Gap States Contribution in the Non-Linear Optical Response of Glassy Semiconductors

Due to lattice disorder, glassy semiconductors have energy levels in their bandgaps (gap states) that can be populated by sub-gap illumination or due to recombination of photo-excited carriers. The non-linear optical (NLO) response induced by high-intensity femtosecond (fs) laser pulses develops together with the gap states excitation. These effects in non-crystalline semiconductors have not yet been well studied. In this work, we use two realizations of the pump-probe method [1,2] to study the NLO response of chalcogenide glassy semiconductors of the systems As
₄₀
S
_x
Se
_1-x
and As
₄₀
Se
_x
Te
_1-x
with fs resolution in time upon illumination by fs laser pulses with the peak wavelengths λ
_p
of 0.79 and 1.57 μm.