Photothermal Spectroscopy of Fluid and Solid Samples

This dissertation presents theoretical and experimental studies of the photothermal spectroscopy in solids and fluids. In particular, theoretical investigations of the photothermal spectroscopy in optically dense fluids and in solids are presented. Experimental investigations of photothermal lensing spectroscopy in flowing fluids and of photothermal deflection spectroscopy in solid semiconducting samples are also presented. The theory of photothermal spectroscopy in optically dense fluids presented here is the most complete theory of the subject todate. The theory is applicable to pulsed (arbitrary pulse length) or cw (modulated or unmodulated) excitation, stationary or flowing media. All three detection techniques, that is, photothermal phase-shift spectroscopy, photothermal deflection spectroscopy, and photothermal lensing spectroscopy are considered. The theory of photothermal deflection spectroscopy in solid samples presented here is applicable to a sample deposited on a substrate and in contact with a fluid medium. The probe beam passes through the fluid medium. Only modulated cw excitation has been considered. Extensive investigation of the dependence of the signal on various parameters has been considered. The experimental investigation of the photothermal lensing spectroscopy are the first systemic investigations in a flowing medium and provide a qualitative verification of the theory. The photothermal deflection spectroscopy experiments on silicon, GaAs, and GaAs multiple quantum well samples also provide a good qualitative verification of the theory.