Bridging the Modeling-Sampling Gap for Mid-Infrared Reflectance Spectroscopy of Small Particles, Films, and Fibers

<p>The concentration dependency of the mid-infrared (MIR) absorbance of bacterial spores was determined. Linear relationships (R² &ge; 0.99) were observed between the concentrations of spores and the baseline corrected peak absorbance for the amide absorbance regions, at coverages of less than 1 monolayer. Optical constants were calculated from these measurements, differing by a factor of 2-4 less than that in the literature. To test if the origin of the reduced cross-section was an electric field effect related to the surface selection rule, polystyrene spheres' characteristics were studied using FT-IR reflection microspectroscopy; results show that absorption has a non-linear, stair-step-like dependence on particle coverage and a wavelength dependence that can be explained by electric field standing waves (EFSW) caused by the mirrored substrate.</p> <p>The same effect is found to cause progressive weakening of the observed intensity as a function of increasing wavelength in sub-monolayer coverage measurements. Thus differences seen between optical properties of particles calculated using the specular-reflection method versus those calculated using traditional aerosol methods are addressed herein given these data. A simple multilayer method for estimating particle absorption coefficients is demonstrated that compares well with reported bulk polystyrene ellipsometric values. Another simple method, based on sub-monolayer coverage spectra, is suitable for spectral classification analysis, but only semi-quantitatively determines absorption coefficients.</p> <p>An IR camera sensitized to spectral regions tuned for detection of crime-scene blood was developed. Adaption of an IR camera with a modulated light source and utilizing digital lock-in amplifier techniques permitted differentiated response due to diffuse reflection and thermal emission. Using the AC response generated by a modulated light source is advantageous over the conventional DC response via enhancing the chemical contrast in the image which enables detection of stains of interest. We also exploit a "like-detects-like" filtering approach to demonstrate a method of using a broadband thermal detector for chemical identification applications.</p>

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Campus Access Dissertation

Discipline thesis:degree_discipline

Chemistry and Biochemistry

Year

2010

Author dc:creator

• Brooke, Heather

Contributors dc:contributor

• Michael L. Myrick

• Chemistry
• Physical Sciences and Mathematics
• Forensic Blood Detection
• Infrared Imaging
• Infrared Spectroscopy
• Optical Constants
• Reflectance
• Scattering

Statement dc:rights

• © 2010, Heather Brooke

Repository record dc:identifier

https://scholarcommons.sc.edu/etd/145

OAI identifier oai:identifier

oai:scholarcommons.sc.edu:etd-1146