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Ongoing technological advancements in the field of mid-infrared (MIR) spectroscopy continuously yield novel sensing modalities, offering capabilities beyond traditional techniques like Fourier transform infrared spectroscopy (FT-IR). One such advancement is MIR dispersion spectroscopy, utilizing a tunable quantum cascade laser and Mach–Zehnder interferometer for liquid-phase analysis. Our study assesses the performance of a custom MIR dispersion spectrometer at its current development stage, benchmarks its performance against FT-IR, and validates its potential for time-resolved chemical reaction monitoring. Unlike conventional methods of IR spectroscopy measuring molecular absorptions using intensity attenuation, our method detects refractive index changes (phase shifts) down to a level of 6.1 × 10–7 refractive index units (RIU). This results in 1.5 times better sensitivity with a sevenfold increase in analytical path length, yielding heightened robustness for the analysis of liquids compared to FT-IR. As a case study, we monitor the catalytic activity of invertase with sucrose, observing the formation of resultant monosaccharides and their progression toward thermodynamic equilibrium. Anomalous refractive index spectra of reaction mixtures, with substrate concentrations ranging from 2.5 to 25 g/L, are recorded, and analyzed at various temperatures, yielding Michaelis–Menten kinetics findings comparable to the literature. Additionally, the first-time application of two-dimensional correlation spectroscopy on the recorded dynamic dispersion spectra correctly identifies the mutarotation of reaction products (glucose and fructose). The results demonstrate high precision and sensitivity in investigating complex time-dependent chemical reactions via broadband refractive index changes. [ABSTRACT FROM AUTHOR]

Gallium ion (Ga+) beam damage induced indium (In) precipitation in indium gallium arsenide (InGaAs)/indium aluminium arsenide (InAlAs) multiple quantum wells and its corresponding evolution under electron beam irradiation was investigated by valence electron energy loss spectroscopy (VEELS) and high‐angle annular dark‐field imaging (HAADF) in scanning transmission electron microscopy (STEM). Compared with argon ion milling for sample preparation, the heavier projectiles of Ga+ ions pose a risk to trigger In formation in the form of tiny metallic In clusters. These are shown to be sensitive to electron irradiation and can increase in number and size under the electron beam, deteriorating the structure. Our finding reveals the potential risk of formation of In clusters during focused ion beam (FIB) preparation of InGaAs/InAlAs quantum well samples and their subsequent growth under STEM‐HAADF imaging, where initially invisible In clusters of a few atoms can move and swell during electron beam exposure. LAY DESCRIPTION: In this paper, the evolution of Ga+ implantation induced In precipitation in InGaAs/InAlAs multiple quantum wells under electron beam irradiation was investigated by valence electron energy loss spectroscopy (VEELs), energy dispersive X‐ray spectroscopy (EDXs) and high‐angle annular dark‐field (HAADF) imaging technique based in a probe aberration corrected scanning transmission electron microscope. In contrast to Ar+ ion bombardment, the projectile of focused Ga+ ions is able to trigger the clustering of In interstitials in InGaAs/InAlAs multiple quantum wells, which allows the formation of metallic In precipitates. Afterwards, by exploiting an extensive electron beam rastering on the region of In precipitation, the increase of electron irradiation time could lead to a pronounced swelling of In cluster size. Especially for the region contains In precipitates of several atoms, where the morphology of In cluster is invisible in atomic image. The continuous electron irradiation could give rise to the promotion of In clustering, allowing the structure of In precipitates been resolved by HAADF image. Our finding reveals the potential risk of formation of In precipitates during focused Ga+ ion beam bombarded InGaAs/InAlAs semiconductors and the subsequent evolution of In clustering under electron beam rastering. These findings emphasise the need for caution when studying FIB prepared In‐based III–V quantum well specimens using TEM even in the In(Ga,Al)As system, as the initially formed In‐rich clusters are so small they can remain invisible for some time. [ABSTRACT FROM AUTHOR]

Light-duty vehicle emission regulations worldwide set limits for the following gaseous pollutants: carbon monoxide (CO), nitric oxides (NOX), hydrocarbons (HCs), and/or non-methane hydrocarbons (NMHCs). Carbon dioxide (CO2) is indirectly limited by fleet CO2 or fuel consumption targets. Measurements are carried out at the dilution tunnel with "standard" laboratory-grade instruments following well-defined principles of operation: non-dispersive infrared (NDIR) analyzers for CO and CO2, flame ionization detectors (FIDs) for hydrocarbons, and chemiluminescence analyzers (CLAs) or non-dispersive ultraviolet detectors (NDUVs) for NOX. In the United States in 2012 and in China in 2020, with Stage 6, nitrous oxide (N2O) was also included. Brazil is phasing in NH3 in its regulation. Alternative instruments that can measure some or all these pollutants include Fourier transform infrared (FTIR)- and laser absorption spectroscopy (LAS)-based instruments. In the second category, quantum cascade laser (QCL) spectroscopy in the mid-infrared area or laser diode spectroscopy (LDS) in the near-infrared area, such as tunable diode laser absorption spectroscopy (TDLAS), are included. According to current regulations and technical specifications, NH3 is the only component that has to be measured at the tailpipe to avoid ammonia losses due to its hydrophilic properties and adsorption on the transfer lines. There are not many studies that have evaluated such instruments, in particular those for "non-regulated" worldwide pollutants. For this reason, we compared laboratory-grade "standard" analyzers with FTIR- and TDLAS-based instruments measuring NH3. One diesel and two gasoline vehicles at different ambient temperatures and with different test cycles produced emissions in a wide range. In general, the agreement among the instruments was very good (in most cases, within ±10%), confirming their suitability for the measurement of pollutants. [ABSTRACT FROM AUTHOR]

We have demonstrated a quantum cascade laser (QCL) with a generation frequency of about 3.8 THz, grown by metal-organic vapor phase epitaxy. The multilayer heterostructure for QCLs consists of 185 repetitions of an active module containing four GaAs/Al0.15Ga0.85As quantum wells. The threshold current and threshold voltage of the fabricated QCL were 2.25 kA/cm2 and 19.7 V, respectively. The QCL oscillations were carried out in the multimode regime, and the detection of terahertz radiation continued with an increase in the laser temperature up to 60 K. [ABSTRACT FROM AUTHOR]

An experimental investigation of the dissociation of CO2 in a symmetric pin-to-pin dielectric barrier discharge (DBD) is presented. The reactor geometry allows for an accurate control of the number of filaments (microdischarges) and is used to study the impact of one single filament on the CO2 dissociation. We show the number of filaments per half cycle follows a power-law as a function of the injected power and does not depend on pressure, flow or other process parameters. It is shown that for pressures between 200 and 700 mbar approximately 0.5 W per filament is required and the charge transferred per filament remains constant at 0.5 nC. Furthermore, the dependence of CO2 conversion on only specific energy input (SEI) is shown to be valid down to a single filament. Additionally, by using quantum cascade laser absorption spectroscopy the absolute number of CO molecules produced per filament is measured and is found to be in the range from 5.1011 to 2.1012. The conversion degree of CO2 into CO is estimated to be lower than 0.1% within a single filament and increases with SEI. In the presence of a couple of filaments, the maximum energy efficiency obtained is 25%. A comparison of the conversion degrees in pin-to-pin DBD and plane-to-plane DBD configuration shows that these two reactor geometries follow the same power law. This means the geometry is not the most important parameter in CO2 dissociation in DBDs, but the SEI and thus the number of filaments ignited per unit of time. This result means that the dependence of conversion degree on the SEI can be extended to a single filament. This observation leads to the conclusion that the SEI appears to be valid as a universal scaling parameter down to very low values. [ABSTRACT FROM AUTHOR]

Quantum cascade lasers (QCLs) and interband cascade lasers (ICLs) are widely used as light sources in tunable laser absorption spectroscopy because they emit in the mid-infrared region where many strong and characteristic absorption bands are present. In this paper, we compare the performance of these lasers emitting at about 2310.1 cm–1 to determine an optimal light source for detecting isotopic ratios of carbon dioxide (CO2). Our results show that the QCL has a higher relative intensity noise of up to 15 dBc/Hz compared to the ICL over the entire measured frequency range. In addition, it has a higher frequency fluctuation. However, the maximum tuning range of the QCL is up to 5.2 cm–1 compared to up to 3.8 cm–1 for the ICL. Both lasers lose more than half of their tuning range when the tuning rate is increased to 10 kHz. When measuring the isotope ratio of CO2, an uncertainty in the δ 13 value of σ 13 C , min ICL = 0.17 ‰ was achieved with the ICL and of σ 13 C , min QCL = 0.42 ‰ with the QCL, both at an integration time of 0.2 s. In summary, the QCL is more appropriate for applications that require a larger spectral tuning range, such as the measurement of a complex gas mixture, while the ICL has an excellent signal-to-noise ratio and is therefore better suited for applications that require higher precision. [ABSTRACT FROM AUTHOR]

Featured Application: With RobustATR, we have developed an exceedingly compact and robust infrared attenuated total reflectance (IR-ATR) accessory uniquely integrating substrate-integrated hollow waveguides (iHWG) facilitating efficient coupling to quantum cascade laser (QCL) light sources. This sensing platform is particularly suited for real-world application scenarios. Small and compact mid-infrared devices are of increasing importance, as there are several applications demanding on-site and real-time measurements in harsh real-world scenarios. The RobustATR, an innovative infrared attenuated total reflectance (IR-ATR) accessory, has been developed and tested with exemplary analytes integrating a single-wavelength Fabry–Pérot quantum cascade laser as light source for testing the feasibility of a potentially miniaturized overall sensor design. Successful direct coupling of the laser radiation via substrate-integrated hollow waveguide (iHWG) coupling elements to the sensor interface could be shown, whereby exemplary analytes of environmental and medical relevance were tested, revealing the future potential for real-world applications. [ABSTRACT FROM AUTHOR]

Given the exquisite capability of direct, non-destructive label-free sensing of molecular transitions, IR spectroscopy has become a ubiquitous and versatile analytical tool. IR application scenarios range from industrial manufacturing processes, surveillance tasks and environmental monitoring to elaborate evaluation of (bio)medical samples. Given recent developments in associated fields, IR spectroscopic devices increasingly evolve into reliable and robust tools for quality control purposes, for rapid analysis within at-line, in-line or on-line processes, and even for bed-side monitoring of patient health indicators. With the opportunity to guide light at or within dedicated optical structures, remote sensing as well as high-throughput sensing scenarios are being addressed by appropriate IR methodologies. In the present focused article, selected perspectives on future directions for IR spectroscopic tools and their applications are discussed. These visions are accompanied by a short introduction to the historic development, current trends, and emerging technological opportunities guiding the future path IR spectroscopy may take. Highlighted state-of-the art implementations along with novel concepts enhancing the performance of IR sensors are presented together with cutting-edge developments in related fields that drive IR spectroscopy forward in its role as a versatile analytical technology with a bright past and an even brighter future. [ABSTRACT FROM AUTHOR]

Quantum cascade lasers are versatile light sources in the mid-infrared range for molecular spectroscopy which find a wide range of applications from high-resolution studies to sensing. While devices with either high power or narrow spectral linewidth have previously been reported, there is still a lack of sources combining both of these characteristics which are particularly important for precision measurements of weak spectroscopic transitions. In this article, we describe and characterize a novel master-oscillator power-amplifier distributed-feedback quantum cascade laser designed to fill this gap. At an output power of 300 mW, the device features a free-running linewidth of 1.3 MHz, measured with a frequency discriminator technique, at an emission wavenumber of 2185 cm − 1 . This linewidth is sufficiently narrow to enable a further reduction by a tight lock to a high-Q oscillator. [ABSTRACT FROM AUTHOR]

An innovative mid-infrared spectroscopic sensor system based on quantum cascade lasers has been developed. The system combines the versatility of substrate-integrated hollow waveguides (IHWGs) with the robustness of attenuated total reflection (ATR) crystals employed as internal reflection waveguides for evanescent field sensing. IHWGs are highly reflective metal structures that propagate infrared (IR) radiation and were used as light pipes for coupling radiation into the ATR waveguide. The combined IHWG-ATR device has been designed such that the utmost stability and robustness of the optical alignment were ensured. This novel assembly enables evanescent field absorption measurements at yet unprecedently harsh conditions, that is, high pressure and temperature. Combining these advantages, this innovative sensor assembly is perfectly suited for taking ATR spectroscopy into the field where the robustness of the assembly and optical alignment is essential. Graphical Abstract [ABSTRACT FROM AUTHOR]

We have designed and demonstrated a quantum cascade laser (QCL) based standoff system that utilizes an uncooled mercury cadmium telluride (MCT) detector with lock-in signal processing for chemical identification at a distance of 12.5 meters in indoor ambient light conditions. In the system, a tunable quad-QCL operating (1 MHz) in quasi-continuous wave mode between 8.45 and 10.03 μm (∼1182 to 1000 cm−1) serves as the active mid-infrared source for remotely interrogating mineral, powder, and thin film oil samples including powder mixtures (6, 12.5, 25, and 50%) of crystalline quartz (SiO2) in KBr. Light as reflected from a given sample is collected using a 10-inch (25.4 cm) Dall Kirkham telescope and coupled with ZnSe optics to an uncooled MCT detector. The mixture dependence of the highly transparent KBr and strongly absorbing quartz was found to fit a modified version of the Schatz reflectance model for compacted powder mixtures. All reflectance spectra reported are relative to an Au-coated diffuse reflector. A NIST traceable polystyrene standard reflector was also used to determine the QCL wavelength tuning range and calibration. Graphical Abstract [ABSTRACT FROM AUTHOR]

Quantum cascade lasers are sophisticated devices mostly based on InGaAs/AlInAs/InP heterostructures to improve thermal performance. Their structure consists of a core containing hundreds or even thousands of thin layers, covered on both sides with thick cladding waveguides. Such a laser design creates enormous stresses in the core and can cause degradation of the entire device. An alternative to the thick InP claddings are thin, highly doped InGaAs layers used as plasmonic waveguides. This solution allows to achieve a mode confinement above 50 % even at only 150 nm of the waveguide layer, which is extremely difficult in the case of standard designs. The article presents theoretical simulations concerning the influence of the InGaAs plasmonic layer on the mode confinement. [ABSTRACT FROM AUTHOR]

In this paper, we review the progress of the development and application of external cavity quantum cascade lasers (ECQCLs). We concentrated on ECQCLs based on the wide tunable range for multi-component detection and applications. ECQCLs in the mid-infrared band have a series of unique spectral properties, which can be widely used in spectroscopy, gas detection, protein detection, medical diagnosis, free space optical communication, and so on, especially wide tuning range, the tuning range up to hundreds of wavenumbers; therefore, ECQCLs show great applications potential in many fields. In this paper, the main external cavity structures of ECQCLs are reviewed and compared, such as the Littrow structure, the Littman structure, and some new structures. Some new structures include the intra-cavity out-coupling structure, multimode interference (MMI) structure, and acousto-optic modulator (AOM) control structure. At the same time, the application research of ECQCLs in gas detection, protein detection, and industry detection are introduced in detail. The results show that the use of diffraction gratings as optical feedback elements can not only achieve wide tuning, but it also has low cost, which is beneficial to reduce the complexity of the laser structure. Therefore, the use of diffraction gratings as optical feedback elements is still the mainstream direction of ECQCLs, and ECQCLs offer a further new option for multi-component detection.

GaInAs/AlInAs superlattice play an important role in the epitaxial structure of mid-wave infrared quantum cascade lasers. This paper find the optimal deoxidation temperature point for an InP/Ga 0.31 In 0.69 As/Al 0.64 In 0.36 As quantum cascade laser (QCL) epitaxial process combining MBE (for active cores) and MOCVD (for waveguide cladding) co-growth, and investigate the effect of thermal annealing on this superlattice. Comprehensive multi-technical analysis including atomic force microscopy (AFM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and photoluminescence (PL) confirmed that slow annealing of the structure at a temperature of 480 °C can be properly optimized. The crystal quality and surface smoothness were confirmed, and the changes in element content of the ternary alloy under thermal reaction were analyzed. These results provide an extremely effective reference value for the QCL secondary epitaxial waveguide layer. • Determination of secondary epitaxial deoxygenation temperature point in MBE and MOCVD integrated growth of InP/GaInAs/AlInAsQCLs • Effect of slow thermal annealing on GaInAs/AlInAs superlattices. • Comprehensive analysis of complex and multiple crystal structures of ternary alloys by diversified characterisation tools. [ABSTRACT FROM AUTHOR]

Background and Aims: The main goals were to determine the effectiveness of two commonly used communication-related Quality of Life (QoCL) measures, and the impact of aphasia-related factors on quality of life (QoL) and QoCL in persons with aphasia (PWAs). Method: Twenty-one PWAs ranging from 47 to 91 years of age with post-onset periods of 2 months to 14 years were tested using standardized and criterion-measure tools to assess their language and cognitive functions, QoL, and QoCL. Additionally, participants completed a demographics questionnaire, which also included information on their stroke and the kinds of therapies they had received. Assessments were conducted over two sessions with randomized order of test administrations to control fatigue and order effects. Results and Discussions: Correlation-matrix was used to determine the strength of relations between test measures. The impact of QoL related factors (viz., aphasia severity, cognitive functioning, time post-onset, and therapy received) on QoCL was examined using ANOVAs. The ASHA Quality of Communication Life Scale (ASHA-QCL) had more significant correlations with other QoL measures than the ASHA-Functional Assessment of Communication Skills (ASHA-FACS). Aphasia severity, cognitive deficits, and therapy received contributed significantly to QoL and QoCL in PWAs. Conclusions: Evaluating overall QoL may not fully reveal the QoCL in PWAs. Measuring QoCL specifically is crucial in aphasia interventions, and it is equally important to use sensitive tools that can capture the QoCL effectively. ASHA-QCL was more effective than ASHA-FACS in capturing the QoCL. QoCL must be considered even when working with PWAs with severe aphasias and/or mild cognitive deficits.

Small and compact mid-infrared devices are of increasing importance, as there are several applications demanding on-site and real-time measurements in harsh real-world scenarios. The RobustATR, an innovative infrared attenuated total reflectance (IR-ATR) accessory, has been developed and tested with exemplary analytes integrating a single-wavelength Fabry–Pérot quantum cascade laser as light source for testing the feasibility of a potentially miniaturized overall sensor design. Successful direct coupling of the laser radiation via substrate-integrated hollow waveguide (iHWG) coupling elements to the sensor interface could be shown, whereby exemplary analytes of environmental and medical relevance were tested, revealing the future potential for real-world applications.

Quantum cascade lasers are versatile light sources in the mid-infrared range for molecular spectroscopy which find a wide range of applications from high-resolution studies to sensing. While devices with either high power or narrow spectral linewidth have previously been reported, there is still a lack of sources combining both of these characteristics which are particularly important for precision measurements of weak spectroscopic transitions. In this article, we describe and characterize a novel master-oscillator power-amplifier distributed-feedback quantum cascade laser designed to fill this gap. At an output power of 300 mW, the device features a free-running linewidth of 1.3 MHz, measured with a frequency discriminator technique, at an emission wavenumber of 2185 cm−1. This linewidth is sufficiently narrow to enable a further reduction by a tight lock to a high-Q oscillator.

Background and Aims: The main goals were to determine the effectiveness of two commonly used communication-related Quality of Life (QoCL) measures, and the impact of aphasia-related factors on quality of life (QoL) and QoCL in persons with aphasia (PWAs). Method: Twenty-one PWAs ranging from 47 to 91 years of age with post-onset periods of 2 months to 14 years were tested using standardized and criterion-measure tools to assess their language and cognitive functions, QoL, and QoCL. Additionally, participants completed a demographics questionnaire, which also included information on their stroke and the kinds of therapies they had received. Assessments were conducted over two sessions with randomized order of test administrations to control fatigue and order effects. Results and Discussions: Correlation-matrix was used to determine the strength of relations between test measures. The impact of QoL related factors (viz., aphasia severity, cognitive functioning, time post-onset, and therapy received) on QoCL was examined using ANOVAs. The ASHA Quality of Communication Life Scale (ASHA-QCL) had more significant correlations with other QoL measures than the ASHA-Functional Assessment of Communication Skills (ASHA-FACS). Aphasia severity, cognitive deficits, and therapy received contributed significantly to QoL and QoCL in PWAs. Conclusions: Evaluating overall QoL may not fully reveal the QoCL in PWAs. Measuring QoCL specifically is crucial in aphasia interventions, and it is equally important to use sensitive tools that can capture the QoCL effectively. ASHA-QCL was more effective than ASHA-FACS in capturing the QoCL. QoCL must be considered even when working with PWAs with severe aphasias and/or mild cognitive deficits. [ABSTRACT FROM AUTHOR]

Minerals play an important role in the oil sands extraction efficiency. It is thus important to assess the major mineral abundance in oil sands ores. This paper presents the application of tunable quantum cascade lasers for mid-infrared reflectance spectroscopy on oil sands minerals. The investigations and results show a new tool to determine oil sands mineral type and to determine potentially quartz and clay contents. [ABSTRACT FROM AUTHOR]

Currently semiconductor lasers in the wavelength range from 20 to 60 μm are scarce. HgTe/CdHgTe heterostructures is a potential basis for alternative sources of coherent radiation in this range. We propose that in such structures carrier heating is the main mechanism, which quenches stimulated emission under high excitation intensity. Lower-energy optical excitation is one way to reduce this negative effect. We compare output power vs excitation intensity at pumping wavelengths of 2.3 and 10.6 μm. Comparison shows that longer wavelength leads up to 3 order of magnitude higher total output power at the same number of photons in pulse. At the same time, for structures designed for the wavelengths above 20 μm, the heating is observed even under 10.6 μm pumping. We debate excitation by quantum cascade lasers with low energy of photons to be the main route for further development of HgTe/CdHgTe sources for 20–60 μm wavelength range. [ABSTRACT FROM AUTHOR]

Acquisition of classical absorption spectra of liquids in the mid-IR range with quantum cascade lasers (QCLs) is often limited in sensitivity by noise from the laser source. Alternatively, measurement of molecular dispersion (i.e., refractive index) spectra poses an experimental approach that is immune to intensity fluctuations and further offers a direct relationship between the recorded signal and the sample concentration. In this work, we present an external cavity quantum cascade laser (EC-QCL) based Mach–Zehnder interferometer setup to determine dispersion spectra of liquid samples. We present two approaches for acquisition of refractive index spectra and compare the qualitative experimental results. Furthermore, the performance for quantitative analysis is evaluated. Finally, multivariate analysis of a spectrally complex mixture comprising three different sugars is performed. The obtained figures of merit by partial least squares (PLS) regression modelling compare well with standard absorption spectroscopy, demonstrating the potential of the introduced dispersion spectroscopic method for quantitative chemical analysis. [ABSTRACT FROM AUTHOR]

We demonstrate the performance of a dual frequency comb quantum cascade laser (QCL) spectrometer for the application of vibrational Stark spectroscopy. Measurements performed on fluorobenzene with the dual-comb spectrometer (DCS) were compared to results obtained using a conventional Fourier transform infrared (FT-IR) instrument in terms of spectral response, parameter estimation, and signal-to-noise ratio (S/N). The dual-comb spectrometer provided similar qualitative and quantitative data as the FT-IR setup in 250 times shorter acquisition time. For fluorobenzene, the DCS measurement resulted in a more precise estimation of the fluorobenzene Stark tuning rate ((0.81 ± 0.09) cm−1/(MV/cm)) than with the FT-IR system ((0.89 ± 0.15) cm−1/(MV/cm)). Both values are in accordance with the previously reported value of 0.84 cm−1/(MV/cm). We also point to an improvement of signal-to-noise ratio in the DCS configuration. Additional characteristics of the dual-comb spectrometer applicable to vibrational Stark spectroscopy and their scaling properties for future applications are discussed. [ABSTRACT FROM AUTHOR]

Here, we present a short overview of our implementation of label-free digital pathology by infrared (IR) imaging. We address the major issues to overcome for clinical translation. First, we elucidate that label-free IR imaging not only identifies cancer in tissue sections but also is even able to provide differential diagnostics as exemplified for colorectal and lung cancer. We obtained sensitivities and specificities far above 90% as compared to the gold standard histopathology. The information is obtained label-free, automated and observer independent. We showed that the spectral patterns observed in the infrared corresponds directly to protein alterations in tissue. This was achieved by integrating IR imaging with laser capture microdissection and subsequent proteome analysis. Furthermore, we demonstrated that IR imaging could replace immunohistochemical marker panels for differential diagnosis. Following one of the most important steps towards translation was the reduction of the measurement time, which now matches the time consumed for immediate diagnostics. Finally, we integrate deep neural networks for the automated annotation. All hurdles has been overcome and label-free digital pathology is ready to validate now the approach in clinically relevant unmet medical needs. This will facilitate acceptance of the approach by clinicians and pave the road for clinical translation. [ABSTRACT FROM AUTHOR]

The function of membrane proteins is highly impacted by their membrane environment. One suitable approach to get insights into the interaction-induced dynamics of membrane proteins and lipid membranes is time-resolved infrared (IR) spectroscopy. Conclusions about environmental influences to the system can be drawn by correlating the observed kinetics to the well-characterized photocycles of light-driven transmembrane proton pumps like bacteriorhodopsin (BR). For the investigation of photoreceptor-membrane interactions, also minor changes in the absorption spectra must be resolved. Therefore, we applied IR laser spectroscopy using tunable quantum cascade lasers (QCLs) as IR light source. Several QCLs were implemented in a home-built spectrometer and provide a tunability in a broad spectral region covering protein, chromophore and lipid vibrational modes. Kinetics of the BR photocycle were monitored at single wavenumbers. This study demonstrates the high potential of QCL-based spectroscopy for the application to membrane protein studies. [ABSTRACT FROM AUTHOR]

Abstract Extended wavelength tuning of an IH-QCL (integrated heater quantum cascade laser) is exploited for simultaneous detection of methane and acetylene using direct absorption spectroscopy. The integrated heater, placed within few microns of the laser active region, enables wider wavelength tuning than would be possible with a conventional DFB (distributed feedback) QCL. In this work, the laser current and heater resistor current are modulated simultaneously at 25 kHz to tune the laser over 1279.6–1280.1 cm−1, covering absorption transitions of methane and acetylene. The laser is characterized extensively to understand the dependence of wavelength tuning on modulation frequency, modulation amplitude and phase difference between laser/heater modulation. Thereafter, the designed sensor is validated in both room-temperature static cell experiments and non-reactive high-temperature-measurements in methane-acetylene-argon gas mixtures in the shock tube. Finally, the sensor is applied for simultaneous detection of methane and acetylene during the high-temperature pyrolysis of iso-octane behind reflected shock waves. [ABSTRACT FROM AUTHOR]

[Display omitted] • A carbon isotope spectrum logging system is designed to identify isotope reversal phenomenon. • Compare the δ13C of CO 2 obtained from the oxidation of methane and ethane. • Mid-infrared laser and long-path cell are utilized for high-precision detection. • Nonlinear dynamic mapping ability of BP is improved through sparrow search algorithm. • Optical subsystem is placed in a thermostat to suppress the influence of temperature dependence. In the process of oil and gas exploration and development, carbon isotope ratio can reflect the maturity of oil and gas and predict the recovery factor, and the isotope ratio in the composition of shale gas is particularly important. Thus, a carbon isotope spectrum logging system was designed and exploited based on tunable diode laser absorption spectroscopy (TDLAS) technology under the fundamental frequency absorption band of 12CO 2 and 13CO 2 molecules, and a quantum cascade laser (QCL) with center wavelength of 4.35 μm was applied. For further detection sensitivity, wavelength modulation spectroscopy (WMS) technology was combined to suppress background noise through the modulation of QCL. A multi-pass gas cell (MPGC) with an optical path length of 41 m was utilized for lower limit of detection (LoD). In order to suppress the temperature dependence of the absorption spectrum, the optical subsystem was placed in a high-precision thermostat to maintain a stable temperature, so as to achieve high-precision and high-stability detection. Meanwhile, sparrow search algorithm-back propagation (SSA-BP) was applied for concentration prediction of 12CO 2 and 13CO 2. Taking advantage of the excellent optimization ability, fast convergence speed and high stability of SSA, the problem that BP neural network algorithm is highly dependent on initial value can be solved to some extent. Sensor performance was validated through calibration and stability experiments. The LoD of 12CO 2 reached a minimum of 0.618 parts-per-billion (ppb) with an 88 s averaging time, and the LoD of 13CO 2 reached 0.181 ppb when the averaging time was 96 s. Besides, the standard deviation of carbon isotope ratio obtained by this system was ∼ 0.61 ‰. The results illustrate that this self-developed sensor has a bright prospect in the field of shale gas isotope detection. [ABSTRACT FROM AUTHOR]

In growing competition between universities from all over the world, the evaluation of student's experience in the university becomes very important and crucial for management decisions. The article discusses the results of applying the method of measuring the quality of university life (QCL - quality of college life), developed by American researchers of higher education on the basis of sociological studies of quality of life. This technique provides a comprehensive assessment of student satisfaction with university experience and can be used not only for internal monitoring and management decision-making, but also for inter-institutional comparisons.

The paper presents one of the laser absorption spectroscopy techniques as an effective tool for sensitive analysis of trace gas species in human breath. Characterization of nitric oxide, carbonyl sulphide and ethane, and the selection of their absorption lines are described. Experiments with some biomarkers showed that detection of pathogenic changes at the molecular level is possible using this technique. Thanks to cavity enhanced spectroscopy application, detection limits at the ppb-level and short measurements time (

Terahertz band has recently attracted the attention of the communication society due to its huge bandwidth and very high-speed wireless communications capability. It has been utilized in a variety of disciplines including physics, biology and astronomy for years; and the main concerns have always been obtaining highly efficient and high-power terahertz sources. Today, these problems are still the most important issues in establishing an operable wireless terahertz communication link. In this paper, recent studies in the field of terahertz source design are investigated based on the terahertz output power and efficiency. Solid-state sources and optical sources were comparatively reviewed with optical photoconductive material (OPM)-based methods which are combined with the terahertz antennas in the design phase generally. For wireless communication, the most suitable frequencies are between 0.3 THz and 1 THz due to the attenuation profile of the atmosphere. For this reason, based on the recently published studies, it has been observed that OPM and resonant tunneling diode-based sources are the most promising terahertz sources in terms of efficiency and power. Key issues and the main problems of terahertz photoconductive antennas which are the base of OPM method were also discussed in this paper. [ABSTRACT FROM AUTHOR]

Mid-infrared (MIR) laser spectroscopy was used to detect the presence of residues of high explosives (HEs) on fabrics. The discrimination of the vibrational signals of HEs from a highly MIR-absorbing substrate was achieved by a simple and fast spectral evaluation without preparation of standards using the classical least squares (CLS) algorithm. Classical least squares focuses on minimizing the differences between the spectral features of the actual spectra acquired using MIR spectroscopy and the spectral features of calculated spectra modeled from linear combinations of the spectra of neat components: HEs, fabrics, and bias. Samples in several combinations of cotton fabrics/HEs were used to validate the methodology. Several experiments were performed focusing on binary, ternary, and quaternary mixtures of TNT, RDX, PETN, and fabrics. The parameters obtained from linear combinations of the calculated spectra were used to perform discrimination analyses and to determine the sensitivity and selectivity of HEs with respect to the substrates and to each other. However, discrimination analysis was not necessary to achieve successful detection of HEs on cotton fabric substrates. The RDX signals (mRDX > 0.02 mg) on cotton were used to calculate the limit of detection (LOD). The signal-to-noise ratios (S/N) calculated from the spectra of cotton dosed with decreasing masses of RDX until S/N ≈ 3 resulted in a LOD of 15–33 µg, depending on the vibrational band used. Linear fits generated by comparing the mass dosed RDX with the fraction predicted were also used to calculate the LOD based on the uncertainty of the blank and the slope. This procedure resulted in a LOD of 58 µg. Probably the most representative value of the method LOD was calculated using an interpolation of a threshold determined using the predicted average value for the blank plus 3.28 times the standard deviations (p-value threshold) for low surface dosages of RDX (LOD = 40 µg). The contribution demonstrates that to achieve HE detection on fabrics using the proposed algorithm, i.e., determining the presence/absence of HEs on the substrates, the library must contain the spectra of HEs, substrates, and potential interferents or that these spectra be added to the models in the field. If the model does not contain the spectra of the fabric components, there is a high probability of finding false positives for clean samples (no HEs) and a low probability for failed detection in samples with HEs. More work will be required to demonstrate that these new approaches to HE detection work on real-world samples and when contaminating materials are present in the samples. [ABSTRACT FROM AUTHOR]

Abstract A compact high-resolution spectroscopic sensor using a thermoelectrically (TE) cooled continuous-wave (CW) room temperature (RT) quantum cascade laser (QCL) operating at 4.6 μm, is employed for simultaneous detection of three main isotopic species (14N15N16O, 15N14N16O and 14N14N16O). To enable a high-precision analysis of N 2 O isotopic species at ambient mixing ratios, a liquid nitrogen-free preconcentration unit is built to trap and load atmospheric N 2 O. The absorption spectra of 14N15N16O, 15N14N16O, and 14N14N16O between 2188.6 cm−1 and 2189 cm−1 are measured, and the respective ratios of the rare to the abundant isotopologues abundances are demonstrated. Moreover, spectroscopic parameters of pressure-broadening coefficient for selected absorption lines have been determined, and a good agreement is obtained by comparing with HITRAN database. Graphical Abstract Unlabelled Image Highlights • A liquid nitrogen-free preconcentration unit is built to trap and load atmospheric N 2 O. • CW-QCLs are used for developing analytical instrumentation based on high-resolution laser absorption spectroscopy. • Three main isotopic species (14N15N16O, 15N14N16O and 14N14N16O) in the atmosphere are measured simultaneously. [ABSTRACT FROM AUTHOR]

Water vapor is an important gas species in atmosphere. In this work, we present a three-line tunable diode laser absorption spectroscopy (TDLAS) gas sensor for water vapor detection based on direct absorption spectroscopy. A continuous wave quantum cascade laser (QCL) is employed as the light source with a wavelength near 7.15 µm. The output wavelength of the QCL is tuned to scan across three absorption lines of water vapor simultaneously in the detection. A detection limit of 10.7 ppm v (parts per million by volume) is obtained in 30-s integration time with a 40 cm gas cell. This detection limit could be further improved if wavelength modulation spectroscopy (WMS) or a multi-pass gas cell is introduced to the system. [ABSTRACT FROM AUTHOR]