UC Irvine

Time-resolved, surface-enhanced, coherent anti-Stokes Raman spectroscopy (tr-SECARS) is

ideally suited for preparing and interrogating vibrational coherences on single molecules.

We have succeeded in the rst demonstration of this concept through measurements carried

out on molecules attached to gold nanosphere pairs which act as plasmonic nano-dumbell

antennae. The tr-SECARS traces provide unique signatures of coherent evolution in discrete

ensembles. The signals are characterized by phase and amplitude noise, which can be cast in

terms of amplitude probability distribution functions (PDF), which allow rigorous distinction

between single, few, and many molecule coherences. We give a brief background on tr-CARS,

the experimental system for carrying out tr-SECARS and the analysis of the results in terms

of PDFs. The analysis makes it clear that we have, for the rst time, observed the coherent

vibrational motion of a single molecule.