Few-Cycle Laser Pulses: The Carrier-Envelope Phase, Its Role in the THz Emission from Laser-Generated Plasmas and a New Way to Measure It

Terahertz emission from laser-generated air plasmas has recently been identified as an interesting source for THz radiation. High intensities and a large bandwidth of the THz pulses can be achieved. We briefly review several mechanisms which were employed to generate the quasi-static dipole moment needed for the optical rectification process. This leads us to a discussion of a specific application of THz emission from an air plasma, namely the investigation of the carrier-envelope phase of few-cycle optical pulses. Such pulses of a duration of less than 10 fs induce a spatial charge asymmetry in the plasma directly via non-linear tunneling ionization. The asymmetry, and with it the emission of the THz radiation from the plasma, depend on the carrier-envelope phase, with the consequence that one can determine the phase by measurement of the amplitude and polarity of the THz pulse.