Measuring the spectrum of terahertz pulses using the first-order autocorrelator based on Fabry-Perot cavity

Abstract

Ultrashort terahertz (THz) pulse has a broad spectral bandwidth and essential applications in material identification and disease diagnosis. In this work, the cascaded Fabry-Perot interferometer is proposed to construct a Fabry-Perot cavity based first-order autocorrelator(FPAC) for measuring the spectrum of the ultrashort THz pulse. The FPAC is made up of two pieces of uncoated high resistivity float zone silicon wafers and can be regarded as three tandem Fabry-Perot interferometers/etalons. It can be demonstrated numerically that without any coating process to measure the spectrum of the THz pulse. Using the home-built FPAC, the spectrum of THz pulses generated by dual-color femtosecond laser filament and the THz transmission spectrum of the penicillin sodium tablet is measured, experimentally demonstrating the validity of the FPAC in THz spectrum detection. Compared to other THz spectrum detection methods, such as the Fourier transform spectrometer and THz time-domain spectral system, the FPAC has a more compact structure due to the utilization of the common-path interference setup, which can be used in narrow space for in situ detection.