Taking six-dimensional spectra in finite time

Abstract

Pump-probe spectroscopies use ultrafast laser pulses to excite molecules, and then probe them with a time-delayed pulse. If more laser pulses are used, information beyond excited-state spectra can be gained. For example, four-pulse techniques can explore how vibrations or electronic excited states are coupled. However, adding even more pulses usually comes at a price—that of very long experimental times to collect all of the data. Spencer et al. (1) now report on a six-pulse laser spectroscopy that obtains intricate details on the coupling between electronic states to vibrational motions, a key issue in the observation of quantum coherence in proteins (2–5). This method takes advantage of the ingenious gradient-assisted photon-echo spectroscopy (GRAPES) developed (6) for four-pulse spectroscopy that speeds acquisition times by tilting the beams to introduce time delays and sampling along a line rather than a point.