Abstract

We investigate the dynamics of coherent optical phonons in single-crystal Tellurium after high-density excitation of free electrons by intense femtosecond laser pulses. The experiments are performed in a standard time-resolved pump-probe setup using pulses of a Ti-Sapphire oscillator that are amplified in a 6.8 kHz dye amplifier. The pulse duration is <100 fs, much shorter than the oscillation period of the A1 optical phonon mode of Tellurium, leading to an impulsive and selective excitation of this phonon via the “displacive excitation” mechanism.¹ The coherent lattice vibrations are detected via transient reflectivity changes that show clearly-resolved oscillations as a function of pump-probe delay, as shown in the inset of Fig. 1. The main plot shows Fourier spectra of the oscillating signal contribution, obtained after subtraction of the slowly-varying background, at various excitation densities.

© 1996 Optical Society of America