Plasma evolution regulations with the change of initial conditions of femtosecond laser and an optical detecting scheme is verified numerically

Abstract

The plasma channel evolution tendencies are studied numerically with the change of initial conditions based on the Nonlinear Schrodinger Equation. Then, the accuracy of an optical scheme to detect the plasma density inside the filaments is certified numerically. A Gaussian beam with pulse width 50fs, radius 2.5mm ranging energy from 10mJ to 50mJ at interval of 10mJ are simulated to yield plasma channel. With the augment of energy, firstly, the beginning position of plasma channel tend to be drew back gradually whereas the end position of the channel can be putted forward in a gradient form instead of continuously. Secondly, the number of peaks add one each time when the energy increase 10mJ. Lastly, the radius of plasma channel barely changes with initial energy up from 10mJ to 50mJ. On the other hand, plasma channel produced by a Gaussian beam with pulse width 50fs, energy 50mJ ranging the radius from 2.5mm to 10mm at interval of 2.5mm are simulated. With the increase of initial beam waist, the plasma channel length becomes shorter. The channel becomes broader and broader whereas the length of the channel becomes shorter. In order to verify the rationality of the approximation, Nornaraki detecting scheme through interference of the probe laser has been tested with the numerical simulation. As a consequence, the integral of refractive index along the radius direction can be replaced by the product of average refractive index and plasma channel diameter.