Pulsed-Laser Excited Photothermal Study of Glasses and Nanoliter Cylindrical Sample Cell Based on Thermal Lens Spectroscopy

• Main Author: Joshi, Prakash Raj
• Format: Others
• Published: DigitalCommons@USU 2010
• Subjects: pulsed-laser; photothermal study; glasses; nanoliter cylindrical sample cell; thermal lens spectroscopy; Analytical Chemistry
• Online Access: https://digitalcommons.usu.edu/etd/680; https://digitalcommons.usu.edu/cgi/viewcontent.cgi?article=1676&context=etd

The research in this dissertation presents Pulsed-Laser Excited photothermal studies of optical glasses and cylindrical sample cell. First, a study of a photothermal lens experiment and the finite element analysis modeling for commercial colored glass filters is done. The ideal situation of a semiinfinite cylinder approximate model used to describe the photothermal lens experiment requires the boundary condition that there is no transfer of heat from the glass to surrounding when the glass is excited with a laser. The finite element analysis modeling for photothermal signal with coupling heat with surrounding shows the thermal heat transfer between the glass surface and the coupling fluid. This work shows that the problem can be resolved by using pulsed laser excitation where the signal decay is faster than the heat diffusion to the surrounding, and finite element analysis modeling to correct the likely deviation from semi-infinite cylinder approximate models. Second, finite element analysis modeling of a photothermal lens signal also shows that there are slow and fast components of signals, which are detected by using a fast response detector and is explained to be due to the axial and radial transfer of heat. A semi-analytical theoretical description of the mode-mismatched continuous and pulsedlaser excitation thermal lens effect that accounts for heat coupling both within the sample and out to the surrounding is presented. The results are compared with the finite element analysis solution and found to be an excellent agreement. The analytical model is then used to quantify the effect of the heat transfer from the sample surface to the air coupling fluid on the thermal lens signal. The results showed that the air signal contribution to the total photothermal lens signal is significant in many cases. Third, surface deformation phenomena are quite common when glasses are excited by laser. Finite element analysis modeling of a surface deformation phenomenon is done. A thermal lens reflection experiment is carried out and results are compared with modeling. The effect of coupling fluid on sample is taken in to account to make more accurate measurement of thermophysical properties of solid sample. Fourth, a novel apparatus for performing photothermal lens spectroscopy is described which uses a low-volume cylindrical sample cell with a pulsed excitation laser. Finite element analysis modeling is used to examine the temperature profile and the photothermal signal. The result of finite element analysis is compared with the experimental result. The experimental photothermal lens enhancement has been found to be that predicted from theory within experimental error.