The work presents the results of laboratory experiments on controlling the filamentation domain of a focused femtosecond laser beam with a spatially structured (using a deformable mirror) wavefront. We studied aberration beams consisting of coherent nested annular subapertures obtained with a specific shape of a deformable mirror determined from theoretical estimates. This makes it possible to create inhomogeneities in distribution of the optical field amplitude during propagation of the laser beam, which can subsequently become seeds for the light filaments formation. This regime of high-power radiation filamentation control does not require compensation for distortions in the initial beam profile, but on the contrary, it is based on the controlled introduction of preliminarily calculated wavefront aberrations.
Optical properties of different commercial plastics for fused deposition modeling 3D printing are defined at room temperature in the spectral range 0.2˗1.2 THz. We compare absorption coefficients and refractive index of ABS, PETG, and SBS printed 1-4 mm plates. Different types of optical elements for controlling high-power THz radiation are studied. A comparison is made of the efficiency of attenuation of linearly polarized THz radiation with homemade band-pass polarizers obtained by etching copper from a flexible polyimide substrate. Filters and polarizers created using 3D printing or by deposition of polymer matrix with magnetic particles under external field are cost-effective and can be easily changed or replaced. Comparison between plastic insets, filters based on magnetic particles, and polyimide film filters are made.
The results of experimental and theoretical studies of behavior spectral profile of second harmonic (SH) radiation with a central wavelength of 475-477 nm during its formation in a nonlinear KDP crystal, depending on the phase matching angle and radiation intensity are presented. It is shown that a change in the propagation angle of fundamental radiation to one or the other side of phase matching angle by 16– 20 min leads to a spatially inhomogeneous broadening of the second harmonic spectrum up to two times and a shift of its maximum (averaged over the beam cross section) to shorter wavelengths from the central wavelength.
We present the thorough studies of dielectric properties of BiB3O6 (BIBO) crystal in the subterahertz range. We observe a large birefringence Δn = nZ −nX = 1.5 and the values of absorption coefficients of all three axes to be less than 0.5 cm−1 at the frequency of 0.3 THz. The difference from visible range in angle Φ between the dielectric axis z and crystallophysical axis χ is found to be more than 6°. The simulated phase-matching curves in the xz plane of the crystal show the optimal value of the angle θ to be around 25.5°±1° for an efficient millimeter-wave generation under the pump of 1064 nm laser radiation.
The results of experimental studies of conditions for THz emission generation in laser filament created by focused ultrashort laser pulse of Ti: Sapphire complex are presented. The influence of magnitude and direction of applied external electric field, energy and polarization of pump radiation in one- and two-color optical schemes on the intensity, divergence, and polarization of THz radiation are investigated. THz spectra is estimated and optimal generation conditions are discussed.
In this work, self-seeded lasing pulse duration of the В2Σ+u – X2Σ+g transition of molecular nitrogen ion in air laser plasma at different pump pulse focusing conditions was investigated. Pumping was carried out at the central wavelength of 950 nm, with 60 fs duration (FWHM), and 10 mJ energy. It was shown that lasing pulse duration increases from 1.15 to 4.6 ps, and unsaturated gain coefficient decreases from 6.7 to 4.2 with decreasing pump pulse intensity when geometrical focus length was increased. An explanation for picosecond lasing duration at femtosecond seed amplification is proposed.
Potential efficiency of the THz wave generation by down-conversion of the visible emission in nonlinear β-BBO crystal is estimated. Eight types of interactions are found possible. Four interaction types were realized in the carried-out experiments. Optical damage threshold under fs pumping was estimated.
The paper presents the results of experimental and theoretical studies of the role of avalanche ionization in the process of highly nonlinear generation of electron-hole pairs in the interaction of intense femtosecond laser radiation with dosimetric crystals LiF:Mg,Ti. We assume that the effective formation of defects of hole-interstitial type, which consist of molecular halogen ions placed in one cationic and two anionic vacancies, distinguished by high-temperature peaks in the thermally stimulated luminescence curves, is feasibly connected with avalanche ionization processes occurring in the regions of passage of light filaments. The calculated dependences of the plasma density on time during the laser pulse made with taking into account the avalanche ionization for this type of crystals show that the contribution of avalanche ionization to the electron-hole plasma density is comparable to that of the multiphoton tunneling mechanism.
THz generation experimental results in a filament plasma produced by focusing ultrashort Ti:Sapphire laser pulses at a wavelength of 950 nm are reported. A study of structure and time-resolved dynamics of forming the laser filament is carried out. THz radiation dependence from filament length and pump energy is also given. Optimal conditions for efficient THz generating were found.
This paper presents model study and experimental results on frequency conversion of Ti:Sapphire laser operating at 950 nm into the long-wavelength THz range in a β-BBO crystal. The generating spectrum in the range of 0.2 - 0.8 THz is studied in detail.
A latest results obtained in THL-100 hybrid femtosecond laser system operating in the visible spectral range are presented and the ways of the peak power increase of the laser beam are discussed.
The effect of astigmatism on laser air filamentation was studied numerically and experimentally. Limited supply of energy to the filament is shown to be the main feature of aberrational focusing, which facilitated the organization of quasi-solitons in the post-filament region. Quasi-solitons are realized due to the balance between linear diffraction and Kerr nonlinearity in the presence of background environment around zones with increased intensity. A highly directional SC of visible light is formed outside the visible filament zone in the resulting spatial quasi-solitons.
The results of studies on the formation of a volume discharge in an electric-discharge XeCl laser with a maximum specific pumping power of 4.7 MW/cm3 are presented. It is shown that with a half-cycle duration of discharge current of 20 ns, the radiation pulse duration on the base is 100 ns. A good agreement between the experimental and numerical results obtained with the XeCl laser was demonstrated. Plasma-chemical processes occurring in a volume discharge at a maximum electron concentration in the plasma of ~ 7×1015 cm-3 are considered.
One way to obtain a multi-terawatt laser beams in the visible spectrum rang is direct amplification of the pulse in the output amplifier. Such method is being developed in IHCE SB RAS based on THL-100 hybrid laser system. This system uses solid-state and gas active media, namely: Ti:Sa femtosecond front-end and photodissociative XeF(C-A) amplifier. The front-end generates a transform-limited radiation pulse of 50 fs duration or a positive-chirped 50 ps pulse (FWHM) on second harmonic (475 nm). The XeF(C-A) amplifier can amplify the energy of front-end pulse up to 2-3 J. A compressor is required to recompress the amplified 50 ps radiation pulse to the transform-limited pulse duration. In this paper, we present the calculated parameters of the compressor based on the diffraction gratings and experimental data of the output radiation pulse compression of the front-end. The compressor optics scheme, its parameters and adjustment technique are presented. The compressing possibility of 50 ps second harmonic pulse to a duration of 75 fs in the grating compressor at a pulse energy of 7 mJ and a 1 cm beam diameter are demonstrated.
The results of formation conditions studies of a highly directional supercontinuum (SC) in a visible spectrum range obtained upon aberration spherical-mirror focusing of a radiation pulse with a wavelength of 940 nm, duration of 70 fs, and energy of 8–15 mJ are presented. It is shown that after visible filament there are two directed white light beams diverging relative to each other at an angle of 1.40 . Formation every light beam occurs through a gradual conversion of the spectral composition from long wavelength to short wavelength (to 350 nm) in a spatially stable structure similar to a soliton with a transverse dimension ≤ 300 μm. The nature of the appearance these beams is due to formation of two zones with higher intensity before meridional plate owing to the distortion of the wavefront of the laser beam in conditions of the astigmatism and the Kerr effect. In result two minima in the phase distribution located outside the beam axis are realized, which lead to the appearance of two off-axis areas with higher radiation intensity and as a consequence of this the formation of two highly directional laser beams.
The results of multiterawatt laser beam formation of a visible range in THL-100 hybrid laser system based on titanium-sapphire front-end and photochemical XeF(C-A) boosting amplifier are presented. The front-end delivers at the second harmonic centered around 475 nm up to 20 mJ energy in 50 fs and to 7 mJ in 50 ps pulses. The active medium of the XeF(C-A) amplifier is produced in a XeF2/N2 mixture irradiated by the VUV radiation from electron beam excited xenon. The laser system is described and the latest results are presented.
The results of the formation and amplification of positive chirped 0.1 ns laser pulse at a central wavelength of 470 nm in the laser system THL-100 are presented. It is shown that a front-end allows forming a radiation pulse with a Gaussian intensity profile and the energy up to 7 mJ. At amplification in XeF(C-A) amplifier of the pulse with 2-5 mJ energy a saturated mode is realized and 3.2 J output laser beam energy is reached.
Results of experimental studies of the chemical HF laser with a non-chain reaction are presented. The possibility of the total laser efficiency of 5 % is shown when a traditional C-to-C pumping circuit with the charging voltage of 20-24 kV is used. It is experimentally shown that the specific radiation output energy of 21 J/l is reached at the specific pump energy of 350 J/l in SF6/H2 = 14/1 mixture at the total pressure of 0.27 bar.
The results of multiterawatt laser beam formation of a visible range in THL-100 hybrid laser system based on titanium-sapphire front-end and photochemical XeF(C-A) boosting amplifier is presented. The front-end delivers up to 20 mJ energy in 50 fs pulses at the second harmonic centered around 475 nm. The active medium of the XeF(C-A) amplifier is produced in a XeF2/N2 mixture irradiated by the VUV radiation from electron beam excited xenon. The laser system is described and the latest results are presented.
The development of effective discharge pulse-repetition KrF laser is informed. Research the possibility of forming in this laser long laser pulse with input pump energy for a few half periods of the discharge current are presented. In the repetitively pulsed regime (up to 100 Hz) laser provides laser pulses with energy of 1 J and duration of 60 ns at the base. The maximum total efficiency of the laser is 3%. The results of studies on the formation in this laser of narrowband radiation with a wide spectral band tuning are reported. The possibility of forming a radiation pulse with a linewidth 2 pm, energy 0.15 J and spectral tuning region 247.5-249.6 nm are demonstrated.
We present the results of studies of energy accumulation during the non-destructive interaction of extremely intense near infrared laser radiation with model wide band gap dielectric crystals of lithium fluoride, when the intensity of pulses is sufficient for effective highly nonlinear absorption of light and for the excitation of the electron subsystem of matter and the energy of pulses is still not sufficient for significant heating, evaporation, laser breakdown or other destruction to occur. We studied the emission of energy in the form of light sum of thermally stimulated luminescence accumulated under conditions of self-focusing and multiple filamentation of femtosecond laser radiation. It was established that it's the F2 and F3+ color centers and supplementary to them centers of interstitial type which accumulate energy under the action of a single femtosecond laser pulses. When irradiated by series of pulses the F3, F3- and F4 centers additionally appear. F2 centers are the main centers of emission in the process of thermally stimulated luminescence of accumulated energy. The interstitial fluoride ions (I-centers) are the kinetic particles. They split off from the X3- centers in the result of thermal decomposition of latter on the I-centers and molecules X20. I-centers recombine with F3+ centers and form F2 centers in excited state. The latter produce the characteristic emission spectrum emitted in the form of thermally stimulated luminescence.
Evolution of spatial and energy characteristics start pulse with energy of 0.8 mJ in duration of 2 ps in the XeF(С-A) amplifier of THL-100 laser system have been studied experimentally and by numerical simulation. Laser radiation energy E = 2 J was obtained experimentally. In that work we present the 3D-model amplification of conically diverging laser beams, that takes into account the spatial inhomogeneity of the pump, and the geometry of THL-100 laser system amplifier. Description and the test results of the model are submitted. At the start pulse energy 0.8 mJ, the calculated radiation energy at the XeF(С-A) output reaches 2.4 J. Simulation results shows that, maximal intensity of the laser radiation in this mode reaches P = 60 GW/cm2. The evolution of the energy and space-time structure of the laser beam in the amplifier was investigated. It is shown that in the ideal case (excluding the processes of nonlinear interaction of laser beam with an active medium), at the start pulse energy of 5 mJ, the energy of the laser radiation at the output of the amplifier is increased to Eout = 3.8 J. In this mode, the maximal radiation intensity reaches a value of I = 148 GW/cm2.
Ab-initio study on modification of commerce terahertz spectrometer with time resolution Z-3 (Zomega, USA) by substitution of ZnTe and GaP detectors and LT-GaAs generator for homemade of pure and S-doped GaSe is carried out. It was established that in spite of not optimized parameters pure and doped GaSe:S(0.3 mass%) crystal are comparable, relatively, in generation efficiency and detection sensitivity to commerce units due to lower nonlinear optical loss and much higher damage threshold. The advantages are in force from pump fluences of below 5 mJ/cm2 for pure GaSe. The closer S-doping to optimal concentration, the lover fluences resulting in the advantages. Pure and S-doped GaSe demonstrate higher reliability and larger dynamic range of operation. Recorded absorption spectra well match known spectra.
Model study of not phase matched and phase matched optical rectification or down-conversion of Ti:Sapphire laser pulses at 950 nm into THz and far-IRrange in pure and S-doped GaSe single crystals is carried out. First, the ordinary and extraordinary wave dispersions of the GaSe refractive indices were measured by terahertz time-domain spectroscopy (THz-TDS). Measured data were approximated in the form of Sellmeier dispersion equations for 0.62 – 2000 μm range with using available shorter wave data.
The influence of the optical inhomogeneities effect of the prism stretcher elements on the spatial, angular and spectral parameters of the transmitted radiation and the degree of change in the phase aberrations of the laser beam during its propagation in the stretcher are studied. It is shown that the prism material does not allow transmitting of a required diameter of 75 mm without linear distortions of the beam. The maximum intensity and beam diameter allowing to amplify the picosecond pulses in XeF(C-A) amplifier are determined.
The experimental results of the inversion population mechanisms study in the resonant electronic transition B3Πg–A3Σu+ of nitrogen ions by optically pumped of air and pure nitrogen by femtosecond laser pulse at a wavelength of 950 nm are presented. It is shown that the inversion results from selective settling of N2+(B2Σu+, v' =0) excited state by multiphoton excitation of the autoionization states of the nitrogen molecule with energy of 18.7 eV. Seed photon for superradiance at transitions of molecular nitrogen ions are photons the axial supercontinuum occurring in the filament on the respective wavelengths. The mode of the superradiance at a wavelength λ = 358.4 nm referred to the transition of the CN molecules was realized.
The paper presents the results of theoretical and experimental studies of the second harmonic generation process in the Ti:sapphire femtosecond complex, which includes a generator of the femtosecond pulse, stretcher, regenerative amplifier, two multi-pass amplifiers, compressor and second-harmonic generator. This complex provides the 50-fs pulses with energy of 20 mJ and it is used as a master oscillator in THL-100 hybrid laser system, which operates in the visible region at a wavelength of 475 nm. Experiments and calculations for various beam parameters of the fundamental harmonic, such as radiation intensity, spatial profile of the beam and the level of the noise component were performed. It is theoretically shown that in the absence of the noise component in the beam of the fundamental wave a good uniformity of the second harmonic should be observed. When making the amplitude heterogeneities in the first harmonic even greater heterogeneities in the second harmonic are appeared. It is experimentally shown that with increasing of energy beam the inhomogeneity of the second harmonic beam increases.
Results of experimental measurements and numerical simulations of the N2 and XeF2 gas pressure effects on the gain characteristics are presented in the paper. It is experimentally and theoretically is shown that maximum total gain (5-6)×104 achieved at a pump energy E = 240 J, 0.2 Torr XeF2 and 0.5 atm N2 pressure. Increasing and decreasing of N2 pressure leads to decrease of the gain. The possibility of the XeF(C-A) amplifier operation in a generator mode is discussed and the theoretical study results of generation are presented. It is shown that an annular laser radiation with energy up to 8.5 J can be obtained. The study results of the influence on the laser energy of N2 and XeF2 pressure and reflectance coefficient of output mirror are presented.
Detailed model study of THz generation by CO2 laser down-conversion in pure and solid solution crystals GaSe1-xSx is carried out for the first time. Both forward and backward collinear interactions of common (eo-e, oe-e, oe-o, oo-e, ee-o) and original (ee-e, oo-o) types are considered. Possibility of realization, phase matching angles and figure of merits are estimated for line mixing within 9 μm and 10 μm emission bands, as well between them. Dispersion properties of o- and e-wave refractive indices and absorption coefficients for GaSe, GaS and GaSe1-xSx crystals were preliminary measured by THz-TDS, approximated in the equation form and then used in the study. Estimated results are presented in the form of 3-D figures that are suitable for rapid analyses of DFG parameters. The most efficient type of interaction is eo-o type. Optimally doped (x = 0.09-0.13) GaSe1-xSx crystals are from 4 to 5 times more efficient at limit pump intensity than not doped GaSe crystals.
The study results of a high-quality radiation formation in the UV and IR spectral ranges for using in lidar systems to detect the vapors of nitric oxide and complex molecules, including data radicals, are discussed. The influence of the existing cavity losses on the radiation formation in the dispersion cavity is studied.The development of KrF laser with a broad spectral band adjustment of 247.5-249.5 nm and high energy are presented about. The possibility of pulse formation with duration of 30 ns in CO2 laser is shown.
The modified Bridgman method with heat field rotation was used to grow ε-polytype single crystals of pure and 1, 2 and 10 mass % S-doped GaSe or solid solution crystals GaSe1-xSx, x = 0.002, 0.091, 0.412. The interaction of ultrashort laser pulses of ∼ 100 fs duration at 800 nm and 2 μm with the grown crystals was studied at room temperature. Up to 3.4-fold advantage of S-doped crystals in limit pump intensity (no decrease in the transmission) was found under 800 nm pump at S-content increase up to 10 mass %. The advantage became a half less at 2 μm pump due to a decrease of two-photon absorption in pure GaSe crystals. The spectral dependence of transient absorption is recorded with 37 fs resolution and interpreted. It was ascertained that first observable damage of high quality crystals is caused by dissociation of submicrometer thick surface layer to initial elements and do not influence the frequency conversion efficiency until alloying of dissociated Ga. Local microdefects, multiphoton absorption and transient transmission processes are identified as key factors responsible for damage threshold.
The design and characterization of a THL-100 multi-terawatt hybrid laser system based on a Start-480M titaniumsapphire
starting complex and photochemical XeF(C-A) amplifier with a 25-cm aperture are described. The first
experiments results are presented. A laser beam peak power of 14 TW at 475 nm wavelength has been attained.
Damage threshold of non-linear GaSe crystals under IR fs (Ti:Sapphiere 800 nm laser and 1.1-2.9μm OPG) and ns (2. 79
Er3+:YSGG and 10.6μm CO2 laser) pulse pumping is studded in details. Local micro defects and field induced effects (GaSe dissociation, multiphoton absorptions and transient transparency origin effects) are identified as responsible for damage threshold in this case. Local (including nano scaled) defects and thermal effects are identified as reason of damage threshold under ns pulse pumping.
Development of KrF laser system for lidar designed for detection of the compound molecules containing a nitric
oxide is presented. The system consists of the master oscillator and the amplifier operating at pulse repetition rate up to
100 Hz. Laser radiation having energy up to 0.2 J and bandwidth of 2 pm is smoothly tuned in a spectral range of 247.6-249.5 nm.
Terawatt hybrid (solid state/gas) laser (THL-100) system on the basis of Ti:sapphire starting complex (50 fs, 5 mJ)
and photochemical XeF(C-A) amplifier with the aperture of 24 cm is presented. Laser system is built at Institute of High
Current Electronics SD RAS, Tomsk, Russia. The design and peculiarities of optical pumping of XeF(C-A) amplifier,
methods of pump power measuring, gain distribution across the active volume are discussed. The results of numerical
modeling of the output parameters simulation are presented and one compared with first experimental results.
Terawatt hybrid laser (THL-100) system on the basis of Ti:sapphire starting complex and final amplifier with
gaseous optically driven active media on XeF(C-A) molecules is presented. Laser system is built at Institute of High
Current Electronics SB RAS, Tomsk, Russia. It consists of Ti:sapphire starting complex and photochemical XeF(C-A)
amplifier. The active media of amplifier pumped by VUV radiation has 24 cm aperture and 110 cm length. The results
of numerical modeling of the output parameters and first experimental results are presented in this paper.
A high power accelerator for photolytically pumped XeF (C-A) short pulse amplifier is described. The 450 keV, 250 ns (FWHM) radial e-beam is injected into cylindrical 30 cm diameter gas chamber through the 15×120 cm four foil windows. Total energy of e-beam penetrated foils is 3.7 kJ. E-beam pumped energy absorbed in argon (3 bar) is about 3 kJ.
In present paper the results of an experimental research of a qualitative radiation formation with pulse duration of 3.5 and 0.15 nanoseconds in one discharge block of XeCl laser with pump pulse duration of 35 ns at use resonator with SBS mirror are presented.
KEYWORDS: Mirrors, High power lasers, Excimers, Optical amplifiers, Gas lasers, Quartz, Laser systems engineering, Pulsed laser operation, Xenon, Diffraction
In the present paper the perspectives using of excimer media for formation of a short high power laser radiation pulses are discussed. Research results of Gas Laser Laboratory of IHCE SD RAS, Tomsk, Russia in this area are shown.
KEYWORDS: Mirrors, High power lasers, Excimers, Xenon, Optical amplifiers, Gas lasers, Laser systems engineering, Excimer lasers, Quartz, Femtosecond phenomena
Presently an excimer mediums continue are examined as one of variants for formation of powerful and over
powerful pulses of laser radiation with duration from units of nanosecond up to tens femtosecond. The researches on
such powerful installations as "NIKE" (USA) and << SUPER ASHURA >> (Japan) proceed in this direction. The main
advantage of excimer mediums is the opportunity to work in a frequency mode, absence of restriction on the size of
active area, high uniformity of a gas working medium, high efficiency (up to 10 %) and wide spectral range of laser
radiation (KrF, XeCl ~ 2nm, XeF (C-A), Xe2Cl ~ 50-100 nanometers). Research in area of high quality laser beams formation in excimer mediums and its amplification in high power
amplifiers are carried out the long time in Institute of High Current Electronics SB RAS, Tomsk, Russia. The wide aperture XeCl laser system of MELS-4k is used for these investigations. Last time we take part in program on development of high power excimer laser system with a petawatt level of power. This system supposes the formation and
amplification high quality laser beams with different pulse duration from units of nanosecond up to tens femtosecond.
We research the possibility of laser beams formation in excimer mediums with ps-ns pulse duration having the low noise
and divergence near to diffraction limit. In other hand, we are developing the wide aperture XeF(C-A) amplifier with
optical pump on base electron accelerator. According to our estimations of the XeF(C-A) amplifier based on the
converter of e-beam energy to the Xe2* fluorescence at 172 nm will allow to obtain up to 100 TW peak power in a 30 fs pulse.
In the present paper the results of an experimental research of a qualitative radiation formation with pulse
duration of 3.5 and 0.15 nanoseconds in one discharge block of XeCl laser with pump pulse duration of 35 ns at use
resonator with SBS mirror are presented.
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.
Results of experimental and theoretical investigations of discharge XeCl laser with 35 ns (FWHM) radiation pulse
duration are presented. Laser generates the laser pulse energy of O.6 J with 2% total electric efficiency and 100 Hz pulse
repetition rate. Calculated laser radiation parameters and discharge parameters have a good agreement with experimental
results. Influence of basic plasma-chemical processes in discharge on laser output and efficiency is shown. Maximal
laser efficiency relatively pumping power was 3.5%.
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
Results of experimental and theoretical investigations of discharge XeCl laser with 30 ns (FWHM) radiation pulse duration are presented. Laser generates the laser energy of 0.35 J with 2.2% total electric efficiency. Calculated laser radiation parameters and discharge parameters have a good agreement with experimental results. Influence of basic plasma-chemical processes in discharge on laser output and efficiency is shown. Maximal laser efficiency relatively pumping power was 3.7%.
A 300 J/210 ns XeCl laser system has been developed. Five lasers in MOPA chains characterized by different pumping techniques are described. Also, the main experimental results of the Photons are given.
Influence of the discharge burning conditions on output radiation parameters and overall performance of a discharge pumped XeCl laser with pump pulse duration of 20 ns is experimentally investigated. It is shown that a 3.9 J/l•atm maximal specific output laser energy from the active medium is realized in the discharge consisting of the
strongly pronounced macro heterogeneities. Laser efficiency of a 2.7 % is reached at discharge current density of a 1.2-1.4 kA/cm2.
The construction of XeCl laser excited by e-beam is described and its radiation parameters are presented. Laser distinguishes from others lasers having similar radiation energy by the small weight and dimensions. Laser excitation fulfills the electron accelerator on base Marx generator with vacuum isolation. The experiments were performed using a gas mixture of Ar-Xe-HCl with pressure of 2-3 bar. A plane-plane lasers optical cavity was used. 120 J output with optical pulse duration ~250 ns (FWHM) on a wavelength of 308 nm have been extracted from 25 cm laser aperture. The heterogeneity of laser intensity distribution was within the limits of 10%.
Output radiation performances of XeCl laser with 10x10x80 cm3 active medium dimensions depending on pumping circuit parameters, intensity and uniformity of preionization have been researched. It was shown that radiation pulse duration and accordingly discharge uniformity depend first of all from preionization homogeneity and not from its intensity.
Results of experimental and theoretical investigations of pump discharge and generation of XeCl laser with 0.21 J laser energy, 2.7% electric efficiency nad 20 ns (FWHM) pulse duration are presented. The influence of step ionization, dissociative attachment and recombination processes on an active volume spatial uniformity and radiation parameters is shown.
A 250 J/210 ns four-stage XeCl laser system named Photons has been developed. Five lasers in MOPA chains characterized by different pumping techniques are described. Also, the main experimental results of the Photons are given.
A four-stage XeCl laser system named Photons has been developed for studying laser interaction with materials. The Photons are outlined and preliminary results characterizing the system are given. The master oscillator Photon-1 can provide “seed” light with laser energy of about 40mJ, pulse duration of about 250ns and good beam quality of nearly diffraction-limited divergence angle and narrow line width less than 1 cm-1 for whole system. The output energy of laser system of 251J has been obtained by four-stage amplification. The synchronization among five lasers is realized by the combination of low voltage timer, high voltage synchronic generators and compensated cables. The demonstration shows Photons good operation with low jitter of less than ±20ns.
Experimental results of long-pulse generation in X-ray preionized XeCl lasers with a 9 x 7 cm2 and 5.4 x 3 cm2 apertures are described. Lasers operate at Ne-Xe-HCl mixture with pressure up to 4 atm. Paper-oil pulse forming lines and rail-gap switch for discharge pump was used. An 2 - 10 J output with optical pulse duration of 250 - 300 ns (FWHM) have been extracted. Problems and peculiarities of long laser pulse formation are discussed.
Experimental results of long-pulse generation in X-ray preionized XeCl lasers with the 9x7 cm2 and 5.4x3 cm2 apertures are described. The lasers operate in the Ne-Xe-HCl mixture with the pressure up to 4 atm. Paper-oil pulse forming lines and a rail-gap switch for the discharge pumping were used. A 3.5 and 10 J output with the optical pulse duration of 250-300 ns (FWHM) has been extracted.
Output radiation performances of XeCl laser having 5.5 1 active medium volume depending on electric circuit parameters, intensity and uniformity of preionization are researched. The maximum output radiation energy of 7 J and pulse duration of 160 ns were obtained only in the presence of modulation of discharge current. It is shown that first of all laser efficiency depend on preionization homogeneity and not from its intensity. The largest laser output realized only in case the small percentage of Xe in gas mixture (≤0.25%).
This paper reports on experimental results and simulation of XeCl-laser with short laser pulse duration. Experimental investigation was aimed at obtaining of maximal lasing power and efficiency. The processes taking place in plasma and in resonator were simulated. Temporal evolutions of plasma particle density as well as simulation rates of processes of ionization, recombination, attachment and formation of XeCl molecules in excited states were obtained. Simulation dependencies have been analyzed; mechanisms of initial parameter effect on lasing power have been established.
Formation of high quality laser beam and the reasons of wave front distortion in electric discharge XeCl laser had been investigated. The influence of macro and micro-inhomogeneities in active volume on radiation divergence is discussed. Possibility of amplification of diffraction limited laser beam practically without distortion is shown.
An X-ray preionized XeCl laser with a large aperture (9x7 cm) is described. Laser operates at Ne-Xe-HCl mixture with pressure up to 4 atm. Paper-oil pulse forming lines and rail-gap switch for discharge pump was used. 10 J output with optical pulse duration up to 300 ns (FWHM) have been extracted from active volume 5.4 l with an electric efficiency 1.2%.
An experomental study of stimulated Raman conversion of high-coherent XeCl laser radiation in H2 has been carried out. About 50 vibrational-rotational components were realized with a circularly polarized laser beam pump. High spatial and temporal coherence of conversed radiation was obtained. Quantum efficiency of conversion in first vibrational Stokes was achieved 95%.
Formation of a diffraction limited divergence and obtaining a high contrast of radiation in electric-discharge XeCl laser system due to SBS are investigated. Possibility of a correction of laser beam wave-front distortion on an astigmatic and a spherical aberrations and on a refractive coefficient non-uniformity in optics elements and atmosphere is shown. Correction of laser beam wave-front having the 20- fold distortion of diffraction limited angle using phase- conjugate Brillouin mirror allowed to obtain the initial angle of 2 X 10-5 rad divergence of laser beam. Use the threshold conditions of Brillouin scattering allowed to increase the XeCl laser radiation contrast from Pgen/Pnoise approximately 4 up to Pgen/Pnoise equals 106 - 107.
Development of a long-pulse master oscillator with pulse duration of 300 ns (FWHM) is reported. The oscillator is made on the base of a long-pulse spark preionized XeCl-laser pumped by a self-sustained discharge using a double- discharge circuit. The pre-pulse is formed by a generator with an inductive energy storage and a semiconductor opening switch. The laser produces up to 1,5 J in pulse with total duration up to 450 ns.
Influence of active medium non-uniformity of 300 ns pulse pump electric discharge XeCl laser on divergence of amplified radiation has been investigated. It was shown that in case of 100 - 200 kW/cm3 pump power the laser active media allows to amplify the diffraction limited laser beam practically without distortion. In case of 400 - 500 kW/cm3 pump power after 120 ns of discharge burning the micro- and macro-inhomogeneities appeared. These inhomogeneities increased the amplified radiation divergence. It was established that basic reason of a divergence degeneration was inhomogenity of gain profile in active medium. In our case amplification increased when the macro-inhomogeneities developed and the absorption increased when the micro- inhomogeneities developed in local regions of active medium.
KEYWORDS: Optical amplifiers, Laser systems engineering, Oscillators, Diffraction, High power lasers, Gas lasers, Excimers, Molecules, Optical components, Amplifiers
High power XeCl laser system and experimental results of diffraction limited laser beam amplification are described. Beyond the preamplifier, the 5 cm X 6 cm laser beam contained 50% of the radiation energy in the diffraction core. At the output from the system an irradiation brightness of 2 X 1014 W/cm-2cr-1 was obtained. Minimum divergence near 0.05 mrad of output beam was restricted to turbulence of air and optics elements. A numerical model of the amplification of the radiation, taking onto account the influence of the amplified spontaneous emission, was developed.
KEYWORDS: Optical pumping, Laser energy, Hydrogen fluoride lasers, Plasma, Energy efficiency, Diodes, Chemical lasers, Electron beams, Ions, Gas lasers
The results of experimental and theoretical investigations on a pulsed, chemical e-beam pumped, non-chain HF laser with a 25 I active volume are submitted. It is shown that there are conditions of anomalous behavior of the output radiation which could be explained by the existence of a space-charge effect in the plasma.
The experimental research results of an laser radiation in excimer lasers and laser systems with output aperture up to 25 X 25 cm2 and output laser energy up to 200 J is described. The laser beam divergence 0.01 mrad have been obtained. The problems of the diffraction limited divergence formation of laser beam are discussed.
The review of the papers devoted the research of excimer lasers with SBS medium is presented. The possibilities of using SBS for phase-conjugation, pulse compression, formation of narrow-band and highly directed radiation are discussed.
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