Studies of nonlinear absorption and aggregation in aqueous solutions of rhodamine 6G using a transient thermal lens technique

Dual-beam transient thermal lens studies were carried out in aqueous solutions of rhodamine 6G using 532 nm pulses from a frequency-doubled Nd:YAG laser. The analysis of the observed data showed that the thermal lens method can effectively be utilized to study the nonlinear absorption and aggregation which are taking place in a dye medium.

Photoacoustic signal saturation and optical limiting in C70-toluene solution

Pulsed photoacoustic studies in solutions of C70 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 C70 solution. We demonstrate that the nonlinear absorption leading to optical limiting is mainly due to reverse saturable absorption.

A Study of Photoacoustic Effects and Optical Limiting in the Solution of C60 in Toluene

Pulsed photoacoustic studies in solution of C60 in toluene have been made using the 532 nm radiation from a frequency doubled Nd:YAG laser. Though C60 is found to exhibit the phenomenon of optical limiting, the results on photoacoustic measurements do not give any indication of multiphoton transitions as suggested in some of the earlier works. Results of photoacoustic measurements show that excited state absorption is the dominant process responsible for optical limiting while phenomena like nonlinear scattering may contribute to a lesser extent.

Investigations of Optical Interaction Processes in Certain Photonic Materials Using Z-scan and Thermal Lens Techniques

International School of Photonics, Cochin University of Science and Technology