I have some questions regarding a fabry perot interferometer. (they aren’t problems as such however I have had a good look around the internet and am struggling to find what I’m looking for). 1) Why is it that a circular fringe pattern is observed. How does a single source interfere with itself and is there variation in the pattern for a given wavelength as the distance between the plates is varied. 2) Am I correct in thinking that the term fringe visibility can only be used when the source is not monochromatic – e.g if there are two wavelengths present, at a given distance between the two plates, two independent ring systems are produced and fringe visibility refers to whether the bright and dark bands of each system coincide or not, and this is dictated by the distance between the plates. But then my next question is… 3) If the source is monochromatic and so changing the distance can not influence the fringe visbiity, what oservable affects does it give arise to? Thanks a lot for any assistance on this. Really Appreciated.