Non-invasive Raman spectroscopy with wavefront shaping and wavelength modulation to quantify methanol in bottled spirits

Abstract Non-destructive, on-site screening methods capable of molecular analysis directly through commercial packaging remain a significant challenge for safety, security, and quality assurance. Here, we introduce an original non-invasive photonics approach based on Raman spectroscopy that combines wavefront shaping with wavelength modulation. The wavefront shaping acts to limit the signal contribution from the packaging, while wavelength modulation further suppresses fluorescence to enhance the method’s sensitivity. As a result of this judicious combination, we are able to enhance the signal-to-noise ratio of the Raman scattering obtained through the packaging up to 12-fold. We demonstrate the capability of the system by quantifying methanol in bottled spirits. Our method achieves quantification of methanol through coloured spirit bottles with a limit of detection of 0.2% (v/v) methanol in 40% ethanol, well below the reported maximum tolerable methanol concentration of 2% (v/v). In contrast to previous approaches, this method remains robust across a diverse range of coloured glass bottles, validated by measurements on real spirit bottles and samples. More broadly, this geometry establishes a versatile Raman sensing platform for assessing authenticity, composition, and contaminants directly through packaging.