Time investigation and enhancement of the photothermal lens effect in the mode-matched configuration

The geometrical configuration of the dual-beam photothermal lens (PTL) experiment has a major role in the PTL sensitivity. This work examines the mode-matched configuration in terms of temporal evolution of PTL signal amplitude. The main results concern the improvement of the PTL signal under specific conditions with the mode-match arrangement considered in several previous works as less sensitive, but less influenced by the aberration effects. The amplitude of the obtained PTL signal is considerably increased to be of the same order of magnitude as that given by the mode-mismatched configuration. This occurred by reducing the probe beam waist at the sample to probe a part of temperature gradient area having a photothermal thin lens behavior. The experimental PTL signal is positive and presents low optical aberrations and a linear dependence with the excitation power. For the purpose of verifying the reliability of this experimental setup, the thermal diffusivities and the absorption coefficients of paraffin oil and ethanol were measured and compared to the results reported in literature.