Ultrafast differential-transmission spectroscopy of excitons in strained ZnSe layers and Zn1-xCdxSe/ZnSe quantum wells

摘要

Abstract: The nonlinear optics of excitons in ZnSe-based heterostructures is investigated by means of fast femtosecond and narrow-band picosecond differential transmission spectroscopy. Pulse lengths amount to 100 fs and 1 ps, respectively. Results taken at Zn$-1$MIN@x$/Cd$- x$/Se/ZnSe quantum wells, ZnSe layers with ZnS$-x$/Se$-1$MIN@x$/ cladding, and ZnSe epilayers are presented and discussed. Because of strain relaxation the usual bleaching of the excitonic absorption observed in quantum wells and waveguide-type structures reverses into an induced absorption in case of thick ZnSe epilayers. This phenomenon is discussed by use of a simple empirical model for the optical absorption of a set of inhomogeneously broadened Lorentz oscillators which react on the local exciton density with a nonlinear damping and a reduction of the oscillator strength. Additionally, a very fast change in transmission observed in the waveguide-type structures is discussed in terms of the resonant optical Stark effect.!14