Abstract

In this paper we describe a device for efficiently converting pump radiation, such as the λ_p = 1.064 μm radiation from a Nd:YAG laser, to idler radiation at a desired wavelength λ_i, using an optical parametric oscillator (OPO) which incorporates additional stages of three-wave mixing. In the conventional OPO each converted pump photon produces only one idler photon. We can extract a second idler photon by internally converting a signal photon of frequency ω_s = ω_p – ω_i using difference-frequency mixing (DFM). We suppose that the OPO is singly resonant at ω_s and insert a DFM crystal in the cavity after the OPO crystal. The DFM crystal is phase-matched for the process ω_s – ω_i → ω_d. The DFM interaction also plays the role of an optical parametric amplifier (OPA) for the idler radiation. Thus, the ideal output of the OPO-DFM device consists of two photons of frequency ω_i and one photon of frequency ω_d per pump photon. If ω_d > ω_i, one or more additional idler photons can be extracted by successive DFM/OPA stages outside the cavity, the first such external conversion being pumped at ω_d and generating a frequency ω_d2 – ω_d → ω_i. For conversion of 1.064 μm radiation to 3.9 μm radiation one internal and one external DFM process are possible. The other wavelengths generated are λ_s = 1.463 μm, λ_d = 2.342 μm, and λ_d2 = 5.861 μm. The OPO and internal DFM process can be carried out using two successive quasi-phasematched χ⁽²⁾ gratings on a wafer of periodically poled LiNbO₃ (PPLN). The external DFM process can be carried out using AgGaS₂, with the ω_d2 radiation polarized orthogonally to the other two waves.

© 1996 Optical Society of America