Measurement of a phonon resonance in a GaSe crystal using THz free induction decay

The relaxation time and absorption and emission profiles of the 0.59 THz TO phonon resonance in a ε-GaSe single crystal were measured using terahertz free induction decay, observed directly as a sequence of decaying sinusoidal oscillations in the time-domain signal following single-cycle pulse excitation. The phonon line profile was also measured using frequency-domain transmission with the resolution of 0.25 GHz and was found to be Lorentzian.