Center for Relativistic Laser Science

2019 123rd KCS

Femtosecond laser has brought a dramatic development on time-resolved spectroscopy to understand the complex photochemical reactions in nature. In time-resolved spectroscopy, an impulsive pump pulse generates a non-equilibrium state, and its time evolution is monitored by a probe pulse. The time delay between the pump and probe is generated by adjusting the optical path-length difference between the two pulses conventionally. Because the experiments with mechanical time-delay have to record the data at a fixed time-delay, they require high time costs to observe slow reaction dynamics and to obtain a high resolution time-domain vibrational spectrum.

Recently, we have demonstrated dual frequency-comb (DFC) based time-resolved spectroscopy. [1-2] Frequency comb being a special type of mode-locked laser has equally spaced spectral lines fixed at the frequencies specified by the laser repetition frequency and a offset frequency. When the repetition rates of two frequency combs are slightly detuned, the time-delay between them are automatically generated. The time-delay generated by DFC does not change the phase-front of the delayed beam, so that it enables wave mixing experiments such as transient absorption and two-dimensional spectroscopy even at nanosecond time delay. The use of single-point photodetector and intrinsically fast time-delay scan rate are also unique properties of DFC spectroscopy. Here, we present three DFC-based time-resolved spectroscopy, and derived them theoretically based on frequency-comb field-adapted perturbation theory. [3]

[1] JW. Kim, B. Cho, T. H. Yoon and M. Cho, J. Phys. Chem. Lett., 9, 1866-1871 (2018)

[2] JW. Kim, T. H. Yoon and M. Cho, J. Phys. Chem. B, 122, 9775-9785 (2018)

[3] JW. Kim, J. Jeon, T. H. Yoon and M. Cho, Phys. Chem., (2019)