Self-focusing and pulse sharpening of sub-picosecond laser pulse in n-InSb

The self-focusing and pulse sharpening of an intense short pulse laser in n-type indium antimonide, a semiconductor with non-parabolic energy band, is studied. The nonlinearity arises through the dependence of electron effective mass on quiver velocity and gives effective permittivity a saturating function of intensity. A laser beam with Gaussian transverse intensity profile undergoes periodic self-focusing. The faster self-focusing of the peak of the pulse causes significant sharpening of the pulse in course of propagation. For 10.6 mu m CO2 laser of picosecond pulse length and intensity similar to 1 - 2 GW/cm(2), significant self-focusing and pulse length shortening occurs over a length of 0.6 mm.