Hyperspectral Imaging Using Laser Excitation for Fast Raman and Fluorescence Hyperspectral Imaging for Sorting and Quality Control Applications

Florian Gruber,Stefan Kaskel,Philipp Wollmann,Wulf Grählert

doi:10.3390/jimaging4100110

Florian Gruber, Stefan Kaskel + Show 2 more

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https://doi.org/10.3390/jimaging4100110

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Abstract

A hyperspectral measurement system for the fast and large area measurement of Raman and fluorescence signals was developed, characterized and tested. This laser hyperspectral imaging system (Laser-HSI) can be used for sorting tasks and for continuous quality monitoring. The system uses a 532 nm Nd:YAG laser and a standard pushbroom HSI camera. Depending on the lens selected, it is possible to cover large areas (e.g., field of view (FOV) = 386 mm) or to achieve high spatial resolutions (e.g., 0.02 mm). The developed Laser-HSI was used for four exemplary experiments: (a) the measurement and classification of a mixture of sulphur and naphthalene; (b) the measurement of carotenoid distribution in a carrot slice; (c) the classification of black polymer particles; and, (d) the localization of impurities on a lead zirconate titanate (PZT) piezoelectric actuator. It could be shown that the measurement data obtained were in good agreement with reference measurements taken with a high-resolution Raman microscope. Furthermore, the suitability of the measurements for classification using machine learning algorithms was also demonstrated. The developed Laser-HSI could be used in the future for complex quality control or sorting tasks where conventional HSI systems fail.

Highlights

Hyperspectral imaging (HSI) technologies are increasingly being used in the fields of remote sensing [1], agriculture [2,3], pharmaceuticals [4,5], and medicine [6,7]
Methods use broadband lighting for a sufficient excitation in the whole spectral range of interest, while other methods, such as laser-induced fluorescence (LIF) and Raman his, are not very common in the field of macroscopic HSI, they are widely used for microscopic imaging [13,14,15]
The experiments carried out show that the described Laser-HSI system makes it possible to measure the Raman or fluorescence spectra of relatively large sample areas, with a high spatial resolution and in a relatively short amount of time

Summary

Introduction

Hyperspectral imaging (HSI) technologies are increasingly being used in the fields of remote sensing [1], agriculture [2,3], pharmaceuticals [4,5], and medicine [6,7]. Hyperspectral imaging methods are mainly used in the ultraviolet (UV), visible (VIS) and near-infrared (NIR) spectral ranges, because they are reasonably inexpensive, readily available, and ideally suited and proven for on-line or in-line quality control [11,12]. These methods allow a fast and extensive inspection of samples or continuous processes. Common HSI methods use broadband lighting for a sufficient excitation in the whole spectral range of interest, while other methods, such as laser-induced fluorescence (LIF) and Raman his, are not very common in the field of macroscopic HSI, they are widely used for microscopic imaging [13,14,15].

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