Abstract
Rapidly tunable, high-repetition-rate picosecond near-infrared (near-IR) optical parametric oscillators (OPOs) are of great interest for applications such as Coherent Anti-Stokes Raman Scattering microscopy [1]. Such OPOs, typically pumped in the green, pose major challenges in terms of the material damage threshold while operating at high power in combination with high repetition rates, making the choice of the nonlinear material a critical factor. Here we report a stable picosecond OPO based on periodically-poled potassium titanyl phosphate (PPKTP) crystal in a fan-out grating design, enabling rapid grating tuning close to room temperature. The green pump radiation for the OPO is obtained by single-pass second harmonic generation of a picosecond Yb-fiber laser in a 30-mm-long LiB 3 O 5 (LBO) crystal under type I (oo→e) noncritical phase-matching. The picosecond green source provides up to 9 W of average power at 532 nm in 16.2 ps pulses at 79.5 MHz repetition rate with FWHM spectral bandwidth of 0.6 nm [2]. The OPO is configured in standing wave X-cavity with a 30-mm-long PPKTP crystal containing grating periods ranging from Λ=9.00 to 10.85 μm in a fan-out design as the gain medium. The green pump beam is focused to a waist radius of wo∼63 μm at the center of the PPKTP crystal, corresponding to a focusing parameter of ξ∼0.3.
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