Two-photon direct frequency comb spectroscopy with chirped pulses

Thanks to the high peak intensities of ultrashort pulse trains that make up an optical frequency comb, conversion to much shorter wavelengths is readily available. Therefore direct frequency comb spectroscopy may offer the possibility of extending high-resolution spectroscopy to spectral regions that are unexplored so far. In this work, we investigate the impact of a chirp, i.e., a varying frequency across the pulses, on the excitation rate obtainable with two-photon direct frequency comb spectroscopy. Using the cesium 6 ²S1/2-8 ²S1/2 two-photon transition at $822$ nm, we show that destructive interference of various quantum paths reduces the excitation rate with the inverse of the time bandwidth product of the exciting pulses.