An Optical Parametric Oscillator in the Mid-IR Range Based on a Fan-out Periodically Poled Structure of Lithium Niobate with a Narrow-Band Seeding Laser

The results of experimental studies of the effect of narrow-band seeding radiation of a gas laser on the spectral width of the oscillation line of an optical parametric oscillator (OPO), which is based on a fan-out structure of a periodically poled lithium niobate (PPLN) crystal, are presented. The use of a seeding He–Ne laser made it possible to reduce the generation threshold for the OPO by a factor of 1.53, from 120 μJ (29.5 mJ/cm2) to 78 μJ (19 mJ/cm2). When the modes of the He–Ne laser were optimally matched in the OPO cavity, the width of the spectral line of the signal wave decreased by a factor of 4.65 and equaled 0.481 nm.