Optimization of Electrooptical Sampling of THz Pulse With a Chirped Broadband Probe Pulse in Thick EO Crystal

Electrooptic (EO) sampling is a method in THz time-domain spectroscopy. In previous studies, a thick EO crystal with a broadband probe pulse is used to meet the requirements of THz detection with a large time window and high-precision frequency spectrum. However, the broadband probe pulses are significantly broadened in the time domain during the transmission in thick EO crystals due to group velocity dispersion, which distorts the EO signal. In this article, a negative prechirp of broadband (10 fs in full-width at half-maximum) laser pulse is utilized to compensate the dispersion and enhances the detected signals. In the experiments, we use an interdigital photoconductive antenna to generate typical THz pulses in the region of 0.1-3 THz. The measurement results confirm that the prechirp of -2100 fs
²
is more effective to optimize the detected signals in ZnTe crystal with a thickness of 3 mm and enhances the EO signal by 71%, and the frequency redshift caused by the filter effect of the electrooptical response function is decreased. Meanwhile, the experimental results show that the enhancements of different prechirps depend on the frequency components of THz pulses and the frequency-dependent optimization of EO sampling is effective, which is consistent with the simulation results. This technique is helpful to optimize the EO sampling in thick ZnTe crystals to obtain the large time window and higher signal-to-noise ratio of EO sampling.