Contents 1. Introduction
In the last decade, filamentation generated by intense femtosecond laser pulses has a lot of potential applications, such as THz radiation and atmosphere diagnosis [1], [2]. Most filamentation experiments have been performed with multi-cycle femtosecond laser pulses (≥50 fs) at TW energy scale. In 2010, D. Laban et al predicted that self-focusing distance should change by as the carrier-envelope phase (CEP) shifted rad with 6.3 fs few-cycle laser pulses, but without clearly evidence experimentally [3]. Here, filament in air generated by CEP stabilized few-cycle laser pulse is studied. By periodically changing the CEP of few-cycle laser pulses, a CEP dependent oscillation of voltage signal which is proportional to the mean free electron density in the filamentation in a circular loop system has been found. To the best of our knowledge, it is a clear evidence of CEP effect on the free electron density in filament.
