Time dependence of CO_2 laser pulses recorded in the mixed detector regime of the photon drag and Seebeck effects in n-doped GaAs

摘要

In this paper, we present experimental work on the temporal profiling of transversly excited atmosphere (TEA) CO_2 laser pulses by using a particular kind of semiconductor photodetector. The detector exploits the combined effects of two fast sensing mechanisms, namely, the electron temperature related Seebeck and photon drag effects, and one slow mechanism, the phonon related Seebeck effect. The design of the photodetector is such that the typical emitted TEA CO_2 laser pulses (100 ns peak pulses in combination with a microsecond long tail) induce a transit response between the fast and the slow sensing mechanisms. In the fast regime, the output voltage is proportional to the temporal evolution of the pulse intensity. Starting from the falling edge of the pulses, this proportionality changes its characteristics gradually such that the output voltage becomes proportional to the time dependence of the laser pulse energy. All experimental results are backed by a theoretical model and numerical simulations.