Optics miniaturization strategy for demanding Raman spectroscopy applications

Abstract

Abstract Raman spectroscopy provides non-destructive, label-free quantitative studies of chemical compositions at the microscale as used on NASA’s Perseverance rover on Mars. Such capabilities come at the cost of extremely high requirements for instrumentation. Here we present a centimeter-scale miniaturization using cheap non-stabilized laser diodes, densely-packed optics, and non-cooled small sensors, while the performance is comparable with expensive bulky research-grade Raman systems. It has excellent sensitivity, low power consumption, perfect wavenumber, intensity calibration, and 7cm-1 resolution within the 400–4000 cm-1 range using a built-in reference. We present solutions to Raman miniaturization challenges: laser temperature and power stabilization, reduction of sensor dark noise, compensation on pixel-to-pixel quantum efficiency variation, laser optical isolation and high spectral resolution. Moreover, shifted-excitation Raman difference spectroscopy (SERDS) and spatially offset Raman spectroscopy (SORS) functions are compatible. High performance and versatility are demonstrated in use cases including quantification of methanol in beverages, in-vivo Raman measurements of human skin, quantification of p-coumaric acid and serine in bacterial fermentations, chemical Raman mapping at sub-micrometer resolution, quantitative SERS mapping of the anti-cancer drug methotrexate and in-vitro bacteria identification by Raman mapping. We foresee that the miniaturization will allow realization of super-compact Raman spectrometers for integration in smartphones and medical devices, democratizing Raman technology.