Determination of initial carrier-envelope phase of few-cycle optical pulses

Using the THz emission from air plasma, the method of determining the initial carrier -envelope phase (CEP) of few-cycle pulses was proposed. In air plasma, the evolution of the generated THz waveform can be used to probe the variation of the CEP of propagating intense few-cycle pulses. In the intense few-cycle laser fields, the inversions position and the number of inversions of the THz waveforms was found dependent on the initial CEP regularly. The calculation based on the transient photocurrent model indicates that the number of inversions of the THz waveforms is either two or one for all the initial CEP for a range of moderate input pulses energies. Under varied input pulse energies, the value of initial CEP is 0.5 constantly when the two inversions of the THz waveforms change to one. This provides a method of measuring the initial CEP of the driving few-cycle pulses.