(Received November 29, 1984)
A new technique for PAS was proposed where the secondary steady light (λ2) modified the primary signal at wavelength (λ1). This technique was applied to the CdS: Cu system. Quenching and enhancement of PAS by the secondary light was observed depending on the absence or introduction of Cu impurities. The importance of the nonradiative decay process from a Cu related level to the native acceptor level was thus clarified.