Laser induced refractive index inhomogeneities and absorption saturation effects in CdS

We have studied an optically-induced index inhomoganeity in CdS. Using ∼10 mW of focused laser radiation whose frequency is near the band gap, a reduction in index as large as one part in 10³was observed which resulted in induced lenses with focal lengths as short as 1 mm. We also find large absorption saturation and highly efficient recombination radiation (green edge emission) accompanying the index effects. Changes in optical transmission of two orders of magnitude and quantum conversion efficiencies of ∼50 percent were measured. The effects occur in selected samples near liquid nitrogen and liquid hydrogen temperature. Various mechanisms for the inhomogeneities are discussed. The effect is ultimately attributed to the presence of compensated Cd acceptor vacancies which act, directly or indirectly, as absorbing centers. The relevance of these effects to laser-induced index inhomogeneities occurring in LiNbO3and LiTaO3is discussed.