A line‐scan hyperspectral Raman system for spatially offset Raman spectroscopy

Abstract

Spatially offset Raman spectroscopy (SORS) is a technique that can obtain subsurface layered information by collecting Raman spectra from a series of surface positions laterally offset from the excitation laser. Currently optical fiber probes are used as major tools in SORS measurement, which are either slow (single fiber probe with mechanical movement) or restricted in selecting offset range and interval (fiber probe array). This study proposes a new method to conduct SORS measurement based on a newly developed line-scan hyperspectral Raman imaging system. A 785-nm point laser was used as an excitation source. A detection module consisting of an imaging spectrograph and a charge-coupled device camera was used to acquire line-shape SORS data in a spectral region of À592 to 3015 cm À1 . Using a single scan, the system allowed simultaneous collection of a series of Raman spectra in a broad offset range (e.g. 0-36 mm in two sides of the incident laser) with a narrow interval (e.g. 0.07 mm). Four layered samples were created by placing butter slices with thicknesses of 1, 4, 7, and 10 mm on top of melamine powder, providing different individual Raman characteristics to test the line-scan SORS technique. Self-modeling mixture analysis (SMA) was used to analyze the SORS data. Raman spectra from butter and melamine were successfully retrieved for all four butter-on-melamine samples using the SMA method. The line-scan SORS measurement technique provides a flexible and efficient method for subsurface evaluation, which has potential to be used for food safety and quality inspection.

Raman spectroscopy: techniques and applications in the life sciences

“…Following this, a popular approach to SORS was to use an annular collection scheme, whereby one fixed offset could be collected from all points in the circle around the excitation point with the radius being the desired offset. This is usually implemented by using ring-fibers with a fixed value of offset chosen for a particular application [391,392], though other approaches such as line-based SORS [393] or using a digital micro-mirror device (DMD) placed at a sample-conjugate plane [394] …”

Line-Scan Hyperspectral Imaging Techniques for Food Safety and Quality Applications

“…Line-scan hyperspectral imaging techniques provide a flexible and efficient method for spatially resolved spectroscopy measurement [11,12]. The method collects a series of spectra all together in a broad offset range with a narrow spatial interval using one CCD exposure (Figure 1b).…”

“…Measurement methods using optical fiber probes are either slow (single fiber probe with mechanical movement) or restricted in offset range and interval selection (fiber probe array) for acquiring the spatially resolved spectra. Line-scan hyperspectral imaging techniques provide a flexible and efficient method for spatially resolved spectroscopy measurement [11,12]. The method collects a series of spectra all together in a broad offset range with a narrow spatial interval using one CCD exposure (Figure 1b).…”

Recent advances in linear and non‐linear Raman spectroscopy. Part XI

“…Qin et al reported the development of a line‐scan hyperspectral Raman system for spatially offset Raman spectroscopy (SORS). The line‐scan SORS measurement technique provides a flexible and efficient method for subsurface evaluation, which has potential to be used for food safety and quality inspection . Timmermans and co‐workers described the integration of confocal Raman microscope into a dualbeam focused ion beam scanning electron microscope (FIB SEM).…”