Dynamics of photoluminescence quenching in GaAs induced by a strong THz field

A photoluminescence (PL) quenching under strong-field (up to 150 kV/cm) picosecond terahertz pulses in a semi-insulating GaAs crystal illuminated by femtosecond laser radiation was studied. We showed that the optical-terahertz time-delay dependence of the PL quenching significantly depends on the optical pump fluence. For high fluences (>200 μJ/cm2), the quenching interval is governed by the terahertz pulse duration (1–2 ps), in agreement with previous studies, whereas for fluences ≲100 μJ/cm2, it is determined by the recombination time (∼80 ps) of photoexcited carriers. This difference is mainly attributed to terahertz field screening by photoexcited electrons in GaAs. A simple model of hot electron density dynamics accounting for nonradiative recombination and the carrier-density-dependent terahertz field strength was found to successfully describe the time-delay quenching at moderate optical fluence (50–120 μJ/cm2). For high fluences, the terahertz pulse dynamics under screening by photoexcited carriers was calculated to qualitatively explain the observed time-delay quenching dependence.