Automated fluorescence rejection using shifted excitation Raman difference Spectroscopy

Sample fluorescence is detrimental to Raman spectroscopic analysis. Several algorithms are proposed to achieve automatic fluorescence rejection (AFR) based on shifted excitation Raman difference spectroscopy. The algorithms are mathematically linear and can be automated. The methods are based on a wavelength-tunable laser and the measurement and calibration of both the Raman and the excitation spectra. Applying the AFR methods to highly fluorescent samples significantly reduces the fluorescence background and reveals weak Raman features unidentifiable using traditional methods. Fixed pattern "noise" associated with the background can be completely removed. The merits of each algorithm are discussed and the best excitation frequency shift to perform the analysis is found to be comparable to the widths of major Raman peaks.