Capturing the Spectral Fingerprint

TU Graz-physicist Birgitta Schultze-Bernhardt intends to use the START Prize funds to further develop electronic fingerprint spectroscopy (ELFIS) for application in the UV range. (Source: FWF / Hoffmann)

Electronic fingerprint spectroscopy (ELFIS), is the name of the new measuring method that Birgitta Schultze-Bernhardt now wants to develop further in the framework of the START programme of the Austrian Science Fund (FWF). The aim is to study light-induced chemical reactions, for example those triggered by the ultraviolet light of the sun in atmospheric trace gases. Understanding photochemical processes in the atmosphere can be the basis for successful measures against climate change.

The core of ELFIS is the combination of two so-called frequency combs. An optical frequency comb is created when a laser (usually working in the infrared range) emits ultrashort laser pulses with simultaneously different optical frequencies, i.e. different colours, at constant intervals. This tool was invented by Theodor Hänsch, who was awarded the Nobel Prize in Physics for it in 2005. Hänsch was Birgitta Schultze-Bernhardt’s doctoral supervisor and long-time collaborator at the Max Planck Institute of Quantum Optics, where Schultze-Bernhardt worked intensively on frequency comb spectroscopy from 2006 to 2012. In this spectroscopic method, the frequency combs are sent through a material sample, and the molecules inside the material absorb the frequency combs to varying degrees. The result is a kind of fingerprint that provides information about the chemical components of the sample and its optical properties. Dual-comb spectroscopy is currently growing into one of the most popular laser measurement techniques because it can be used to measure the vibrations and rotations of molecules in the infrared spectral range.

ELFIS should make such observations possible in the UV range in the future, since the frequencies in this spectrum excite not only molecular vibrations but also electrons. “And electrons are crucial for every chemical bond,” explains Schultze-Bernhardt. However, such investigations would require a laser that emits directly in the UV range, which is not yet available. “We therefore use non-linear processes to shift the light from a particularly powerful laser source into this high-energy range and generate two UV frequency combs. In other words, we convert infrared light into ultraviolet light,” she says. Initial attempts to do so have already been successful.

In a first phase, a spectrometer is currently being developed that operates in the visible (green) spectral range and can detect trace gases such as nitrogen dioxide. Finally, a spectrometer in the near UV spectral range could be realistic within a year. At the end of the phased plan, Schultze-Bernhardt hopes to have a spectrometer “with which we will be able to view light-induced processes in a broad spectral range, in real time with high spectral and temporal resolution at the same time.” (Source: TU Graz)

Links: Dual Comb Spectroscopy (B. Schultze-Bernhardt), Institut of Experimental Physics, Graz University of Technology, Graz, AustriaLeading Women Programme at Graz University of Technology, Graz, AustriaSTART Programme, Austrian Science Fund FWF, Vienna, Austria


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