Abstract

Transient degenerate four-wave mixing is a powerful technique for studying the ultrafast phase relaxations of photoexcited carriers. We report here the measurements of dephasing times of hydrogenated amorphous Si (a-Si:H), a-Ge:H, a-As₂S₂, a-As₂Se₂, a-Se, and polysilane [a-(SiH₂)_n]. The ultrafast dephasing time is measured by the two-beam self-diffraction technique (see Fig. 1).^1,2 The advantage of this technique is that dephasing times much less than the laser pulse width can be readily measured. For the measurements we used an amplified colliding-pulse mode-locked (CPM) laser with a pulse duration of 80 fs, energy per pulse of 5 μJ, and wavelength of 620 nm (2 eV).

© 1991 Optical Society of America