Laser Supported Absorption Wave (LSAW) is an important content in laser propulsion research, which can be divided into Laser Supported Detonation Wave (LSDW) and Laser Supported Combustion Wave (LSCW) according to that whether the wavefront of LSAW is separated from the wavefront of Precursor Shock Wave or not. Maintaining LSAW need the incident laser with certain energy, in result the laser threshold of LSDW is higher than that of LSCW.
In 1965, the pneumatic dynamics model is proposed by Paйзep firstly, in which LSDW is regarded as a strong discontinuity without thickness transmitting with supersonic speed, where the incident laser is completely absorbed so that the wave is forward. LSDW compresses the gas in front of it, with the result that the gas ionizes by temperature increasing and absorbs laser, then becomes the new wavefront. Based on the fluid mechanical formula of one-dimension LSDW, influence of incident laser intensity on the speed of LSDW and the pressure, temperature and intensity of gas behind LSDW is analyzed in this paper, primarily the range and trend of the speed of LSCW and the parameters of gas behind LSDW are deduced in theory. The speed of LSDW is in direct ratio with 1/3 of incident laser intensity, and the pressure and temperature of gas behind wave is in direct ratio with 2/3 of incident laser intensity.
Along with laser power increasing, the speed of LSCW is gradually close to the speed of precursor shock wave, at the moment LSDW comes forth. While the ratio of the speed of LSAW to sonic speed is more than 1, LSAW is LSDW. Or else, while the ratio of the speed of LSAW to sonic speed is less than 1, LSAW is LSCW. On the basis of speed formula of LSDW and sound speed formula in gas, the threshold of the laser intensity to keep LSDW is discussed in this paper, and the theoretically calculated results are compared with experimental results reported in some documents.
In fact, because that plasma is composed of positively charged ions and negatively charged electrons, and the charged particles have Coulomb interaction, which bring about that the internal energy and the pressure of gas is somewhat different from ideal gas, plasma should not simply be discussed as ideal gas. In view of the internal Coulomb interaction of plasma, the speed of LSDW is increasing and the pressure and temperature of gas behind wave is descending. Finally, the deviations of plasma with Coulomb interaction from ideal gas are put forward, and how to correct these deviations is analyzed.