Development of Fabry-Perot etalons with an optical switch for terahertz laser pulses

Tsubouchi, Masaaki; Kumada, Takayuki   

We have introduced a novel etalon device for THz laser pulses to generate THz laser pulse trains. The etalon usually consists of a pair of the high reflective mirrors. Therefore, a large amount of input light is reflected by the input mirror, and cannot be transferred to the pulse train efficiently. We have solved this intrinsic problem of the etalon by using an optical switch. Our THz etalon consists of a thin silicon (Si) plate as an input coupler and a glass coated by the indium tin oxide (ITO) as an output coupler. The Si plate is transparent for THz light, and the ITO membrane strongly reflects it. After the THz pulse transmits the Si plate, the Si is irradiated by a UV light pulse to generate the plasma sheet which strongly reflects the THz light. The UV light operates as an optical switch which traps the THz pulse in the etalon cavity. The small portions of THz light are transmitted through ITO in each round trip, and form the pulse train. In this study, we have demonstrated the THz etalon, and efficiently obtained the THz pulse trains which have comb-shaped spectra.