a the spectrum of human skin from excitation by 670 nm is presented at wavelengths from 848 to 960 nm no fluid was added between the skin and optical window 180 it is observed that the peak signal value is about 450 000 counts there is a raman line of water at about 3400 cm u2212 1 which for excitation at 670 nm produces a peak in the neighborhood of 872 nm it is not readily observed in fig4 a as the fluorescence signal dominates in magnitude in fig4 b relative counts scattered signal from the sample minus a background taken with no sample are again presented for 670 nm excitation but microscope immersion oil richard allan scientific m2000 has been introduced between the human skin and the optical window 180 so great was the suppression of fluorescence that the raman line of water is now observed without any impairment fluorescence is often the largest source of random noise in spectroscopy of biological samples in particular the variance of the fluorescence counts is very often the limiting random noise in raman spectroscopy of biological samples in fluorescence spectroscopy the fluorescence from some chemicals can greatly interfere with the observation of fluorescence from the desired chemical therefore a means of suppressing fluorescence from targeted chemicals is exceptionally valuable in human skin the fluorescence observed at an excitation of 670.