Relative Intensity Correction of Raman Systems with National Institute of Standards and Technology Standard Reference Material 2242 in 90°-Scattering Geometry

Abstract

The U.S. National Institute of Standards and Technology (NIST) has certified a set of Standard Reference Materials (SRMs) that can be used to accurately determine the spectral sensitivity of Raman spectrometers. These solid-state reference sources offer benefits such as exact reproduction of Raman sampling geometry, simple implementation, and long-term stability. However, a serious drawback of these SRMs is that they are certified only in the backscattering (180°) configuration. In this study, we investigated if and how SRM 2242 (applicable for 532 nm) can be employed in a 90°-scattering geometry Raman system. We found that the measurement procedure needs to be modified to comply with the certified uncertainty provided by NIST. This requires a change in the SRM illumination that is possible only if we polish the side surfaces. In addition, we need to account for the polarization configuration of the Raman system by choosing the appropriate polarization of the excitation beam. On top of that, the spatial inhomogeneity of the luminescence light needs to be taken into account, as well as its behavior while traveling through the SRM bulk. Finally, we show in a round-robin test that the resulting uncertainty for the quantification of Raman spectra using the modified technique is on the order of ± 1.5 percentage points.