Fraunhofer-Institut für Photonische Mikrosysteme IPMS

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Non-resonant MOEMS mirror for laser cavity-length tuning

2023 , Dreyhaupt, André , Oswald, Lucas , Graßhoff, Thomas , Hugger, Stefan , Grahmann, Jan

High resolution spectroscopy via tunable lasers usually requires CW operation with mode-hop-free wavelength tuning. To suppress mode hopping by laser resonator-length tuning, Fraunhofer IPMS developed a novel electrostatic non-resonant translational micromirror. The combination of this device with a MOEMS grating within an external-cavity MIR QCL results in a miniaturized module that meets the requirements of high-resolution spectroscopy. The translational micromirror features a 5-mm aperture, an arbitrary actuator stroke of up to 120 µm and multiple independent electrostatic actuators to compensate for tip or tilt up to 350 µrad. We compare characterization and FEA simulation data, demonstrating the unique characteristics and the operational capability for a variety of applications.

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Microoptoelectromechanical systems-based external cavity quantum cascade lasers for real-time spectroscopy

2018 , Butschek, Lorenz , Hugger, Stefan , Jarvis, Jan-Philip , Härtelt, Marko , Merten, André , Schwarzenberg, Markus , Grahmann, Jan , Stothard, David , Warden, Matthew , Carson, Christoph , Macarthur, John , Fuchs, Frank , Ostendorf, Ralf , Wagner, Joachim

We report on mid-IR spectroscopic measurements performed with rapidly tunable external cavity quantum cascade lasers (EC-QCLs). Fast wavelength tuning in the external cavity is realized by a microoptoelectromechanical systems (MOEMS) grating oscillating at a resonance frequency of about 1 kHz with a deflection amplitude of up to 10 deg. The entire spectral range of the broadband QCL can therefore be covered in just 500  ms, paving the way for real-time spectroscopy in the mid-IR region. In addition to its use in spectroscopic measurements conducted in backscattering and transmission geometry, the MOEMS-based laser source is characterized regarding pulse intensity noise, wavelength reproducibility, and spectral resolution.

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Real-time spectroscopy enabled by external cavity QCLs with MOEMS diffraction gratings

2017 , Butschek, Lorenz , Hugger, Stefan , Jarvis, Jan-Philip , Härtelt, Marko , Merten, André , Grahmann, Jan , Boskovic, Dusan , Fuchs, Frank , Ostendorf, Ralf , Schilling, Christian , Rattunde, Marcel , Wagner, Joachim

In this contribution, we report on real-time mid-IR spectroscopy enabled by rapidly tunable External Cavity Quantum Cascade Lasers (EC-QCLs). High speed spectral scanning in a Littrow-type resonator is realized by employing a resonantly driven micro-opto-electro-mechanical-systems (MOEMS) grating as wavelength selective element. Oscillating at a frequency of 1 kHz with mechanical amplitudes of up to 10°, the MOEMS grating is able to cover the whole spectral range provided even by broad-gain QCL chips in just 500 ms. In addition to the high spectral scanning frequency, the MOEMS approach also allows for a miniaturized and rugged design of the EC-QCL. An evaluation of this laser source with regard to spectral reproducibility of consecutive scans, pulse intensity noise, and spectral resolution will be given. Furthermore, we present spectroscopic measurements in backscattering as well as in transmission geometry, demonstrating the real-time capability in different scenarios.

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Widely tuneable quantum cascade lasers for spectroscopic sensing

2015 , Wagner, J. , Ostendorf, R. , Grahmann, Jan , Merten, André , Hugger, S. , Jarvis, J.P. , Fuchs, F. , Boskovic, D. , Schenk, Harald

In this paper recent advances in broadband-tuneable mid-infrared (MIR) external-cavity quantum cascade lasers (EC-QCL) technology are reported as well as their use in spectroscopic process analysis and imaging stand-off detection of hazardous substances, such as explosive and related precursors. First results are presented on rapid scan EC-QCL, employing a custom-made MOEMS scanning grating in Littrow-configuration as wavelength-selective optical feedback element. This way, a scanning rate of 1 kHz was achieved, which corresponds to 2000 full wavelength scans per second. Furthermore, exemplary case studies of EC-QCL based MIR spectroscopy will be presented. These include time resolved analysis of catalytic reactions in chemical process control, as well as imaging backscattering spectroscopy for the detection of residues of explosives and related precursors in a relevant environment.

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Advances of MOEMS-based external cavity QCLs

2019 , Härtelt, Marko , Hugger, Stefan , Butschek, Lorenz , Schilling, Christian , Merten, André , Schwarzenberg, Markus , Dreyhaupt, André , Grahmann, Jan , Rattunde, Marcel , Ostendorf, Ralf

The combination of broadly tunable quantum cascade laser chips in an external cavity (EC-QCL) with a micro- electromechanical system (MEMS) scanner with integrated diffraction grating as wavelength-selective element allows for the development of extremely compact and robust spectroscopy systems. Resonant MOEMS grating scanners enable spectral tuning rates of hundreds of wavenumbers per millisecond and consequently broad-band spectroscopy with millisecond temporal resolution. Also non-resonant (quasi-static) MOEMS grating scanners are possible, providing scanrates of tens of Hz as well as static setting of arbitrary wavelengths, as common for mechanically driven EC lasers, while keeping the small MOEMS footprint, ruggedness, and low power consumption. Here, we give a progress report on the latest developments on MOEMS-based EC-QCLs made by Fraunhofer IAF and IPMS. We will highlight two of our latest developments: A non-resonant MOEMS EC-QCL version that allows arbitrary scan frequencies up to few ten Hertz, as well as static operation. Furthermore, we present the application of a resonantly driven cw-MOEMS-EC-QCL with cavity-length control to enable fast high-resolution spectroscopy over a spectral range of >100 cm-1, offering new possibilities for spectroscopy on complex gas mixtures.

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Towards a compact, portable, handheld device for contactless real-time standoff detection of hazardous substances

2018 , Carson, Christopher , Macarthur, John , Warden, Matthew , Stothard, David , Butschek, Lorenz , Hugger, Stefan , Jarvis, Jan-Philip , Härtelt, Marko , Ostendorf, Ralf , Merten, André , Schwarzenberg, Markus , Grahmann, Jan , Ratajczyk, Marcin

Here we report our recent achievements towards a compact, portable, handheld device for contactless real-time detection and identification of explosives and hazardous substances via reflectance spectroscopy in the 7.5 mm - 10 mm spectral region. The mid-IR spectroscopic measurement principle relies on selective illumination of the target using broadly tunable external cavity quantum cascade lasers (EC-QCLs). A resonant micro-opto-electro-mechanical systems(MOEMS) grating enables fast wavelength tuning in the external cavity, allowing the full spectral scan to be completed in <1 ms. The diffusely backscattered light's intensity dependence on illumination wavelength provides spectroscopic information to identify threat compounds via our spectral database, containing a large number of materials relevant in a security context. We present a handheld portable, albeit tethered, device capable of real-time identification of hazardous substances at a range of 1 m. We will outline future improvements to increase the system's usability, such as integrated computing power, automated focusing to that allow use over a range of detection distances and spatial scanning for background subtraction.

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Hyperspectral image analysis for standoff trace detection using IR laser spectroscopy

2016 , Jarvis, J.P. , Fuchs, F. , Hugger, S. , Ostendorf, R. , Butschek, L. , Yang, Q. , Dreyhaupt, A. , Grahmann, J. , Wagner, J.

In the recent past infrared laser backscattering spectroscopy using Quantum Cascade Lasers (QCL) emitting in the molecular fingerprint region between 7.5 um and 10 um proved a highly promising approach for stand-off detection of dangerous substances. In this work we present an active illumination hyperspectral image sensor, utilizing QCLs as spectral selective illumination sources. A high performance Mercury Cadmium Telluride (MCT) imager is used for collection of the diffusely backscattered light. Well known target detection algorithms like the Adaptive Matched Subspace Detector and the Adaptive Coherent Estimator are used to detect pixel vectors in the recorded hyperspectral image that contain traces of explosive substances like PETN, RDX or TNT. In addition we present an extension of the backscattering spectroscopy technique towards real-time detection using a MOEMS EC-QCL.

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Quasi-statischer MOEMS-Gitterscanner zum spektralen Durchstimmen eines MIR-Quantenkaskadenlasers

2019 , Merten, André , Schroedter, Richard , Dreyhaupt, André , Graßhoff, Thomas , Schwarzenberg, Markus , Hugger, Stefan , Schilling, Christian , Grahmann, Jan , Ostendorf, Ralf

Breitbandig durch stimmbare Infrarotstrahlung im mittleren Wellenlängenbereich von etwa 3bis 10 mm bzw. 1000 bis 3200 Wellenzahlen kann effizient zur Spektroskopie gasförmiger, flüssiger oder fester Stoffe und Gemische verwendet werden. In diesem Beitrag wird ein neuartiges quasi-statisches mikro-opto-elektromechanisches (MOEMS) Gitter zur spektralen Durchstimmung einer Infrarotlichtquelle auf Basis eines Quantenkaskadenlasers (QCL) vorgestellt. Das Konzept vereint die Vorteile breitbandiger Quellen mit denen kohärenter Laserquellen in einem miniaturisierten Aufbau. Das quasistatische Antriebsprinzip erlaubt im Gegensatz zur resonanten Bewegung das Scannen mit vorgegebenen Trajektorien und einstellbarer Geschwindigkeiten und damit eine höhere spektrale Auflösung. Zur Stabilisierung der Bewegung wird MOEMS-Bauelement mittels integrierter Positionssensoren geregelt. Dieser Beitrag stellt die dynamischen Eigenschaften eines MOEMS-Mikrospiegels mit integriertem Beugungsgitter, sowie die damit gewonnenen experimentellen Ergebnisse beim Durchstimmen eines QCL im Bereich von 4150 bis 4600 nm Wellenlänge vor.

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Miniaturisierte Laserlichtquelle für Infrarotspektroskopie

2017 , Merten, A. , Dreyhaupt, A. , Hugger, S. , Butschek, L. , Grahmann, J. , Schwarzenberg, M. , Ostendorf, R. , Jarvis, J. , Härtelt, M.

Breitbandig durchstimmbare Infrarotstrahlung im mittleren Wellenlängenbereich von etwa 3 bis 10 mm bzw. 1000 bis3200 Wellenzahlen ist ein hochinteressantes Mittel zur spektroskopischen Untersuchung gasförmiger, flüssiger oderfester Stoffe und Gemische. In diesem Beitrag wird eine weit durchstimmbare Infrarotlichtquelle auf Basis eines Quantenkaskadenlasers(QCL) und eines mikro-opto-elektro-mechanischen (MOEMS) Gitters vorgestellt. Dieses Konzeptvereint Vorteile breitbandiger Quellen mit Vorteilen kohärenter Laserquellen in einem miniaturisierten Aufbau. Als mögliche Anwendungen werden aktuell berührungslose und zerstörungsfreie Echtzeit-Identifikation explosiver Substanzen sowie online und inline Detektion von Öl-Kontaminationen in Wasser untersucht und entwickelt.

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Recent advances and applications of external Cavity-QCLs towards hyperspectral imaging for standoff detection and real-time spectroscopic sensing of chemicals

2016 , Ostendorf, R. , Butschek, L. , Hugger, S. , Fuchs, F. , Yang, Q. , Jarvis, J. , Schilling, C. , Rattunde, M. , Merten, A. , Grahmann, J. , Boskovic, D. , Tybussek, T. , Rieblinger, K. , Wagner, J.

External-cavity quantum cascade lasers (EC-QCL) are now established as versatile wavelength-tunable light sources for analytical spectroscopy in the mid-infrared (MIR) spectral range. We report on the realization of rapid broadband spectral tuning with kHz scan rates by combining a QCL chip with a broad gain spectrum and a resonantly driven micro-opto-electro-mechanical (MOEMS) scanner with an integrated diffraction grating in Littrow configuration. The capability for real-time spectroscopic sensing based on MOEMS EC-QCLs is demonstrated by transmission measurements performed on polystyrene reference absorber sheets, as well as on hazardous substances, such as explosives. Furthermore, different applications for the EC-QCL technology in spectroscopic sensing are presented. These include the fields of process analysis with on- or even inline capability and imaging backscattering spectroscopy for contactless identification of solid and liquid contaminations on surfaces. Recent progress in trace detection of explosives and related precursors in relevant environments as well as advances in food quality monitoring by discriminating fresh and mold contaminated peanuts based on their MIR backscattering spectrum is shown.

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