Key points are not available for this paper at this time.
Observations have been made of the two-photon excitation of an electron from the valence to the conduction band in CdS (E₆=2. 5 eV) using a pulsed ruby laser (=1. 78 eV). The radiative recombination emission from exciton and impurity levels subsequent to the simultaneous absorption of two quanta of =1. 78 eV was observed as a function of laser intensity and compared to the emission excited by single-quanta absorption for photons of >E₆. It was found that the intensity of the recombination radiation is proportional to {I₀}^n for single-quanta excitation and {I₀}^2n for double-quanta excitation, where I₀ is the excitation intensity and n is a constant which differs for different groups of emission lines. The observed cross section for double-quanta excitation is compared with theory utilizing the band parameters of CdS.
Braunstein et al. (Mon,) studied this question.