  We provide conclusive demonstration of vibrational pumping under Surface
Enhanced Raman Scattering (SERS) conditions by performing anti-Stokes/Stokes
ratio measurements down to 10 K using dried silver colloids, the dye rhodamine
6G and 676 nm laser excitation. The method we propose allows the measurement of
the SERS cross sections for different modes and the determination of the
asymmetry between the anti-Stokes and Stokes SERS cross sections.
