Answer to Question #155617 in Optics for Huzaifa Rehman

Question

What is the physical significance (importance) of free spectral range (δνr) of the resonator in real laser systems?

Answer 1

the free spectral range 

For a resonator, it is the frequency spacing of the modes of the axial resonator. The free spectral range is inversely proportional to an optical pulse's round-trip time. 

For a Fabry–Pérot interferometer, it is the frequency used to spacing the system's peaks of transmission. When the extensive free spectral range is more, it leads to a bandwidth that is larger for a resonator bandwidth spectral resolution that is poor.