Search

Tunable laser spectroscopy (TLS) combined with mid-infrared imaging is a powerful tool for a sensitive and quantitative visualization of gas leaks. This work deals with standoff methane leak detection within 2 m by an interband cascade laser (3270 nm wavelength) and an infrared camera. The concept demonstrates visualization of methane leakage rates down to 2 ml/min by images and sequences at frame rates up to 125 Hz. The gas plume and leak can be localized and quantified within a single image by direct absorption spectroscopy (DAS). The HITRAN database allows a calibration-free, pixelwise determination of the concentration in ppm*m. The active optical imaging concept showed pixelwise sensitivities around 1 ppm*m.

Mid-infrared imaging and tunable laser spectroscopy were combined to obtain a hyperspectral gas camera for detecting methane leaks. With the setup a detection limit of better than 10 ppm-m and a leakage flow rate of less than 0.5 ml/min methane has been achieved.

Laser haben durch die Fortschritte in der Herstellung, Qualität und breiten Anwendbarkeit erfolgreich Einzug die optische Online- und Inline-Prozessanalysentechnik gehalten. Es wird gezeigt, welche Möglichkeiten sich durch den Einsatz von laserbasierten Methoden für die Gasanalytik ergeben. Dies wird anhand von Beispielen aus der Infrarotspektroskopie und Raman-Spektroskopie demonstriert. Mit der Raman-Spektroskopie in hohlen photonischen Kristallfasern lassen sich geringe Gaskonzentrationen mit Messzeiten im Sekundenbereich detektieren. Mit Quantenkaskadenlasern können Methanemissionen im Spurenbereich aus der Ferne nachgewiesen werden und mithilfe von Lasern und nichtlinear-optischen Komponenten lassen sich hochempfindliche ungekühlte Infrarotdetektoren für die Gasanalyse realisieren.

Bulk high-throughput experiments allow the exploration of unknown alloy systems for novel permanent magnet phases. This multilevel concept is threefold. Search field prioritization is based on physical, technological, and economic aspects to identify promising systems in advance. Efficient synthesis is based on heterogeneous nonequilibrium states to scan the most interesting part of the phase diagram of one alloy system by one sample. An efficient analysis is based on the characteristic domain structure of hard magnetic phases to evaluate the magnetic properties and industrial relevance of the novel phases. The efficiency of the elaborate concept is demonstrated for the well-known ternary system Fe-Nd-B and then applied to discover novel phases for permanent magnets.

Pulsed nonlinear-optical upconversion is used for mid-infrared signal detection. A setup for both mid-infrared generation and upconversion based on a single pump laser enables sensitive light detection and is utilized for gas spectroscopy. With the demonstrated pulsed setup, quantum efficiencies above 80 % for the upconversion of a Gaussian beam signal and 25 % for the upconversion of backscattered radiation are achieved and in agreement with theoretical predictions. Combined with efficient background suppression due to spectral and temporal gating, this results in highly sensitive detection of the infrared signals. As a demonstration of application, the presented system is used for methane sensing in an open path geometry, highlighting the potential for stand-off leak detection with a concentration resolution better than 1.5 ppm·m.

Bulk high-throughput experiments allow the exploration of unknown alloy systems for novel permanent magnet phases. This multilevel concept is threefold. Search field prioritization is based on physical, technological, and economic aspects to identify promising systems in advance. Efficient synthesis is based on heterogeneous nonequilibrium states to scan the most interesting part of the phase diagram of one alloy system by one sample. An efficient analysis is based on the characteristic domain structure of hard magnetic phases to evaluate the magnetic properties and industrial relevance of the novel phases. The efficiency of the elaborate concept is demonstrated for the well-known ternary system Fe-Nd-B and then applied to discover novel phases for permanent magnets.

Signal upconversion by sum frequency generation is presented as a tool for fast, low-noise sensing of infrared radiation. Methane detection is demonstrated for laser-based and thermal illumination. Applicability towards further laser-based detection methods is considered.

The primary all- trans to 13- cis chromophore isomerization of the light driven chloride pump halorhodopsin has been studied by means of transient absorption spectroscopy in the visible and mid-infrared regime at a time resolution of better than 100 and 220 fs, respectively. The picosecond vibrational dynamics are dominated by two time constants, i.e., 2 and 7.7 ps in accordance with the biphasic decay of the retinal excited electronic state and electronic ground state formation with 1.5 and 6.6 ps. The transient vibrational spectra of the participating electronic states strongly suggest the existence of two distinct S 1 populations as a result of an early branching reaction. It is shown that the 13- cis product is formed with the fast time constant, whereas the all- trans educt state is repopulated via both time constants. Concomitant protein dynamics are indicated by spectral changes on a similar time scale in the amide region.

Femtosecond time-resolved transient absorption spectroscopy was employed to characterize for the first time the primary photoisomerization dynamics of a bacterial phytochrome system in the two thermally stable states of the photocycle. The 85-kDa phytochrome Cph1 from the cyanobacterium Synechocystis PCC 6803 expressed in Escherichia coli was reconstituted with phycocyanobilin (Cph1-PCB) and phycoerythrobilin (Cph1-PEB). The red-light-absorbing form Pr of Cph1-PCB shows an approximately 150 fs relaxation in the S(1) state after photoexcitation at 650 nm. The subsequent Z-E isomerization between rings C and D of the linear tetrapyrrole-chromophore is best described by a distribution of rate constants with the first moment at (16 ps)(-1). Excitation at 615 nm leads to a slightly broadened distribution. The reverse E-Z isomerization, starting from the far-red-absorbing form Pfr, is characterized by two shorter time constants of 0.54 and 3.2 ps. In the case of Cph1-PEB, double-bond isomerization does not take place, and the excited-state lifetime extends into the nanosecond regime. Besides a stimulated emission rise time between 40 and 150 fs, no fast relaxation processes are observed. This suggests that the chromophore-protein interaction along rings A, B, and C does not contribute much to the picosecond dynamics observed in Cph1-PCB but rather the region around ring D near the isomerizing C(15) [double bond] C(16) double bond. The primary reaction dynamics of Cph1-PCB at ambient temperature is found to exhibit very similar features as those described for plant type A phytochrome, i.e., a relatively slow Pr, and a fast Pfr, photoreaction. This suggests that the initial reactions were established already before evolution of plant phytochromes began.

The currently highest-performance Fe-Nd-B magnets show limited cost-effectiveness and lifetime due to their rare-earth (RE) content. The demand for novel hard magnetic phases with more widely available RE metals, reduced RE content or, even better, completely free of RE metals is therefore tremendous. The chances are that such materials still exist given the large number of as yet unexplored alloy systems. To discover such phases, an elaborate concept is necessary which can restrict and prioritize the search field while making use of efficient synthesis and analysis methods. It is shown that an efficient synthesis of new phases using heterogeneous non-equilibrium diffusion couples and reaction sintering is possible. Quantitative microstructure analysis of the domain pattern of the hard magnetic phases can be used to estimate the intrinsic magnetic parameters (saturation polarization from the domain contrast, anisotropy constant from the domain width, Curie temperature from the temperature dependence of the domain contrast). The probability of detecting TM-rich phases for a given system is high, therefore the approach enables one to scan through even higher component systems with one single sample. The visualization of newly occurring hard magnetic phases via their typical domain structure and the correlation existing between domain structure and intrinsic magnetic properties allows an evaluation of the industrial relevance of these novel phases.

The currently highest-performance Fe-Nd-B magnets show limited cost-effectiveness and lifetime due to their rare-earth (RE) content. The demand for novel hard magnetic phases with more widely available RE metals, reduced RE content or, even better, completely free of RE metals is therefore tremendous. The chances are that such materials still exist given the large number of as yet unexplored alloy systems. To discover such phases, an elaborate concept is necessary which can restrict and prioritize the search field while making use of efficient synthesis and analysis methods. It is shown that an efficient synthesis of new phases using heterogeneous non-equilibrium diffusion couples and reaction sintering is possible. Quantitative microstructure analysis of the domain pattern of the hard magnetic phases can be used to estimate the intrinsic magnetic parameters (saturation polarization from the domain contrast, anisotropy constant from the domain width, Curie temperature from the temperature dependence of the domain contrast). The probability of detecting TM-rich phases for a given system is high, therefore the approach enables one to scan through even higher component systems with one single sample. The visualization of newly occurring hard magnetic phases via their typical domain structure and the correlation existing between domain structure and intrinsic magnetic properties allows an evaluation of the industrial relevance of these novel phases.

Laser spectroscopy is a powerful tool for analyzing small molecules, i.e. in the gas phase. In the mid-infrared spectral region quantum cascade lasers (QCLs) have been established as the most frequently used laser radiation source. Spectroscopy of larger molecules in the gas phase, of complex mixtures, and analysis in the liquid phase requires a broader tuning range and is thus still the domain of Fourier transform infrared (FTIR) spectroscopy. However, the development of tunable external cavity (EC) QCLs is starting to change this situation. The main advantage of QCLs is their high spectral emission power that is enhanced by a factor of 10(4) compared with thermal light sources. Obviously, transmission measurements with EC-QCLs in strongly absorbing samples are feasible, which can hardly be measured by FTIR due to detector noise limitations. We show that the high power of EC-QCLs facilitates spectroscopy beyond simple absorption measurements. Starting from QCL experiments with liquid samples, we show results of fiber evanescent field analysis (FEFA) to detect pesticides in drinking water. FEFA is a special case of attenuated total reflection spectroscopy. Furthermore, powerful CW EC-QCLs enable fast vibrational circular dichroism (VCD) spectroscopy of chiral molecules in the liquid phase - a technique which is very time consuming with standard FTIR equipment. We present results obtained for the chiral compound 1,1'-bi-2-naphthol (BINOL). Finally, powerful CW EC-QCLs enable the application of laser photothermal emission spectroscopy (LPTES). We demonstrate this for a narrowband and broadband absorber in the gas phase. All three techniques have great potential for MIR process analytical applications.

Femtosecond time-resolved optical absorption experiments reveal that the changes of the excited electronic state dynamics observed between bacteriorhodopsin wild type and the single mutant R82A are...

Sensitive and fast identification of drugs or drug precursors is important and necessary in scenarios like baggage or container check by customs or police. Fraunhofer IPM is developing a laser spectrometer using external cavity quantum cascade lasers (EC-QCL) to obtain mid-infrared (IR) absorption spectra in the wavelength range of the specific vibrational bands of amphetamines and their precursors. The commercial EC-QCL covers a tuning range of about 225 cm -1 within 1.4 s. The system could be used for different sample types like bulk samples or liquid solutions. A sampling unit evaporates the sample. Because of small sample amounts a 3 m long hollow fiber with an inner volume smaller than 1ml is used as gas cell and wave guide for the laser beam. This setup is suitable as a detector of a gas chromatograph instead of a standard detector (TCD or FID). The advantage is the selective identification of drugs by their IR spectra in addition to the retention time in the gas chromatographic column. In comparison to Fourier Transform IR systems the EC-QCL setup shows a good mechanical robustness and has the advantage of a point light source. Because of the good fiber incoupling performance of the EC-QCL it is possible to use hollow fibers. So, a good absorption signal is achieved because of the long optical path in the small cell volume without significant dilution. In first laboratory experiments a detection limit in the microgram range for pseudo ephedrine is achieved.

Bacteriorhodopsin, reconstituted with a sterically "locked" retinal chromophore, BR5.12, has frequently been used to elucidate elementary photoinduced processes in the native pigment bacteriorhodopsin. In this work, the vibrational response of BR5.12 to photoexcitation is investigated by means of femtosecond time-resolved mid-infrared and UV-vis spectroscopy. The electronically excited state of BR5.12 decays with a time constant of 18 ps. Neither in the UV-vis nor in the mid-IR spectral region are indications found for chromophore photoproducts, besides the full recovery of the electronic ground state. However, vibrational bands are observed at around 1660 and 1550 cm(-1) in the protein amide I and amide II band regions, respectively. They are formed within a few picoseconds or even instantaneously. Thus, they appear faster than the S1 decay and persist for at least 130 ps, i.e., for much longer than the S1 lifetime. These findings strongly suggest that the observed bands must be assigned to protein vibrations and that they are not caused by a photoinduced temperature rise. Thus, for the first time, ultrafast protein vibrational changes are detected in BR5.12, that are not associated with isomerization. Possibly they can be related to the enhanced chemical reactivity of photoactivated BR5.12 reported in the literature. In wild-type bacteriorhodopsin, bands with very similar spectral and kinetic characteristics are observed, suggesting that they might originate from a similar mechanism which is not isomerization. A plausible mechanism is a polarization induced protein conformational change, as discussed in the literature.

Sensitive and fast detection of explosives remains a challenge in many threat scenarios. Fraunhofer IPM works on two different detection methods using mid-infrared absorption spectroscopy in combination with quantum cascade lasers (QCL). 1. stand-off detection for a spatial distance of several meters and 2. contactless extractive sampling for short distance applications. The extractive method is based on a hollow fiber that works as gas cell and optical waveguide for the QCL light. The samples are membranes contaminated with the explosives and real background. The low vapor pressure of TNT requires a thermal desorbtion to introduce gaseous TNT and TATP into the heated fiber. The advantage of the hollow fiber setup is the resulting small sample volume. This enables a fast gas exchange rate and fast detection in the second range. The presented measurement setup achieves a detection limit of around 58 ng TNT and 26 ng TATP for 1 m hollow fiber. TATP - an explosive with a very high vapor pressure in comparison to TNT or other explosives - shows potential for an adequate concentration in gas phase under normal ambient conditions and thus the possibility of an explosive detection using open path absorption of TATP at 8 μm wavelength. In order to lower the cross sensitivities or interferents with substances with an absorption in the wavelength range of the TATP absorption the probe volume is checked synchronously by a second QCL emitting beside the target absorption wavelength. In laboratory measurements a detection limit of 5 ppm*m TATP are achieved.

Spectroscopic concentration measurements of oxygen at high pressures are limited by the effect of pressure broadening and line mixing. These effects strongly depend on the gas mixture in which the oxygen concentration has to be determined as the pressure broadening coefficients of different gases vary over a large range. Line broadening coefficients of the oxygen a-band for a large number of different gases are well known in the literature, but up to now there is, to our best knowledge, no experimental data available which describes the line broadening of oxygen in hydrogen. In respect to a possible application for online-monitoring of oxygen in hydrogen electrolysis we have measured the pressure broadening coefficient of the oxygen P9P9 line in hydrogen and compared with the theoretical model. To confirm the result, also measurements of the well known broadening coefficient of oxygen in helium were accomplished. Measurements were obtained using laser absorption spectroscopy with vertical-cavity surface-emitting lasers in a Herriott-Cell with 15 m path length adapted for vacuum pressures.

Stand-off and extractive explosive detection methods for short distances are investigated using mid-infrared laser spectroscopy. A quantum cascade laser (QCL) system for TATP-detection by open path absorption spectroscopy in the gas phase was developed. In laboratory measurements a detection limit of 5 ppm*m was achieved. For explosives with lower vapor pressure an extractive hollow fiber based measurement system was investigated. By thermal desorption gaseous TATP or TNT is introduced into a heated fiber. The small sample volume and a fast gas exchange rate enable fast detection. TNT and TATP detection levels below 100 ng are feasible even in samples with a realistic contaminant background.

We present an overview of the current status of laser diodes used in remote sensing application including novel laser types such as single mode emitting DFB lasers operating at wavelengths up to 3 μm and quantum cascade lasers for mid infrared absorption spectroscopy. In particular we will focus on applications of these devices in the frame of safeguard measures and home security.

The all-trans to 13-cis photoisomerization of the retinal chromophore in bacteriorhodopsin (bR) acts as a strong steric and electronic perturbation for the protein environment, thereby driving the proton pump mechanism. Photoexcitation and torsional movement are expected to be paralleled by various intra- and intermolecular relaxation processes. According to femtosecond (fs) time-resolved optical absorption spectroscopy the electronic ground state is reached after about 500 fs (J) [1-4], which then relaxes on a 3 ps time-scale to the K-state with the chromophore in 13-cis configuration.

The vibrational dynamics of the retinal chromophore all-trans–to–13-cis photoisomerization in bacteriorhodopsin has been studied with mid-infrared absorption spectroscopy at high time resolution (about 200 femtoseconds). After photoexcitation of light-adapted bacteriorhodopsin, the transient infrared absorption was probed in a broad spectral region, including vibrations with dominant C–C, C=C, and C=NH stretching mode amplitude. All photoproduct modes, especially those around 1190 reciprocal-centimeters that are indicative for a 13-cis configuration of the chromophore, rise with a time constant of ∼0.5 picosecond. The results presented give direct vibrational-spectroscopic evidence for the isomerization taking place within 0.5 picosecond, as has been suggested by previous optical femtosecond time-resolved experiments but questioned recently by picosecond time-resolved vibrational spectroscopy experiments.

For the first time, the marker-bands for the retinal chromophore isomerization in the fingerprint region were studied. Their temporal evolution clearly shows that with a time constant of ca. 500 fs isomerization essentially has taken place. The vibrational pattern characteristic for a 13-cis chromophore configuration is established before K-formation (cp. the step-scan FTIR BR570-K difference spectrum (15)). Further molecular processes as structural relaxation and vibrational cooling are suggested to contribute to the time constant of 1-2 ps, observed for the partial recovery of the bleach signals.

The environmental scanning electron microscope (ESEM) offers improved capabilities for coupling a scanning electron microscope (SEM) with an in situ laser device compared with conventional SEMs. Such coupling generally enables, for example, the observation of laser glazing effects or high-temperature behaviour as well as thermal shock behaviour of materials and devices. In an ESEM, decomposition caused by high-temperature gas reactions can additionally be studied while monitoring the gaseous environment online with a mass spectrometer attached to the specimen chamber. In this work, we demonstrate the capabilities of an in situ laser system suitable for heating specimen in an in situ deformation stage, thus enabling the further study of the mechanical properties of materials far beyond temperatures accomplished by thermal heating stages.