Stimulated Raman scattering (SRS) microscopy is a label-free quantitative chemical imaging technique that has demonstrated great utility in biomedical imaging applications ranging from real-time stain-free histopathology to live animal imaging. However, similar to many other nonlinear optical imaging techniques, SRS images often suffer from low signal to noise ratio (SNR) due to absorption and scattering of light in tissue as well as the limitation in applicable power to minimize photodamage. We present the use of a deep learning algorithm to significantly improve the SNR of SRS images. Our algorithm is based on a U-Net convolutional neural network (CNN) and significantly outperforms existing denoising algorithms. More importantly, we demonstrate that the trained denoising algorithm is applicable to images acquired at different zoom, imaging power, imaging depth, and imaging geometries that are not included in the training. Our results identify deep learning as a powerful denoising tool for biomedical imaging at large, with potential towards in vivo applications, where imaging parameters are often variable and ground-truth images are not available to create a fully supervised learning training set.

Chloride salts have been proposed to exist on the surface of Europa based on some geochemical predictions of the ocean composition as well as some interpretations of data from the Galileo spacecraft. To help elucidate our understanding of Europa’s surface composition, we have conducted a study of frozen chloride salt brines prepared under simulated Europa surface conditions (vacuum and temperature) using both near-infrared (NIR) and Raman spectroscopies. The latter was used to determine the hydration states of various chloride salts as a function of the temperature, while NIR spectroscopy of identically prepared samples was used to provide reference reflectance spectra of the identified hydrated salts. We further investigated the stability of the formed hydrated salts under vacuum and ultraviolet (UV) irradiation. Our results indicate that, at temperatures ranging from 80 to 233 K, (i) NaCl·2H2O is formed from the freezing of NaCl brines, (ii) freezing of KCl solutions does not form KCl hydrates, (iii) freezing of MgCl2 solutions forms a stable hexahydrate, and (iv) freezing of CaCl2 solutions forms a hexahydrate. Dehydration of the salts was observed as temperatures were increased, leading to a succession of hydration states in the case of CaCl2 (hexahydrate → tetrahydrate → dihydrate). Similarly, UV irradiation is also found to induce progressive loss of water from the hydration shell of NaCl, CaCl2, and MgCl2 hydrates.

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