Asymmetric self-focusing of a laser pulse in plasma

An intense short-pulse laser propagating through a plasma undergoes self-pulse distortion due to the combined effects of nonlinearity-induced self-focusing and dispersion. The nonlinearity arises as a result of relativistic mass variation. The low-intensity front of the pulse converges mildly, while the high-intensity later portions self-focus strongly. However, at the intensity maxima, the self-focusing effect is masked by the saturation effect of the nonlinear refractive index. The group velocity is also a function of intensity; as a result, the front of the pulse becomes sharpened, while the tail tends to be broadened.