Abstract

Thermal lens is a well-known method that allows the measurement of absorption coefficients with high sensitivity and versatility. In a pump-probe version of the technique, the pump beam induces a thermal lens in the absorbing medium which is monitored by a collinearly propagating probe beam. Usually the pump and the probe beam are tightly focused onto the sample. In this configuration, increasing the path-length of the sample much over the confocal distance of the focused pump beam does not enhance the amplitude of the signal. This usually limits the advantages of the thermal lens technique to sample thickness of a few millimeters. Furthermore, the thermal lens signal is proportional to the power and not to the fluence of the pump field, which removes the need to focus the beams to obtain the thermal lens signal.

© 2001 Optical Society of America