Graduation Year

2005

Document Type

Thesis

Degree

M.S.

Degree Granting Department

Physics

Major Professor

Dennis Killinger.

Keywords

Laser absorption, Spectroscopy, Optical waveguide

Abstract

Long path optical waveguides can be used in optical absorption measurements to increase the optical path length and, thus, the overall absorption of a sample. Recently, 1m long coiled Liquid Waveguide Capillary Cells (LWCC) have been used by analytical spectroscopists to measure the absorption strength of weakly absorbing liquids. However, most of these measurements have used conventional light sources such as Xenon or Halogen lamps and not spectroscopic laser sources. In this thesis study, we used a LWCC absorption waveguide and a laser light source to measure, for the first time to our knowledge, the optical transmission through several water or liquid samples. It was found upon using the LWCC waveguide, the coherent laser light source tended to produce larger variability (>ł15%) in the measurements of transmission readings than that for a conventional absorption cell or a conventional light source.

This was especially evident when the LWCC waveguide was chemically cleaned with an acid and a base solution between each sample run as directed by the manufacturer. The non-coherent optical sources, Halogen lamp and Xenon arc lamp, produced more stable (ł3%) transmission measurements. Finally, using a Helium Neon laser scattered off a diffuse reflecting surface was found to produce moderate variability (ł7%), but this was much less than the coherent Helium Neon laser alone. It was concluded that the use of the coherent source was more susceptible than the non-coherent source to small changes in the reflectivity or index of refraction along the wall of the coiled LWCC waveguide. Our results are consistent with recent work by Barwicz and Haus, and by Lytle and Splawn who saw a large dependence of the transmission through a hollow straight waveguide upon changes in the polarization and input angle of the laser beam directed into the waveguide.

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