Optimisation of a compact single-laser-dual-beam thermal lens apparatus

Abstract

The experimental parameters that determine the thermal lens signal and the length of the optical system are considered in order to develop a simple and compact single-laser-dual-beam set-up for thermal lens spectrometry. The results, expressed in terms of signal amplitude and signal to noise ratio, show that they depend on the focal length of the focusing lens, the distance between the sample cell and the detector, the size of the aperture used to sample the thermal lens signal and the relative power of the pump and probe beams. The performance of the apparatus is optimised in the shortest configuration for which the length of the optical system is less than 0.9 m from the laser head. A minimum detectable absorbance of 8.4 × 10^–6 is obtained in ethanol with only 4 mW of excitation power available at the sample cell.