Intense self-compressed, self-phase-stabilized few-cycle pulses at 2 μm from an optical filament

We report the compression of intense, carrier-envelope phase stable mid-IR pulses down to few-cycle duration using an optical filament. A filament in xenon gas is formed by using self-phase stabilized 330 μJ 55 fs pulses at 2 μm produced via difference-frequency generation in a Ti:sapphire-pumped optical parametric amplifier. The ultrabroadband 2 μm carrier-wavelength output is self-compressed below 3 optical cycles and has a 270 μJ pulse energy. The self-locked phase offset of the 2 μm difference-frequency field is preserved after filamentation. This is to our knowledge the first experimental realization of pulse compression in optical filaments at mid-IR wavelengths (λ>0.8 μm).