Free spectral range calculator





About this calculator

This calculator computes the free spectral range of an optical resonator, which is the frequency interval between its resonance frequencies defined as

FSR=c2ngLFSR = \dfrac{c}{2n_gL}

where cc is the speed of light in vacuum, ngn_g is the group index of the resonator material, LL denotes the physical length of the resonator and the factor 2 is included due to light's double-pass through the resonator in a single round-trip.

This calculator also gives the FSR in wavelength units if the correct center wavelength is supplied.