Coherent dual-comb spectroscopy at high signal-to-noise ratio

Two coherent frequency combs are used to measure the full complex response of a sample in a configuration analogous to a dispersive Fourier transform spectrometer, infrared time domain spectrometer, or a multiheterodyne laser spectrometer. This dual-comb spectrometer retains the frequency accuracy and resolution of the reference underlying the stabilized combs. We discuss the specific design of our coherent dual-comb spectrometer and demonstrate the potential of this technique by measuring the overtone vibration of hydrogen cyanide, centered at THz ( nm). We measure the fully normalized, complex response of the gas over a THz bandwidth at MHz frequency resolution yielding resolution elements. The average spectral signal-to-noise ratio (SNR) over the THz bandwidth is for both the magnitude and phase of the measured spectral response and the peak SNR is . This peak SNR corresponds to a fractional absorption sensitivity of and a phase sensitivity of microradians. As the spectral coverage of combs expands, coherent dual-comb spectroscopy could provide high-frequency accuracy and resolution measurements of a complex sample response across a range of spectral regions. Work of U. S. government, not subject to copyright.