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Spectrometry
Published in Chandrasekhar Roychoudhuri, Causal Physics, 2018
The Fabry–Perot (FP) spectrometer is a very useful high-resolution instrument, and hence we will derive the basic causal time-evolving and time-integrated response function for it. The mathematical logic is the same as that for the grating, except for the number N. For a grating N is determined unequivocally by the total number of slits (steps) in the grating that is actively illuminated by the beam to be analyzed. For an FP we will use the finesse number N = πR/(1 − R) where R is the intensity reflectance of the two mirrors (not the resolving power R). Operationally, finesse is the ratio of the free-spectral range of the FP, νfsr, divided by the width of the fringe δν, which is indicative of the resolving power of the instruments ν/δν. Just like grating step delay τ, FP also has a step delay given by the round-trip time between the FP mirror pair, τ = (2d/c) = (1/ νfsr), where d is the separation between the FP mirrors. To appreciate the definition of finesse, the reader is referred to any basic book on optics [1.34]
Basic Laser Processes
Published in Mark Steven Csele, Laser Modeling, 2017
In a cavity such as this, an integral number of half-wavelengths must fit within the cavity giving rise to discrete longitudinal modes separated by a constant frequency called the free spectral range (FSR) of the cavity. FSR(Hz)=c2nl
Spectrometers
Published in Daniel Malacara-Hernández, Brian J. Thompson, Fundamentals and Basic Optical Instruments, 2017
In multiple-beam interference, which includes both Fabry–Perot interferometers and diffraction gratings, there can be an overlapping of orders. The free spectral range is the spectral interval between such overlaps. The finesse is the ratio of the free spectral range to the spectral slit width.
Switchable Fabry–Perot filter for mid-infrared radiation
Published in Liquid Crystals, 2019
U. Chodorow, R. Mazur, P. Morawiak, J. Herman, P. Harmata, P. Martyniuk
An important parameter of the resonator is the distance between adjacent resonant frequencies FSR (free spectral range). This is the range in which one can switch the filter without covering the adjacent passbands: