Photoionization in precursor of laser-induced plasma by ultraviolet radiation

Summary form only given. In the initial stage of laser-induced plasma, a laser absorption layer propagates with the shock wave that corresponds to a combustion layer in chemical detonation. The structure has been recognized as a Laser Supported Detonation (LSD). A previous study show that a precursor electron ahead of a shock wave has been investigated until LSD termination with using a two wave Mach-Zehnder interferometer. Results of this study demonstrate that the laser heated sustained the LSD wave. Since laser heating induces the shock wave in the LSD, the LSD is difficult to sustain in separating the front of shock wave from the laser heating layer. The result suggests that the generation of the precursor electrons produces the preheated layer ahead of the shock wave. In other words, the precursor electrons play an important role in shock wave propagation. Besides, photoionization by Ultraviolet (UV) radiation behind the shock wave generate the electrons. In the present study, we estimated UV photons generating behind the shock wave and photon absorption depth ahead of shock wave for different gases. First, to evaluate UV photons emission from plasma, we measured a number density of electrons and the electron temperature and estimated the absorption layer and the radiation volume. And high-purity argon was used as the test gas for comparison with air. Argon gas is one of the inert gases and its ionization and excitation processes a re simple comparing with air. As a result, the argon plasma e mitted a single photon in 10^-9 to 10^-4 seconds, which were higher values as compared with air plasma. Result reveal that the large number of photons emitted from plasma sustains in 1 ong LSD regime. Secondly, we estimated the photon absorption depth ahead of shock wave. It takes into account the absorption by atom (Argon) and molecular (Oxygen). The confirm of the mechanism of photoionization offered by Zhelezniak et al.