Date Approved

2008

Degree Type

Open Access Thesis

Degree Name

Master of Science (MS)

Department

Chemistry

Committee Member

Dr. Donald Snyder, Chair

Committee Member

Dr. Marshall Thomsen

Committee Member

Dr. Timothy Brewer

Abstract

Absorption of energy from a modulated laser beam by a transparent substrate leads to cyclic thermal expansion and contraction of the surface at the pump beam focus. This minute distortion of the surface forms a transient optical lens structure, which can be monitored by the changes it induces in a second laser beam reflected at an angle off the same focal point. The Surface Thermal Lensing (STL) technique is based on detecting the modulated interference pattern that results from interaction of the probe beam wavefront as it reflects from both the flat surface surrounding the transient lens and the curved lens surface itself. Since a variety of physical properties for a polymer change sharply as the solid is heated through the glass transition temperature, changes in the STL signal can be used to detect Tg in spatially resolved surface regions as small as the focal point of the pump laser. This report will examine the relationship between the magnitude of the STL signal and such instrument parameters as pump beam intensity and chopping frequency, and the thermo-mechanical properties of several transparent polymers.

Included in

Chemistry Commons

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