Phase-sensitive terahertz emission from gas targets irradiated by few-cycle laser pulses

The effect of the carrier envelope phase (CEP) of few-cycle laser pulses on terahertz (THz) emission from gas targets is investigated by analysis and two-dimensional particle-in-cell simulations. For linearly polarized (LP) light, the THz amplitude depends on the CEP phase sinusoidally. For circularly polarized (CP) light, the THz amplitude is independent of the phase, but its polarization plane rotates with the phase. By measuring the THz amplitude or polarization direction, one can determine the CEP of LP or CP laser pulses, respectively. We find that when the ionization degree of atoms is lower than 10%, the phase dependence of the THz radiation is insensitive to intensity and duration of the laser pulse, which is preferable for the phase determination.