Abstract

Resonatorless absorptive switching and self-pulsing have been observed in bulk ZnSe when excited by square input pulses at 476.5 nm on a time scale from ~1 μs to >1 s. Beyond a critical intensity of ~7 kW/cm² the material begins to switch repeatedly between a transmission of ≥60% and ≤5%. This switching and self-pulsing behavior is a local phenomenon (resonatorless). This bistable behavior is based upon band gap renormalization, band filling, and plasma screening. Through absorption there is an increase in the temperature. This results in a shifting of the band edge to longer wavelengths. This further increases the absorption. At some point the incident photons become completely absorbed and a switching to an “off” state results. At this point a relatively large number of electron-hole pairs are created. Depending on the thermal and electron-hole pair concentration dynamics, a filling of the available states eventually results and the absorption decreases. Thermal diffusion then allows for local cooling, the band gap shifts to shorter wavelengths, and a switching to the “on” state results. This modulation of the absorption continues, and one sees a sequence of pulses (self-pulsing) in the transmission.

© 1992 Optical Society of America