Materials studies with TeraHz beams

Abstract

Summary form only given. Far-infrared time-domain spectroscopic studies of the dielectrics crystalline sapphire and quartz and fused silica and the semiconductors silicon, gallium arsenide and germanium are discussed. The present results extend from 0.2 to 2 THz and cover a previously neglected frequency range. For sapphire and quartz, the measured absorptions are consistent with the earlier work below 0.5 THz. Above 1 THz significantly more absorption was measured for sapphire, while for quartz the present values are in reasonable agreement. The results on high-purity fused silica are consistent with the most transpartent fused silica measured to date. For GaAs two weak absorption features have been resolved at 0.4 and 0.7 THz. Measurements on germanium demonstrate the dominant role of intrinsic carriers; the measured absorption and dispersion are well fit by the simple Drude theory. In contrast, for silicon there is strong disagreement with the earlier work. In the THz-frequency range the absorption is extremely sensitive to carrier density. The measurements indicate that intrinsic silicon is an exceptional THz optical material, more transparent than crystalline quartz.