Laser-Induced Probe-Beam Defocusing at the Band Edge of CdSxSe1−x Mixed Crystal at Room Temperature

Abstract

A room temperature measurement is made of the IR‐pump‐laser induced external defocusing of a Gaussian shaped probe‐beam transmitted at a fixed wavelength at the band edge of CdSxSe1−xmixed crystal (x = 0.65). From the probe‐beam expansion factor the negativ dispersive change at the band edge resulting from the excess free‐carrier concentration Ne generated by the IR‐pump‐beam via two‐photon interband absorption is calculated and compared with the value ob‐tained in a pump‐beam selfdiffraction experiment. Already at Ne = 1.3 × 1016 cm−3 a dispersive change of −Δn = 1 × 10−4 is found. Moreover, at the band edge an increase of the probe‐beam transmission is measured indicating a maximum absorptive change which is about four times smaller than k Δn. Therefore, at higher excitation levels the higher transmission signal expected will be limited by defocusing.