Switching of a gaas bistable etalon: External switching on and off, regenerative pulsations, transverse effects, and lasing

Switching between states of an intrinsic bistable device is usually accomplished by changing the input intensity II, increasing it above the switch-up value It or below the switch-down value With a constant input intensity satisfying I<↓ II < I↑, switching can be actuated by external pulses. Switch-on by a 10-ps, 600-nm, 1-nJ pulse in less than the 200-ps detector response time is attributed to screening of the GaAs free excitons by hot carriers. Switch-off in <20 ns by a 7-ns, 600-nm, 300-nJ pulse is attributed to heating the etalon and increasing I4, until it exceeds the constant II. Under certain con-ditions the competition between excitonic and thermal effects causes the etalon to switch on and off repeatedly in a relaxation oscillation fashion. These regenerative pulsations could be the basis of an all-optical oscillator. The transverse profile has been examined for switching actuated by intensity modulation of the input. Whole-beam switching is observed, i.e., when switch-on occurs, it occurs out to large radii simultaneously. Computer simulations show whole-beam switching for strong diffractive coupling but show radially dependent switching for weak diffraction, neglecting transverse diffusion. The same etalon emits a near-band-gap laser pulse when pumped sufficiently by an above-band-gap pulse, serving as a wavelength converter. All of these modes of operation of the GaAs etalon, i.e., switchable memory, oscillator, and wavelength converter, could be useful in all-optical logic and computing systems.