Date of Award

1998

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Bioinformatics & Computational Biology

First Advisor

Alois J. Adams, Ph.D.

Abstract

Diode lasers are semiconductor devices and as such are small, relatively inexpensive, and modest in power requirements. They are being used more and more in a variety of spectroscopic measurement systems. Diodes can be configured to provide a single wavelength for Raman measurement or be tuned over a 10-20 nm range for absorption studies. Most commercial diode-based Raman systems currently employ lasers with output powers in the 100-1000 mW range. There are obvious strategic and economic advantages associated with low power diode chemical analyzers, especially those being developed for on-line industrial and environmental monitoring. A diode-based Raman measurement system which uses a low power off-the-shelf diode laser has been developed. The current prototype uses a 10 mW visible (670 nm) diode laser which is temperature and current stabilized and is configured in a pseudo-external cavity configuration for enhanced signal levels at the sample. Additional optical methods increase the collection of scattered light. The optical source/sample collector system has been used with both a standard photomultiplier based and a cooled CCD array. Spectra have been obtained in the 200-4000 cm⁻¹ range for numerous neat solutions. The potential for tracking the degree of saturation of C=C double bonds using a low power diode system was explained by measuring the 1646 cm⁻¹ peak in various cyclohexene-dibromocyclohexane mixtures. Results with the cooled CCD spectrometer confirm that the process is linear on a molecular basis. A mathematical model which integrates all the instrumental factors impacting a Raman measurement has been developed and presented. Several key parameters in the model have been confirmed by empirical methods. Based on the model, a low cost monitor designed for following the degree of unsaturation of a chemical process is proposed, including the expected results and the description of operation. It includes the use of an ellipsoid of revolution for collecting the Raman scatter from the sample, which can enhance the collection by 10 to 100 times compared to a typical lens optical system.

Download

Included in

Optics Commons

Share

COinS