Methods for Modeling and Diagnosis of Nonlinear Absorption in Photothermal and PhotoacousticSpectrometry of Homogeneous Fluids
AIP Conference Proceedings: Photoacoustic and Photothermal Phenomena
F. Scudieri and M. Bertolotti
Practical aspects of nonlinear signal characterization and modeling are presented. Experiments use apparatuses with well-known and validated excitation beam waist radiuses produced by lasers with controlled modes. Excitation laser attenuation methods that do not cause beam walk off are used. Computer hardware requirements and digital signal processing schemes for optimum data collection are given. The basis for modeling is ground and excited state absorption and relaxation kinetics. Analysis is based primarily on the kinetic model for optical excitation and subsequent excited state relaxation. To obtain accurate model results, the irradiance dependent excitation laser profile and the subsequent hydrodynamic relaxation of the spatially and temporally distorted heating rate distribution resulting from nonlinear absorption, and metastable state relaxation, are incorporated. This heating rate is used to calculate the temperature change distribution and subsequently the optical elements needed to model the experimental photothermal signals. Computer software tools used to aid in the process are discussed.
Methods for Modeling and Diagnosis of Nonlinear Absorption in Photothermal and Photoacoustic Spectrometry of Homogeneous Fluids Stephen E. Bialkowski and Agnès Chartier Photoacoustic and Photothermal Phenomena, F. Scudieri and M. Bertolotti, Ed., AIP Conference Proceedings 463 46‐49 1999