Time-resolved Raman spectroscopy for non-invasive detection through non-transparent materials

A study was conducted to demonstrate the use of time-resolved Raman spectroscopy (TRRS) for non-invasive detection through non-transparent materials. TRRS techniques relied on short laser pulses and gated detection to make the discrimination, while deeper Raman photons arrived at the detector later and helped in the selective collection of these photons by delaying the opening of a short detector gate. The short gate width used in TRRS considerably reduced fluorescence and it was found that TRRS measurements using an intensified charge-coupled device (ICCD) device to create a gate of 250 ps, provided better selectivity over spatially offset Raman spectroscopy (SORS) in sub-surface measurements on a mm-cm depth scale. The ability to obtain chemical information through opaque, diffusely-scattering layers showed the potential for a number of fields, including forensics and security screening.