2018 BFY III Abstract Detail Page

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Abstract Title: W14: Quantitative analysis of Fraunhofer diffraction patterns: an exercise in model fitting, optics, and electronics
Abstract: Observing the locations of the minima in a single-slit diffraction pattern is a standard introductory experiment in wave optics. However, measuring and mathematically modeling how the intensity of the Fraunhofer diffraction pattern varies spatially leads to a much richer experience for sophomore-level students. In this workshop, we describe how to measure diffraction patterns using a photodiode mounted on a computer-controlled motorized stage. By moving the photodiode across the diffraction pattern from a single slit, students can map out the intensity point by point. They then determine the slit width by fitting a Fraunhofer diffraction model to their measurements. We use this relatively simple experiment to introduce students to nonlinear model fitting using standard Python libraries within the Jupyter Notebook environment.

This experiment can also develop student skills in other areas. Learning to control the motorized stage from a computer via a serial port can introduce students to interfacing (we use the pySerial Python library). Students can strengthen their laboratory electronics skills by designing and building a photocurrent-to-voltage converter using an op-amp and a feedback resistor. In addition, this experiment can illustrate the connection between Fraunhofer diffraction and the Fourier transform, particularly if students compare diffraction patterns from single slits of varying width or from multiple slits.
Abstract Type: Workshop
Contributed Paper Record: Contributed Paper Information
Contributed Paper Download: Download Contributed Paper

Author/Organizer Information

Primary Contact: Jerome Fung
Wellesley College
106 Central St.
Science Center
Wellesley, MA 02481
and Co-Presenter(s)
Lauri Wardell

Workshop Documents

Workshop Doc 1: Download the Workshop Doc 1