Optical parametric oscillators in the presence of strong two-photon absorption for extended applications of nonlinear optical materials

We show that two-photon absorption (TPA) strongly affects backward and forward optical parametric oscillation (OPO) in certain wavelength ranges. After introducing a normalized coefficient of TPA, we have obtained a simple expression for the threshold intensities in the presence of TPA, that is the same for both configurations of OPO. The threshold intensities increase as the TPA coefficient increases. At the same time, the conversion efficiencies decrease. We have shown that even if the threshold intensity is just increased by a very small factor due to TPA the conversion efficiency can be reduced considerably. We have considered several nonlinear optical materials as examples to illustrate the trade-off among different parameters such as the TPA coefficient vs. pump wavelength, and, the pulse energy density vs. crystal length. Our results are important for implementing optical parametric oscillators in the extended wavelength ranges, such as visible, mid-IR, far-IR, mm and THz. (C) 2001 Elsevier Science B.V. Alt rights reserved.