Evaluating stability of a Raman spectrometer for long‐time experiments

Abstract

Raman spectroscopic measurements spanning several hours to days are increasingly common and important. The stability of a Raman spectrometer becomes crucial when comparing spectra recorded at different occasions in such time‐intensive experiments. In this work, series of Raman spectra of benzene and emission spectra of neon were acquired using a standard Raman spectrometer operating in a typical air‐conditioned laboratory, with synchronized measurements of ambient parameters (pressure, temperature, humidity, etc.) subject to continuous unsystematic environmental drifts. The time‐dependent fluctuations of positions and intensities of selected bands in the series of spectra recorded over tens of hours displayed variations of up to ±0.3 cm−1 in the band positions and up to 2% in the associated Raman intensities, with experiments over longer time periods prone to more pronounced fluctuations. After accounting for change in the laser power fluctuations, the intensity variations were reduced to about 1%. Both the variations in the band positions and intensities showed practically no correlation with either of the ambient parameters or the refractive index of air. Tiny drifts in the laser wavenumber (on the order of 0.01 cm−1), attributed to the change in the refractive index of the laser cavity associated with the variations in the ambient pressure, were too small to account for the observed fluctuations in the band positions.

Unlocking ultimate precision of intensity and area ratio measurements in Raman spectroscopy: Insights from simulation, experimentation, and theory and implications for isotope ratio analysis

“…To investigate the influence of nonlinearity of the detector sensitivity 54 and drift 41,58 on σ α I and σ α A , which are not accounted for in theory or simulation, we conducted 14-50 repeated measurements of CO 2 at 30 MPa and 21 C under various analytical conditions (e.g., I, S, k, and n read ).…”

“…When averaged over multiple experimental conditions, the correlation coefficient was close to 0, indicating a lack of reproducibility (Table S12). Because the frequency of the semiconductor laser depends on the refractive index of air (n ref ), 58 to investigate the correlation between n ref and 13 I þ F:D: =I þL F:D: , n ref was calculated from T r , H, and P r using the Ciddor equation 76 assuming a CO 2 concentration of 450 μmol/mol. Nevertheless, no correlation was found between 13 I þ F:D: =I þL F:D: and n ref (Figure S8).…”

“…Fluctuations in T r affect various components of the Raman system. Consequently, the measured α I might vary in a complex way, for example, through thermal expansion of the components holding the optical elements, 41 changes in the properties of the polymer film used in the filter, 77 variations in the wavelength of the laser, 58 and temperature dependence of the source follower amplifier. 78 The dependence and response speed might differ for each product.…”