Rapid 3D chemical‐specific imaging of minerals using stimulated Raman scattering microscopy

Abstract

Raman microscopy, which offers chemical‐specific imaging, has important applications in geological sciences. Conventional Raman imaging, however, is challenged by long acquisition times and can be overwhelmed by sample fluorescence. Here, we present the first applications of stimulated Raman scattering (SRS) microscopy, a nonlinear optical Raman technique, to samples of mineralogical interest. Combined with second harmonic generation microscopy, SRS offers a multimodal tool for rapid imaging of mineral samples with chemical specificity, structural sensitivity, and excellent three‐dimensional resolution. Our spectral focusing implementation allows for very rapid scanning of Raman spectral lineshapes, with an adjustable spectral resolution (set here to 25 cm−1) and an overall tuning range of 400–4500 cm−1. In mineralogical applications, this wide‐tuning range offers hyperspectral imaging of both trapped organics, via the CH region (~2900 cm−1), and the lower frequency (<1000 cm−1) ‘fingerprint’ modes important for mineral identification. The simultaneously acquired second harmonic generation image reveals details of the local crystallinity of non‐centrosymmetric minerals such as quartz. As opposed to single‐spectral‐point imaging, we emphasize the importance of tuning over the Raman lineshape while imaging, to unambiguously distinguish the resonant Raman response from nonresonant background signals. Based on the range of samples studied here, we believe that multimodal SRS microscopy will become a valuable imaging tool in the earth sciences, particularly in mineralogy, petroleum, and mineral resources research. ©2017 Her Majesty the Queen in Right of Canada Journal of Raman Spectroscopy ©2017 John Wiley & Sons, Ltd.