Ultrahigh sensitivity stimulated Raman gain spectroscopy

Using a synchronously pumped mode-locked dye laser system, we have obtained a factor of 300 improvement in signal to noise ratio (
S/N
) over previous CW experiments using stimulated Raman gain spectroscopy, and achieved an
S/N = 200 000
for a 1 s integration time in bulk benzene. This result confirms the sensitivity of the picosecond Raman gain approach and would allow the detection of a monolayer using a pump intensity of 100 MW/cm
²
.