Figure 5.

Features of Raman spectroscopy. (a) Schematic representation of the Raman shift from light scattering. It can be observed that an incident monochromatic laser with a wavenumber of 18,797 cm⁻¹ is scattered at a wavenumber of 15,385 cm⁻¹. The resulting wavenumber change of 3400 cm⁻¹ is due to the vibrational energy changes of the molecules. (b) Effect of long-pass and band-pass filters on generated signals. Recorded signals from light scattering are generated by anti-Stokes Raman scattering, Stokes Raman scattering, and Rayleigh scattering. Rejection filters are required to eliminate Rayleigh signals. They work by allowing and attenuating signals at specified frequencies to measure Raman spectra. Collection geometries in Raman spectroscopy: (c) Backscattered geometry, (d) Transmission geometry, and (e) Right-angle geometry. Backscattered and Transmission geometries require Rayleigh rejection filters to eliminate the noise resulting from Rayleigh scattering and back-reflected excitation light. Unlike the former two geometries, the configuration of right-angle geometry yields little noise, and, hence, rejection filters are not required.