Femtosecond pulse propagation in argon: A pressure dependence study

We present a numerical study of self-focusing and optical breakdown of focused femtosecond pulses in argon using an extended nonlinear Schrödinger equation for the field coupled to an equation for the electron density generated via multiphoton ionization. Using the pressure as a control parameter we are able to identify different regimes of femtosecond pulse propagation from a low-pressure regime dominated by plasma effects $(p\lesssim 1\mathrm{atm})$ to full blown self-focusing collapse arrested by normal group velocity dispersion at high pressures $\left(p\gtrsim 100\mathrm{atm}\right).\mathrm{}$ In the intermediate region $\left(p\sim 1-10\mathrm{atm}\right)$ the dynamics of the pulse propagation is affected by both self-focusing and plasma effects and can lead to multiple collapse events and also stabilized propagation.