The role of nonlinear optical absorption in narrowband difference-frequency terahertz-wave generation

We present a general analysis of the influence of nonlinear optical absorption on terahertz generation via optical-difference frequency generation when reaching for the quantum conversion efficiency limit. By casting the equations governing the process in a suitably normalized form, including either two-photon- or three- photon absorption terms, we have been able to plot universal charts for phase-matched optical-to-terahertz conversion for different values of the nonlinear absorption coefficients. We apply our analysis to some experi- ments reported to date in order to understand to what extent multiphoton absorption could have played a role and also to predict the maximum achievable conversion efficiency at higher peak pump intensities