The full width at half maximum of the peaks is called the bandwidth and the ratio of the line width to the distance between the peaks (the FSR) is called the Finesse, F. As the reflectivity of the mirrors is increased the modulation peaks become sharper and decrease in width. The mirror reflectivity does not affect the FSR, it affects the number of bounces and improves the quality of the modulation (more perfect bounces = better modulation). You will notice that the mirror reflectivity is not part of these equations. If the absorption and scattering losses are small, the reflection spectrum of the etalon is 1 - T. As seen on the right in our online etalon designer. The transmission spectrum of an etalon will have a series of peaks, where constructive interference occurs, spaced by the 'free spectral range' or FSR. Constructive and destructive interference occurs based on the angle of the beam (θ) the optical thickness of the etalon (nd) and the wavelength(λ). During one return bounce the phase changes by 2πx2ndCOS(θ)/λ, where θ is the angle of the beam in the etalon. Light that enters the etalon undergoes multiple reflections and the interference of the light emerging from the etalon during each bounce causes a modulation in the transmitted and reflected beams. The Fabry Perot interferometer consists of two parallel flat semi-transparent mirrors separated by a fixed distance. Use our simple web based etalon calculator to determine the thickness and coating reflectivity to meet your requirements. These devices require high quality, very flat optical surfaces and extreme parallelism to achieve high performance, making them a good match for the polishing and metrology at LightMachinery.Įtalons can be made from a wide variety of materials including Fused Silica, Silicon and even Air. Solid etalons, air spaced etalons, piezo tunable etalons, Gire Tournois etalons, LightMachinery has extensive expertise in the manufacturing and testing of all kinds of Fabry Perot etalons from 1mm square to 100mm in diameter.
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