Photoacoustic signal saturation and optical limiting in C-70-toluene solution

Pulsed photoacoustic studies in solutions of C-70 in toluene are made using the 532-nm radiation from a frequency-doubled Nd:YAG laser. It is found that contrary to expectation, there is no photoacoustic (PA) signal enhancement in the power-limiting range of laser fluences. Instead, the PA signal tends to saturate during optical power-limiting phenomenon. This could be due to the enhanced optical absorption from the photoexcited state and hence the depletion of the ground-state population. PA measurements also ruled out the possibility of multiphoton absorption in the C-70 solution. We demonstrate that the nonlinear absorption leading to optical limiting is mainly due to reverse saturable absorption. (C) 1997 Society of Photo-Optical Instrumentation Engineers.