Light-modulated reflectance in CdS

Reflectance spectra of CdS modulated by a second, intense light beam, show detailed structure due to excitons. This structure results from screening induced by the free carriers generated by the intense light beam. By maximizing the effect we were able to obtain considerably better resolved spectra than previous photo- or electro-reflectance measurements had given. A good theoretical fit was possible with a choice of reasonable parameters.