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We have experimentally studied combination breakdown (electric and optical breakdown or electro-optical breakdown) of krypton under low vacuum (p ~ 101 to 105 Pa) during simultaneous exposure to nanosecond laser pulses (λ ~ 213, 266, 355, 532, 1064 nm, τ 0.5 ~ 18 ns, I 0 ~ 109 to 1011 J/cm2) and a constant electric field (E ~ 0–13.2 kV/cm). We have demonstrated a substantial change in the ratio of the optical and electric components of the breakdown threshold I 0 (E) for different gas pressures and photon energies, as well as the presence of a synergistic effect, manifested in the many-fold decrease in the threshold values for the components of the combination treatment. The results obtained can be used to assess the breakdown processes in gas-discharge devices.

The results of studying the effectiveness of using photopolymerizable compositions (PPC) in various-purpose laser-plasma facilities with regard to the transportation and fine dosing of the working medium, as well as providing a long service life and reliability, are presented. The characteristics of the pulsed and continuous laser radiation curing of PPC and mixtures thereof are discussed in terms of the spectral-energetic characteristics of the incident radiation. The thresholds of nanosecond laser ablation in the UV and near-IR regions, specific ejected mass, momentum coupling coefficient, and efficiency of conversion of laser radiation energy into the kinetic energy of the laser-induced gas-plasma ablation jet for PPC in the liquid and solid states. The highest efficiency of generation of the gas-plasma ablation jet was achieved for the laser irradiation of initially liquid PPC at a wavelength of 355 nm, a wavelength optimal for the photopolymerization of PPC.

The efficiency of laser ablation of photocuring compositions that are working substances of various laser-plasma facilities is investigated for the first time. A substantial difference in spectral-energetic laser ablation thresholds, specific mass consumption, momentum coupling coefficient, and conversion efficiency of the laser energy to the kinetic energy of gas-plasma flow for liquid and solidified phases is demonstrated. Application of this class of working media allows not only solving problems related to laser ablation of a target, transport, fine dosing, and obtaining long lifetime and reliability of laser-plasma-based technological setups, but also considerably broadens the range of their operational characteristics.

We report the results of experimental investigation of thermophysical and gas-dynamic characteristics of the gas-plasma flows induced by ultrashort (45 - 60 fs) laser pulse irradiation (the radiation wavelength l = 400, 800 nm) of a titanium target in vac- uum (~5 ´ 10 -4 mbar). The use of combined interferometric tech- nique and complex experimental data processing allowed us to esti- mate the momentum coupling coefficient (Cm ~ 10 -4 N W -1 ), the efficiency of laser energy conversion to the kinetic energy of the gas-plasma flow (65 % - 85 %), the spatiotemporal distributions of the particle density (ne = 10 18 - 10 20 cm -3 ) and velocity (GuH = 4 - 9 km s -1 ), the static (10 6 - 10 8 Pa) and total (10 7 - 10 11 Pa) pres- sure and temperature (T = 7 - 50 kK) in the flow. Our data are compared with published data obtained by other methods.

The use of ultrashort laser pulses is a way to increase recoil momentum under laser ablation of materials, because, in this case, the energy deposition per unit volume of the target material is substantially higher due to reduced heat dissipation. By using methods of combined interferometry, we estimated the specific impulse (∼200–900 s), momentum coupling coefficient (∼2 × 10−5−3 × 10−4 Ns/J), laser-energy conversion efficiency to kinetic energy of the gas-plasma flow (∼0.05–0.82), and degree of the gas-plasma flow monochromaticity (∼0.72–0.92) under femtosecond (τ ∼ 45 fs, λ ∼ 800 nm) ablation of refractory metals (Ti, Zr, Mo, and Nb) in vacuum.

Thermophysical and gasdynamic characteristics of gas-plasma flows induced by ultrashort laser pulses interacting with a thinfilm copper target in vacuum were studied experimentally. Using combined laser interferometry and complex processing of experimental data, we estimated the momentum coupling coefficient and the efficiency of laserenergy conversion to kinetic energy, spatiotemporal distributions of the number density and velocities of particles, pressure, and temperature in the gas-plasma flow. We provide comparative analysis of presented data with those found in the literature, which were obtained by other meth� ods.

A combination of interferometric techniques is used to determine the specific impulse (~250–300 s), specific mechanical recoil momentum (momentum coupling, 1–3∙10–4 N∙s/J), efficiency with which the laser energy is converted to kinetic energy of the gas-plasma fl ow (~0.1–0.55), and degree of monochromaticity (~0.75–0.82) of the gas-plasma flow during femtosecond (τ ~ 45 fs, λ ~ 800 nm) ablation of copper in vacuum. The experimental results are compared with published data covering a wide range of laser interaction parameters.

The opto-mechanical characteristics, such as the specific mechanical recoil momentum, the specific impulse, and the energy efficiency, of the laser ablation of flat polymer targets ((C2F4) n , (CH2O) n ) have been determined experimentally for the first time for the case of excitation with femtosecond pulses (τ ∼ 45–70 fs) of UV-IR (λ ∼ 266, 400, 800 nm) laser radiation (I 0 up to 1015 W/cm2) under normal atmospheric and vacuum (p ∼ 10−4 mbar) conditions. The efficiency of mechanical recoil momentum generation is analyzed for various regimes of the laser irradiation.

We present the results of an experimental study of the ablation spectral energy thresholds for a number of polymer materials ((C2F4) n , (CH2O) n ) exposed to femtosecond (τ0.5 ~ 45–70 fs) laser pulses (λ ~ 266, 400, 800 nm) under atmospheric conditions and under vacuum (p ~ 10–2 Pa). We have analyzed the energy thresholds and the efficiency of optical, thermophysical, and gasdynamic processes in laser ablation vs. the laser pulse duration and photon energy.

New information on particle distribution over velocities, the mean-mass velocity, and the degree of monochromaticity of gas-plasma flow under femtosecond (τ ∼ 45 fs, λ ∼ 800 nm) laser ablation is obtained for several metals (Ti, Zr, Mo, Nb, Cu) in vacuum (p ∼ 5 × 10−2 Pa) by means of combined interferometry.

We describe an optical diagnostics module and the instrumental and methodological features of ultrahigh vac- uum experiments investigating the optical characteristics of condensed media in the short-wavelength (hν ~ 3.5-25 eV) range of the spectrum of probing synchrotron radiation. We give a brief presentation of the re- sults of an experimental determination of the spectral dependence of the luminescence quantum yield and the luminescence excitation spectrum of ablatable polymer dielectrics on the Kurchatov synchrotron radiation source at values of the probing radiation power density (I0 ~ 10 12 photons/cm 2 ⋅sec) that are below threshold for extended surface vaporization and a surface temperature of the condensed targets equal to 77-300 K. Introduction. In photonic power systems with high power density (optical accelerators and plasmatrons, laser plasma injectors, thermionic plasma optical converters, etc.) (1-3), plasma active media, including optical ablation media, at high temperatures (Te ~ 1-5 eV), are a source of broadband short-wavelength radiation with maximum in- tensities in the UV (UVC) and vacuum UV (VUV) regions of the spectrum. The temperature of the structural ele- ments of such power systems in the cycle for different pulsed periodic conditions may vary from cryogenic to phase transition temperatures. Therefore to calculate the heat and mass exchange characteristics, here we need data on the spectral reflection and absorption coefficients, the luminescence quantum yield for the structural materials in the UV- VUV regions of the spectrum over a broad temperature range, taking into account the technologically attainable level of surface treatment. As we know, measurement of the optical characteristics of condensed media in the vacuum UV region of the spectrum presents significant experimental complications, first of all due to the lack of sufficiently bright (at least 1 μW/mrad 2 ⋅nm) and broadband radiation sources in this region of the spectrum and secondly due to the need to make precision measurements under vacuum. Spectroscopy studies of condensed media in the vacuum UV region of the spectrum are conducted mainly using gas-discharge sources with a line emission spectrum, which limits the experimen- tal options in this spectral range both with respect to the number of available frequencies and with respect to the spectral brightness of the probing sources (2, 3). Using synchrotron radiation helps solve this problem. The high spec- tral density, the continuous (from the IR to the x-ray region) emission spectrum, the sharp directionality, and the high degree of polarization, the possibility for accurate determination of the spectral and energy characteristics of the source of probing radiation enable efficient use of synchrotron emitters as a working tool in optics and metrology with the maximum degree of monochromatization of short-wavelength radiation for existing vacuum UV monochromators. The goal of this work was to analyze the instrumental and methodological features of study under ultrahigh vacuum of luminescence excitation spectra and luminescence quantum yield of polymers over a broad range of photon energies for UV-VUV radiation and over a broad temperature range.

Using the methods of combined interferometry, we obtained new data on the momentum coupling coefficient and conversion efficiency of radiation energy into kinetic energy of a gas-plasma stream during femtosecond laser ablation (τ ∼ 45 fs, λ ∼ 800 nm) of several metals (Ti, Zr, Mo, Cu) in vacuum (p ∼ 5 × 10−2 Pa).

A pulsed–periodic source of high-power (∼1 MW/cm2) short-wave UV radiation with a developed luminous body and a high radiance temperature (∼30 kK) in the UV and near-VUV spectral region is described. The emitting plasma in the source is heated as a result of shock-wave interaction of counter-propagating supersonic dense-plasma streams formed by erosion-type magnetoplasma compressors.

A light-erosion generator of high-enthalpy gas-plasma streams of complex chemical composition has been developed on the basis of a plasma-dynamic broadband lamp-type source of short-wave UV radiation with a high power density of ∼1 MW/cm2 and a luminance temperature of ∼3.5 eV. The results of studies in a vacuum and a gas at a finite pressure show that the generator ensures the finely controlled characteristics of the mass flow rate: the velocity is v~ = 2–10 m/s and the mass consumption ratio is m. ≅ 2–3 mg/J.

The brightness-spectrum and energy parameters in the VUV range of the spectrum (hν ∼ 9–70 eV) of the surface laser plasma of polymeric targets in vacuum are determined experimentally. Using the experimental technology of double open and closed ionization chambers (as radiation detectors) requiring no absolute energy calibration in a wide range of regulation parameters of the effect of standard laser frequencies, we obtained new data on multifactor radiative gasdynamic processes of effect which are needed to determine emission and mass-output characteristics of the targets irradiated under vacuum.

The design of a double ionization chamber is described and an example of its use for the quantitative detection of pulse radiation fluxes in the vacuum ultraviolet region (hν ∼ 9–70 eV) in strong magnetic fields is given. The chamber features a high time resolution and good electromagnetic noise immunity.

A description is given of a pulse-periodic iodine laser pumped by high-power nonmagnetic plasma-dynamic flashlamps and incorporating a thermal closed circulation system for the active medium (n-C4F9I–C6F14 mixture) based on a condensation–evaporation cycle. An investigation was made of the energy balance and the output characteristics of the laser under single-pulse and pulse-periodic conditions at a repetition frequency of 17–50 mHz. The laser output energy was ~ 0.5 kJ, the pulse duration was 35–40 μs, the angular divergence was ~ 0.56 mrad, and the efficiency in terms of the electrical energy deposited in the pumping system was ~ 1 %. Stimulated emission during the complete laser pulse was achieved at the frequency of the unperturbed F' = 3 →F = 4 electronic transition in the hyperfine structure of the iodine atom.

The results of combined electrooptical breakdown (DC E~0-13.2 kV/cm + laser λ-213, 266, 355, 532, 1064 nm, τ0,5~18 ns, I0~109-1011 W/cm2) of gases (He, Ne, Ar, Kr) and their binary and triple mixtures at subatmospheric pressure (101-105 Pa) experimental investigation are presented for the first time. Thresholds of optical, electrical and combined electrooptical breakdown for those were experimentally determined. The possibility of breakdown threshold components decrease at simultaneous optical and electrical impact on the gas, and the possibility of lowering the thresholds of the combined breakdown of doped gases have been investigated.

The results of experimental and theoretical research of optical and thermophysical characteristics of refractory dielectric materials (SiO/sub 2/, BNC, Al/sub 2/O/sub 3/) in a field of intensive (I/spl sim/10/sup 6/-10/sup 9/ W/cm/sup 2/) coherent radiation (with standard laser wavelengths) and wideband thermal powerful VUV-IR radiation are presented.

An investigation was made of the lasing properties of broadband optically pumped active media utilizing the perfluoralkyl mercury halides CF3HgCl, CF3HgBr, CF3HgI, and i -C3F7HgBr. Low-temperature lasing (T ≲ 100 °C) was obtained for the first time using mercury monoiodide (λg ≈ 444 nm) produced by the photodissociation of CF3HgI, and the laser activity of the i - C3F7HgBr molecule was demonstrated. It was found that active media utilizing the perfluoralkyl mercury halides have energy characteristics which are not inferior to those of active media utilizing mercury dihalides, but that they can lase efficiently at a considerably lower temperature (T ≈ 120–135 °C).

It is a brief review of studies of lasing and energy-spectral characteristics of gas lasers utilizing — the excimer-like mercury halide vapor HgX2 (X=C1, Br, I), inert gas halogenides — XeF (B-X), (C-A) and molecules of the stable halogens (I2, Br2), optically pumped by wide-band UV-VUV radiation of high-current radiative discharges.

A description is given of the first mercury halide photodissociation laser pumped by wide-band thermal radiation from a plasma and emitting three-color visible radiation. Simultaneous lasing was observed for ionic-covalent electronic B–X transition in molecules of mercury monochloride λl≈558 and 559 nm, monobromide (λl≈502 and 504 nm), and monoiodide (λl≈443 and 444 nm). The laser radiation energy was ~0.3J emitted in the form of ~2.5μsec pulses and the lasing efficiency was ~0.07%.

A description is given and the results are reported of the first photoionization-recombination laser using atomic xenon excited by thermal ionizing radiation from a plasma. The pump source was a multichannel plasmadynamic discharge in magnetoplasma compressors, which was ignited in the active medium of the laser. When the composition of the working mixture was optimal (Xe:Ar = 1:250) and the total pressure was 1 atm, the output energy was ~?0.5 J in the form of pulses of ~?10 ?s duration and the maximum specific output energy represented by laser radiation was 1?2 J/liter. The unsaturated gain was 27 m???1. A kinetic laser scheme was proposed and analyzed. It allowed for the processes of photoionization, ion conversion, dissociative recombination, interaction of excited states with electron and buffer gases, etc. An important role played by heating of the active medium during pumping was demonstrated and it explained the observed characteristics of the spatial and temporal structure of the lasing process, particularly bleaching of large volumes of the active medium. The potential output energy of the laser was considered and specific constructions were proposed to attain a lasing efficiency amounting to a few percent.

A study was made of a perfluoropropyl iodide photodissociation laser pumped by the radiation emitted from a localized plasmadynamic discharge of the "plasma focus" type. An erosion magnetoplasma compressor was used as the plasma source. When the electrical energy input was 8 kJ, the specific energy output in the form of stimulated radiation was ~0.1 J/cm3 and the radiation power was ~0.2 MW. Experiments carried out without an illumination enclosure yielded an estimate of the laser efficiency which was ~0.35–0.45%. A comparison was made with a similar flashlamp-pumped laser. The result demonstrated advantages of the use of high-current plasmadynamic discharges for the optical excitation of photodissociation lasers.

An investigation was made of the radiation emitted in the wavelength range 1500–200 nm from a focus of a magnetic erosion plasma compressor. It was found that a discharge of this type was a promising optical laser-pumping source.

The results of calculating the properties of an equilibrium plasma of plastic at a temperature of from 1 to 100 eV are given, according to which it is possible to model the radiation-gas-dynamic processes in the multigroup approximation. The techniques for determining the radiative absorption coefficient provided for calculating the photoionized spectra in the vacuum ultraviolet while taking into account the observed similarity in cross section, individual consideration of the contributions of numerous calculations (up to 100 per ion) of the excited states, bremsstrahlung photo-processes, negative ions, etc. The results of the calculations are discussed.

An analysis of possible ways of enhancing the brightness of ultraviolet radiation emitted by quartz light sources led to a proposal of a new lamp in which an electric-discharge plasma is heated as a result of shock-wave thermalization of directional kinetic energy when a high-velocity plasma stream is decelerated in a gaseous medium, which also acts as a filter of the hard component of the plasma emission spectrum. This approach made it possible to construct quartz light sources characterized by an output radiation flux density in the short-wavelength ultraviolet range (180–250 nm) corresponding to the radiation emitted by a black body at a temperature of 40 kK.

A description is given of a high-power pulse-periodic radiation source with an extended luminous body and a high brightness temperature (~30×103 K) in the visible and near infrared parts of the spectrum. It is designed for laser and photochemical studies. A plasma is heated by a dynamic method based on thermalization of the kinetic energy of high-velocity plasma streams formed by magnetoplasma compressors of the erosion type; shock deceleration is the thermalization process. The results are reported of an experimental investigation of the spectral, energy, and dynamic characteristics of various shock deceleration configurations for plasma streams in vacuum and in gases (air, xenon), together with the spectral luminescence and lasing characteristics of molecular iodine vapor subjected to pulsed photoexcitation with radiation from the new plasmadynamic source.

This paper presents data on the continuous spectrum of CH/sub 2/O plasma for quantum energies of 1-1000 eV as well as its thermodynamic functions. The partial composition of the multicomponent plasma was calculated from a Sach-Eckert system of equations, taking the weak nonideality into account by the Debye equation, supplemented by the conditions of quasineutrality and maintaining the relationship between the number of particles of the various elements. Photoionization of the excited states having a principal quantum number greater than that for the ground state of the outer electron was calculated by the more approximate quantum defect method. To calculate the remaining highly excited states, integral relationships were used. The authors calculated the absorption coefficients averaged over the 16 spectral intervals which are necessary for making calculations in a multigroup approximation. It is shown that for calculations of the phenomena in a polyformaldehyde plasma having parameters lying principaly within the limits of the ranges indicated, a linear interpolation in logarithmic coordinates and the extrapolation of the data are recommended.

A new method is proposed for initiating long ( 0.5 m) spark discharges over the surface of an insulator: it does not require the use of "hard" electrical circuits (i.e., having a high U0/L0 value) or high operating and ignition voltages (U 25 kV), but provides temporally and spatially stable plasmas of a specified geometrical shape and, in particular, in the form of strictly linear plasma channels. An experimental investigation was made of the dynamics of formation and of the energy and spectral-brightness characteristics of high-current radiating discharges of a new type in the form of surface discharges having a linearly stabilized streamer (spark) channel. Discharges of this type can be used as high-power open sources of continuous pulse-periodic radiation of large size and having a high ( 40 kK) brightness temperature in the ultraviolet spectral region.

Double ionization chambers were used in a study of 10–70 eV radiation emitted from a plasma focus in an erosion-type magnetoplasma compressor. The maxima corresponded to the recombination of electrons terminating at the ground state of singly, doubly, triply, and multiply charged ions. The plasma focus emitted 45% of its total energy in the 12–70 eV range and could therefore be used as an efficient source of far ultraviolet radiation in establishing a population inversion in a medium by photoionization of the inner-shell electrons.

The authors determine similarity criteria and obtain relations relating instrument characteristics to the parameters of both the plasma formations and the shock waves which are formed due to such discharges. The results of this analysis can be used for studying and generalizing experimental data and for creating new, special-purpose, electrophysical devices based on magnetoplasma compressor discharges.

The lamp was placed in an illuminator which provided low inductance current supply to the electrode terminals. The body of the cell, which carried the return current, consisted of two brass cylinders separated by an isolator with holder clamps at opposite ends for making electrical contact with the electrode terminals of the lamp. Openings with a diameter of !0 mmwere made in the body of the illuminator in the central portion of the lamp and near the electrode region to allow for observation of the lamp emission. Measurement of the electrical parameters of the discharge circuit with the coaxial pump showed that when the discharge energy was varied from 50 to 200 J, the maximum value of the discharge current was 10-30 kA with a currant pulse length of 0.8-1.0 ~sec and a rise time of 0.4-0.5 ~sec. The energy losses in the elements of the discharge circuit accounted for 25% of the energy stored in the supply capacitor. The peak value of the power in the pulse sp was varied from was 40-150 MW, while the specific electrical power delivered to the lamp Pdl' 3 to 60 MW/cmSo

An experimental investigation was made of the radiation-gasdynamic interaction of high-power vacuum ultraviolet radiation fluxes with optical materials. Wide-band ultraviolet and vacuum ultraviolet radiation was generated by cumulation of hypersonic oppositely directed plasma jets formed by magnetoplasma compressors of the erosion type. A description is given of the apparatus and method used to measure the transmission characteristics of optical materials in the ultraviolet and vacuum ultraviolet parts of the spectrum. The results are given of measurements of the optical properties of quartz, lithium fluoride, and magnesium fluoride in the spectral range 250–120 nm after direct contact with a light-emitting plasma and under conditions of formation of an optically dense (in respect of hard vacuum ultraviolet radiation) gas layer. It is shown that, in principle, it is possible to construct sources of ultraviolet and vacuum ultraviolet radiation with a high brightness temperature of 30 kK in which the light-emitting medium is isolated by transparent walls.

A bleaching-wave laser (utilizing an ether solution of coumarin 6 and 1,4-diphenylbutadiene) was pumped by a flashlamp-type source utilizing magnetoplasma compressors. When the bleaching wave propagated in the solution at a velocity of ~ 1 km/s, cw lasing was obtained for 30–40 μs with an output energy of 1.2 J in the 517 ± 5 nm range. Estimates were made of the threshold pump intensity and of the internal losses in the bleaching-wave laser. It was found that, compared with a laser without a bleaching wave (utilizing an ethyl solution of coumarin 6), a bleaching wave improved greatly (under the same excitation conditions) the output energy and the directionality of the radiation.

A description is given of the first photodissociation laser utilizing the B–X electronic transition in mercury chloride (λ = 558, 559 nm). Wide-band optical radiation (representing thermal radiation of a plasma) was used to pump HgCl2 vapor. The energy of the laser output pulses reached 2.1 J and the duration was 7.6μsec. The laser efficiency, relative to the stored energy, was 0.1%.

An investigation was made of an XeF laser (λ ≈ 490 nm) with a 100 mm aperture and an active medium over 1 m long. An active mixture was formed by the flow of Ar, N2, and Kr buffer gases transmitted by polycrystalline XeF2. The use of a plane-plane resonator increased considerably the efficiency of utilization of the active volume. Measurements were made of the gain of the active medium for two configurations of the optical pump source at different XeF2 pressures. The dependences of the output energy on the resonator mirror transmission and on the XeF2 concentration were determined experimentally. An increase in the active length of the laser to 1.5 m and the use of a two-channel pump source increased the average (over the laser volume) specific output energy to 5 J/liter. A mixture of the XeF2:N2:Kr = 1:100:300 composition at a pressure P = 1.1 atm provided a record (for excimer lasers emitting in the visible range) energy of El = 45 J per pulse.

A report is given of lasing achieved for the first time in optically pumped molecular bromine (D' 3Π2g→A' 3π2u, λL ≈ 292 nm). It was pumped by thermal vacuum ultraviolet radiation emitted by plasmadynamic discharges of magnetoplasma compressors, formed directly in the laser active medium. An output energy of ~ 1.1 J was obtained per laser pulse of ~ 5-μs duration from a Br2:Ar ≈ 1:450 active mixture at a pressure of ~ 4 atm. A comparison was made of the experimental output parameters of optically pumped Br2, I2, and XeF (B–X) lasers when their geometries and excitation energies were identical.

Lasing was obtained for the first time in mercury monohalides at active medium temperatures ≲ 100°C. Stimulated emission due to the B–X electronic transition in mercury monobromide (λl ~ 502 nm) and mercury monochloride (λl ~ 552 and 558 nm) was excited by broad-band optical pumping of CF3HgBr and CF3HgCl vapors by radiation from a linearly stabilized surface discharge.

An effect of external static electric field on emission of radiation from non-ideal plasmas of erosion focus has been experimentally observed. An order-of-magnitude increase in radiation intensity for spectral interval hv = 40 − 350 eV with electric field increasing up to 103V/cm has been found for plasmas with ξ Z ≃1 , where ξ is the number of electrons in Debye sphere, Z = 2 − 3 is the stage of ionization. The energy emitted has been several times higher than the black body energy for the same spectral interval at maximum electric field achieved. The effect vanishes at ξ Z ≃10 .

A description is given of the first photodissociation laser utilizing the B–X electronic transition in mercury iodide (λ = 442, 443, 444 nm) with wide-band optical pumping of HgI2 vapor by thermal radiation from a plasma. The pump source was a linearly stabilized surface discharge with a brightness temperature Tb ≈ 25kK in the ultraviolet part of the spectrum. Laser pulses of 0.5J energy and 3.5μsec duration were generated.