Dual-Comb Coherent Raman Spectroscopy With Near 100% Duty Cycle

Dual-comb coherent Raman spectroscopy is a powerful tool for rapidly probing vibrational signatures of molecules in the fingerprint region. However, >99% of its incident laser energy is unused and wasted since the duty cycle of its spectral acquisition is only less than 1% due to the mismatch between the interval of the laser pulses (>1 ns) and the coherence lifetime of molecular vibrations (similar to 3 ps). Here we demonstrate similar to 100% duty-cycle dual-comb coherent Raman spectroscopy with a "quasi"-dual-comb source. This is made possible by rapidly modulating the cavity length of one of the frequency combs and accurately measuring the group delay between pump and probe pulses by two-color interferometry for calibrating the phase of each Raman active mode in the sample. Specifically, we use the method to show a record high spectral acquisition rate of 100000 spectra/s with even higher sensitivity than conventional slower dual-comb coherent Raman spectroscopy.