Abstract-Terahertz hyper-Raman time-domain spectroscopy of gallium selenide and its application in terahertz detection

Applied Physics Letters

Sen Mou, Andrea Rubano, Domenico Paparo

Experimental setup: BS, beam splitter; L, lens; CH, triggered chopper; DL, delay line; PL, air plasma; F, BG39 colored filter; MC, monochromator; PM, photomultiplier tube; Si, silicon plate.

https://aip.scitation.org/doi/abs/10.1063/1.5115986

We report the observation of Terahertz (THz) hyper-Raman generation in a gallium selenide crystal. This nonlinear optical process derives from the four- and five-wave-mixing of femtosecond optical pulses and intense, subps, broadband terahertz pulses. The wavelength spectrum of the resulting signal displays two pronounced frequency sidebands close to the optical second-harmonic central frequency 2ωL$2{\omega }_L$, where ωL is the optical central frequency of the fundamental beam. The two sidebands develop around the central frequency at the (anti-) Stokes side of ωs,a=2ωL∓ωT${\omega }_{s,a}=2{\omega }_L\mp {\omega }_T$, where ωT is the THz central frequency. This nonlinear optical process is used for the coherent detection of intense and broadband terahertz waves. The proposed technique shows a good linear response of up to 90 kV/cm and a better efficiency in detecting the lowest terahertz frequencies, as compared to the standard electro-optic sampling performed in two different nonlinear crystals.

The authors acknowledge funding from the “Ministero Istruzione Università e Ricerca” and “Consiglio Nazionale delle Ricerche.”