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Physics Fanatic Focuses Eye on Optics

Senior Physics and Mathematics major Michaela Conley recently presented her research entitled A Study of Optical Rotation and Linear Polarization to the Kentucky Association of Physics Teachers (KAPT) Physics and Astronomy spring meeting on March 4, 2006 and Lexington Community College.

Optical Rotation and Linear Polarization

Conley did the research in a directed study course with Dr. Amer Lahamer in order to fulfill the degree requirements for her physics major. With the suggestion from Dr. Lahamer Conley attempted to reproduce the findings in an article out of the Journal of Biomedical Optics. "The presentation at the KYPT was a result of the course," said Conley. Presenting at the KYPT helped Conley "gain recognition within Physics circles," she said.

Beyond all the scientific terms used to explain this research, Conley explained that "the main issue behind the experiment I conducted was the detection of glucose levels in diabetic patients. The question has been raised," she said "would it be possible to develop a noninvasive method of glucose detection? Because glucose is a chiral substance in theory it should be possible for us to pass a beam of light through the finger, for example, and be able to determine from the optical rotation and linear polarization effects what concentration of glucose is present. Although this idea may not be plausible in reality, it is worth investigating."

Conley began studying optical rotation and linear polarization in the fall of 2005. She has continued to expand her research on this topic as part of her senior seminar project.

Conley said that the most enjoyable part of doing this research has been "realizing that what I'm doing might actually have some real significance in the world. It wasn't just a class exercise that I was going to get graded on."

Look for Conley's research in the future. "If I can get good results with the part of this project I'm doing for senior seminar, the results might get published. I think that's pretty cool..."

Read Conley's abstract below:

A Study of Optical Rotation and Linear Polarization

Michaela Conley and A. S. Lahamer
Physics Department
Berea College
Berea, KY 40404


The capability to measure polarization properties of multiply scattered light yields several experimental observables such as optical rotation and the degree of (linear, circular) polarization that can be used to characterize turbid media such as noninvasive detection of chiral glucose molecules in turbid biological tissues. Our experiment was to quantify the surviving linear polarization fraction and the optical rotation imposed upon a linearly polarized light beam which was passed through a reference solution of polystyrene microspheres and (l(-), d(+)) arabinose (chiral), mixture (racemic), and glycerol (achiral) substances. A chopped unpolarized HeNe laser beam of light was passed through a linear polarizer situated at to the vertical. The ray then passed through a photoelastic modulator (PEM) with its modulation axis horizontal, a modulation frequency of 50 kHz, and a retardation of 3.469 rad. The light then passed through the sample solution. A pinhole aperture was placed at to the incident beam. This aperture was then followed by another linear polarizer also called an analyzer set at which varied from to in intervals. Another pinhole aperture was placed between the analyzer and the photomultiplier tube (PMT). The signal detected at the PMT was then sent through a pre-amplifier to the lock-in amplifier where it was compared to a reference signal from the chopper. A plot of the 2f/dc ratio (the lock-in 2f reading divided by the reference dc reading) versus the analyzer angle was made for each substance. The surviving linear polarization was extracted from the fits of the data for each of the substances. The optical rotation was found to be (-3.60 .87) for the chiral l-arabinose. The polystyrene and glycerol solutions produced an optical rotation of (1.97 .81) and (2.70 1.57) respectively. This technique has the potential to allow the extraction of the effect of the chiral constituent from depolarizing backgrounds. These preliminary values are in relatively good agreement with the values found in literature (Journal of Biomedical Optics July 2002).

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