Abstract

Since the demonstration of the ac-Stark effect of excitons in multiple quantum wells,¹ resonant coherent optical nonlinear phenomena of extended Bloch electrons has been studied extensively. In solid materials, such electronic states usually have very short dephasing times and rapidly lose the phase memory of coherent optical excitation. Thus, we usually need ultrafast short pulses to observe such coherent optical processes. The coupling between biexciton and phonon is very weak in CuCl,² and the linewidth of the biexciton state is very narrow. Therefore, the biexciton state is a good candidate to demonstrate resonant coherent optical nonlinearity in the steady-state regime. In this report, we present dear evidence of ac-Stark splitting of the Bloch-type electronic state, namely, the ac-Stark splitting of the Γ₁-biexciton state in CuCl resulting from coherent mixing of the Z₃ exciton-polariton and the biexciton with highresolution two-photon polarization spectroscopy.³

© 1991 Optical Society of America