Coherent control in molecular systems:

The goal of using light to selectively break chemical bonds, and more generally to guide molecular processes via quantum interference effects, has been pursued since the development of the laser. A great deal of recent progress has been made in this direction, and examples of ultrafast laser control of coherent molecular state superpositions ('wave packets') have begun to extend beyond model two-atom systems to both gas- and solid-phase polyatomics. Recent years have also brought many technological advances in this field, including the advent of elegant ultrafast pulse shaping techniques and the implementation of feedback-controlled learning algorithms. These advances allow manipulation of molecular systems even in cases where the controlled molecule is too complex to reasonably model with theory.

We will apply these experimental ultrafast techniques to several small (~3-10 atom) neutral molecular systems to exert control, through well-timed pulse sequences and cleverly designed pulse shapes, over the excitation and dissociation of these molecules. By combining these ultrafast laser techniques with molecular beam techniques, these coherent control experiments will begin in the isolated molecule regime, with experiments directed toward selectively breaking specific chemical bonds. Ultimately, however, we are interested in discovering how our ability to control these processes is affected by interaction with surrounding media. Therefore, we will quickly direct experiments towards more complex regimes in which the controlled molecule is either embedded within an isolated cluster of solvent molecules, or completely dissolved into solution.

Ultrafast probing of energy transfer in capped colloidal nanoparticle systems:

A second set of experiments will be initiated probing the dynamics of energy transfer in capped colloidal metal nanoparticle systems. These systems, whose inherently size-dependent properties can be synthetically 'tuned,' have several current and potential applications ranging from highly sensitive analytical probes in single molecule spectroscopies to synthetic light-harvesting assemblies for use as optoelectronic materials. We will use ultrafast pump-probe techniques to view and understand the transfer of energy between the nanoparticle core and chromophores tethered to the particles. Multi-pulse nonlinear ultrafast spectroscopies will be critical tools used to follow the time dynamics of these nanoparticle systems.