Nonlinear absorption of a picosecond pulse in a-Si: H

The results of a nonlinear-absorption research in a film of a -Si: H are reported. The absorption is induced by a picosecond laser pulse with quantum energy only slightly exceeding the band gap width of the material. Picosecond pulses obtained by optical methane and hydrogen pumping and stimulated Raman scattering were used in experiments for resonance excitation of the sample. The total absorption is shown to be the sum of the free carrier absorption and absorption by holes trapped on local levels in the “tail” of the conduction band.