Nonlinear optical studies in tetraphenyl-porphyrin-doped boric acid glass using picosecond pulses

We report the results of our studies on the nonlinear optical response of t hin films of tetraphenyl porphyrin doped in boric acid glass for picosecond -duration pulses. The fluence-dependent transmission measurements show that the sample exhibits reverse saturation behavior at 532 nm and saturable ab sorber action at 683 nm. By fitting the nonlinear transmission data at thes e wavelengths to a rate equation model, values for sigma (S)(e) and sigma ( L) the excited singlet and ground state cross sections were obtained. The l arge value (approximate to 8) for sigma (S)(e)/sigma (L) makes it a potenti al material for optical limiting at 532 nm, whereas at 683 nm the ratio L-s igma/sigma (S)(e) approximate to 4.3. Intensity dependence of degenerate fo rward four-wave mixing at 683 nm was also investigated to establish the ord er and magnitude of the nonlinearity. The forward four-wave mixing signal a t 683 nm showed a cubic dependence on the input intensity, establishing the third-order nonlinearity. A value of 4 x 10(-12) esu for the third-order s usceptibility \chi ((3))\ was estimated from the measured efficiency. The t ime response of the nonlinearity was measured by the pump-probe transmissio n experiment, resulting in a decay constant of about 1.8 ns for the repopul ation of the ground singlet state at 683 nm.