Propagation of High Power Short Pulse Laser in a Tunnel Ionizing Inhomogeneous Gas

Abstract

An intense short pulse laser with a Gaussian radial profile, propagating through a gas of axially inhomogeneous density, produces plasma via tunnel ionization. The plasma has radial as well as axial inhomogeneity. The former causes defocusing of the laser due to nonlinear refraction as the refractive index is minimum on axis. The axial inhomogeneity causes stronger defocusing in regions of higher density. The rapid temporal evolution of the plasma density gives rise to phase modulation and frequency upshift of the laser. The effect is most pronounced at the front end of the pulse. The self-defocusing of the laser reduces the ionization rate and frequency upshift. The results are compared with a recent experiment and found to be in reasonable agreement.