Press release

Quantum-inspired terahertz spectroscopy with visible photons.

Experimental AuCau for quantum op:cial layer thickness measurement in the terahertz spectral range by measuring visible photons © Fraunhofer ITWM

Even the application-oriented institutes of the Fraunhofer-Gesellschaft cannot do without their own basic research. The Fraunhofer Institute for Industrial Mathematics ITWM in Kaiserslautern, for example, is working on the detection of terahertz waves based on new quantum optical methods. Already a year ago, the renowned journal "Science Advances" reported on first successes. Now, the OPTIMAS researcher and head of the Department of Materials Characterization and Testing at Fraunhofer ITWM Prof. Dr. Georg von Freymann and his colleagues succeeded in reaching the next milestone.


Technically challenging spectral range.

Embedded in the lead project QUILT (Quantum Methods for Advanced Imaging Solutions), several Fraunhofer institutes are working on quantum-based measurement systems for different spectral ranges. In doing so, they are exploiting the properties of correlated photons in the still young research field of quantum sensor technology. This is because, despite the steady advancement of terahertz technology in recent years, detection in this spectral range without cooling or expensive pulsed lasers remains a major technical challenge. For the visible spectral range, on the other hand, we carry high-resolution detectors around with us almost daily - in the form of smartphones - in our pockets.

Quantum optical measurement method for layer thickness
A new measurement method can help here: With the help of quantum optical methods, the properties of photons (light particles) in the terahertz spectral range can be transferred to the visible photons, which are easier to detect. The physical principle behind this is that pairs of correlated photons of different wavelengths are generated in a nonlinear crystal - in this case one of them in the visible and one in the terahertz spectral range. Subsequently, these photons are first separated and then cleverly superimposed again, with the terahertz photons transferring their properties to the visible photons.
If the terahertz photons come into contact with a sample in the meantime, they also pass on the collected information about the sample. This method has the advantage that already sophisticated detectors can be used to find the information obtained via the terahertz photons.

Next milestone: spectroscopy
The Kaiserslautern researchers were already able to observe this so-called quantum interference in the terahertz spectral range using visible photons a year ago, demonstrating for the first time the measurement of layer thicknesses. Now, building on their previous findings, they have succeeded in using this measurement method for spectroscopic investigations as well and determining ingredients hidden in wax plates.
For this purpose, they prepared wax plates under controlled conditions with different concentrations of α-lactose monohydrate and para-aminobenzoic acid as additives. These were then placed in the part of the beam path through which only the terahertz photons pass. By measuring the visible photons, it was thus possible to determine the type and amount of additive - without having to detect the terahertz radiation itself.
The scientific success of the Kaiserslautern physicists was published in the journal "Optica," published by the Optical Society, and is freely available online here.

 

Questions answered:

Prof. Dr. Georg von Freymann,

TU Kaiserslautern 
Department of Physics,

Chair of Optical Technologies and Photonics.


Phone: 0631 205-5225 


E-mail: georg.freymann(at)physik.uni-kl.de 

 

Press contact via Fraunhofer Institute ITWM:

Ilka Blauth Fraunhofer Institute for Industrial Mathematics ITWM

Fraunhofer-Platz 1

67663 Kaiserslautern

Phone +49 631 31600-4674

presse(at)itwm.fraunhofer.de

www.itwm.fraunhofer.de

Experimental AuCau for quantum op:cial layer thickness measurement in the terahertz spectral range by measuring visible photons © Fraunhofer ITWM