Molecules Brilliantly Illuminated

An artistic view of frequency conversion from near-infrared to mid-infrared through a nonlinear crystal. (Source: A. Gelin)

Molecules are the building blocks of life. They control our bio­rhythm, and they can also reflect our state of health. Researchers led by Ferenc Krausz at the Labora­tory for Atto­second Physics LAP – a joint venture between Ludwig-Maxi­milians-Univer­sität LMU and the Max Planck Institute for Quantum Optics MPQ in Munich – want to use brilliant infrared light to study molecular disease markers in much greater detail, for example to faci­litate early stage cancer diag­nosis. The team has developed a powerful femto­second light source which emits at wave­lengths between 1.6 and 10.2 micro­meters. This instrument should make it possible to detect organic molecules present in extremely low concen­trations in blood or aspirated air.

Myriads of molecules react in highly specific ways to light of certain wave­lengths in the mid-infrared region. By absorbing particular wave­lengths, each type of molecule in a sample imprints a specific signa­ture on the trans­mitted beam, which serves as a molecular finger­print. With a source of broadband mid-infrared light one detects the finger­prints of many molecular structures at once – in a sample of blood or aspirated air, for example. If the sample contains marker molecules that are asso­ciated with specific disease states, these too will reveal their presence in the spectrum of the trans­mitted infrared light. LAP physicists have now con­structed such a light source, which covers the wave­lengths between 1.6 and 10.2 microns. The laser system exhibits watt-level average output power, and is well focusable which results in a highly brilliant infrared light source. This feature enhances the ability to detect mole­cules present in extremely low concen­trations. In addition, the laser can produce trains of femto­second pulses, which makes it possible to carry out time-resolved as well as low-noise and highly- precise measure­ments.

At present, infrared spectro­scopy is often based on the use of inco­herent light, which provides coverage of the whole mid-infrared region. However, the relatively low brilliance of the beam produced by inco­herent sources markedly reduces the ability to detect very weak molecular finger­prints. Synchro­tron radiation produced in particle acce­lerators can alter­natively be used, but such faci­lities are in short supply and are ex­tremely expensive. However, laser-based methods can generate even brighter beams than synchro­trons do. The physicists have now succeeded in building a coherent light source which produces brilliant laser light over a broad spectral region in the infrared range. That used to be the major drawback of laser sources. Moreover, the new system has a much smaller footprint and is far less costly than a synchro­tron: it fits on a large table.

“Of course, there is still a long way to go until we can diagnose cancer at much early stage than at present. We need a better under­standing of disease markers and we have to design an effi­cient way to quantify them, for example,” says Marcus Seidel, one of the researchers involved in the project. “But now having signi­ficantly improved light sources available, we can begin to tackle these issues.” Moreover, the new laser system will find appli­cations in areas beyond the bio­sciences. After all, the precise obser­vation of molecules and their trans­formations is at the core of both chemistry and physics too. (Source: LMU)

Reference: M. Seidel et al.: Multi-watt, multi-octave, mid-infrared femtosecond source, Sci. Adv. 4, eaaq1526 (2018); DOI: 10.1126/sciadv.aaq1526

Link: Laboratory for Attosecond Physics LAP, Ludwig-Maximilians-Universität München, Garching, Germany

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