Full vibrational spectroscopy for simultaneous mechanical, structural and chemical analysis

Abstract

Abstract The light scattered inelastically from molecular vibrations occurring at different temporal and spatial scales carries intrinsic physical information about the illuminated sample. Mechanical, structural and chemical properties can be simultaneously retrieved by analyzing the full vibrational spectrum in different frequency ranges, yet strong elastic scattering near the laser frequency typically overwhelms the low-frequency region. Here, we present a method for measuring the full vibrational spectrum from 0.1 to  > 3,500 cm −1 using a Birefringence-Induced Phase Delay filter with high extinction ratio and ultranarrow bandwidth for efficient elastic suppression. Our multimodal, label-free approach enables the simultaneous acquisition of Brillouin, ultra-low-frequency Raman (ULFR), and Raman spectra from the same illumination voxel. We demonstrate the method acquiring Brillouin, ULFR, and Raman spectra from active pharmaceutical ingredients, revealing previously inaccessible distinctions in the amorphous forms of indomethacin and its mixtures with polyvinylpyrrolidone excipients. We further extended our approach to full vibrational imaging by acquiring maps of an ibuprofen tablet. Our findings demonstrate the high sensitivity and specificity of the multimodal platform to analyze chemical content while investigating mechanical and structural heterogeneities. Results open promising avenues in biomedical research and material science where key physical properties can be optically retrieved simultaneously at diffraction-limited spatial resolution.