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Infrared sensing made visible: Combining infrared light sources and upconversion sensors for improved sensitivity in medical applications and gas analysis

Periodic Reporting for period 2 - Mid-TECH (Infrared sensing made visible: Combining infrared light sources and upconversion sensors for improved sensitivity in medical applications and gas analysis)

Reporting period: 2017-01-01 to 2018-12-31

The Mid-TECH project is an MSCA Innovative Training Network, providing training for 15 Early Stage Researchers (ESRs) working towards a doctoral degree. The project Consortium comprised 6 academic institutions and 2 companies, and was coordinated by Technical University of Denmark (DTU). The Mid-TECH programme aimed to combine novel mid-infrared (mid-IR) light sources, mid-IR upconversion detection and mid-IR applications.

The mid-IR wavelength range is an emerging and important new research frontier. Its general importance relates to a multitude of mid-IR industrial and biomedical sensor applications. Chemical fingerprints of most complex molecules such as those found in food, human tissue or combustion compounds all have vibrational absorption features in the mid-IR, thus identifiable through mid-IR spectroscopy. Incidentally, also the fundamental absorption bands of gas molecules are located in the mid-IR enabling novel instrumentation for mid-IR gas spectroscopy allowing for measurement of small concentrations. This is relevant for applications like “leak-tests” or remote sensing of greenhouse gases.

The main obstacle for the exploitation of the mid-IR optical range has been a lack of efficient mid-IR light sources and sensitive mid-IR detectors/imaging. In Mid-TECH we have gathered the best European academic and industrial partners to show that in a combined effort, both technological shortcomings can be overcome, paving the way for novel instrumentation for industry and society.

Mid-TECH has had an ambitious set of objectives both in relation to science and training:

• Train a group of 15 highly skilled ESRs forming a new generation of networked scientists
• Develop and discover new technologies for the mid-IR
• Technology transfer from university to industry
• Promote new innovation and entrepreneurial behaviour
• Demonstrate novel instrumentation for society and industry

Main actions: The Mid-TECH programme has produced almost 50 ISI indexed publications and 50+ conference contributions, the equivalent of approximately 500 pages of digested research results, covering diverse aspects of mid-IR technologies and applications. In the context of an ITN project, it is interesting to note that one third of the published Mid-TECH ISI publications have more than one beneficiary/partner on the authors’ list, underlining the collaborative and synergetic nature of Mid-TECH. For a comprehensive overview, please refer to the list of publications at the Mid-TECH website.

Scientifically the ambitious objectives formulated in the Mid-TECH application have been very successful. Deviations have been mostly in the form of “to what extent” an objective has been accomplished. This we find reasonable; otherwise, we would not have been ambitious enough. Mid-TECH has been highly experimental in nature and has produced a long list of new light sources and sensing principle, addressing novel mid-IR applications.

The training activities in the form of summer schools, secondments and training at host universities have been completed and formed the basis of the ESRs’ PhD theses.
The Mid-TECH project has motivated the development of novel laser light sources in previously inaccessible spectral regions out to 18 µm, and in particular at wavelengths beyond 4 µm, where conventional laser technologies are not easily available, and where existing sources cannot meet the demands for many applications because of limited output power or the inability to operate at all time scales. High power diode lasers with fast single mode properties have been devised with several nm tuning for new applications.

Upconversion detection and imaging has been explored experimentally in different configurations for mid-IR detection and hyperspectral imaging. The extreme fast response of the nonlinear crystal used has allowed Mid-TECH to demonstrate imaging from CW down to the 100 femtosecond regime, thus opening new avenues for ultra-fast imaging. A comprehensive theory has been developed guiding future initiatives. Upconversion of mid-IR Optical Parametric Oscillators (OPOs), Quantum Cascade Lasers and thermal radiation has been realised; each described in terms of their characteristic parameters. High spectral brightness, broadband mid-IR super continuum lasers have been combined with upconversion using a highly versatile and stable electronical locking scheme, to lock two independent, pulsed, light sources together at the 50 picosecond scale. This has allowed for a new generation of upconversion implementations.

The unique combination of OPO sources or Quantum Cascade Lasers (QCLs) with upconversion techniques during the Mid-TECH has opened up new avenues for the realization of imaging and spectroscopy systems having new capabilities in the mid-IR, and their exploitation for various applications including medical diagnostics, safety, and environmental monitoring. A prominent example of such instrumentation is a novel mid-IR upconversion device based on illumination with a high-power picosecond OPO, which now provides mid-IR upconversion imaging at video frame-rate for the first time.
A long list of novel instrumentation and findings have been realised during Mid-TECH. Below are listed a few examples central to the objectives set out in the Mid-TECH programme.

A video-frame rate upconversion imaging system has been realized using a standard CCD camera, in synchronism with the crystal rotation of an upconversion system. This system is capable of acquiring 64 kpixels upconverted mid-infrared images in a mere 2.5 ms, without the need for post-processing. This approach is generic in nature and constitutes a major simplification in realizing video-frame rate hyperspectral imaging in the mid-IR.

Based on the mentioned setup, a pilot study on oesophageal tissues samples from a tissue microarray was presented in the 3 to 4 µm wavelength range using computer-assisted classification. Comparing the stained sections evaluated by a pathologist to those obtained by either Fourier Transformed IR (FTIR) spectroscopy or by 3 to 4 µm upconversion hyperspectral imaging, based on machine learning, shows great promise for future research pointing towards potential clinical translation.

An improved upconversion detector which outperforms an InGaAs-based Avalanche Photodetector (APD) for long-range Differential Absorption Lidar (DIAL) measurements of atmospheric methane (CH4) has been demonstrated in close collaboration with the German Aerospace Center (DLR) near Munich, Germany. The backscatter signals from the atmosphere in ranges of several kilometres were detected by both the upconversion detector developed in Mid-TECH and the existing InGaAs APD, implemented in DLR’s instrumentation. It was experimentally confirmed that the upconversion detector achieves better performance in terms of signal-to-noise, thus constituting a novel alternative for climate research.
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Mid-TECH ESRs and supervisors at Berlin summer school March 2016