Surface Laser Plasma in Laser Treatment of Materials in High Pressure Gases
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SURFACE LASER PLASMA IN LASER TREATMENT OF MATERIALS IN HIGH PRESSURE GASES
A. SMIRNOV*, C. DUPUY**, *Institute of Metallurgy, Moscow, USSR **Institut de Science Odeillo,
G. FLAMANT** USSR Academy of Sciences,
Leninsky Pr. 49,
et de Genie des Materiaux et Procedes,
66120 Font-Romeu,
CNRS,
117334 BP.5,
FRANCE
ABSTRACT Using holographic interferometry the surface laser plasma generation in high pressure gases has been investigated. Additional information about the generation of surface cover laser plasma, optical breakdown in the presence of aerosol particles and condensation front forming in high pressure gases is given.
INTRODUCTION The modification of the physical parameters of different materials by laser-plasma treatment is a well known technology. These operations include heat treatment (surface hardening), annealing, welding, cutting, hole drilling (piercing), etc. The synthesis of new materials and surface deposition of materials by chemically active surface laser plasma (SLP) in high pressure gas is another important direction of the recent scientific research. It is of practical importance to take the advantage of the SLP thermochemical and thermal target interaction in the most effective way. Experiments show that the use of gaseous media of a controllable composition and pressure can change the character of laser-target interactions. This offers the possibility of evolving new processes of material treatment. The processes of laser-plasma treatment are found to play a substantial role in modifying of surface properties of a material. Further investigations of the laser-plasma treatment of materials are closely connected with the research on thermodynamic phenomena in the solid state and on different phenomena in SLP [1,2]. The main phenomena in SLP is concerned to be chemical processes at the surface of materials during laser-plasma treatment. Many articles discuss the generation of SLP and optical breakdown (OB) in gases [3,4]. Some of them are based on holographic interferometry experiments [5,6]. This paper is devoted to the peculiarity of SLP, optical breakdown (OB) generation and condensation front (CF) forming during laser treatment of materials in high pressure gases. SLP and OB were visualized by double exposure holographic interferometry.
EXPERIMENTAL
The holographic interferometer was bound to visualize the variation of the refractive index in the layer of laser target interaction to measure 3 it. The experimental equipment consisted of: a Nd+ -glass pulsed laser (10-100 J, duration l.5ms), for target treatment, a Q-switched Ruby laser (0.5 J, duration 20 ns), and a holographic interferometry set-up. Five different types of targets, made of Ti (20-24 mm in diameter, 2 mm thick), 2 Zr (15-17 mm in diameter, 2mm thick), W2 0 3 (10xl5mm , I mm thick), A1 2 0 3 (15 mm in diameter, 10mm thick), plexiglass (20 mm in diameter, 1 mm thick) were installed in a high pressure chamber at different angles (0, W/6, W/4, 3 w/3) with respect to the Nd+ -glass pulsed laser beam direction. The chamber
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