Bench-top IR spectromicroscope quality rivals synchrotron

29 Mar 2018

France-developed laser source for infrared chemical imaging is a promising tool for detailed early medical diagnosis.

A new type of bench-top, optical fibre-based laser source can be used used for high spatial resolution infrared micro-spectroscopy and chemical imaging rivaling, and in some regard even surpassing, the performances achieved at large-scale synchrotron facilities, say its developers.

Sébastien Février, reader at the University of Limoges, France and researcher at XLIM (a joint unit between the French research agency CNRS and the university), and his team have demonstrated the device, as reported in Optica.

Synchrotrons are accelerator facilities that provide powerful infrared light used for analyzing the chemical content of biological tissues with micrometer scale resolution.

This high precision chemical imaging technique enables an early diagnosis of pathologies such as cirrhosis and cancer. However, up to now, the very high cost of ownership and limited availability of synchrotron sources has hindered the deployment of chemical imaging technique in the hospital.

Février commented, “Replacing the synchrotron with a compact laser source, which covers the wavelength range identified as relevant by initial synchrotron studies, could unleash the potential of this technique and ease its implementation in the hospital, thus accelerating access to diagnosis and treatment.”

The development has involved a consortium including researchers from XLIM and the synchrotron Soleil in Saclay as well as engineers from the company Novae, a start-up founded in 2013 by researchers from the University of Limoges.

Novae targets industrial and scientific markets such as laser-based bio-imaging and materials micro-processing. The infrared laser is now part of Novae’s portfolio of products. The infrared laser called “Coverage” is part of Novae’s portfolio of products.

Effective and economical

The abstract of the Optica paper explains the operation of Fourier-transform infrared spectromicroscopy and the advantages of the new Limoges technique:

“This technique combines the spatial resolution of optical microscopy with the spectral selectivity of vibrational spectroscopy. Synchrotron sources can provide diffraction-limited beams in the infrared, and therefore synchrotron-based FTIR spectromicroscopy is nowadays an indispensable tool for biology and materials science studies where high spatial resolution is required,” it states

“To date, the low brightness of thermal emitters or high temporal coherence and narrow bandwidth or tunability of laser sources have hindered the progress of bench-top FTIR spectromicroscopy.

But Fevrier’s Limoges and XLIM group says it has demonstrated “that fiber-based supercontinuum sources in the mid-infrared enable fast spectral mapping of localized material properties with close to diffraction-limited resolution (3×3×3 μm), paving the way to table-top, on-demand, fast, and highly spatially resolved studies.

“We have illustrated these capabilities by imaging thin sections of human liver samples and compare the results and performance with those obtained using a synchrotron source.”

Fevrier’s group concludes, "We have demonstrated, in focusing on the spectral region centered on 3.5 μm, the possibility of performing infrared spectromicroscopy measurements using a custom supercontinuum laser source. Our study shows that the Signal-to-Noise Ratio obtainable with [our] laser source is comparable to or surpasses those available with a synchrotron source in shorter acquisition times even at very small aperture sizes.

“Although the spectral bandwidth of the presented supercontinuum laser is highly limited in comparison to the thermal and especially the synchrotron source, it is clear that specific applications will benefit from the possibility of diffraction-limited infrared spectromicroscopy using such bench-top sources. These bench-top sources will enable faster turnaround and open the way for the application of FTIR spectromicroscopy in time-sensitive, on-demand applications such as medical diagnosis.”