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Effect of two-photon absorption on optical parametric oscillation

For the first time, we show that two-photon absorption strongly affects backward and forward optical parametric oscillation in certain wavelength ranges. We have introduced a normalized coefficient of two-photon absorption. We have obtained a simple expression for the threshold intensities in the presence of two-photon absorption, that is the same for both configurations of optical parametric oscillation. The threshold intensities increase as the two-photon absorption coefficient increases. As 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 two-photon absorption the conversion efficiency can be reduced considerably. We have considered several nonlinear optical materials as examples to illustrate how to optimize the performance of optical parametric oscillators in the presence of strong two-photon absorption in the extended wavelength ranges.