A single and simple mathematical expression of the signal for cw-laser thermal lens spectrometry

Since the discovery of the thermal lens effect, several theoretical models have been put forward for cw-laser thermal lens spectrometry and different expressions of the thermal lens signal have been derived for various optical configurations including single-beam or dual-beam situations. This review focuses primarily on the successive mathematical expressions reported so far for both steady-state and time-resolved measurements, with the aim of comparing them in order to propose a single and convenient relation that accurately accounts for the sensitivity and the temporal behaviour of the thermal lens efrect.