Resonance Raman spectroscopy measures
resonance-enhanced Raman spectra. This resonance-enhancement enables chromophores
within molecules to be targeted with molecular specificity, by tuning the Raman
pump pulse onto an electronic transition of the sample. The apparatus has a ca 2 ps time resolution with > 10 cm-1 spectral
resolution. The ULTRA OPAs allow
independent tuning of the pump and probe beams from the UV to near-IR.
The figure shows a typical layout for a
time-resolved Raman spectroscopy experiment, with OPAs driven by the 800 nm
output (red) of a titanium sapphire amplifier. The pump laser (blue) initiates a change
within the sample, the dynamics of which are probed by a second time delayed
beam (green) “probe” beam. Raman scatter (green dotted line) from the sample is
collected and directed to the spectrometer with CCD detector. A Kerr gate
system driven by a time delayed third beam from the laser output can be used to
remove fluorescence background from the Raman signal.