Doubly resonant raman scattering induced by an electric field

By applying a variable electric field to a 30-35 Å GaAs/${\mathrm{Ga}}_{0.65}$ ${\mathrm{Al}}_{0.35}$As superlattice we have achieved tunable doubly resonant Raman processes, in which both the incident and the scattered light are in resonance with electronic transitions. The resonances, which involve states of the field-induced Stark ladder, manifest themselves as strong enhancements in the intensity of Raman scattering associated with the longitudinal optical phonon of GaAs. The dependence of the double resonances on field and photon energy provides direct information on the superlattice states, in very good agreement with results of photocurrent and photoluminescence experiments.