Spectral Narrowing Techniques for Optical Parametric Oscillators at Near and Mid-IR Region

The authors present advanced experimental methods of spectral narrowing in optical parametric oscillators. One of the studied approaches relies on the use of a volume Bragg grating in the resonators of optical parametric generators. The other approaches are based on injection seeding techniques employing different seed lasers (namely, a narrow-linewidth He-Ne laser and a tunable diode laser). Both methods demonstrated significant narrowing of the spectral line. Using the volume Bragg grating, it was possible to reduce the width of the optical parametric generator line from 180 nm to 640 pm, and the tuning range was 67 nm. The output power of this configuration was 689 mW at 5 kHz and pulse duration 8 ns. The injection seeding was carried out at an idler wave (He-Ne laser at $3.39\ \mu \mathrm{m}$) and at a signal wave (diode laser at $1.538\div 1.544,\ \mu\mathrm{m}$). In both cases, the linewidth after seeding was approximately the same and amounted about 0.5 nm.