Kerr-lens mode-locked bidirectional dual-comb ring laser for broadband dual-comb spectroscopy

Fourier-transform spectroscopy is an indispensable tool for analyzing chemical samples in scientific research as well as the chemical and pharmaceutical industries. Recently, its measurement speed, sensitivity, and precision have been shown to be significantly enhanced by using dual-frequency combs. Moreover, recent demonstrations of inducing nonlinear effects with ultrashort pulses have enriched the utility of dual-comb spectroscopy. However, wide acceptance of this technique is hindered by its requirement for two frequency combs and active stabilization of the combs. Here, we overcome this predicament with a Kerr-lens mode-locked bidirectional ring femtosecond-pulse laser that generates two broadband frequency combs with slightly different pulse repetition rates and a tunable yet highly stable rate difference. Since these combs are produced by one and the same laser cavity, their relative coherence stays passively stable without the need for active stabilization. To show its utility, we demonstrate broadband dual-comb spectroscopy with the single laser.