Tunable filter for Hyperspectral Raman Imaging

Sebastien Blais-Ouellette, CEO and Founder of Photon etc. talks to AZoNano about tunable filter technology for hyperspectral Raman imaging. 

Photon etc’s tunable filter technology is quite unique - can you discuss the principles behind how this system works?

The key element of our Bragg Tuneable Filter is the use of volume holographic gratings in a non-dispersive configuration to filter light one wavelength at a time. These holograms allow us to continuously vary the resonant wavelength by changing the angle of the incident light, making it possible to continuously tune the image wavelength. By scanning the entire visible or SWIR region, we can build unique hyperspectral imagers having a very high efficiency and a high spectral resolution.

Laser Line Tunable Filter by Photon etc.

How did the features of your filter technology help in the design of your Raman imaging systems?

These two important features, high efficiency and spectral resolution, of our technology are paramount for Raman imaging. First, the very high efficiency, up to 80%, is perfectly suited to the faint Raman signal. For traditional spectrometer-based systems, it is a constant challenge to keep a high throughput while having the spectral resolution compatible with Raman spectroscopy.

It is on the other hand completely natural with the Bragg Tuneable Filter. In addition, the customizable spectral resolution and spectral range give us the possibility of changing them according to the application. For example, a researcher developing graphene will not have the same needs in terms of excitation and acquisition wavelengths compared to someone trying to observe Raman shifts in biological tissues.

How does your Raman system differ from other Raman Microscopy systems?

Basically, our Imagers acquire full megapixel images at a single wavelength, and scan the wavelength, while traditional systems scan the sample to reconstruct the image. The main problem with traditional Raman imaging systems is therefore the speed.

Even with the most efficient scanning systems, tens of thousands of movements are necessary to reconstruct even small (200 x 200) images, compare to a few hundred spectral channels for typical Raman spectra.  

Our modus operandi is usually called “global imaging” by comparison to “push-broom” or raster scanning systems. The gain in speed is also improved by the possibility of selecting small spectral regions around relevant Raman peaks instead of gathering the complete spectrum for each point of the image like traditional spectrometer based technologies. In other words, maps that would take hours to acquire, can be done in minutes with our technology.

The RIMA Raman hyperspectral imaging system by Photon etc.

What research sectors has this technology already been used in?

At the moment, Raman imaging is mainly used by material scientists, biomedical researchers and some drug developers. This is due to the limitations in terms of speed, as discussed above, but applications such as live Raman imaging for surgery applications, forensics and anti-counterfeiting will now be able to use this technology with great efficiency.

Two natural consequences of global imaging are very appreciated by material scientist. The evenly distributed illumination and the low illumination density allow a better understanding of the physical properties of nanomaterial or photovoltaic for example.

In biological application on the other hand, the lower illumination density decreases the phototoxicity. This allows studies over longer period, or with higher wavelength excitation lasers.

What kind of nanomaterials have you used to explore the performance of your technology in Raman imaging?

Carbon nanotubes and graphene were the main focus as a start. First, we have a long experience with carbon nanotubes since a few years ago we had developed resonant Raman spectroscopy systems to characterize radial breathing modes of these particles.

The successes of this project was in fact one of the main arguments for developing an imaging system. In the case of graphene, we know that spectroscopists have been avoiding Raman imaging because it is too slow, but also that if accessible, it would render maps of defects, purity, layer thickness, and many other features.

How will your technology help the spectroscopy market?

For years, Raman spectroscopists have been using non-imaging technologies mainly because the acquisition time of a spectral data cube was prohibitive, so they were limited to point spectroscopy in their research. We now offer them a solution to this problem.

What are the current issues with the application of Raman Spectroscopy in the pharmaceutical industry with relation to diagnostics?

Once again, diagnostics cannot afford to be time-consuming, and up until now, Raman imaging was too slow to imagine the deployment of Raman analyzers in the clinical domain. Of course, there are still enhancements to be done to get there, but the core technology we have developed will get us there.

Can you ­provide some background on Photon etc. and your range of analysis products?

Photon etc. aims to provide each researcher, engineer and technician with access to the latest innovations in optical and photonic instrumentation. As pioneers in Bragg-based hyperspectral imaging, we offer state-of-the-art hyperspectral imaging systems for both macroscopic and microscopic applications. Furthermore, our experience has led us to develop high-end infrared scientific cameras and tunable laser sources.

Where can we find further information on your technology?

Of course, our website is a rich source of information, but you can also contact us directly for more information, [email protected], we are always glad to talk about our technology and even more to learn about new applications we never thought of!

About Sebastien Blais-Ouellette, Ph.D

An Astrophysicist by training, Sébastien Blais-Ouellette is the President and Founder of Photon etc.

While working in the Astronomy Department of the California Institute of Technology (Caltech), he developed a new optical tunable filter technology that allows unique hyperspectral imaging systems.

With numerous scientific papers and patents, and the management of a high tech business, Dr. Blais-Ouellette balances business development and technological activities.