CW optical parametric oscillator for the mid-IR range

We report the development of a cw optical parametric oscillator (OPO) for the mid-IR range. The oscillator uses a 50-mm long periodically poled lithium niobate crystal in a ring resonator. The OPO is pumped by an ytterbium fibre laser with a wavelength of 1.064 μm. At a pump power of 10 W, the OPO generates continuous radiation with a wavelength of 3.6 μm and a power of 2.8 W. The pump power depletion in the OPO is 94 %. The idler wave frequency of the OPO is stabilised using a precision laser wavelength meter. The rms error of the idler wave frequency in the stabilisation regime is 3 MHz. A simple theoretical model for the operation of a cw OPO is proposed, based on an empirical characteristic of the OPO, i.e., the pump depletion, and on a quantum description of three interacting light waves. The power characteristics of the operating OPO are in good agreement with those predicted by the theoretical model.