This window helps calculating important parameters of confocal and non-confocal Fabry-Perot interferometers. 

The first section converts between the mirror spacing and the free spectral range (FSR). The free spectral range can be entered/seen in frequency and wavenumber units. 

• confocal_FSR_frequency = c/(4*mirror_spacing) 
• plano_FSR_frequency = c/(2*mirror_spacing) 
• wavenumber = frequency/c

The second section converts between the reflectivity finesse anf the mirror reflectivity: 

• finesse = pi*sqrt(confocal_reflectivity)/(1-confocal_reflectivity)/2 
• finesse = pi*sqrt(plano_reflectivity)/(1-plano_reflectivity)

The third section converts mirror reflectiviy and cavity losses into FPI throughput, and vice versa: 

• confocal_throughput = 0.5*(1-losses/(1-reflectivity))^2 
• plano_throughput = (1-losses/(1-reflectivity))^2

With these values it is possible, e.g. to estimate the minimum resolvable bandwidth (MRB) of a Fabry-Perot interferometer. Approximately the following equation applies: 

• MRB = FSR/finesse