A confocal scanning Fabry-Perot interferometer has mirrors of power reflectance set…
PHYSICS · Multi-part · Fermi University Physics · Optics & Photonics · Interference and diffraction · Interference and diffraction
What an Instrument Can See, Ch Multiple beams: the stack as a matrix and the etalon as a filter
Problem
A confocal scanning Fabry-Perot interferometer has mirrors of power reflectance R=0.980 set d=75.0 mm apart (air, n=1), figured flat to λ/60 at the He-Ne wavelength λ=633 nm. Scanning it across a single-frequency He-Ne laser line gives a transmission peak of full width at half maximum 40 MHz on the frequency axis, read off using the confocal free spectral range c/4d.
((a)) Estimate the reflectance-limited finesse FR, the figure-limited finesse Ffig, and their quadrature combination F, and hence the instrument's frequency resolution.
((b)) State what can and cannot be concluded about the true linewidth of the laser from the measured 40 MHz width, and identify which limit dominates the instrument's resolution.