NEW ADVANCES IN MID-IR PULSE SHAPING AND ITS APPLICATION TO 2D IR SPECTROSCOPY AND GROUND-STATE COHERENT CONTROL

Abstract

Pulse shaping directly in tre mid-IR opens up many new experiments in both Ic oherent control and multidimensional IR spectroscopy. This technological advance is very recent, and so only the most rudimentary uses have been implemented so far [4, 5]. In fact, coherent control and multidimensional spectroscopies might be combined to strongly complement one another. In coherent control methods using feedback, the bottleneck is often understanding how the process is optimized by the pulses. If 2D IR spectroscopy were used in conjunction with coherent control experiments (and truncated pulse sequences), the vibrational pathways selected by the control path could be monitored, lineshapes could be monitored to understand how solvent dephasing alters selectivity, and energy transfer could be mapped to understand how inter-molecular relaxation inhibits the excitation process. Understanding these processes will likely lead to improved control strategies. Coherent control strategies might also be used to enhance 2D IR spectra [7]. In NMR spectroscopy, radio-frequency control over nuclear spins allows for precise control over pulse sequences. Similar methodology might be possible in multidimensional spectroscopy with pulse shaping. For instance, cross-peaks might be enhanced using shaped pulses that preferentially excite the combination bands. With pulse shaping, implementing coherent control and 2D IR spectroscopy may be straightforward. At least in principle, combining coherent control and 2D IR spectroscopy is just a matter of computer programming, whereby the shaped pulse is incorporated into the 2D pulse sequence, or the 2D pulse sequence just follows a shaped pulse. Whether or not these experiments are possible, it is clear that even with the rudimentary experiments performed so far, mid-IR pulse shaping is an insightful new tool to apply toward understanding and manipulating the vibrational modes of molecules.