Generation of carrier-envelope phase-stable two optical-cycle pulses at 2 μm from a noncollinear beta-barium borate optical parametric amplifier.

We report on the generation of two optical-cycle, carrier-envelope phase-stable pulses with energy of 15 μJ at central wavelength of 2 μm. Pulses of 15 fs (2.3 optical cycles) duration are obtained by difference-frequency generation, which at the same time provides passive carrier-envelope phase stabilization, and noncollinear optical parametric amplification in beta-barium borate crystal, which is shown to provide broad phase-matching bandwidth if seeded by pulses in the 1.6-2.6 μm wavelength range. Pulse compression is achieved by means of a simple propagation through the optical setup and by precisely controlling the initial chirp of the pulses to be frequency downconverted.