Numerical modeling of the transmission of breakdown plasma generated in water during laser shock processing

The transmission of breakdown plasma generated in water during laser shock processing experiments was investigated theoretically. A numerical model based on a rate equation formalism has been developed to calculate the characteristics (peak irradiance and duration) of the laser pulses transmitted through the breakdown plasmas generated in water. Results are in good agreement with previous experimental data for 25 ns-1064 nm laser pulses. Above 10 GW/cm(2), the transmitted peak irradiance saturates and the transmission starts to decrease. The results have been extended to shorter wavelengths (532 and 355 nm). At 1064 nm, the breakdown process is dominated by avalanche ionization, whereas for shorter wavelengths, multiphoton ionization plays the major role.