Unlocking a lower shot noise limit in dual-comb interferometry

Optimizing the signal-to-noise ratio (SNR) is critical to achieve high sensitivities across broad spectral ranges in dual-comb interferometry. Sensitivity can be improved through time-averaging, but only at cost of reduced temporal resolution. We show that it instead possible use high-bandwidth detection combined with frequency-domain averaging multiple copies beat note. By controlling signal and noise stationarity properties, one even reduce fundamental shot contribution compared normal, single copy, operation where integration time matched to, or larger than repetition period. In principle, Na aliased will improve SNR by up Na, equivalently, acquisition a factor Na. demonstrate interferometry using = 5 aliases, achieving predicted fivefold reduction power density low frequencies. Over full spectrum, unaveraged relative intensity limits SNR, we measure 1.65× fold improvement CO2, corresponding 2.7× for given precision.