1315 nm. This solid-state oscillator enables ps-synchronization to other laser systems. A homemade automatic stabilization of the OPO idler wave as to wavelength and pointing ensures long-term stable operation of the whole system. The active medium of the SOFIA amplifiers is a mixture of C3F7I and He. The SOFIA pulses are frequency-tripled in two KD*P crystals and then serve as the driver in a two-stage optical parametric amplification scheme in which chirped broadband Ti:sapphire laser pulses are amplified (OPCPA). [ABSTRACT FROM AUTHOR]

New values of a number of kinetic constants of processes proceeding in oxygen-iodine laser media are presented. The total probabilities of formation of I2( X, 15 ≤ v ≤ 24) and I2( X, 25 ≤ v ≤ 47) molecules in the course of quenching of I* atoms by I2( X) are found to be 0.9 and 0.1, respectively. The quantum yield of singlet oxygen in the reaction O(1 D) + N2O → N2 + O2( a1Δ) is close to 100%. The quenching rate constants of I2( A’) by O2, H2O, CO2, I2, and Ar and of I(2 P1/2) by O(3 P), O3, NO2, N2O4, and N2O are presented. [ABSTRACT FROM AUTHOR]

Abstract: Iodine flow rate (IFR) measurement is an essential diagnostic tool in the research and optimization of chemical oxygen–iodine laser (COIL) system. Venturi meter or absorption spectroscopy was used to monitor IFR. But it is difficult for Venturi meter to precisely measure IFR. Simple absorption spectroscopy has trouble monitoring IFR due to the contamination on diagnostic windows and aerosol scattering. An advanced absorption spectroscopy for measuring IFR was described in this paper. The method utilizes two wavelengths (e.g. 470nm and 365nm) to distinguish between iodine vapor absorption and other optical losses (e.g. contamination and aerosol scattering). It can easily eliminate the influence of the serious contamination and aerosol scattering on IFR measurement and obtain a reliable IFR. The method is about to apply in COIL studies as a routine diagnostic tool. [Copyright &y& Elsevier]

AbstractUsing the PALS iodine laser system, Au ions with the charge state up to 58+ and with the kinetic energy as high as ~300 MeV were generated. The production of these ions was tested in dependence on the laser frequency (1?, 3?), on the irradiation/detection angles (0?, 30?), on the focus position with regard to the target surface, and on the target thickness (500??m, 200??m, 80??m). A larger amount of the fastest ions was produced with 1? than with 3?, the most of the fast ions were recorded in the direction ~10?from the target normal, the optimum focus position is in front of the target and should be set on with a precision of 50??m. The forward emission is weaker than the backward one for both of the thinner targets (which burn through) at our experimental conditions. [ABSTRACT FROM AUTHOR]

AbstractInteractions of laser driven plasma jets with He and Ar gas puffs was investigated experimentally by means of three-frame interferometric/shadowgraphic system and three-frame X-ray pinhole camera. A defocused iodine laser beam using the Prague Asterix Laser System (PALS) interacting with massive planar Cu targets generated high-speed well-collimated plasma jets. The PALS third harmonic (0.438??m), with pulse duration of 250?ps (full width at half maximum), and energy of 100?J was employed in two irradiation geometries: with an incidence normalto the target surface and with an obliqueone (30?with respect to the target normal), in order to minimize the heating of the ambient gas by the laser beam. The results of these interaction experiments, in particular, those obtained in case of the oblique incidence geometry, are presented and discussed. They show the effect of the double shock formation in ambient gases: starting by the ablative plasma action, followed by that of the jet. [ABSTRACT FROM AUTHOR]

The process of laser beam homogenization in a gas medium placed in front of a thin metallic foil has been studied. Experiments were performed using the Prague Asterix Laser System iodine laser [Jungwirth et al., Phys. Plasmas 8, 2495 (2001)] working at 0.44 μm wavelength and irradiance of about 1015 W/cm2. Homogenization was detected both by directly analyzing the transmitted laser beam and by studying the shock breakout on the foil rear side. Results show that the gas ionization by the laser pulse induces a strong refraction and produces an effective smoothing of large-scale intensity nonuniformities. [ABSTRACT FROM AUTHOR]

Investigations of powerful laser pulse action on planar flyer targets consisting of the layers of different materials are of importance from the basic as well as the applied physics point of view. One important aspect of this research deals with optimization of inertial fusion targets design. Here, the role of a thin heavy metal layer as a protector against preliminary heating of compressed thermonuclear fuel by thermal X-ray radiation can be mentioned as one particular topic to be properly understood. In this paper, the results of our studies of such a thin layer influence on the laser-produced energy deposition in the flyer foils as well as on the hydrodynamic motion of the foils as a hole will be reported. A 0.4 μ m thick gold layer was located between an aluminum layer of 6 μ m thickness and mylar layer with thickness of 2.5 μ m, used here as an ablator. For comparison, the flyer target without the gold layer but of the same area density was employed. Two different target constructions were used: (1) with a 2 mm gap separating the foil and the massive targets for measuring the foil velocity and (2) with gaps of 50, 100 and 200 μ m for laser energy transfer efficiency measurements. Targets were irradiated by laser beam energies of ∼100 J in the case of the first harmonic, and by laser beam energies ∼120 J in the case of the third one using the Prague Asterix Laser System iodine laser. The interaction spot radius of 200 μ m and the laser pulse duration of ∼250 ps were employed in these experiments. A three-frame interferometric and shadowgraphic system was set-up as to measure velocities of the rear side of the foils and to determine electron density distributions at different stages of plasma evolution. Volumes of craters produced by collisions of accelerated foils with a massive aluminum block were used as an indicator of the laser energy transfer efficiency into the foils of both types. These experiments have shown that the presence of the thin gold layer causes a decrease of the flyer velocity by a factor of ∼1.2 for both the harmonics. However, in the case of the first harmonic, the energy transfer into the flyer with the gold layer is higher (compared with the flyers without the gold layer) only for the targets with smaller gaps. In the case of the third harmonic, about 10% decrease in the amount of energy transferred into the foil with the gold layer was observed. [ABSTRACT FROM AUTHOR]

Abstract: A chemical method of atomic iodine generation followed by iodine injection into the supersonic nozzle of Chemical Oxygen–Iodine Laser (COIL) was studied experimentally. This method is based on the reaction of gaseous hydrogen iodide (or deuterium iodide) with fluorine atoms formed in a preceding reaction between molecular fluorine and nitrogen oxide. Iodine atoms are generated in specially designed reactors and then injected into the primary gas flow in the COIL cavity. Concentration profiles of atomic iodine along the primary gas flow or perpendicularly to it were measured in dependence on the flow rates of reaction gases. Very high concentrations of atomic iodine (up to 3.2×1015 cm−3) were measured in the laser cavity when the primary gas contained no singlet oxygen, O2(1Δg). Yields of atomic iodine related to either F2 or HI were rather high (I/F2 ⩽100%, I/HI⩽60%). A small signal gain on the I∗–I laser transition was measured when atomic iodine was injected into the primary gas containing singlet oxygen. The measured gain was lower than the gain estimated from the determined concentration of atomic iodine, temperature, and O2(1Δg) yield measured upstream the iodine admixing. This difference was ascribed to the O2(1Δg) quenching by some product of DI oxidation (probably the radical ). [Copyright &y& Elsevier]

Investigations of plasma jets produced by the action of a defocused laser beam on planar metallic targets and the interaction of supersonic plasma jets with dense gases (He and Ar) are presented. The experiment was carried out at the iodine laser facility (Prague Asterix Laser System (PALS)) using the third harmonic of laser radiation (0.438 µm) with a pulse duration of 250 ps (FWHM). In order to optimize the plasma jet parameters, the laser beam energy and the focal spot radius were changed in the ranges of 13-160 J and 35-600 µm, respectively. Besides, the focal point was located both before and inside the targets. The study was performed with the use of target materials of different mass densities (Cu, Ag and Ta). Finally, the optimized Cu plasma jets were used for shock wave generation in ambient gases of different pressures.Information about the geometry of plasma expansion, plasma dynamics and electron density distributions was obtained by means of a 3-frame laser interferometric system. Additionally, a Photonic Science PE7051 x-ray pinhole camera and the crater replica method for the reconstruction of crater parameters were used.Our experiment has shown that the plasma jet forming is a fundamental process which accompanies the expansion of the laser plasma produced by irradiating a massive planar target, made of a material of a relatively high atomic number, with a partly defocused laser beam. One can suppose that there are no laser energy limitations for the plasma jet creation. Illustrations of applications of such plasma jets for astrophysical and inertial confinement fusion investigations are also presented. [ABSTRACT FROM AUTHOR]

Quenching of excited iodine atoms (I(5p5, 2P12)) by nitrogen oxides are processes of relevance to discharge-driven oxygen iodine lasers. Rate constants at ambient and elevated temperatures (293−380 K) for quenching of I(2P12) atoms by NO2, N2O4, and N2O have been measured using time-resolved I(2P12) → I(2P32) 1315 nm emission. The excited atoms were generated by pulsed laser photodissociation of CF3I at 248 nm. The rate constants for I(2P12) quenching by NO2and N2O were found to be independent of temperature over the range examined with average values of (2.9 ± 0.3) × 10-15and (1.4 ± 0.1) × 10-15cm3s-1, respectively. The rate constant for quenching of I(2P12) by N2O4was found to be (3.5 ± 0.5) × 10-13cm3s-1at ambient temperature. [ABSTRACT FROM AUTHOR]

We present a series of experimental results, and their interpretation, connected to various aspects of the hydrodynamics of laser produced plasmas. Experiments were performed using the Prague PALS iodine laser working at 0.44 μm wavelength and irradiances up to a few 1014 W/cm2. By adopting large focal spots and smoothed laser beams, the lateral energy transport and lateral expansion have been avoided. Therefore we could reach a quasi one-dimensional regime for which experimental results can be more easily and properly compared to available analytical models. [ABSTRACT FROM AUTHOR]

We present a stabilized semiconductor laser system designed to operate as a fiber-optic front-end master oscillator of a pulsed high-power iodine laser Prague Asterix Laser System (PALS). The replacement of the PALS master oscillator is a part of a broader effort to rebuild PALS into a laser generating shorter pulses with higher pulse power by the technique of optical parametric chirped pulse amplification. With an operating wavelength of 1315.15 nm the stabilized laser master oscillator is based on a telecommunication single-frequency distributed feedback diode. The frequency stabilization is derived from transitions in thermally dissociated iodine. Locking to the selected transition is fully automatic and the control system employs a unique combination of control loops derived from temperature and absorption to overcome the problem of narrow locking range of a single absorption line. [ABSTRACT FROM AUTHOR]

Abstract: The chemical oxygen–iodine laser (COIL) is the only chemical laser based on electronic transitions. It is essentially a low pressure, high flow rate system requiring high capacity vacuum pumps for its operation in its standard form. Since, the output power of COIL systems is a direct function of the input fuel rate, power scale up of these systems is a definite possibility which can be utilized in numerous civil and defense applications. However, scaling up and field applications necessitates exploration of possible means of reduction in size of vacuum systems for which an efficient ejector based pressure recovery system qualifies to be the prime candidate. In this paper, the gas dynamic aspects of a two-stage peripheral air ejector system suitable for a 500W class COIL employing a flow rate of ∼3 gm/s have been presented. The experimental results with this developed ejector system for the simulated flow conditions of the laser under vacuum have indicated a start up pressure in excess of ∼50Torr in the first stage and more than ∼600Torr in the second stage. The experimentally observed flow parameters at various locations in the flow field have been validated with the computational results obtained employing Fluent 6.1 software using 2-D axi-symmetric formulation. [Copyright &y& Elsevier]

One of the main goals of the study of plasmas generated by short or ultrashort laser pulses is the estimation of a complex parameter as the evaluation of the plasma temperature. Considering the laser-target and laser-plasma interactions as nonequilibrium processes, it is not possible to define a unique plasma temperature because the behavior of the different subsystems such as ions, electrons, neutral particles, and photons is not uniformly correlated, and the physical parameters can be different in different values of the plasma plume. In this work different experimental setups and techniques and different empirical and theoretical approaches are compared by using a Nd:YAG laser with an intensity of 1010 W/cm2 and an iodine laser with an intensity of 1015–1016 W/cm2. Time-of-flight measurements have been performed with an ion-energy analyzer and by using a number of Faraday cups in order to measure the velocity and the kinetic energy of ions and electrons emitted by the plasma. The obtained results have been relevant to confirm that by using a Nd:YAG laser the plasma ion temperature in the plasma core is about 400 eV. The electron emission indicates the presence of hot electrons with an energy of about 1 keV. These results will be compared with the ones obtained with the powerful iodine laser at Prague Asterix Laser System. [ABSTRACT FROM AUTHOR]

High-throughput operation of a supersonic chemical oxygen-iodine laser (COIL) is achieved with an advanced mixing nozzle. The mixing nozzle consists of a staggered arrangement of thin wedges lying across the flow duct, and looks like the letter "X" when it is viewed from the side. A 32.9% chemical efficiency is measured experimentally with this nozzle and buffer-gas precooling. Computational fluid dynamics (CFD) calculations are conducted to understand the rapid mixing capability of the nozzle. A series of streamwise vortices generated by the alternating wedges greatly enhances the mixing process in the supersonic stream and the rapid formation of the gain medium. The temperature and Mach number of the flow field are estimated from the gain-profile measurement of the I (²P1/2) to I (²P3/2) transition. Good agreement with the CFD calculations is seen. [ABSTRACT FROM AUTHOR]

The use of supersonic nozzles for the driver nitrogen in an ejector nozzle bank (ENB) for chemical-oxygen iodine laser (COIL) resulted in the elimination of the chocking effect for the primary oxygen flow and formation of a low temperature gain medium. The ENB generates a supersonic gain medium with a Mach number greater than 2.2, and a temperature less than 200 K. The potential recovered pressure was 90 Torr with a small signal gain greater than 10-2 cm-1. With a 5 cm gain length for this nozzle, the output power was 1.2 kW with a chemical efficiency of 23.4%. A strong decay of I(2 P1/2) emission, (concentration), along the gain medium flow was observed . [ABSTRACT FROM AUTHOR]

Abstract The composition of various gas effluents and their flow parameters viz. flow rate, pressure and Mach number are very crucial in determining the output of high power infrared gas lasers. PC based real time gas Flow Control and Analysis (FCA) System which is the heart of the high power infrared gas lasers such as CO2 Gas Dynamic Laser (10.6m), Hydrogen Fluoride-Deuterium Fluoride (2.73.4m) and Chemical Oxygen Iodine Laser (1.315m) has been developed and successfully tested for its applications in Chemical Oxygen Iodine Laser (COIL). The system has been realized using the state of the art PCI bus based high-speed data processing electronics, a personal computer and electro-pneumatic components. The system has demonstrated its capability of controlling the flow rates in the range of 1-6500 lpm (in case of nitrogen) with a response time of 50 msec which is mainly limited by the response of the electro-pneumatic valves and pressure reducers used in the present system. The developed system also has the potential to monitor, estimate and display various flow parameters at critical locations of the laser system. More than 600 successful power runs of the COIL have been given using the developed FCA system. [ABSTRACT FROM AUTHOR]

The high-power iodine laser system PALS (λ0=1.315 μm at the fundamental laser frequency, 1ω, and λ1/3=0.438 μm at the third harmonic frequency, 3ω), with a maximum laser intensity IL of up to about 3×1016 W/cm2, was used to generate highly charged Ta ions. Maximum ion charge states slightly above z=50+ were determined by using an electrostatic ion energy analyzer and the maximum energy of emitted ions, estimated from the ion collector signals, was even higher than Ei=22 MeV, as determined by track detectors. Charge-state distributions, as well as charge-energy distributions were evaluated for both 1ω and 3ω laser frequencies. The focus position with regard to the target surface (in addition to the focus spot size) determines not only the laser power density deposited and the amount of produced ions, but it also directly influences the mechanisms of ion generation. Highly charged ions with the charge states above 50+ can be generated either by using a sufficiently high laser intensity (about 1×1016 W/cm2) or, at lower laser intensities (IL>2×1014 W/cm2), in the case where the conditions for the relativistic self-focusing are met. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The demonstration and characterization of a multiwatt all gas-phase iodine laser (AGIL) are described. A 20-cm subsonic reactor was used to produce NCI(a¹Δ) for a series para. metric studies of the I[sup *] (2 P[sub 1/2]) - I (²P[sub 3 /2] ) small-signal gain and extracted power dependence on reactant flow rates and reaction time. The highest measured gain was 2.5 × 10[sup -4] cm[sup -1] and the highest power observed was 15 W. [ABSTRACT FROM AUTHOR]

The iodine laser PALS operated at the fundamental 1ω[sub0] and third harmonic 3ω[sub0] frequencies (wavelengths 1315 run and 438 nm, respectively) was used for the generation of plasmas of various Z-number targets. The investigation were performed at energies up to 800 J and 250 J for 1ω[sub0] and 3ω[sub0], respectively, in the 400 ps pulses. In these conditions attention is paid to the application of the solid state nuclear track detectors of the PM-355 type for measurements of parameters of ions emitted from the laser produced plasmas. Detector samples were masked with different A1.-foil filters for making possible a rough estimation of ion energy. Track densities of the order of magnitude > 10[sup7] tracks/cm² were observed on the uncovered detectors and on detectors masked with 0.75 and 1.5 µm thick A1.-foils. It confirms that Ag-, and Ta-ions of energy in the MeV range were emitted from the targets irradiated with the laser pulses. The ion streams were estimated on the basis of the track densities for different experimental conditions. The results were compared with those obtained with the use of ion collectors. [ABSTRACT FROM AUTHOR]

The crater formation process is studied in the "laser - Al solid target" interactions on the PALS (Prague Asterix Laser System) iodine laser facility. A great variety of laser beam parameters are used to irradiate massive aluminum targets. Large laser energies available (up to 600 J) open a possibility to investigate the process of crater formation for physical conditions different from the earlier studies for the lower laser energies. Comparison with the earlier results is presented. A simple theory LSM (laser simulation method) has been applied for the analysis of the experimental results. This model leads to a universal relation (scaling law) for the crater relative volume. Our work expands the study of crater formation to the "virtual" macroparticle velocities exceeding 100 km/s. The scaling law is derived here for this previously unexplored region. An alternative method of studying crater formation is also proposed. [ABSTRACT FROM AUTHOR]

Experimental results have demonstrated that the use of ejector-nozzle concepts can allow to achieve simultaneously high chemical efficiency and high pressure recovery in a chemical oxygen iodine laser. The estimated small-signal gain of the gain medium generated by these nozzle banks was from 0.5 to 0.8 %/cm. In laser experiments with all nozzle banks (NB-1-NB-5), Pitot pressures of the order of 80 Torr and Mach numbers of ∼2 in the cavity-mixing chamber have been achieved. The geometry of a given ejector-nozzle bank and gas-flow conditions affect the power extraction and chemical efficiency. The main factors for high efficiency and high power are small mixing scale, high area for the oxygen flow, dilution of chlorine by helium, and the arrangement of nozzles. A chemical efficiency of 25% at a power level of ∼900 W was obtained for NB-1 having the smallest mixing scale, parallel injection of all flows, and dilution of oxygen by helium. The highest power of ∼1.2 kW with a chemical efficiency of 19.5% and 160 W/cm[SUP2] of specific output power was achieved with NB-5 having the largest area for the oxygen flow and dilution of oxygen by helium. [ABSTRACT FROM AUTHOR]

During the operation of a chemical oxygen iodine laser (COIL) with an unstable resonator of a large Fresnel number, as the output power increases, an instability of the output laser beam will appear, behaving mainly as far-field beam spot drift and deformation. In order to interpret this phenomenon, thermal expansion analysis on the scraper with finite element analysis method and a simulation of the output beam mode of this kind of laser by the method of Fast Fourier Transform were developed. From the experimental measurement and the calculation, we proposed that the presence of the nonuniform temperature distribution of scraper causes the front surface of the scraper to tilt and bulge due to thermal expansion. As the output power is increasing, all the mirror surfaces, especially the scraper''s, will absorb more and more heat, causing thermal expansion of the mirror front surface to occur more seriously, thus resulting in the tilting and deformation of the far-field beam spot. The initial misalignment of the direction is also an important factor leading to the far-field beam spot drift and deformation. [Copyright &y& Elsevier]

The possibility of obtaining a high specific input energy in an electron-beam sustained discharge ignited in oxygen gas mixtures O2 : Ar : CO (or H 2) at the total gas pressures of 10–100 Torr was experimentally demonstrated. The specific input energy per molecular component exceeded ~6 kJ l -1 atm -1 (150 kJ mol -1) as a small amount of carbon monoxide was added into a gas mixture of oxygen and argon. It was theoretically demonstrated that one might expect to obtain a singlet delta oxygen yield of 25% exceeding its threshold value needed for an oxygen–iodine laser operation at room temperature, when maintaining a non-self-sustained discharge in oxygen gas mixtures with molecular additives CO, H2 or D2. The efficiency of singlet delta oxygen production can be as high as 40%. [ABSTRACT FROM AUTHOR]