Abstract
The birefringence of LiInS2 (LIS) crystals in the THz frequency region is investigated by THz time-domain spectroscopy (THz-TDS). The experimental results indicate that LIS has large birefringence and low absorption in the THz frequency region. The optical properties of LIS are quantitatively determined. A sharp absorption caused by a TO-phonon resonance is observed at around 1.70 THz when the Z-axis is parallel to the polarization of the incident THz wave. A temporal separation of the transmitted THz pulses with different polarization components is realized by changing the orientation of the LIS crystal with respect to the polarization of the incident THz pulses. By controlling the relative phase and amplitude of the temporally separated THz pulses, THz polarization pulse shaping caused by birefringence in LIS crystal is demonstrated.
Highlights
Terahertz (THz) radiation covers the frequency range from approximately 100 GHz to 10 THz [1]
THz time-domain spectroscopy (THz-TDS) [10] is one of the pivotal techniques to elucidate dynamic processes in the materials occurring on time scales of femtoseconds to picoseconds
We investigated LIS crystals which were cut along three crystallographic a, b- and c-axes with different thickness
Summary
Terahertz (THz) radiation covers the frequency range from approximately 100 GHz to 10 THz [1]. In THz-TDS systems, a broadband THz pulse is generated with a femtosecond laser pulse of typically 100 fs pulse duration in a photoconductive device [11] This broadband THz pulse is detected with a delayed probe pulse in amplitude and phase after being transmitted through the sample. In our THz-TDS experiments, a high-speed asynchronous optical sampling (ASOPS) system operates with mode-locked Ti:sapphire 1 GHz femtosecond oscillators as pump and probe lasers. The transmitted time-domain electric field of the THz pulses through the air and LIS crystal are recorded with a 100-MS/s 14-Bit A/D converter (Gage CS8327: OCT-832-007), which is triggered by a crosscorrelation signal between pump and probe laser generated by two-photon absorption in a GaP diode [22].
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