Polarization and energy stability of filamentation-generated few-cycle pulses

Polarization properties and energy stability are measured for few-cycle pulses that are generated by filamentation in dual Ar-filled tubes in tandem. The dual-tube geometry enhances the contribution of self-phase modulation to spectral broadening. The polarization extinction ratio (I(perpendicular)/I(parallel) is improved for the beam transmitted through the second tube compared to the first tube and of the incident laser beam. Polarization control of few-cycle pulses is realized in simple fashion by a half-wave plate placed prior to the dual-tube assembly. We show that intensity clamping in the filament affords a major advantage in accomplishing a significant reduction in energy fluctuations compared to those inherent in the incident laser beam.