Abstract

Subpico-second pulses of terahertz electromagnetic radiation are generated by femtosecond optical pulses incident on a large-aperture biased photoconductor. The key advantage of a large-aperture biased photoconductor is the ability to generate high power pulses by increasing the size of the aperture of the photoconductor to accept very high optical energies and high applied bias voltages. This power scaling feature of large-aperture photoconductors has been studied by others using the 8-μJ, 620-nm optical pulses from an amplified CPM laser system. Applied bias fields up to 7 kV/cm were used on semiconductors having 0.5-4 mm electrode gap spacings. We present the results of the generation of terahertz electromagnetic pulses using the amplified 800-nm, 150-μJ, 200-fs optical output from a 5-Hz laser system incident on the biased surfaces of GaAs and InP wafers. Wider gap spacings and larger optical energies permit further investigation into the power scaling and saturation properties of the photoconductors. Our use of 1.5-eV rather than 2-eV photons permits a comparison of results as a function of photon energy.

© 1992 Optical Society of America