Effects of initial focusing on the blueshifting of high-power laser pulses

高パワーレーザーパルスの青方偏移に対する初期集光の効果

Koga, J. K.

Koga, J. K.

Since the advent of high power short pulse lasers, there has been a broad interest in the propagation dynamics of high power pulses in neutral gases. When high power ultra-short laser pulses are focused in neutral gases to sufficient irradiance levels, the gas is ionized and plasma forms. Experiments with a laser pulse focused in a gas chamber have shown a total blue-shift of the laser pulse, which was fixed and independent of the gas when the power is above the critical power for self-focusing. By directly solving Maxwell's equations including higher order gas polarization and using a semi-analytical method for pulse propagation we study the generation of plasma by high irradiance laser pulses propagating in a neutral gas and determine the effect of initial focusing angle on the blue-shift of the laser pulse. By varying the initial focusing angle we find that below a specific angle the blue-shift is nearly fixed and above the specific angle the shift changes with the initial angle.