Raman scattering is an excellent tool to probe matter for the research of its dynamical properties particularly in the aim of its integration in non linear optical applications. However, only few efforts have been devoted to the connection of the Raman scattering measurements with the nonlinear optical properties of inorganic materials such as LiNbO 3 (LN) and LiTaO 3 (LT). Such a relation requires at the first glance the determination of the Raman polarisability tensor elements whose absolute or relative measurement is experimentally very difficult. In the present study, we described a simple method based on crystal rotation, which leads us to measurements of the scattering efficiencies and their relative phase. More specifically, we characterized a congruent lithium niobate and we recorded its Raman spectra in the backscattering geometries e.g. for the following configurations (x(yy)x , x(yz)x , x(zy)x , x(zz)x). The measured spectra were fitted by using the Lorentz or Fano functions. The parameters deduced from the fit are presented as functions of rotation angles of crystal. This allows us to validate the selection rules and to determinate the relative phase and as the absolute values of the Raman tensor elements.

The present study highlights self-consistently helpful improvements dedicated to overcoming the difficulty resulting from the fitting procedure of integrated Raman intensities recorded according to the rotation crystal method described earlier. To this end, the anisotropy factors of Raman polarizabilities and the corresponding relative phases are determined within the framework of the exact mathematical derivation of the phase factors. These are the relevant parameters of the Raman efficiency relations which are numerically difficult to obtain from the fitting of the integrated areas. The present theoretical approach is then applied to the modes of the A(1) and Ey symmetry species of the lithium niobate (LN) crystal point group. All the expressions of the Raman absolute intensities of the A(1) and Ey irreducible representations initially imply three parameters to be determined from the fitting computations. However, from the derived analytical expressions of the phase differences, the number of parameters involved in the fitting procedure is reduced from 3 to 2, thus improving the statistics of the numerical treatment.

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Fluorescence excitation‐emission matrix (EEM) and synchronous scanning fluorescence (SF), coupled with parallel factor (PARAFAC) analysis, principal component analysis (PCA) and Linear discriminant analysis (LDA) methods were used to differentiate 49 lager beer samples and monitor the effects of temperature and sunlight exposition on their composition. EEMs were decomposed into independent fluorescent components. The beer samples were characterized by the presence of excitation/emission (exc/em) peaks at 290/350, 315/345, 340/410, 375/455, 360/420, 400/460, and 437/525 nm, which were ascribed, according to the known beer fluorescent components, respectively to aromatic amino acids, vitamin B6 (pyridoxal), vitamin B6 (pyridoxic acids), vitamin B3, iso‐α‐acids, vitamin B1, and vitamin B2. The variation of the relative concentration of iso‐α‐acids in the different beer brands presented the same trend with that of their relative IBU, thus revealing the potency of our method in the assessment of beer bitterness. The impact of temperature and sunlight was assessed by separately monitoring the modifications of the EEMs after 5 h exposition to 40°C temperature and sunlight respectively. Noticeably a variation of the peaks intensity of the iso‐α‐acids, carbonyl and polyphenols compounds were observed, accompanied by a decrease of the alcohol content, thus indicating beer aging. This method can be useful for the identification and monitoring of beer state during the technological production cycle and storage. Practical Application The present work demonstrates the potency of the fluorescence technique used together with chemometric methods to give valuable information on beer bitterness. Development of rapid quantitative methods for beer bitterness assessment is of great importance for brewing industries.

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