Acousto-optic frequency combs for heterodyne interferometry

We demonstrate the capability of a frequency shifting loop seeded with a CW laser to generate a coherent optical frequency comb. Our system produces a spectrum that contains near 1000 modes, with a frequency spacing between them easily reconfigurable in the kHz-100 MHz range, without high-speed electronics. In order to show the potentiality of this kind of frequency combs for precise spectroscopy, we report the measurement of the complex amplitude of the resonance peaks of a Fabry-Perot cavity, with sub-MHz resolution.