Abstract

Using our newly developed techniques of terahertz optics,¹ we have generated well-collimated beams of freely propagating subpicosecond electromagnetic pulses. By comparing the high speed response of different receiver-transmitter combinations, we have optimized the system so that the terahertz pulses are detected with subpicosecond resolution and with signal-to-noise ratios of more than 1000:1. With this terahertz source, time domain spectroscopic measurements of single crystals of sapphire, quartz, MgO, and high resistivity silicon have provided the most accurate characterization of their terahertz dielectric properties to date. When the terahertz beams propagate through as little as 20 cm of laboratory air, a 50-ps duration oscillatory structure appears after the main subpicosecond pulse. This structure is caused by the absorption and dispersion of several strong resonance lines in water vapor. Using a controlled ambient atmosphere for the terahertz beam path, we have made the most accurate measurements to date of the absorption strengths of the nine strongest lines of water vapor in the spectral region from 0.2 to 1.5 THz.

© 1989 Optical Society of America