Patent ID: 7145651

Claim:
A method for extracting a Raman signal from a fluorescence background in a Raman/fluorescence emission from a material, the method comprising: (a) exciting the Raman/fluorescence emission from the material by a laser light source; (b) measuring a Raman/fluorescence spectrum of the Raman/fluorescence emission using a spectrometer, wherein the spectrometer comprises a wavelength tunable optical filter for selecting a wavelength component of the Raman/fluorescence spectrum and a photo detector for measuring the Raman/fluorescence spectrum in the wavelength component selected by the wavelength tunable optical filter; (c) modulating the wavelength component selected by the tunable filter in such a way that a modulated optical signal with a modulation amplitude representing a derivative of the Raman/fluorescence spectrum at a central wavelength of the tunable filter is detected by the photo detector; (d) scanning the central wavelength of the tunable filter and recording the corresponding modulation amplitude for each wavelength to obtain a difference Raman spectrum; and (e) extracting and amplifying the Raman signal in accordance with the difference Raman spectrum.