Researchers have developed a unique high-resolution imaging method that
can capture mid-infrared spectral images of fast events or dynamic
processes that take place on the order of milliseconds. This spectral
range is used for many applications because it can reveal the detailed
chemical composition of a sample.
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Caption: Researchers developed a new system that uses frequency conversion to shift an entire mid-IR image into the near-infrared wavelength range while preserving the spatial information. The system can be used to look for the chemical specific signatures of cancer and other diseases. Credit: Peter Tidemand-Lichtenberg, DTU Fotonik
“This novel approach could one day be used to prescreen medical biopsies
to identify the ones that need closer examination,” said Peter
Tidemand-Lichtenberg, a member of the research team from DTU
Fotonik in Denmark. “It could be used to look for the chemical
signatures of cancer and other diseases in ways that would increase the
accuracy and speed of diagnoses.”
A multi-institutional group of researchers describe the new imaging
approach in Optica,
The Optical Society’s (OSA)
journal for high-impact research. They also demonstrate some of the
technique’s potential applications by imaging a gas flow and
distinguishing cancerous and normal samples of esophageal tissue.
“Although mid-infrared spectroscopy is recognized as a powerful tool for
chemical analysis, its applicability has been hampered by a lack of
affordable light sources and sensitive detectors,” said
Tidemand-Lichtenberg. “To overcome this barrier, we used an approach
that translates information from the mid-infrared region, where the
chemical signatures are most distinct, to the near-infrared, where
today’s camera technology is most mature and sensitive.”
Practical mid-infrared spectroscopy
The researchers drew on a process known as nonlinear frequency
conversion in which energy is added to a photon to change its
wavelength, and hence its color. Although frequency conversion, or
upconversion, is often used to change the wavelength of a laser’s
output, the researchers from DTU Fotonik developed a detection system
that could shift an entire mid-IR image into the near-infrared
wavelength range while preserving all the spatial information.
The system incorporates a new mid-infrared light source developed by
collaborators from The Institute of Photonic Sciences (ICFO).
This single-wavelength light source can be tuned to different
wavelengths and it also uses frequency conversion to generate the
mid-infrared light. In fact, the researchers used the same pulsed
near-infrared laser for two things: to generate the tunable mid-IR light
and to achieve the image upconversion.
“This approach yields high peak power pulses in perfect synchronism,
eliminating the need for sophisticated temporal control of the pulses,
leading to images with a good signal-to-noise ratio,” explained
Tidemand-Lichtenberg. “In addition, our optical setup is designed in a
way that requires very little post-processing after the images are
Imaging fast events and complex samples
The researchers demonstrated the imaging speed of their new mid-infrared
upconversion spectroscopy approach by tuning the illumination laser to
match the peak absorption of a gas flow and acquiring a video with 40
images per second.
They also conducted a pilot study, headed by the team members from Exeter
University, in which the system was used to evaluate cancerous and
healthy esophageal tissue samples. They found that morphology and
spectral classification using their system matched well with the
standard stained histopathology images.
“Our upconversion imaging approach is generic and constitutes a major
simplification in realizing video-frame-rate, mid-infrared monochromatic
imaging,” said Tidemand-Lichtenberg. “The spectral information provided
by this technique could be combined with machine learning to enable
faster, and possibly more objective, medical diagnostics based on
chemical signatures without the need for staining.”
The research project was funded by the European Commission’s Innovative
Training Networks and involved a collaborative team of researchers from
The Institute of Photonics Sciences (ICFO) in Spain and DTU Fotonik as
well as Exeter University and Gloucestershire
Hospitals NHS Foundation Trust, both from the United Kingdom.
Paper: S. Junaid, S. Chaitanya Kumar, M. Mathez, M. Hermes, N.
Stone, N. Shepherd, M. Ebrahim-Zadeh, P. Tidemand-Lichtenberg, C.
Pedersen, “Video-rate, mid-infrared hyperspectral upconversion imaging,” Optica,
6, 6, 702-708 (2019).
Optica is an open-access, online-only journal dedicated to the
rapid dissemination of high-impact peer-reviewed research across the
entire spectrum of optics and photonics. Published monthly by The
Optical Society (OSA), Optica provides a forum for pioneering
research to be swiftly accessed by the international community, whether
that research is theoretical or experimental, fundamental or applied. Optica
maintains a distinguished editorial board of more than 50 associate
editors from around the world and is overseen by Editor-in-Chief Alex
Gaeta, Columbia University, USA. For more information, visit Optica.
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