Fabry–Pérot filter cavities for wide-spaced frequency combs with large spectral bandwidth

We use low-finesse Fabry–Perot cavities in series to generate frequency combs with a large mode spacing in a way that allows its application to a large optical bandwidth. The attenuation of laser modes closest to the pass bands of the cavity exceeds 70 dB for a filter ratio of m=20 relative to the resonant modes centered within the pass bands. We also identify the best cavity geometry to suppress spurious transmission of higher order transversal modes. Such a thinned out frequency comb can be used to calibrate traditional spectrographs for precision astronomy. In the time domain mode filtering generates a pulse train with a multiplied repetition rate. High-fidelity filtering, as described here, implies small variations of the pulse energies.