ULTRAFAST MULTIDIMENSIONAL SPECTROSCOPY

Our main methodology is the state-of-the-art two-dimensional vibrational spectroscopy (2D-IR) where we impulsively excite selected vibrational modes of the molecule and track their ultrafast relaxation into different vibrational modes, into the modes of an interacting partner molecule, and dissipation into the solvent. Spreading the spectral information in two dimensions allows to reveal the correlations between molecular motions, and to resolve congested spectra arising from multiple molecular conformations. At the same time, the instrument response of our 2D-IR apparatus is fast enough to resolve different relaxation dynamics of these conformations and their inter-conversionkinetics. Figures below schematically summarize how the four-pulse 2D-IR experiments are conducted.

Ultrashort laser pulses are generated in the mid-infrared region by successive frequency conversions (optical parametric amplification and difference frequency generation) of the amplified near-infrared 50 fs pulses. The mid-IR pulses are split into four replica and recombined at the sample, while time delays between them are scanned during the experiment. The emitted non-linear signal is detected by spectral interferometry.

A piece of an optical table, where mid-IR pulse manipulations are performed.
Note, that mid-infrared light is invisible to human eye, and no alignment cards in that region are available!

Once all the signals are collected at different time delays between the pulses, the data is Fourier-transformed to get a two-dimensional spectrum, which carries rich information on ultrafast molecular dynamics.