Ultrafast imaging Raman spectroscopy of large-area samples without stepwise scanning

Elmar Schmälzlin,Daniel Bodenmüller,Benito Moralejo,Maxim E Darvin,Gisela Thiede,Martin M Roth

doi:10.5194/jsss-5-261-2016

Abstract

Abstract. Step-by-step, time-consuming scanning of the sample is still the state-of-the-art in imaging Raman spectroscopy. Even for a few 100 image points the measurement time may add up to minutes or hours. A radical decrease in measurement time can be achieved by applying multiplex spectrographs coupled to imaging fiber bundles that are successfully used in astronomy. For optimal use of the scarce and expensive observation time at astronomical observatories, special high-performance spectrograph systems were developed. They are designed for recording thousands of spatially resolved spectra of a two-dimensional image field within one single exposure. Transferring this technology to imaging Raman spectroscopy allows a considerably faster acquisition of chemical maps. Currently, an imaging field of up to 1 cm2 can be investigated. For porcine skin the required measurement time is less than 1 min. For this reason, this technique is of particular interest for medical diagnostics, e.g., the identification of potentially cancerous abnormalities of skin tissue.

Highlights

When monochromatic light impinges on a sample, the inelastically scattered light is wavelength shifted (Raman effect)
In the field of medical diagnostics, imaging Raman spectroscopy is a promising technique for identifying cancerous parts of tissue (Reble et al, 2014; Zhao et al, 2015)
The setup works in essence as if every single fiber were connected to an individual single-channel spectrograph

Summary

Introduction

When monochromatic light impinges on a sample, the inelastically scattered light is wavelength shifted (Raman effect). Raman lines are extremely faint (only a fraction of 1 × 10−7 of the scattered light is Raman scattering). For this reason, the number of practical applications of Raman spectroscopy was for a long time rather limited. Raman lines appear relative to the laser excitation wavelength. When using excitation light at visible wavelengths, the Raman lines always appear in a range where the absorption of water is negligibly small. Raman spectroscopy works well in aqueous environments This turns out to be a key advantage with regard to biological samples. In the field of medical diagnostics, imaging Raman spectroscopy is a promising technique for identifying cancerous parts of tissue (Reble et al, 2014; Zhao et al, 2015). RiverD International B.V., Rotterdam, the Netherlands, http://www.riverd.com, last access 18 May 2016)

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