Downsampling of optical frequency combs for carrier-envelope offset frequency detection

We explore downsampling of optical frequency combs by way of pulse gating for efficient spectral broadening and f-2f interferometry. We downsample a 250 MHz repetition-rate comb to 25 MHz, thereby enabling detection of the comb's carrier-envelope offset frequency. Pulse gating can both increase timing jitter of the comb's pulse train and induce spurious frequency offsets of the comb's spectrum. To investigate these effects, we characterize the phase-noise spectrum of the downsampled comb, determine the effects of timing jitter deliberately imposed on the pulse gate, and demonstrate the null frequency shift of the comb's optical spectrum to the level of several microhertz.