PROGRESS TOWARD A BETTER UNDERSTANDING OF SIGNAL GENERATION IN LASER-EXCITED PHOTOTHERMAL SPECTROMETRY OF HOMOGENEOUS SAMPLES

This article examines some recent experiments and theories that have a dvanced our understanding of the physical effects following thermal re laxation of the excited state. Experiments which show that the tempera ture-dependent refractive index is composed of density and pure-therma l terms are discussed. The importance of the purely thermal term is th at it allows ultra-fast pulsed excitation sources to be used in photot hermal refraction spectroscopy. This opens up new areas of application s in ultra-fast measurement. The effect of and progress towards the el ucidation of specific volume changes are reviewed. Finally, recent pro gress in understanding nonlinear optical absorption and its effect on the photothermal signal are summarized. (C) 1998 Elsevier Science B.V. All rights reserved.