Terahertz emission from air plasma produced by few-cycle circularly polarized laser pulses

The polarization characters of terahertz emission from air plasma produced by few cycle circularly polarized laser pulses were studied. Terahertz waves were generated from the air plasma produced by focusing the 8.6 fs circularly polarized laser pulses into the air. By measuring the polarization of terahertz waves and the relationship between the polarization and the carrier-envelope phase of driving laser, new methods for terahertz polarization control were developed. The terahertz emission was measured to be elliptically polarized, and its polarization rotated with the carrier-envelope phase of driving laser. This is useful for terahertz polarization control and provides a way to measure the carrier-envelope phase of few-cycle laser pulses in the air.