We report on the realization of a multi-emitter quantum cascade laser system with optimized package volume. A multidimensional bonding of chip-on-substrate units allows for close packaging of several chips. The emission of several chip-on-substrate units with an emission wavelength around 3.9 µm are geometrically combined to achieve a multi-Watt emission power level while obtaining a symmetric beam profile of the emission. A dedicated integrated electronic circuit provides individual pulse control, which enables individual timing for each emitter.
In the present contribution we introduce silver nanowires, a material with outstanding properties. When silver nanowires are coated on surfaces, they form a percolating network. The surface resistance of these coatings can be adapted to individual needs, by changing the amount of silver nanowires on the surface. The coating formulation is versatilely applicable on rigid and flexible, glass and plastic and even curved substrates. Silver nanowires can be processed using standard coating procedures.
Thereby the material properties of silver, such as excellent electrical conductivity and reflection of electromagnetic radiation, and the advantages of nanotechnology are combined: The resulting coatings are electrically conductive, show remarkable reflective properties to electromagnetic radiation in the infrared wavelength range and are transparent in the visible spectral range.
In this paper we will demonstrate the potential of silver nanowires as a reflective coating for electromagnetic radiation on the example of low-e coatings. Such low-e coatings can be used for e.g. windows, where a high reflection of incoming IRradiation is necessary to avoid rising of the interior’s temperature. The reflective properties of silver nanowire based lowe coatings can be individually adjusted by means of the maximum reflection performance within a specific wavelength interval. Furthermore, the reflection properties of silver nanowires show a wavelength dependent performance. Consequently, silver nanowires are a promising material for tailorable reflective coatings especially for electrical, optical and IR systems.
We report on the temporally controlled combination of the emission of multiple quantum cascade laser modules. The combination is demonstrated and allows for temporal pulse shaping at a target position. The laser chips are packaged individually in stand-alone modules that can provide an average optical output power on Watt-level. Timing is provided by integrated microcontrollers which allow for comfortable output synchronization of several modules. Thus we have reached a timing accuracy in the order of better than 10 ns. The operation is demonstrated for a wavelength of λ = 4 μm, but can be easily adapted to other wavelengths that are relevant for sensing, free space communication or directional infrared counter measure applications.
Through the European Defence Agency, the Joint Investment Programme on CBRN protection funded the project AMURFOCAL to address detection at stand-off distances with amplified quantum cascade laser technology in the longwave infrared spectral range, where chemical agents have specific absorptions features.
An instrument was developed based on infrared backscattering spectroscopy. We realized a pulsed laser system with a fast tunability from 8 to 10 μm using an external-cavity quantum cascade laser (EC-QCL) and optical parametric amplification (OPA). The EC-QCL is tunable from 8 to 10 μm and delivers output peak powers up to 500 mW. The peak power is amplified with high gain in an orientation-patterned gallium arsenide (OP-GaAs) nonlinear crystal. We developed a pulsed fiber laser acousto-optically tunable from 1880 to 1980 nm with output peak powers up to 7 kW as pump source to realize an efficient quasi-phase matched OPA without any mechanical or thermal action onto the nonlinear crystal. Mixing the EC-QCL and the pump beams within the OP-GaAs crystal and tuning the pump wavelength enables parametric amplification of the EC-QCL from 8 to 10 μm leading to up to 120 W peak power. The output is transmitted to a target at a distance of 10 – 20 m. A receiver based on a broadband infrared detector comprises a few detector elements. A 3D data cube is registered by wavelength tuning the laser emission while recording a synchronized signal received from the target. The presentation will describe the AMURFOCAL instrument, its functional units and its principles of operation.
Within the framework of the first European Defence Agency (EDA) call for protection against chemical, biological, radiological and nuclear threats (CBRN Protection) we established a project on active multispectral reflection fingerprinting of persistent chemical agents (AMURFOCAL). A first paper on the project AMURFOCAL has been issued last year on the SPIE conference in Warsaw, Poland. This follow up paper will be accompanied by an additional paper that deals specifically with the aspect of the 100 W-level peak power laser system tunable in the LWIR. In order to close a capability gap and to achieve detection at stand-off distances our consortium built a high peak power pulsed laser system with fast tunability from 8 to 10 μm using an external-cavity quantum cascade laser and optical parametric amplification. This system had to be tested against different substances on various surfaces with different angles of inclination to evaluate the ability for an active stand-off technology with an eye-safe laser system to detect small amounts of hazardous substances and residues. The scattered light from the background surface interferes with the signal originating from the persistent chemicals. To account for this additional difficulty new software based on neutral networks was developed for evaluation. The paper describes the basic setup of the instrument and the experiments as well as some first results for this technology.
Remote detection of toxic chemicals of very low vapour pressure deposited on surfaces in form of liquid films, droplets or powder is a capability that is needed to protect operators and equipment in chemical warfare scenarios and in industrial environments. Infrared spectroscopy is a suitable means to support this requirement. Available instruments based on passive emission spectroscopy have difficulties in discriminating the infrared emission spectrum of the surface background from that of the contamination. Separation of background and contamination is eased by illuminating the surface with a spectrally tune-able light source and by analyzing the reflectivity spectrum.
The project AMURFOCAL (Active Multispectral Reflection Fingerprinting of Persistent Chemical Agents) has the research topic of stand-off detection and identification of chemical warfare agents (CWAs) with amplified quantum cascade laser technology in the long-wave infrared spectral range. The project was conducted under the Joint Investment Programme (JIP) on CBRN protection funded through the European Defence Agency (EDA).
The AMURFOCAL instrument comprises a spectrally narrow tune-able light source with a broadband infrared detector and chemometric data analysis software. The light source combines an external cavity quantum cascade laser (EC-QCL) with an optical parametric amplifier (OPA) to boost the peak output power of a short laser pulse tune-able over the infrared fingerprint region. The laser beam is focused onto a target at a distance between 10 and 20 m. A 3D data cube is registered by tuning the wavelength of the laser emission while recording the received signal scattered off the target using a multi-element infrared detector. A particular chemical is identified through the extraction of its characteristic spectral fingerprint out of the measured data.
The paper describes the AMURFOCAL instrument, its functional units, and its principles of operation.
We report on the effects of active and passive cooling on the performance of high power mid-IR QCL modules (λ ≈ 3.9 μm) in quasi-cw mode. In active cooling mode, a thermo-electrical cooler attached with its hot side to a heat sink of constant temperature, a local thermometer in close proximity to the QCL chip (epi-down mounted) as well as a control unit has been used for temperature control of the QCL submount. In contrast, the passive cooling was performed by attaching the QCL module solely to the heat sink. Electro-optical light-current- (L-I-) curves are measured in a quasi-cw mode, from which efficiencies can be deduced. Waiving of the active cooling elements results in a drop of the maximum intensity of less than 5 %, compared to the case wherein the temperature of the submount is stabilized to the temperature of the heat sink. The application of a model of electro-optical performance to the data shows good agreement and captures the relevant observations. We further determine the heat resistance of the module and demonstrate that the system performance is not limited by the packaging of the module, but rather by the heat dissipation on the QCL chip itself.
The paper addresses the topic of the electro-optical energy conversion in mid-infrared high power QCL to support designers of optical countermeasure systems in assessing the utility of QCLs for their applications and in specifying the laser sub-system properly. We propose a quadratic dependence of the optical output power on the pump current (L-I curve) in order to reflect the influence of Stark shifting of the energy levels and of heating of the electrons in the planes perpendicular to the current direction. Formulae are given which relate the L-I model parameters to descriptors of these two effects. The model is simple enough to be implemented in system level simulations of the QCL performance in different modes of operations.
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