2012 BFY Abstract Detail Page

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Abstract Title: W15 - From Jones Matrices to Ellipsometry: Modeling and Measuring the Polarization of Light
Abstract: Every physics lab has a special moment where students, after hours of toil, compare their laboriously collected data with theoretical predictions. At this moment, neat and tidy theoretical predictions are viewed side-by-side with messy and complicated real- world results. How can we make the most of this educational opportunity?

At the University of Colorado Boulder we have partially answered this question by redesigning our senior-level Optics and Modern Physics Lab to emphasize creating, testing, and refining of models, whereby "model" we mean a simplified representation of a more complex system that has predictive power and specified limitations to its validity. By emphasizing modeling, students use the full suite of mathematical and computational tools from their lecture courses to make predictions about the behavior of real-world systems. In the lab, a model-based approach allows for an improved discussion of ¬topics we previously neglected, such as systematic error and understanding various "black box" measurement tools.

A model-based approach can be applied to any experimental setup, but in this workshop we will demonstrate the transformation process from our older polarization lab to a model-based experiment. Students build up models of polarized light, starting with linear polarization and ending with arbitrary states of elliptically polarized light. They model optical components such as polarizing filters and quarter wave plates, and refine idealized models to account for systematic error effects in their actual equipment. In the end, mathematical models are developed that can be used to predict the outgoing light field from a sequence of optical components. Measurements of arbitrary polarization states can also be done using the computational model to fit results of the measured power transmitted through a rotating polarizer. The final challenge implemented during a student project was to use the same measurement techniques and computational modeling to infer the thickness and index of refraction of a thin film, a technique known as ellipsometry.

Mathematica is employed for computational modeling. LabVIEW is used in combination with low-cost USB data acquisition devices for quicker data taking. The experimental setup consists of a commercial HeNe laser, amplified photodetector, rotation stages, linear polarizers, and mounted lenses and mirrors. The equipment can be reused in a variety of optics labs.

At the end of this workshop you will be able to deliver a model-based polarization lab appropriate for the upper-division level. We will also spend a portion of the workshop discussing how your favorite labs at your institution can be adapted to incorporate aspects of modeling, including systematic error, and a deeper understanding of the experimental apparatus.
Abstract Type: Workshop

Workshop Documents

Workshop Document: Download the Workshop Document
Workshop Document (2): Download the Workshop Document (2)
Workshop Document (3): Download the Workshop Document (3)
Workshop Document (4): Download the Workshop Document (4)

Author/Organizer Information

Primary Contact: Ben Zwickl
Univ. of Colorado-Boulder