Theoretical Studies On Laser Induced Plasma Ignition Mechanism And The Threshold Detection

This paper probes into the plasma ignition mechanism and the correlation feature during the process of the interaction between ultra high power density pulse laser with the materials in atmosphere and liquid environment. The plasma ignition threshold of metal is got through experimental and numerical study.The vapour and plasma ignition times of the target are got based on the equation of heat conduction and cascade model. We suppose that the plasma is ignited when 210 generations of new electrons are born in vapour generation time. The influence of temperature on the thermodynamics and optics parameters of material also have been considered in the model. The resulting theory has good agreement with the experiment and overseas report. A blade method to measure the laser spot is given in this paper with validation and error analysis. The plasma threshold of metals in atmosphere and water ambients both are diagnosed with the light deflection and piezoelectric transducer. A Q-switched pulsed Nd:YAG laser operating at infrared (1064nm), visible(532nm) and ultraviolet (355nm) wavelengths has been used. Al,Fe,Cu are used as targets and get a similar results with both method. Theoretical and experimental analyses are applied on the influence of wavelength on the threshold have been done, both of which have shown that the plasma threshold of metals decrease as the laser wavelength increases; The plasma threshold of metals are higher in water than in air and the pressure of the shock wave in water is five times higher than in air.Some references of the studies on the interaction of the laser with the material can be supplied by the result achieved in this paper, and some theoretical and experimental rules on the laser action project is also given...