15min:

MATTHEW J. AMMEND, DAVID A. BLANK, Department of Chemistry, University of Minnesota, Minneapolis, MN 55455.

The dynamics of the local solvent environment are studied during chemically relevant events using the second-generation of resonant pump third-order Raman probe spectroscopy (RaPTORS). This two dimensional spectroscopy employs a nonresonant third-order Raman probe to track the changes in the complete intermolecular response as a function of time after photo-initiated dynamics. Several improvements have been made to the RaPTORS experiment in the current iteration. Although a diffractive optic (DO) is used to create a phase locked local oscillator (LO), the LO has been spatially separated from the beam crossing. This eliminates any unwanted pump-probe signals resulting from interactions between the LO and any of the other four interacting pulses. The non-collinear LO and signal are combined on a second DO, where the relative phase is controlled by translation of the DO normal to the LO. This method of phase selection creates a down-gearing of the phase, with a 2.5 cm translation of the DO rotating the relative phase at 800 nm by 2 , and provides stability of >\frac 200 over the course of several hours. Signals are collected via a balanced detection scheme that provides single shot subtraction of two phase-cycled signals.