Optical Spectroscopy

Ultrafast Nonlinear Laser Spectroscopy

In ultrafast nonlinear laser spectroscopy, we apply multiple laser pulses to probe the dynamics of chemical/physical phenomena in real time. Using these time-delayed laser pulses, we initiate the chemical/physical phenomena and then monitor the progress of the dynamics process. By adjusting the time ordering, propagation directions, and polarizations of those pulses, we can selectively measure the nonlinear signals containing specific dynamic information on the molecules in transition.

The below figure shows an example of nonlinear laser spectroscopy: two-dimensional electronic spectroscopy (2D-ES) applied to probe the dynamics of energy transfer and coherent oscillations in a photosynthetic light harvesting complex, chlorosome. By measuring the third-order nonlinear signal while scanning the time delays between three coherent laser pulses and subsequent Fourier transformation, a 2D spectrum is obtained. By taking a series of 2D spectra while changing the time delay between the second and third pulses (called population time, T), we can keep track of ultrafast energy transfer occurring among the exciton states of chlorosome as well as reveal the coherent oscillations arising from the electronic coherence created among the exciton states.