Shadowgraph Detection And Calculation Of Laser Induced Air Plasma

Laser induced air plasma can be widely used in laser propulsion, reducing air resistance, and laser plasma switch, and it is importance to know the shock wave propagation of laser induced air plasma. In this thesis, shadowgraph technique was used to investigate laser induced plasma in air. The evolution of the shock wave was obtained, and the shock wave speed was presented. The plasma refractive index equation was numerically solved Jacobi iteration method, the refractive index and density distribution of the disturbed region were obtained. Followings are the main contents of this thesis.Experimentally, The experimental system was established to diagnosis the laser induced air plasma by the use of shadowgraph technique. Both TEA CO2 laser and Nd: YAG laser were used in the experiment. By changing the delay time of ICCD camera, we obtained a complete series shadowgraph of laser induced air plasma from the plasma generation to the dissipation of the thermonuclear air dissipated, and the temporal evolution of the shadowgraph was explained. By using various focal lengths, the diameters plasma shock wave and velocity were measured and calculated. By using different attenuators, the relationship between plasma shock wave velocity and diameter with laser energy was obtained.Theoretically, Python for scientific computing is introduced, Jacobi method is used to solving Poisson equations. The equation between the intensity of shadowgraph and refraction index was obtained, the iterative method script based on the Python language was written. The written Script code was used to process the experimental obtained shadowgraph, and the two-dimensional refractive index profile was obtained, based on Gladston-Dale relations thermonuclear shockwave and air density distribution of laser induced air plasma was obtained.