Medium Wavelength Infrared Research Articles

Evaluation of RMS Current in AC Power Wires Using a High-Speed Infrared System

This paper presents a new method of the effective value (RMS) of alternating current (AC) in power wires based on infrared radiation (IR) measurement using a high-speed medium wavelength infrared (MWIR) camera. The method called “2-ω” involves measurement of the 100 Hz harmonic of temperature (T100) and is supported by signal analysis in the frequency domain. The article discusses the issue of non-sinusoidal alternating current, which causes much more difficult analyzes compared to sinusoidal current with a frequency of 50/60 Hz. The simulation and measurement results for different current shapes obtained in typical power systems like: a phase-controlled switching regulator, half-wave and full-wave rectifiers, and finally the nonlinear distortion of the AC current due to saturation of the magnetic core, are presented and confirm the linear relation of T100 ~ I2RMS. The main advantage of proposed method is the independence of the measurement results from environmental conditions.

Tunable High-Sensitivity Four-Frequency Refractive Index Sensor Based on Graphene Metamaterial.

As graphene-related technology advances, the benefits of graphene metamaterials become more apparent. In this study, a surface-isolated exciton-based absorber is built by running relevant simulations on graphene, which can achieve more than 98% perfect absorption at multiple frequencies in the MWIR (MediumWavelength Infra-Red (MWIR) band as compared to the typical absorber. The absorber consists of three layers: the bottom layer is gold, the middle layer is dielectric, and the top layer is patterned with graphene. Tunability was achieved by electrically altering graphene's Fermi energy, hence the position of the absorption peak. The influence of graphene's relaxation time on the sensor is discussed. Due to the symmetry of its structure, different angles of light source incidence have little effect on the absorption rate, leading to polarization insensitivity, especially for TE waves, and this absorber has polarization insensitivity at ultra-wide-angle degrees. The sensor is characterized by its tunability, polarisation insensitivity, and high sensitivity, with a sensitivity of up to 21.60 THz/refractive index unit (RIU). This paper demonstrates the feasibility of the multi-frequency sensor and provides a theoretical basis for the realization of the multi-frequency sensor. This makes it possible to apply it to high-sensitivity sensors.

Experimental Determination of the Dependence Between Spectral Response and Current–Voltage Characteristics for MWIR HgCdTe Detectors

Experimental results are reported for a medium-wavelength infrared (MWIR) HgCdTe photodetector designed in a joint laboratory run by VIGO Photonics S.A. and the Military University of Technology. The parameters of the MWIR detectors fabricated with HgCdTe heterostructures were studied. Advances in the metal–organic chemical vapor deposition (MOCVD) technique enable the growth of HgCdTe epilayers with a wide range of composition and doping, used for uncooled infrared detectors. Device-quality HgCdTe heterostructures were deposited on 2-inch-diameter, low-cost (100) GaAs substrates. The heterostructures obtained were examined measuring the spectral response and current–voltage characteristics in different temperatures. Our intention here was to determine the relationship between electrical and optical results, using thermal analysis of dark current properties and photocurrent and spectral characteristics. The appearance of an additional signal source in certain ranges of reverse voltages was examined. Comparative analysis of the electrical and electro-optical characterization enabled us to isolate the photocurrent originating from different layers of the detector structure. Automated measurement techniques make it possible to correlate current responsivity with current–voltage curves measured as a function of temperature in a range from 10 K to 300 K with ±0.05 K resolution without human exertion. LabVIEW-aided data acquisition enables the averaging of each characteristic several hundred times, eliminates random and human errors, and decreases measurement uncertainty.Graphical

Synthesis, Mesomorphism and the Optical Properties of Alkyl-deuterated Nematogenic 4-[(2,6-Difluorophenyl)ethynyl]biphenyls.

The synthesis and characterization of new deuterated liquid crystal (LC) compounds based on phenyl tolane core is described in this paper. The work presents an alternative molecular approach to the conventional LC design. Correlations between molecular structure and mesomorphic and optical properties for compounds which are alkyl-hydrogen terminated and alkyl-deuterium, have been drawn. The compounds are characterized by mass spectrometry (electron ionization) analysis and infrared spectroscopy. They show enantiotropic nematic behavior in a broad temperature range, confirmed by a polarizing thermomicroscopy and differential scanning calorimetry. Detailed synthetic procedures are attached. Synthesized compounds show a significantly reduced absorption in the near-infrared (NIR) and medium-wavelength infrared (MWIR) radiation range, and stand as promising components of medium to highly birefringent liquid crystalline mixtures.

Interpretation of temperature distribution observed on W-ITER-like PFUs in WEST monitored with a very-high-resolution IR system

During the 2019 experimental campaign, the WEST tokamak was partially equipped with ITER-like plasma facing units (PFUs) made of discrete monoblocks (MBs) in one of the twelve lower divertor sectors. The magnetic field lines can enter the gaps between two MBs and strike their leading edges (LEs) with near normal incidence, leading to high localized heat flux, temperature and thermomechanical stress during both stead-state operation and transients. Exposed leading edges are a particular matter of concern because of potential crack formation, recrystallization or even melting of tungsten. During the 2019 experimental campaign in WEST, five of them were misaligned (vertical misalignment h = 0.30 ± 0.1 mm) with their poloidal leading edges exposed to the plasma heat flux. A medium wavelength IR filter (MWIR: 3.9 ± 0.1 μm) was installed in the very high resolution infrared system, featuring a submillimeter spatial resolution (∼0.1 mm/pixel). This system has a temperature detection threshold of Tthreshold, BB ≈ 250 °C. In this paper, thermal analysis will be presented with a specific focus on overheating of poloidal and toroidal edges using post-mortem measured emissivity maps. The study reveals an unexpected hot spot in the top LE corner of misaligned PFUs at the outer strike point (OSP). Photonic calculations were performed with different emissivity on top and lateral surfaces, in order to consider the complex reflectance characteristics in the toroidal gaps. During this experiment, the Larmor radius (0.35 mm) is comparable to the gap size. Thus, the helical trajectory of the particles may significantly affect the heat load distribution in the edges vicinity. Heat load simulations were performed with ion orbit modeling that consider the Larmor radius, to study its impact on the thermal distribution of the MB. The photonic simulations showed that it was possible to observe a false hot spot at the top LE corner, with both optical approximation (OA) and ion orbit (IO) modeling, due to reflections and different emissivity values.

Very high-resolution infrared imagery of misaligned tungsten monoblock edge heating in the WEST tokamak

Fourteen ITER-like plasma-facing units (PFUs) made of bulk tungsten were installed in the WEST tokamak divertor. Five of which were misaligned with their poloidal leading edges (LEs) exposed to the plasma heat flux: two sharp-edge PFUs and three chamfered PFUs (vertical misalignment h = 0.30 ± 0.1 mm). The parallel heat flux is measured on the outer strike point with a very high-resolution (VHR) infrared camera, featuring a sub-millimeter spatial resolution (~0.1 mm/pixel). A Medium Wavelength IR filter (MWIR) was used to lower the temperature detection threshold (Tthreshold,BB ≈ 250 °C) and extend the IR analysis to the full toroidal Monoblock (MB) length on both outer (OSP) and inner (ISP) strike points. The parallel heat flux derived from the VHR data (~70 MW/m2) is consistent with previous analysis and other measurements (Thermocouple and Fiber Bragg Grating) at the maximum heat flux location (OSP). This corresponds to real temperatures of about 1000 °C on the LE. Values obtained on the LE of the ISP are typically lower than of the OSP by a factor of two. However, a significant discrepancy between modeling and measurement is observed along with the toroidal temperature profile, with a temperature drop in the first 5 mm after the LEs. Visual and microscopic analysis performed on the component show clear evidence of surface state modification caused by plasma exposure: the presence of cracks on the LE, polished surface in its vicinity, and rougher surfaces further away from the LE.

Robust Behavior Recognition in Intelligent Surveillance Environments.

Intelligent surveillance systems have been studied by many researchers. These systems should be operated in both daytime and nighttime, but objects are invisible in images captured by visible light camera during the night. Therefore, near infrared (NIR) cameras, thermal cameras (based on medium-wavelength infrared (MWIR), and long-wavelength infrared (LWIR) light) have been considered for usage during the nighttime as an alternative. Due to the usage during both daytime and nighttime, and the limitation of requiring an additional NIR illuminator (which should illuminate a wide area over a great distance) for NIR cameras during the nighttime, a dual system of visible light and thermal cameras is used in our research, and we propose a new behavior recognition in intelligent surveillance environments. Twelve datasets were compiled by collecting data in various environments, and they were used to obtain experimental results. The recognition accuracy of our method was found to be 97.6%, thereby confirming the ability of our method to outperform previous methods.

Recent progress in MOCVD growth for thermoelectrically cooled HgCdTe medium wavelength infrared photodetectors

The authors report on advanced metalorganic chemical vapour deposition (MOCVD) of Hg1−xCdxTe (HgCdTe) structures for high operating temperature, medium wavelength infrared (MWIR) detector application. MOCVD technology with wide range of composition and donor/acceptor doping and without post grown annealing was proved to be an excellent tool for HgCdTe heterostructure epitaxial growth used for uncooled photodetector design. The interdiffused multilayer process (IMP) technique was applied for the HgCdTe deposition. HgCdTe epilayers were grown at 350°C with Hg source kept at 210°C. The II/VI mole ratio was assumed in the range from 1.5 to 3 during CdTe/HgTe cycles of the IMP process.The MWIR detectors grown by MOCVD exhibit detectivity ∼7.3×1011Jones at λPEAK=3.5μm and T=230K being determined by background limited photodetector (BLIP) condition.

Monolithic Integration of an Active InSb-Based Mid-Infrared Photopixel With a GaAs MESFET

Medium wavelength infrared (MWIR) detectors are of increasing importance in defense, security, commercial, and environmental applications. Enhanced integration will lead to greater resolution and lower cost focal plane arrays (FPAs). We present the monolithic fabrication of an active photopixel made in InSb on a GaAs substrate that is suitable for large-scale integration into an FPA. Pixel addressing is provided by the cointegration of a GaAs MESFET with an InSb photodiode (PD). Pixel fabrication was achieved by developing novel materials and process steps, including isolation etches, a gate recess etch, and low temperature processes, to make Ohmic contacts to both the GaAs and InSb devices. Detailed electrical and optical measurements in an FTIR demonstrated that the PD was sensitive to radiation in the range of 3– $5~\mu \text{m}$ at room temperature, and that the device could be isolated from its contacts using the integrated MESFET. This heterogeneous technology creates great potential to realize a new type of monolithic FPA of addressable pixels for imaging in the MWIR range.

State-of-the-Art HgCdTe at Raytheon Vision Systems

Dark current density data recorded over the past 14 years at Raytheon Vision Systems on short-wavelength infrared (SWIR) and medium-wavelength infrared (MWIR) devices were examined. This included HgCdTe detector arrays grown by liquid-phase epitaxy on CdZnTe and molecular beam epitaxy on both silicon and CdZnTe substrates. This study analyzed zero-bias resistance–area product and current–voltage measurements from test structure assemblies included on every detector wafer. The data span cutoff wavelengths from 1.7 μm to 7.5 μm and operating temperatures from 40 K to 300 K. A basis is derived for a simple manufacturing trend model for a wide range of cutoffs and temperatures. This model uses a function similar to Tennant’s Rule’07 but includes a generation–recombination (GR) term. Dark current densities below the test set limit are extrapolated assuming GR-limited performance. Model assumptions are tested using sensor chip assembly (SCA) median dark current density values at the same inverse cutoff–temperature products. This model allows probabilistic determination of array manufacturability and prediction of yield, and provides a statistical basis for Raytheon’s state-of-the-art performance.

Theoretical modeling of InAsSb/AlAsSb barrier detectors for higher-operation-temperature conditions

InAsSb is considered as an alternative to HgCdTe ternary alloy as far as infrared (IR) detection systems are concerned. Lately, there has been an enormous progress in the development of InAsSb focal plane arrays. High-operating-temperature conditions were successfully achieved with A III B V unipolar barrier structures including InAsSb/AlAsSb and InAs/AlAsSb material systems. The performance of medium-wavelength IR InAsSb-based nB n nn + detectors is examined theoretically. Since there is no depletion layer in the active layer of such devices, the generation-recombination and trap-assisted tunneling mechanisms are suppressed, leading to lower dark currents in bariode detectors in comparison with standard diodes. Detailed analysis of the detector performance (such as dark current, dynamic resistance area product, and detectivity) versus bias voltage and operating temperatures are performed by pointing out optimal working conditions. The theoretical predictions of bariode parameters are compared with experimental data published in the literature. Finally, the bariode performance is compared with standard InAsSb photodiodes operated at room temperature.

Target detection for low cost uncooled MWIR cameras based on empirical mode decomposition

In this work, a novel method for detecting low intensity fast moving objects with low cost Medium Wavelength Infrared (MWIR) cameras is proposed. The method is based on background subtraction in a video sequence obtained with a low density Focal Plane Array (FPA) of the newly available uncooled lead selenide (PbSe) detectors. Thermal instability along with the lack of specific electronics and mechanical devices for canceling the effect of distortion make background image identification very difficult. As a result, the identification of targets is performed in low signal to noise ratio (SNR) conditions, which may considerably restrict the sensitivity of the detection algorithm. These problems are addressed in this work by means of a new technique based on the empirical mode decomposition, which accomplishes drift estimation and target detection. Given that background estimation is the most important stage for detecting, a previous denoising step enabling a better drift estimation is designed. Comparisons are conducted against a denoising technique based on the wavelet transform and also with traditional drift estimation methods such as Kalman filtering and running average. The results reported by the simulations show that the proposed scheme has superior performance.

Theoretical modelling of MWIR thermoelectrically cooled nBn HgCdTe detector

Abstract The paper reports on the medium wavelength infrared (MWIR) unipolar barrier infrared detector (UBIRD) nBn/B-n type (n-type barrier) HgCdTe detector’s photoelectrical performance. The UBIRD nBn/B-n type HgCdTe detector was modelled using commercially available software APSYS. Detailed analysis of the detector’s performance (such as dark current, photocurrent, responsivity, and detectivity) versus bias voltage, operating temperatures, and structural parameters (cap, barrier, and absorber’s doping as well as cap and barrier compositions) were performed pointing out optimal working conditions. Both conduction and valence band alignments of the HgCdTe nBn/B-n type detector structure was simulated stressing their importance on detectors performance. It was shown that higher operation temperature (HOT) conditions achieved by commonly used thermoelectric (TE) coolers allow to obtain detectivities of D* = (3-10)×109 cmHz1/2/W at T = 200 K for detectors with cut-off wavelength of 5.2 μm The differential resistance area product of RA = 0.15-0.4 cm2 at T = 230 K for bias voltage V = 50 mV was estimated. Finally, the state of the art of UBIRD HgCdTe nBn/B-n type detector performance was compared to InAs/GaSb/B-Al0.2Ga0.8Sb T2SLs nBn detector, InAs/GaSb T2SLs PIN and the HOT HgCdTe bulk photodiodes’ operated at near-room temperature (T = 230 K). It was shown that the RA product of the MWIR UBIRD nBn/B-n type HgCdTe detector can reach a comparable level to the state of the art of the HgCdTe HOT bulk photodiodes and two types of type-II superlattice detectors: PIN photodiodes and nBn detectors

Modelling of MWIR HgCdTe complementary barrier HOT detector

The paper reports on the photoelectrical performance of medium wavelength infrared (MWIR) HgCdTe complementary barrier infrared detector (CBIRD) with n-type barriers. CBIRD nB1nB2 HgCdTe/B1,2-n type detector is modelled with commercially available software APSYS by Crosslight Software Inc. The detailed analysis of the detector’s performance such as dark current, photocurrent, responsivity, detectivity versus applied bias, operating temperature, and structural parameters (cap, barriers and absorber doping; and absorber and barriers compositions) are performed pointing out optimal working conditions. Both conduction and valence bands’ alignment of the HgCdTe CBIRD structure are calculated stressing their importance on detectors performance. It is shown that higher operation temperature (HOT) conditions achieved by commonly used thermoelectric (TE) coolers allows to obtain detectivities D∗≈2×1010cmHz1/2/W at T=200K and reverse polarisation V=400mV, and differential resistance area product RA=0.9Ωcm2 at T=230K for V=50mV, respectively.Finally, CBIRD nB1nB2 HgCdTe/B1,2-n type state of the art is compared to unipolar barrier HgCdTe nBn/B-n type detector, InAs/GaSb/B-Al0.2Ga0.8Sb type-II superlattice (T2SL) nBn detectors, InAs/GaSb T2SLs PIN and the HOT HgCdTe bulk photodiodes’ performance operated at near-room temperature (T=230K). It was shown that the RA product of the MWIR CBIRD HgCdTe detector is either comparable or higher (depending on structural parameters) to the state of the art of HgCdTe HOT bulk photodiodes and both AIIIBV 6.1Å family T2SLs nBn and PIN detectors.

Performance modeling of MWIR InAs/GaSb/B–Al0.2Ga0.8Sb type-II superlattice nBn detector

This paper reports on the unipolar medium wavelength infrared (MWIR) InAs/GaSb/B–Al0.2Ga0.8Sb type-II superlattice (T2SL) nBn detector's photoelectrical performance. In our model, the heterojunction barrier-active region (absorber) was assumed to be decisive as the contributing dark current mechanism limiting nBn's detector performance. The voltage drop analysis on the nBn structure was introduced to estimate the bias drop on the heterojunction barrier-active region. It was assumed that the contact n+-barrier heterojunction's layer has an insignificant influence on the electrical properties of the detector. In addition, a bulk-based model with an effective band gap of T2SL material has been assumed in the device modeling. Both current–voltage (I–V) and differential resistance–area product RA(V,T), characteristics of nBn's detector were found to be dominated by diffusion and generation–recombination currents in the zero-bias and the low-bias regions. At medium values of reverse voltages, the dark current was mostly affected by trap-assisted tunneling, whereas the band-to-band tunneling revealed its contribution at high values of reverse bias (V > 0.7 V). The RA(V,T) characteristics' fitting procedure allowed estimation of both diffusion and generation–recombination lifetimes as well as the trap energy level temperature dependence within T2SL energy gap. It was predicted that at T = 77 K, the RA product and detectivity reached values of 1000 Ωcm2 and 4 × 1011 cm Hz1/2 W-1, respectively. The corresponding values at room temperature were 0.01 Ωcm2 and D* = 5 × 108 cmHz1/2 W−1, respectively. Finally, InAs/GaSb/B–Al0.2Ga0.8Sb T2SLs nBn's state of the art was compared to the performance of InAs/GaSb T2SLs PIN photodiodes and the HgCdTe bulk photodiodes operated at near-room temperature. It was shown that the RA product of the MWIR T2SLs nBn detector has reached a comparable level with the state of the art of the HgCdTe bulk photodiodes.

Medium-wavelength infrared gas sensing with electrochemically fabricated porous silicon optical rugate filters

Porous silicon optical rugate filters are electrochemically fabricated to display reflectance peaks in the medium-wavelength infrared (MWIR) region from 4 to 8 μm. Etching conditions are adjusted to create filters with single and multiple infrared reflectance peaks overlapping specific infrared chemical absorbance bands. Additional infrared reflectance peaks are designed into the structures to provide internal optical reference channels. Samples containing optical reflectance features matching the absorbance band of CO2 at 2350 cm−1 are used to demonstrate gas sensing with optical filters, and a structure with a photonic stop band tuned to match the infrared absorbance band of the P=O functional group, found in G-series chemical warfare agents, is fabricated. With adequate electrolyte replenishment, the calibrated etch conditions generated reproducible spectral band features even for relatively long etch durations. This work represents the first example of a porous Si spectral filter prepared to match specific spectral features of molecules in the MWIR ("fingerprint") region.

P to n conversion in SWIR mercury cadmium telluride with ion milling

Exposure to specific damage introduced by either ion implantation or ion milling converts p-type short wavelength infrared (SWIR) HgCdTe to n-type in a manner similar to the conversions in medium wavelength infrared (MWIR) or long wavelength infrared (LWIR) mercury cadmium telluride. However, the depth of conversion for SWIR Hg1−xCdxTe, with x=0.48, is approximately 300% smaller when compared to the depth of conversion for MWIR HgCdTe for an identical degree of ion milling. The depth of conversion, or the n/p junction depth, tracks linearly the extent of surface removals by ion milling when the metal vacancy concentration is held invariant. These results can be correlated to the interaction between metal vacancies and a product of the lattice damage process resulting from ion milling. The observation of a linear dependence of this depth on the degree or time of ion milling rules out the existence of a diffusive barrier in the transfer of this product for both MWIR and SWIR HgCdTe.

Passivation effect on optical and electrical properties of molecular beam epitaxy-grown HgCdTe/CdTe/Si layers

The effects of passivation with two different passivants, ZnS and CdTe, and two different passivation techniques, physical vapor deposition (PVD) and molecular beam epitaxy (MBE), were quantified in terms of the minority carrier lifetime and extracted surface recombination velocity on both MBE-grown medium-wavelength ir (MWIR) and long-wavelength ir HgCdTe samples. A gradual increment of the minority carrier lifetime was reported as the passivation technique was changed from PVD ZnS to PVD CdTe, and finally to MBE CdTe, especially at low temperatures. A corresponding reduction in the extracted surface recombination velocity in the same order was also reported for the first time. Initial data on the 1/f noise values of as-grown MWIR samples showed a reduction of two orders of noise power after 1200-A ZnS deposition.

Curing and properties comparison of an unsaturated polyester resin, varying crosslinking reaction conditions

AbstractIn this work four different curing modes were used to crosslink a general‐purpose unsaturated polyester resin. Styrene was used as monomer and glass fiber mat as reinforcement. The four curing modes included a traditional convection oven, a long‐wavelength infrared (IR) radiation oven, a medium‐wavelength IR radiation oven, or room temperature for an open‐curing condition without oven heating. Some samples were cured using initiator only, and others were cured combining initiator and promoter. For oven curing, chamber temperature was 85°C. For the samples, final curing conversion (using Fourier transform IR spectroscopy), as well as glass transition temperature (Tg), Young's modulus, impact strength, and Shore D hardness were measured and compared. The medium‐wavelength IR radiation oven as curing condition offered the best option for highest conversion, Tg, and mechanical properties. Polym. Compos. 25:662–666, 2004. © 2004 Society of Plastics Engineers.

Recent developments of high-complexity HgCdTe focal plane arrays at leti infrared laboratory

In this article, we present recent developments of the research in France at LETI infrared laboratory in the field of complex third-generation HgCdTe IRCMOS focal plane arrays (FPAs). We illustrate this with three prototypes of FPAs made at LETI, which have involved some technological improvements from the standard process today in production at Sofradir. We present, using molecular-beam epitaxy (MBE) growth, a 128 × 128 dual-band infrared (photodetector)-complementary metal oxide semiconductor (IRCMOS) with a pitch of 50 µm operating within 2–5 µm. Using the more conventional liquid-phase epitaxy (LPE) growth, we show a new generation of high-performance long linear arrays (1500 × 2; pitch, 30 µm) operating in medium-wavelength infrared (MWIR) or long-wavelength infrared (LWIR) bands based on a modular architecture of butted HgCdTe detection circuit and SiCMOS multiplexers. Finally, we present for the first time a megapixel (1000 × 1000) FPA with a pitch of 15 µm operating in the MWIR band that exhibits a very high performance and pixel operability.