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Laser pulses enable high-sensitivity molecular fingerprinting

23 Sep 2015

ICFO and MPQ/LMU develop light source with unprecedented sensitivity to identify tell-tale signs of cancer.

Researchers from the Attoscience and Ultrafast Optics Group led by Prof. Jens Biegert, from Barcelona’s Institute for Photonic Sciences, in collaboration with the Laboratory for Attosecond Physics at the Max Planck Institute for Quantum Optics and Ludwig-Maximilians-Universität in Munich, have developed a “record-breaking” broadband and coherent infrared light source.

The peak brilliance of this light source makes it an ultrasensitive detector for the infrared molecular fingerprint region, ideal for detecting minute changes in the spectral features from cells or tissue which are tell-tale signs of DNA mutation or the presence of cellular malfunctions such as cancer. The group’s work has just been published in Nature.

The mid-range of infrared wavelengths is an extremely important range of the electromagnetic spectrum since the wavelength of such light can resonantly excite molecular vibrations. Consequently, shining this type of electromagnetic radiation through a sample leaves the resonant fingerprints in the spectrum allowing identification. The absence of light sources that cover enough of the infrared spectrum with sufficient brilliance to detect minute concentrations originating from onco-metaboloids has been a significant challenge in cancer detection, says the ICFO and MPQ/LMU group.

Now, the new light source exerts extreme control over mid-wave infrared laser light with unrivalled peak brilliance and single-shot spectral coverage between 6.8µm and 16.4 µm. The emitted radiation is fully coherent and emitted at 100 MHz. Each laser pulse has a duration of 66fs which is so short that the electric field oscillates only twice. These characteristics, in combination with its coherence, make the light source a compact and ultrasensitive molecular detector.

No synchrotron required

Prof. Jens Biegert and his colleagues at ICFO are currently investigating molecular sensitivity for the identification of cancer biomarkers on the single cell level using all optical techniques in the mid-wave infrared wavelength range.

The Nature paper abstract states, “Powerful coherent light with a spectrum spanning the mid-infrared spectral range is crucial for a number of applications in natural as well as life sciences, but so far has only been available from large-scale synchrotron sources. The group has developed a compact apparatus that generates pulses with a sub-two-cycle duration and with an average power of 0.1W and a spectral coverage of 6.8–16.4μm (at −30dB).

“The demonstrated source combines, for the first time in this spectral region, a high power, a high repetition rate and phase coherence. The MIR pulses emerge via difference-frequency generation (DFG) driven by the nonlinearly compressed pulses of a Kerr-lens mode-locked ytterbium-doped yttrium aluminium garnet (Yb:YAG) thin-disc oscillator. The resultant 100 MHz MIR pulse train is hundreds to thousands of times more powerful than state-of-the-art frequency combs that emit in this range and offers a high dynamic range for spectroscopy in the molecular fingerprint region and an ideal prerequisite for hyperspectral imaging as well as for the time-domain coherent control of vibrational dynamics."

About the Author

Matthew Peach is a contributing editor to optics.org.

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