  Coherent anti-Stokes Raman scattering (CARS) spectroscopy with time-delayed
ultrashort pulses and a single-pixel photodetector has shown great potential
for spectroscopic imaging and transient studies in chemistry and biological
research. However, those systems rely on mechanical delay lines or two
asynchronous optical combs with inflexible repetition frequencies, technically
limiting their acquisition speeds. Here, we demonstrate a hybrid dual-comb CARS
system involving a broadband fiber laser and a highly-flexible,
frequency-modulated electro-optic comb. We achieve multiplex CARS spectra
(2800-3200 cm-1), with a moderate resolution (22 cm-1), at a maximum refresh
rate of 1 MHz, limited by the radio-frequency synthesizer we use. Fast
spectroscopic CARS imaging is demonstrated for liquid mixtures. Our system
enables spectral measurements in the high-wavenumber C-H stretching region at a
record speed that is an order of magnitude higher than state-of-the-art
systems, which may open up new opportunities for fast chemical sensing and
imaging.
