Abstract
Carrier-envelope phase (CEP) of single-cycle pulses generated by using four-wave difference frequency
mixing has been investigated. The waveforms of the single-cycle pulses generated through two-color
filamentation were characterized by using frequency-resolved optical gating capable of CEP
determination. We have observed a particular behavior of the phase: the phase of high frequency
components of the generated pulses changes continuously and linearly with the relative phase between
the two-color input pulses, whereas the phase of the low frequency components takes only two discrete
values. The transition of the phase behavior has been clearly observed in the experiment, and reproduced
by a numerical simulation. We have found out that such a phase behavior is a unique feature of singlecycle
pulses generated with a passive CEP stabilization scheme.
