Curved photo reflector12/10/2023 ![]() Tilt or WedgeĮnd mirrors that are not parallel cause a change in the phase of the beam across the etalon. The numbers that are included in the calculator are examples of practical values such as. ![]() Surface figure is usually measured at the HeNe laser wavelength of 633nm and is expressed as fractions of this wavelength. Spherical error is excluded from the rms surface figure and is treated separately. Surface figure is the rms variation of surface away from flat. In our etalon calculator the graph displays both the perfect theoretical transmission and the expected transmission taking into account all the defects in a real etalon. Each one makes a contribution to limiting the finesse and then all these contributions are combined to come up with the expected finesse and transmission. In reality there are other factors that 'limit' the transmission and finesse such as surface irregularity, parallelism, coating scatter. So a perfect etalon with no losses or imperfections will always have a 100% peak transmission. This is like our physics class questions that started by assuming "a mass is sliding down a frictionless incline.". The etalon is assumed to have no losses, like scatter or imperfect surface flatness. In many textbooks, the finesse is calculated using only the parameter R, reflectivity of the mirrors as in F=PI/SQRT( 4R/(1-R)^2). Actual versus Theoretical PerformanceĮtalons are usually described in terms of FSR and finesse. The finesse is a dimensionless quantity and the units of the Bandwidth are the same as the FSR.Īnother quantity, The Coefficient of Finesse, \(F = 4\mathcal)\). ![]()
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