DIFFRACTION EFFECTS IN SINGLE-LASER AND 2-LASER PHOTOTHERMAL LENS SPECTROSCOPY

A simple method for calculating the effects of optical geometry on pho tothermal lens signals is shown. This method is bases on calculating c umulative electric-field phase shifts produced by a series of Gaussian refractive-index perturbations produced by the photothermal effect. T heoretical results are found for both pulsed.-laser and continuous Gau ssian laser excitation sources and both single-and two-laser apparatus es commonly employed in photothermal lens spectroscopy. The effects of apparatus geometry on the resulting signal are shown. Analytical time -dependent signal results are found for small signals. Analytical pump -probe focus geometry results allow direct optimization for certain co nditions. The calculations indicate that the photothermal lens signal is, in general, optimized for near-field detection-plane geometries. ( C) 1997 Optical Society of America.