Few-cycle 1.9-μm pulse generation via collinear spectrum synthesis in multiple-crystal OPA

A multiple-crystal optical parametric amplification (OPA) design is reported for efficiently generating few-cycle 1.9-μm laser pulses. Different spectral regions of the idler pulse are successively amplified in three nonlinear crystals with delicately adjusted phase-matching angles, and a broadband spectrum supporting a three-cycle transform-limited (TL) pulse duration is obtained. Near-TL duration of 21.5 fs is realized by simple compression in a silicon window. Owing to sufficient exploitation of the pump energy in the crystals, total conversion efficiency of 31.3% is achieved with idler pulse energy of 65.8 μJ. The gain bandwidth in multiple-crystal OPA is markedly broadened compared to OPA using a single thick crystal; meanwhile, the high efficiency is preserved. Further energy scaling of the proposed scheme is potentially feasible using dual-chirped OPA geometry.