Experiments in Raman spectroscopy of hair: exciting light and molecular orientation

Hair fibers have been analyzed by Raman spectroscopy to assess the suitability of a range of excitation wavelengths for data collection over extended periods of time. It is found that the optimum excitation wavelength for spectral detail, of these tested, was 780 nm and that this wavelength resulted in little signal degradation over time. It was found that with higher energy excitation sources that the signal intensity of the spectra degraded significantly in short periods of time. This work suggests that near-IR Raman spectroscopy therefore offers the most suitable conditions to analyze the nature of secondary structural feature in hair fibers. In addition, a preliminary exploration of the structural orientation of spectral features of the hair was attempted. Through the use of a linearly polarized excitation source the intensity of the Raman spectral features were observed to change as the alignment of the fiber axis with respect to the plane of polarization was changed. It was found that the spectral features associated with the alpha-helical vibrations decreased in intensity as the fiber axis was rotated from an orientation parallel to the exciting beam.