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Fabry-Perot Etalons

Posted on Jan 21 2011 by Jamie Quinton, Jessica Francis-Staite, Ashley Slattery

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Tags: asell physics, optical physics

Experiment Overview

This experiment is taken by second year physics students and requires three hours to complete. This experiment involves observing interference fringes created by a laser that is shone through a Fabry-Perot etalon interferometer. The laboratory notes lead students from the known condition for interference maxima to a general equation for the radii of interference fringes (rp) as a function of laser wavelength (l), fringe number (p), distance between etalon faces (d) and the focal length of the viewing lens (f), namely

rp = f (pl/d)1/2
Students will measure the position and corresponding ring number of each observed fringe, with these measurements and the above equation they will come to the conclusion that by using the slope of a graph of rp vs p1/2 they will be able to determine the distance d between the two faces of the etalon. Once the distance of the etalon is determined the, students repeat this process using a source of unknown wavelength (typically a green laser), and then apply what they’ve learned in the first part to to determine the wavelength of the second source.
It is also notable that the students who undertake the experiments in our second year physics subject do so in a Round-Robin style, and so some students will do this experiment in the middle of semester, while others will do it at the end, and thus may have differing amounts of background knowledge prior to their experience with this experiment.
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