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Thin Film Fabry-Perot Etalons
Advances in the manufacturing of Fabry-Perot etalons for a wide variety of research and industrial applications have generated affordable products that are very useful for improving experiments in intermediate and advanced physics teaching laboratories. In particular, etalons of solid media (silicon, germanium, and fused silica), with or without thin-film coatings, are now available for experiments that probe the visible and infrared regions of the electromagnetic spectrum. These solid-medium etalons are simple and robust devices that, unlike the traditional air-gap Fabry-Perot interferometers, do not require any adjustment from the student. Further, they can be purchased for less than half of the cost of an air-gap interferometer and perform very well in a laboratory teaching environment with reasonably controlled temperature.
We will present examples of classic experiments where these devices are used. Etalon thicknesses for these type of experiments range from 60 micrometers to a few millimeters and are made of fused silica with thin-film coatings.
At least TWO experiments (possibly a third one under development) will be presented:
1) Sodium D-line Splitting by Two Measurement Methods: introduces students to the splitting of atomic spectral lines due to the spin of the optically active electron in hydrogenic atoms (“fine structure”) as well as selection rules. Participants will measure the sodium D-line splitting by two independent methods: (a) using a Czerny-Turner type spectrometer; and (b) using a thin-film Fabry-Perot etalon, a cellphone camera, and the ImageJ free software. Combining the results, with proper uncertainty propagation, is a great exercise for teaching the weighted average method. Please refer to Figures 1 and 2.
Figure 1: Experimental setup for measurement of the Sodium D-line Splitting by two methods: a Czerny-Turner type spectrometer and using a Thin-film Fabry-Perot Etalon.
Figure 2: Sodium D-line splitting using a Thin-film Fabry-Perot Etalon and a cellphone camera.
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