High duty-cycle spectroscopy and microscopy using optical frequency combs*

Dual-comb spectroscopy (DCS) advanced optical spectroscopy by enabling high-resolution measurements without requiring moving mechanical parts. This technique uses two laser frequency combs that emit ultrashort pulses of light. One comb excites the electrons in a sample and the emitted signal is then interfered with the second comb that has a slightly different repetition frequency. The difference in repetition rates between the combs creates an interferogram, which is analyzed to extract detailed information about the sample’s chemical and physical properties.

 

A significant limitation of dual-comb spectroscopy is its low-duty cycle, which arises when the sample’s decay process occurs faster than the interval between laser pulses. To overcome this issue, we developed a modified DCS technique. By locking the repetition rates of both combs and modulating the phase of one comb, we can generate the interferogram and perform rapid scanning where the signal is nonzero. Additionally, we implemented spatial scanning, enabling high-resolution analysis across the entire sample.