DIFFRACTION FROM ANHARMONIC VOLUME GRATINGS CALCULATED BY 2-DIMENSIONAL FOURIER-TRANSFORMS TO EVALUATE NONLINEAR-OPTICAL ABSORPTION

A general numerical approach is presented to predict the diffraction efficiency of laser-induced anharmonic volume gratings by using two-dimensional Fourier transforms. An explicit calculation is carried out for thermal phase gratings created by two-photon absorption and by one-photon saturated absorption in the steady-state and photochemical-change limits. Calculations are also performed for the probe-beam angular dependence of the diffraction efficiency, which yield a series of maxima centered about the Bragg angles. The results show that for multiphoton absorption and for the limit of weak saturation of one photon, the previously developed quasi-planewave approximation (QPWA) and the present calculation agree well. Under strong-saturation conditions, however, the QPWA fails, and the present numerical method must be used to predict diffraction intensities accurately. © 1990 Optical Society of America.