Laser holographic interferometry of short ultraviolet radiation with high power density interaction with condensed metters

The dynamics and macrostructure of near-surface vapor-plasma fluxes arising from condensed substances evaporation in the field of broadband radiation of the UV-VUV spectrum range are studied using double-exposure laser holographic interferometry and schlieren photography (the Toepler scheme in the light field mode). The experimental setup was created on the basis of the unique scientific facility "Beam-M". Broadband UV and VUV radiation was generated by a plasma-dynamic emitting discharge of an end geometry coaxial erosion-type magnetoplasma compressor with an ablating fluoroplastic plasma-forming insulating sleeve in a gas. To control the emission spectrum of the discharge, gas filters were used (Ar, Ne, air, Ne mixture with 5% air). The emitter operated in the following mode: U = 20 kV, the stored energy W = 3.6 kJ, the energy input to the discharge was up to 3.2 kJ, with 30% in the first half-cycle of current, the maximum current is 160 kA, the half-cycle of discharge is 6 μs; the total radiation energy from the discharge was 1.0-1.2 kJ; the fraction of radiation in the VUV range of the spectrum was about 50% in Ne (hν ≤ 20 eV) and about 45% in Ar (hν ≤ 16 eV). It was shown that the implemented scheme of electromagnetic compatibility and protection ensures reliable synchronization of the electric discharge circuit and optical diagnostics components in the whole range of discharge characteristics. Optical diagnostics of near-surface gas-plasma flows was implemented on the basis of a second harmonic (532 nm) of a solid-state Nd:YAG laser (Solar LQ-115), its versatility was shown for studying various pulsed plasma processes with characteristic changes in gas concentrations of about 1017 - 1018 cm-3 and gradients of 1019-1020 cm-3. On the schlieren-pictures and interferograms, the zones characteristic of the studied type of radiation effects on materials were recorded: the gas-dynamic evaporation mode was realized (plasma piston mode), there was a shock wave in the gas, the contact boundary between the shock-compressed gas and the vapor plasma. The analysis of interferograms indicates that the regime of developed evaporation was preceded by a regime of diffusion evaporation. The use of extended samples allowed us to observe successive stages in the development of gas-dynamic perturbations during evaporation (due to the different distances between the target areas and the discharge). On the interferograms above the target, at different distances from the source of irradiation, 3 types of gas-dynamic perturbations were observed: acoustic wave, simple wave (Riemann wave), and shock wave. The effect of the energy characteristics of the discharge and the spectral composition of the radiation on the evaporation pattern was experimentally shown. © 2017 Lavoisier. All rights reserved.