Efficiency of cascaded third harmonic generation in single quadratic crystal in focused beam

Generation of third harmonic by cascading of two phase-matched or two near phase-matched second order processes in single quadratic crystal with focused fundamental beam is theoretically investigated. The optimized conditions for maximum conversion into third harmonic are found with the help of analytical and numerical investigations. In general the optimal position of focusing depends on the values of the mismatches Deltak(1) and Deltak(2) for both steps of the second order cascading (omega + omega = 2omega; omega + 2omega = 3omega), It is shown that this method of third harmonic generation requires specially chosen Deltak(1.opt) and Deltak(2.opt) and focusing into the center of the nonlinear media in order to obtain best efficiency. (C) 2002 Published by Elsevier Science B.V.