Optical Parametric Device for Efficient Generation of Radiation in the 3.9 Micrometer Range

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 ωs = ωp – ωi using difference-frequency mixing (DFM). We suppose that the OPO is singly resonant at ωs and insert a DFM crystal in the cavity after the OPO crystal. The DFM crystal is phase-matched for the process ωs – ωi → ωd. 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 ωi and one photon of frequency ωd per pump photon. If ωd > ωi, 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 ωd and generating a frequency ωd2 – ωd → ωi. 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 d 2 = 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 ωd2 radiation polarized orthogonally to the other two waves.