Abstract

Within the last year groups at Brown¹ and Berkeley² have reported that second harmonic generation from the centrosymmetric semiconductors Ge and Si shows a strong dependence on the angle of rotation of the sample about its surface normal. The Brown group have performed their experiments using psec pump beams at 1.06 μm and 0.53 μm and have attributed the behavior to a high density, plasma induced phase transition which break the inversion symmetry of the crystal. Since no signal is observed for sub-band gap radiation at 1.06 μm for Si, this is considered to be evidence for the need of a plasma. Tom et al.² using a nsec 0.53 μm pump on Si attribute their (different) results to nonlocal quadrupolar bulk and dipolar surface contributions to the second harmonic polarization density. We report comprehensive studies of both 20 psec and 20 nsec, 1.06 μm induced harmonic generalism from the same (100) and (111) surfaces of Ge and (111) and (110) surfaces of Si.

© 1984 Optical Society of America