Electric breakdown and non-self-sustained electric discharge were triggered and guided by a train of ultrashort sub-TW ultraviolet (UV) pulses overlapped with a long free-running UV pulse of a hybrid Ti:Sapphire-KrF laser facility. Photocurrent sustained by this train is two orders of magnitude higher, and electric breakdown distance is twice longer than those for the discharge triggered by the long UV pulse only. UV filaments of ~100 m length were observed when transporting the laser radiation over the long distance.
Non-self-sustained electric discharge and electric breakdown were triggered and guided by a train of ultrashort sub-TW ultraviolet (UV) pulses overlapped with a long free-running UV pulse of a hybrid Ti:Sapphire - KrF laser facility. Photocurrent sustained by this train is two orders of magnitude higher, and electric breakdown distance is twice longer than those for the discharge triggered by the long UV pulse only. When transporting the laser radiation over the long distance, UV filaments of ~ 100 m length were observed.
The radiation amplification and oscillation are obtained in an electron-beam-pumped Berdysh laser with an active
volume of 10 L in the visible range from 430 to 470 nm at the broadband 42Γ -1,2 2Γ transition in the triatomic Kr2F molecule of interest for amplification of ultrashort laser pulses. It is shown that, along with absorption of laser radiation in the active medium, the amplification dynamics is considerably determined by short-lived absorption induced in the amplifier windows by bremsstrahlung X-rays. For the specific pump power 0.6 ÷ 0.7MW cm-3, the gain, corrected for nonstationary absorption, was ~10-3 cm-1. A scheme of aKr2F amplifier is proposed for amplification of ultrashort pulses
up to multiterawatt peak powers in the active volume ~10 L.
Fluorescence and transient absorption spectra of various rare gas mixtures with additions of fluorine-containing gases
and nitrogen under e-beam pumping are investigated with the original time-gated probing technique. The obtained
results allow us to specify KrF laser kinetics. Weak amplification of radiation at broadband trimer Kr2F transition
(42Γ→1,22Γ) is demonstrated.
Mechanisms of nonlinear absorption and ionization of pure atomic argon and molecular nitrogen gases by UV femtosecond
laser pulses were studied using photogalvanic and photoacoustic techniques. The effect of the intermediate Rydberg
resonance, its dynamic Stark perturbation and ponderomotive upshift of the first ionization potential of argon
atoms and nitrogen molecules by the intense laser pulses has been revealed by observing an increase of a power slope of
ion yield from three to four at increasing laser intensity.
Generation of free-carrier plasma and filamentation of the ultra-short laser pulse were investigated and modeled.
Experimental results of filamentation are supported by numerical model which takes into account accumulation
of refractive index modifications due to multi-pulse exposure. A contact acoustic monitoring technique was
employed to perform spatially-resolved in situ detection of micro-plasma formation and filamentation of focused
femtosecond laser pulses with critical and sub-critical powers in glass. The recorded acoustic signals reveal freecarrier
generation mechanisms associated with the formation of plasma and filamentation of the propagating
laser pulses. Optical opacity of the plasma region, which sets in at the irradiance of a few kJ/cm3 (close to
the dielectric breakdown threshold) using pulse focusing optics with numerical aperture NA = 0.75, reveals its
critical character, and allows the estimation of acoustic pressure in the ~GPa range. The pressure depended on
the irradiance as P ~ I0.59. In the case of loose focusing (NA = 0.035) filamentation of fs-pulses occurred at
sub-critical plasma density with P ~ I. Detection and interpretation of these acoustic signatures thus enable
real-time in situ monitoring of optical ionization, pulse filamentation in bulk dielectrics under the irradiation by
femtosecond laser pulses.
The paper is devoted to R&D of novel experimental technique - laser-driven shock tube (LST) for modeling of
Rayleigh-Taylor (R-T) and Richtmyer-Meshkov (R-M) hydrodynamic instabilities development at the contact surface of
two immiscible liquids under a shock wave (SW) passage. 100-J, 100-ns KrF laser facility GARPUN has been used to
irradiate some opaque liquids. A homogenizing focusing system combined multi-element prism raster and a lens to
provide non-uniformity less then few percents across a square 7*7-mm spot, laser intensities being varied in the range of
q = 0.004 - 2 GW/cm2. Surface plasma blow off produced a planar SW propagated into the liquid. SW amplitudes as
high as 0.8 GPa weakly damping with increasing thickness were measured in dibutyl-phthalate (DBP), which strongly
absorbed UV laser light. Test bench experiments were performed to produce standing acoustic waves as initial
perturbations at the interface between two immiscible liquids.
The multi-stage hybrid laser system producing ultrashort pulses of radiation with peak power ~1014 - 1015 W being now under developing at the Lebedev Physical Institute of the Russian Academy of Sciences is discussed. The distinctive feature of the laser system is direct amplification of ultrashort pulses produced by a solid state laser system, first going through a prism stretcher with negative dispersion, in gas active medium without using a rather expensive and complicated grating compressor of laser pulses. Two hybrid schemes are being developed now based on the amplification of femtosecond pulses of the third harmonic of Ti:Sapphire laser at the wavelength 248 nm in the active medium of KrF laser amplifier, and on the amplification of the second harmonic of Ti:Sa laser at the wavelength 480 nm in the active medium of photochemical XeF(C-A)-laser excited by VUV radiation of an e-beam pumped Xe2 lamp. The final stage of the laser system is supposed to be an e-beam pumped facility with a laser chamber of 60 cm in diameter and 200 cm long in the case of KrF laser, and with another laser chamber of 30-40 cm in diameter put into the former one in the case of XeF(C-A) laser. The parameters of such e-beam facility are close to those of previously developed at the Institute of High-Current Electronics: electron energy ~600 keV, specific input power ~ 300-500 kW/cm3, e-beam pulse duration ~ 100-200 ns. A possibility of using Kr2F as an active medium with saturation energy 0.2 J/cm2 for amplification of ultrashort laser pulses is also under consideration. There was theoretically demonstrated that the energy of a laser pulse at the exit of the final stage of the laser system could come up to ~ 17 J with pulse duration ~50 fs in the case of KrF laser, and ~75 J with pulse duration of 25 fs in the case of XeF laser. Two Ti:Sa laser systems producing 50 fs pulses with energy ~0.5 mJ at the wavelength 248 nm and ~5 mJ at the wavelength 480 nm have been already developed and are being now installed at the Lebedev Institute.
Time-resolved fluorescence of Ar/Kr/F2 mixtures and transient absorption spectra were measured at Berdysh preamplifier module of GARPUN KrF laser facility pumped by 50 A/cm2, 350 keV, 100 ns e-beam. The experiments pursued an aim to obtain additional data on KrF laser kinetics, in particular, on the formation of Kr2F molecules and their influence on the absorption and extraction of KrF laser radiation in large-scale amplifiers. A possibility of femtosecond laser pulses amplification at broad-band Kr2F (42&Ggr;→1,2 2&Ggr;) transition is discussed.
Protective single-layer, AR double-layer, and HR multi-layer fluorine-resistant coatings with damage thresholds as high
as 20 J/cm2 were deposited for the intracavity optics of high-energy KrF lasers by using different deposition techniques.
They were tested by the atomic-force microscopy and IR Fourier spectrometry in regard of microstructure, porosity,
water content, and in prolonged etching by fluorine. The most promising were NdF3-based AR and HR coatings
produced by e-beam evaporation, while outstandingly low water content was demonstrated for MgF2 and Al2O3 layers
deposited by laser evaporation with a preliminary laser treatment of substrates.
Optical damage produced by femtosecond pulsed lasers on dielectric surfaces is extremely precise, allowing the damage mechanisms to be inferred from reproducible damage characteristics. Here nanoscale femtosecond laser ablation is applied to probe the ultrafast dynamics of laser energy deposition including the generation and transport of surface electron-hole or electron-ion plasmas. For shallow surface nano-craters fabricated on quartz and glass surfaces by single 0.53 &mgr;m or 1.05 &mgr;m laser shots, their corresponding well-defined laser intensity thresholds demonstrate pronounced effects of laser wavelength, crystalline state of the dielectric and laser waist radius, indicating equal importance of laser energy deposition and transport phenomena during ablation. Simultaneously, unusually deep surface nanoholes emerge drilled by self-focusing laser beam or forward-scattered highly penetrating short-wavelength radiation from the warm, dense surface plasma.
The multi-stage hybrid laser system producing ultrashort pulses of radiation with peak power ~1014 - 1015 W now under
developing at the Lebedev Physical Institute of the Russian Academy of Sciences is discussed. The distinctive feature
of the laser system is direct amplification of ultrashort pulses produced by solid state laser system, first going through a
prism stretcher with negative dispersion, in gas active medium without using a rather expensive and complicated grating
compressor of laser pulses. Two hybrid schemes are being developed now based on the amplification of femtosecond
pulses of the third harmonic of Ti:Sapphire laser at the wavelength 248 nm in the active medium of KrF laser amplifier,
and on the amplification of the second harmonic of Ti:Sa laser at the wavelength 480 nm in the active medium of
photochemical XeF(C-A)-laser excited by VUV radiation of an e-beam pumped Xe2 lamp. The final stage of the laser
system is supposed to be an e-beam pumped facility with a laser chamber of 60 cm in diameter and 200 cm long in the
case of KrF laser, and with another laser chamber of 30-40 cm in diameter put into the former one in the case of XeF(CA)
laser. The parameters of such e-beam facility are close to those of previously developed at the Institute of High-
Current Electronics: electron energy ~600 keV, specific input power ~ 300-500 kW/cm3, e-beam pulse duration ~ 100-
200 ns. A possibility of using Kr2F as an active medium with saturation energy 0.2 J/cm2 for amplification of ultrashort
laser pulses is also under consideration. There was theoretically demonstrated that the energy of a laser pulse at the exit
of the final stage of the laser system could come up to ~ 17 J with pulse duration ~50 fs in the case of KrF laser, and
~75 J with pulse duration of 25 fs in the case of XeF laser. Two Ti:Sa laser systems producing ~50 fs pulses with
energy ~0.5 mJ at the wavelength 248 nm and ~5 mJ at the wavelength 480 nm have been already developed and are
being now installed at the Lebedev Institute. Preliminary
Fluorine-resistant coatings for fused silica windows of high-energy KrF lasers with damage thresholds as high as 20 J/cm2 have been developed using two comparative deposition techniques: ion-assisted e-beam evaporation and magnetron ion sputtering. They were evaluated by means of atomic-force microscopy, Fourier spectroscopy, and laser-damage testing in large irradiated spots ~ 1 cm at powerful GARPUN KrF laser.
Experiments were performed at 100-J-class GARPUN KrF laser installation on optimization of e-beam pumping and amplification of 20-ns pulses in e-beam-pumped amplifiers with gain volumes of 10 × 10 × 100 cm3 and 16 × 18 × 100 cm3. Amplified spontaneous emission (ASE) was measured in the near field close to the output window and in the far field along the amplifier axis. Suppression of transverse ASE by amplification of a laser signal was also investigated. The experimental data were compared with numerical simulations of e-beam transport using Monte Carlo code and 3-D numerical simulations of large-aperture single-pass and double-pass KrF laser amplifiers. Finally, the verified numerical codes were applied for optimization studies of large-scale KrF amplifiers with output energy up to 10 kJ being developed for Inertial Fusion Energy application.
The process of laser ablation of fused and crystal silica and natural silicates induced by pulsed CO2 laser irradiation (total pulse duration of 35 μs, laser pulse rise time of 0.1 μs, pulse energy of 10 J) has been studied. By action of focused laser radiation at the surface of samples the appearance of erosion plume at the irradiated surface take place. For study of ablation regimes the frame image of laser induced plume by use of high speed photography method with 2 microsecond expose of each frame have been made. It has been observed the formation of two different type of laser plume during laser pulse action. First type plume represents a long narrow plume with the onset close to start of laser pulse. The maximal length of this plume is about of 20 millimeter. The second type of plume represents a conical plume with the onset, which is late from laser pulse start for a few microsecond. The first type plume expands in to laser beam direction. The second type plume expands normal to the surface. The velocity of laser plume particles by means of measurements of moment transferred into samples during laser pulse action has been measured. It has been obtained, that value of this velocity varies in region of (l÷3)103 m/s in dependence of laser fluency value. The appearance of first time plume have a threshold which equal to 0.30 kJ/cm2 whereas the appearance of second type plume have not a such threshold and may take place at low laser fluency. We believe, that the first type plume connects with the selective ablation of SimOn complexes whereas second type plume connects with the thermal heating caused by dissipation of laser energy in to system of low frequency acoustics phonons.
The results of test for radiation resistance of high purity crystals (MgF2, CaF2, BaF2Al2O3, SiO2) and quartz glasses (QU-1, KS-4V, Corning 7940) under action of e-beam are submitted. Energy density of e-beam for a pulse duration 80 ns was within the limits of 0,2-2 J/cm2. More than 104 pulses has been made on samples within one year. Changes of transmission spectra of samples in a range of 100-1000 nm were traced during an irradiation.
The experiments have been performed at 100-J-class GARPUN KrF laser installation, which consists of 20-ns discharge-pumped master oscillator and two stages of e-beam-pumped amplifiers with gain volumes of 10x10x100 cm and 16x18x100 cm. Gain and absorption coefficients were measured in a single-pass scheme, while intrinsic efficiency of about 12% was demonstrated in the saturated double-pass amplification. They were compared with numerical simulations. A numerical code solved a set os simultaneous self-consistent kinetic equations together with amplification of laser radiation and spontaneous emission in large-aperture KrF lasers. Being verfied with the experimental data the code was used to forecast the parameters of IFE-scale KrF amplifiers.
Hydrodynamic regimes of KrF laser interaction with solid and thin-film targets in atmospheric and reduced pressure air were investigated at high-energy GARPUN installation. These experiments were performed with 100-J, 100-ns laser pulses in planar focusing geometry and compared with numerical simulations with ATLANT code to verify the concept of laser-driven shock tube (LST), which could accelerate a gas to hypersonic velocity and produce strong shock waves (SW). Laser beam was focused by a prism raster optical system that provided very uniform intensity distribution at moderate laser intensities q ≤ 1 GW/cm2 over a square spot of ~ 1-cm size. Dynamics of laser-produced plasma and SW in a surrounding gas were investigated by means of high-speed photo-chronograph and streak camera in combination with shadow or schlieren techniques, time and space resolved spectroscopy in a visible spectral range. Both experiments and simulations confirmed that target evaporation and blow-up of expanding plasma are the main mechanisms of UV laser-target interaction in a surrounding gas. Planar shock waves with velocities up to 7 km/s towards the laser beam were observed in a normal density air and up to 30 km/s in a rarefied air. Acceleration of thin CH films of 1 to 50-μm thickness was investigated both in a free-expansion and plasma-confined regimes with the highest achieved velocities up to 4 km/s. The SW damping law in a free space independently on laser intensity and air pressure could be approximated by a power law x ~ tn with a power indexes n1 = 0.85 - 0.95 at the initial stage and n2 = 0.5 - 0.6 later, when a distance of the SW front from a target became comparable with a size of the irradiated spot. Instability growth at contact interfaces between ablative plasma and accelerated film, as well as between plasma and compressed air were observed and compared for various initial irradiation non-uniformities. They were introduced by a grid, which was set in front of the film target.
The laser ablation of fused and crystal silica and natural silicates induced by pulsed CO2 laser irradiation (total pulse time of 35 μs, pulse increase time of 0,1 μs, pulse energy of 10 J) has been studied. By action of focused laser radiation at the surface of samples the appearance of erosion plume at the irradiated surface take place. For study of ablation regimes the frame image of laser induced plume by use of high speed photography method with 2 microsecond expose of each frame have been made. It has been observed the formation of two different type of laser plume during laser pulse action. First type plume represents a long narrow plume with the onset close to start of laser pulse. The maximal length of this plume is about of 20 millimeter. The second type of plume represents a conical plume with the onset, which is late from laser pulse start for a few microsecond. The first type plume expands in to laser beam direction. The second type plume expands normal to the surface. The velocity of laser plume particles by means of measurements of moment transferred into samples during laser pulse action has been measured. It has been obtained, that value of this velocity varies in region of 1-3•103 m/s in dependence of laser fluency value. The appearance of first time plume have a threshold which equal to 0,15 kJ/cm2 whereas the appearance of second type plume have not a such threshold and may take place at low laser fluency. We believe, that the first type plume connects with the selective ablation of SimOn complexes whereas second type plume connects with the thermal heating caused by dissipation of laser energy in to system of low frequency acoustics phonons.
The comprehensive results are presented on the behaviour of high purity synthetic quartz glasses under the action of intensive ionizing radiation (x-rays and energetic electrons) and UV laser radiation with 248-nm wavelength. They are concerned to the application of e-beam-pumped large-size KrF-laser as a driver for the Inertial Fusion Energy.
The behavior of high-purity fluorite crystals under the action of ionising radiation (fast electrons and roentgen) and also intensive KrF- and ArF-laser radiation has been investigated. On the basis of these experimental results and literature data the benefits of high-purity fluorite for manufacturing of windows and other optical elements for excimer lasers were demonstrated.
Here we discuss the results of the experiments performed using the Prague Asterix Laser System (PALS) of wavelength 0.44 μm (3ω of Iodine laser) and energy ≈ 250 J in 450 ps (FWHM). Two sets of experiments were carried out, firstly, generation of high quality shocks which were steady in time and uniform in space using Phase Zone Plates (PZP), to establish the scaling laws of shock pressure Vs. laser intensity for aluminum foil target of thickness 8 μm. Our results show a good agreement with the delocalized laser absorption model. Secondly, measurements of the Equation of State of carbon compressed by shocks at megabars of pressure have been realized. Equation of State were obtained for carbon using the impedance mismatch technique. Step targets allowed the simultaneous measurements of shock velocity in two different materials. Aluminum was used as a reference material and relative EOS data for carbon have been obtained up to ≈ 14 Mbar pressure.
We have suggested a concept of laser-driven shock tube (LST) for generation of hypersonic shock waves (SW) in gases and compression waves in liquids. This novel laboratory technique might be applied to the studies of various fundamental hydrodynamic phenomena such as development of hydrodynamic instabilities at contact interfaces between different liquids and gases accelerated by shock waves, hypersonic gas flow around bodies, effects of strong shock wave refraction and cumulation in time scale of several microseconds and space scale of ten millimeters. These problems are of great importance in Inertial Confinement Fusion, comsology, astrophysics, and aerospace engineering. In this paper we present both numerical simulations and first experimental results to verify the laser-driven shock tube concept for studying of strong SW generation in the air.
The 2D codes "ATLANT-C" (Lagrangian coordiantes) and "NUTCY" (Euler coordinates) have been used for the modeling of experiments performed at laser installations "GARPUN" (KrF-laser with pulse energy about 100 J and duration of 100 ns) and "PICO" (Nd-laser with pulse energy of 30 J and duration of 3 ns). Both laser installations are located at Lebedev Physical Institute, Moscow, Russia.
Time-resolved scintillation technique and absolutely calibrated thermo-luminescence dosimeters have been applied to characterize bremsstrahlung x-ray emission from a large-aperture GARPUN KrF laser module pumped in a transverse geometry by double-sided e-beams stabilized by pulsed magnetic field of 0.1 T. It was produced by electrons with ~300 keV kinetic energy, 50 A/cm2 current density, and 100 ns pulse duration when they passed from vacuum diodes through foil windows into laser chamber and were decelerated in a working gas. Regularization algorithm was developed to reconstruct the bremsstrahlung spectra using experimental data on x-ray transmission through different absorbers. The energy fluence of ionizing radiation escaped onto laser windows has been measured. It was shown that a long-term degradation of optical transmission due to bremsstrahlung x-ray irradiation should be taken into account for KrF laser application in Inertial Fusion Energy.
The comprehensive results are presented on the behavior of high purity synthetic CaF2, MgF2, quartz glass and Al2O3 under the action of intensive ionizing radiation (x-rays and energetic electrons) and UV laser radiation with 248-nm wavelength. They are concerned to the application of e-beam-pumped large-size KrF-laser as a driver in the Inertial Fusion Energy.
The design of a miniature laser shock tube for the study of a wide range of hydrodynamic phenomena in liquids at pressures greater than 10 kbar and supersonic flows in gases with large Mach numbers is discussed.
KEYWORDS: Laser scattering, Magnetism, Scattering, Diodes, Fluorine, Monte Carlo methods, Laser stabilization, Transmittance, Semiconductor lasers, Chemical species
There are several key engineering and physical issues for the development of Krypton Fluoride driver for Inertial Fusion Energy Program. In the frame of this program we have performed experiments with e-beam-pumped KrF laser installation GARPUN on the transportation of relativistic e- beams through aluminum-beryllium and titanium foils and compared them with Monte Carlo numerical calculations. It was shown that 50-micrometers thickness Al-Be and 20-micrometers Ti foils had equal transmittance of 75% for approximately 300 keV, 50 kA/cm2, 100 ns e-beams, being lower than calculated one. In contrast to Ti foil, which surface was strongly etched by fluorine, no surface modification and no fatal damages were observed for Al-Be foils after approximately 1000 laser shots and protracted fluorine exposure. It was shown that applied magnetic field of approximately 1 kGs significantly reduced electron scattering both across and along laser cell at typical pumping conditions with 1.5-atm pressure working gas. The energy fluence of scattered electrons fell down from approximately 100 mJ/cm2 to approximately 1 mJ/cm2 per pulse at 8.5-cm distance from the boundary of injected e-beams. Without magnetic field the scattered electrons were spread up to 20 cm, thus strongly irradiating optical windows and being a cause of additional induced absorption of laser radiation.
Vladimir Zvorykin, S. Arlantsev, Valerii Bakaev, Nikolay Morozov, O. Rantsev, Paul Sergeev, Gleb Sychugov, A. Tserkovnikov, Stephen Obenschain, J. Sethian
Two key engineering issues in the development of a KrF laser driver for Inertial Fusion Energy are high transmitting and long life e-beam window and optical laser windows. We have performed experiments with e-beam-pumped KrF laser installation GARPUN on the transport of relativistic e-beams through Al-Be and Ti foils and compared them with Monte Carlo numerical calculations. It was shown that both 50-?m thick Al-Be foils and 20-?m thick Ti foils had equal transmittance of about 75% for ~3OO keV, 50 A/cm2, 100 ns e-beams. However in both cases the observed transmission was lower than calculated one. In contrast to Ti foil, whose surface was strongly etched by fluorine, no surface modification or fatal damages were observed for Al-Be foil after ~1000 laser shots and protracted fluorine exposure. It was shown that applied magnetic field of ~1kG significantly reduced electron scattering both across and along laser cell at typical pumping conditions with 1 .5-atm pressure working gas. Without magnetic field irradiation of optical windows by scattered electrons resulteu in additional transient and residual induced absorption of laser radiation. The analysis of different optical materials for KrF laser windows and coatings has also been done.
This paper describes gasdynamic regimes of high-power pulsed laser interaction with solid targets in the ambient air of normal and reduced densities in the moderate intensity range 0.1 - 1000 MW/cm2, typical four numerous laser applications. The experiments have been performed with a set of CO, CO2 and KrF laser installations with output energy up to 100 J and pulse durations of 0.1 - 200 microsecond(s) . Supersonic erosion jet formation during target evaporation as well as different types of laser- supported absorption waves, i.e. laser-supported detonation waves, subsonic and supersonic radiation waves have been identified for the variety of radiation wavelength 0.25, 5.0 - 5.6, 10.6 (9.6) micrometer. The results on the gasdynamic regimes determination, being obtained for sufficiently big irradiated spots approximately 1 cm, might be extended for much higher energies available for these types of lasers in large-scale environments.
Experiments on laser-rock-fluid interaction have been carried out by using pulsed CO and CO2 lasers which irradiated rocks typical for oil field: sandstone, limestone, shale and granite. Energy fluence and laser intensity on rock surface were up to 1.0 kJ/cm2 and 107W/cm2, respectively. The dependencies of specific energy consumption (i.e. energy per volume needed for rock excavation) on energy fluence, the number of pulses, saturated fluid, rock material and irradiation conditions have been obtained for various rock samples. The dependencies of momentum transferred to the rock on energy fluence for dry rocks and rocks with surface saturated by water or mineral oil have been measured. High-speed photography procedure has been used for analyzing laser plasma plume formation on a rock surface. Infrared spectra of reflectivity and absorption of rocks before and after irradiation have been measured.
This paper describes a performance of 100 J-class KrF laser system `GARPUN' intended for target irradiation experiments by 100 ns pulses. A controllable space-time distribution in a focal spot reaching 5*1012 W/cm2 produced megabar ablation pressure, which irradiated conical shock wave in solids. It propagated in a quasi-steady manner together with an ablation front that resulted in anomalous high penetration rate of laser radiation throughout the matter. Long-time sample loading together with strong tangential shear flow of compressed layers produced favorable conditions for pressure-induced transformation of the pyrolytic graphite into a diamond-like phase by martensitic mechanism.
Experiments on laser-rock-fluid interactions have been carried out by using pulsed CO and CO2 lasers which irradiated rocks typical for oil field: sandstone, limestone, shale and granite. Energy fluence and laser intensity on rock surface were up to 1.0 kJ/cm2 and 107 W/cm2, respectively. The dependencies of specific energy consumption (i.e. energy per volume needed for rock excavation) on energy fluence, the number of pulses, saturated fluid, rock material and irradiation conditions have been obtained for various rock samples. The dependencies of momentum transferred to the rock on energy fluence for dry rocks and rocks with surface saturated by water or mineral oil have been measured. High-speed photography procedure has been used for analyzing laser plasma plume formation on a rock surface. Infrared spectra of reflectivity and absorption of rocks before and after irradiation have been measured.
The advantages of a high-power KrF laser system 'GARPUN' generating UV radiation of 248 nm wavelength, 100 J energy and 100 ns pulse duration for the production of megabar range ablation pressures are demonstrated. The scaling law for the pressure dependence on laser intensity reaching 5*1012 W/cm2 was established and compared with other wavelengths. High-pressure material investigations were carried out with the emphasis on a shock wave dynamics and equation of state studies. Pressure-induced transformation of the pyrolytic graphite into a diamond-like phase was observed for the first time in laser-target interactions.
A high-power KrF laser system based on a wide-aperture electron-beam pumped excimer laser `GARPUN' with injection-locking from a discharge pumped narrow-band oscillator has been developed. The laser radiation spectral brightness of approximately 5 X 1014 W/cm2 srad cm-1 with narrow linewidth approximately 0.1 cm-1 tunable near (lambda) equals 248 nm, and the output peak power of approximately 1 GW have been obtained.
The unique possibilities ofpowerfu.l gas lasers operating on carbon dioxide for treatment of materials,
for production and heating of plasma, for exploring the atmosphere and other applications have been
represented in numerous studies into the physics of interaction between the infrared laser radiation
and gases, as well as condensed substances.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.