Orientation-Dependent THz Response of m-Plane Sapphire Substrate by Polarization-Sensitive THz Time Domain Spectroscopy

Abstract

The dielectric response of m-plane sapphire (m-sapphire) substrates in the terahertz (THz) frequency is investigated using polarized-sensitive femto-second THz time-domain spectroscopy. We examined the transmitted THz time-domain waveforms with respect to the parallel-polarized THz field by rotating phi angle of m-sapphire substrates. The THz amplitude significantly decreased at the azimuth angle of 0 degrees, 90 degrees, and 180 degrees with roughly equal amplitudes and no propagation time delay. The time delay of 480 fs in the THz pulse oscillations was observed between the azimuth angle of 45 degrees and 90 degrees, possibly due to the birefringence of nonpolar m-sapphire substrate. Strong THz field absorptions around similar to 1 THz frequency at azimuth angles of every 90 degrees could be attributed to low-frequency phonon modes.