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We report a stable, Yb-fiber-laser-based, green-pumped, picosecond optical parametric oscillator (OPO) for the near-infrared based on the nonlinear crystal, PPKTP, using fan-out grating design, and operating near room temperature. The OPO is continuously tunable across 726-955 nm in the signal and 1201-1998 nm in the idler, resulting in a total signal plus idler wavelength coverage of 1026 nm by grating tuning at a fixed temperature. The device generates up to 580 mW of average power in the signal at 765 nm and 300 mW in the idler at 1338 nm with an overall extraction efficiency of up to 52% and a pump depletion >76%. The extracted signal at 765 nm and idler at 1746 nm exhibit excellent passive power stability better than 0.5% and 0.8% rms, respectively, over 1 hour, in good beam quality with TEM00 mode profile. The output signal pulses have Gaussian temporal duration of 13.2 ps with a FWHM spectral bandwidth of 3.4 nm at 79.5 MHz repetition rate. Power scaling limitations of the OPO due to the material properties of PPKTP are studied. © 2015 Optical Society of America OCIS codes : (190.4360) Nonlinear optics, devices; (190.7110) Ultrafast nonlinear optics; (190.4400) Nonlinear optics, materials; (190.4970 Rapid and continuously tunable, high-power, picosecond optical parametric oscillators (OPOs) in the near-infrared wavelength range are highly desirable for the advancement of microscopic techniques such as Coherent Anti-Stokes Raman Scattering (CARS), enabling several applications in biology and medicine [1][2][3]. Such OPOs are typically pumped in the green, which in turn rely on second harmonic generation (SHG) of mode-locked Nd-based solid-state or Yb-based fiber lasers [4]. Although picosecond green sources can provide high average powers, the ability to power scale green-pumped picosecond OPOs together with rapid tuning has been challenging [5]. While power scaling in OPOs depends on the available pump power and optimization of the output coupling However, in all these reports wavelength tuning has been achieved by varying the temperature of the nonlinear crystal, which is a relatively slow process.Here we report a stable, picosecond OPO based on fan-out design in PPKTP, enabling rapid grating tuning by translation of the nonlinear crystal while operating close to room temperature. The OPO, which is synchronously pumped by a mode-locked frequency-doubled Yb-fiber laser in the green, can provide continuous tuning over 726-955 nm in the signal wavelength range together with corresponding idler tuning across 1201-1998 nm. A maximum average power of 580 mW at 765 nm in the signal and 300 mW at 1338 nm in the idler, an overall extraction efficiency of up to 52%, and pump depletion >76% have been obtained. To the best of our knowledge, this is the first report of a picosecond OPO based on PPKTP using a fan-out grating design. The schematic of the experimental setup is shown in Fig. 1. The primary pump source is a mode-locked Yb-fiber laser (Fianium, FP1060-20) delivering ~20 ps pulses at 79.5 MHz repet...

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Abstract:We report the generation of tunable high-repetition-rate picosecond radiation in the mid-infrared using the new quasi-phase-matched nonlinear material of orientation-patterned gallium phosphide (OP-GaP). The source is realized by single-pass difference-frequencygeneration (DFG) between the output signal of a picosecond optical parametric oscillator (OPO) tunable across 1609-1637 nm with input pump pulses at 1064 nm in OP-GaP, resulting in tunable radiation across 3040-3132 nm. Using a 40-mm-long crystal, we have generated up to 57 mW of DFG average power at ~80 MHz repetition rate for a pump power of 5 W and signal power of 0.9 W, with >30 mW over >50% of the tuning range. The DFG source exhibits a passive power stability better than 3.2% rms over 1 hour in good spatial beam quality. To the best of our knowledge, this is the first picosecond frequency conversion source based on OP-GaP.

Abstract:We report the implementation of a compact cascaded multicrystal scheme based on birefringent crystals in critical phasematching, for the generation of continuous-wave (cw) radiation in the deep ultraviolet (UV). The approach comprises a cascade of 4 single-pass second-harmonic-generation (SHG) stages in β-BaB 2 O 4 (BBO) pumped by a single-frequency cw green source at 532 nm. A deep-UV cw output power of 37.7 mW at 266 nm has been obtained with a high passive power stability of 0.12% rms over more than 4 hours. Characterization and optimization of the system in each stage has been systematically performed. Angular phase-matching acceptance bandwidth under tight focusing in BBO, and spectral properties of the deep-UV radiation, have been studied. Theoretical calculations for SHG in the cascaded scheme based on birefringent phase-matching have been performed, and enhancement in UV power compared to single-stage single-pass scheme are studied. Theoretical comparison of BBO with other potential crystals for deep-UV generation in cascaded multicrystal scheme is also presented. 32-34 (1976). 16. J. Reintjes and A. C. Eckardt, "Efficient harmonic generation from 532 to 266 nm in ADP and KD*P," Appl. #260670Phys. Lett. 30(2), 91-93 (1977)