Long-wavelength Infrared Range Research Articles

Narrow-band controllable sources of IR emission based on one-dimensional magneto-optical photonic structures

Creation of controllable narrow-band emission sources for the mid- and long-wavelength infrared ranges is one of the primary tasks of infrared technology. In this paper, we propose and demonstrate non-luminescent (thermal) magnetically controllable sources of infrared emission based on semiconductor magneto-optical photonic structures (MOPS). It is shown that interference effects cause narrow-band thermal emission spectrum of such sources, and magnetic field makes it possible to effectively control the spectral and amplitude characteristics of emissivity in the mid- and long-wavelength infrared range. Influence of the MOPS composition and design on the source emissive characteristics is studied. Using the obtained results, the designs of A3B5 semiconductor compounds based sources with dynamically tunable spectrum and amplitude modulation of emission are proposed. Theoretical modeling has shown the possibility of dynamic control of their emission parameters by achievable magnetic fields. Such sources may be used in environmental monitoring systems, medicine, forensics, infrared spectroscopy, etc.

An improved YOLOv5s method based bruises detection on apples using cold excitation thermal images

Bruising is one of the key factors that causes postharvest losses, which decreases the economic efficiency of fruit. Nevertheless, the detection of bruises still relies mainly on manual work, which is strongly subjective with long labor time and low efficiency. Accordingly, it is necessary to design an efficient fruit bruise detection approach. Thermal imaging (TI) is a fast and effective nondestructive testing technology. However, the commonly applied thermal excitation TI-based bruise detection may lead to a decrease in the shelf life of the fruit. Therefore, this study uses apple as the research object, introduces cold excitation to improve the sensitivity of bruise detection, and then constructs a simple longwavelength infrared range (7.5–13 µm) TI system to acquire the thermal image of bruised apples. In addition, the low signal-to-noise ratio of thermal images also leads to detection performance degradation. Thus, the YOLOv5s network is applied and improved to achieve better detection. The specific methods are described as follows: (1) Since the thermal images have the problem of duplicated RGB data, group convolution is used to reduce the feature duplication computation. (2) The bottleneck structure of YOLOv5s is replaced by the ghost bottleneck (GB), and the number of bottlenecks is reduced to decrease the computational quantity of extracting redundant features of thermal images. (3) The shrinkage module is inserted into the GB, and the threshold is automatically obtained through two fully connected layers without relevant professional knowledge to eliminate noise in the features that may cause performance degradation. The F2 score, mAP and mAP50 of the proposed model are 97.76%, 86.24% and 98.08%, respectively, which are better than those of YOLOv5s. Moreover, the computation and the FPS of the proposed model are 1.31 GFLOPs and 160, which are 31.95% and 121.21% of those of the YOLOv5s, respectively.

Long-wavelength infrared selective emitter for thermal infrared camouflage under a hot environment.

Thermal infrared camouflage as a kind of counter-surveillance technique has attracted much attention owing to the rapid development of infrared surveillance technology. Various artificial optical structures have been developed for infrared camouflage applications under cold ambient environment (low thermal radiation), but the realization of infrared camouflage under a hot environment (high thermal radiation) is also highly desirable and has been rarely reported. Here, a lithography-free, ultra-thin, high performance long-wavelength infrared (LWIR) selective emitter for thermal infrared camouflage in a high radiation environment is proposed and experimentally demonstrated. Experimental results show that our designed selective emitter exhibits average emissivity higher than 90% over the LWIR range from 8 to 14 µm and low emissivity less than 35% outside this window. Numerical simulations were performed to optimize the geometrical structures and reveal that such a selective emission effect is attributed to the combination of multiple hybrid plasmonic resonances. LWIR thermal images show that the selective emitter can perfectly blend into the high radiation backgrounds. Furthermore, it is found that the sample displays angle-independent emission properties, indicating that our emitter offers great potential for application in evading large-angle detection.

Growth of high material quality InAs/GaSb type-II superlattice for long-wavelength infrared range by molecular beam epitaxy

By optimizing the V/III beam-equivalent pressure ratio, a high-quality InAs/GaSb type-II superlattice material for the long-wavelength infrared (LWIR) range is achieved by molecular beam epitaxy (MBE). High-resolution x-ray diffraction (HRXRD), atomic force microscopy (AFM), and Fourier transform infrared (FTIR) spectrometer are used to characterize the material growth quality. The results show that the full width at half maximum (FWHM) of the superlattice zero-order diffraction peak, the mismatching of the superlattice zero-order diffraction peak between the substrate diffraction peaks, and the surface roughness get the best results when the beam-equivalent pressure (BEP) ratio reaches the optimal value, which are 28 arcsec, 13 arcsec, and 1.63 Å, respectively. The intensity of the zero-order diffraction peak is strongest at the optimal value. The relative spectral response of the LWIR detector shows that it exhibits a 100% cut-off wavelength of 12.6 μm at 77 K. High-quality epitaxial materials have laid a good foundation for preparing high-performance LWIR detector.

Ultrafast Silicon Nanomembrane Microbolometer for Long-Wavelength Infrared Light Detection.

The microbolometer is the cornerstone device for imaging in the long-wavelength infrared range (LWIR) at room temperature. The state-of-the-art commercial microbolometers usually have a large thermal time constant (TTC) of over 10 ms, limited by their substantial device heat capacity. Moreover, the minimal pixel size of state-of-the-art bolometer is around 10 μm by 10 μm to ensure sufficient power absorption per pixel. Here, we demonstrate an ultrafast silicon nanomembrane microbolometer with a small heat capacity of around 1.9 × 10-11J/K, which allows for its operation at a speed of over 10 kHz, corresponding to a TTC of less than 16 μs. Moreover, a compact diabolo antenna is leveraged for efficient LWIR light absorption, enabling the downscaling of the active area size to 6.2 μm by 6.2 μm. Because of the complementary metal oxide semiconductor (CMOS)-compatible fabrication processes, our demonstration here may lead to a future high-resolution and high-speed LWIR imaging solution.

Micromachined porous silicon Fabry-Pérot long wavelength infrared filters

Porous silicon Fabry-Pérot (PS-FP) filters operating in the long wavelength infrared (LWIR) range are demonstrated and studied. Porous silicon (PS) offers many advantages for such filters, including improved optical and mechanical properties compared to other LWIR filter materials, and the ability to modulate porosity to form multilayer structures that are compatible with conventional semiconductor technologies. This work discusses the optical and the mechanical characterizations of what are the first MEMS-based suspended PS-FP filters operating in the LWIR range. Methods developed to model and characterize PS-FP filters are discussed, with characterization a challenge for such porous structures considering their low refractive index and low Young’s modulus. The transmittance measurements show that introducing notches at the four corners of the top mirror minimizes the bowing of the top mirror significantly. The stress measurements of attached films show that the lattice mismatch at the PS/silicon interface is likely the key factor controlling the stress in multilayer PS thin films. The micromachining techniques developed to form a resonance cavity within PS-FP filters can also be tuned to reduce the stress mismatch and the absorption loss in the LWIR range. This study shows exciting promise for the use of micromachined PS-based filters for LWIR operation.

High refractive index dispersion of compositionally optimized Ge-Ga-Sb-S sulfide glass for use as molded lens in the long-wavelength infrared range

In an effort to endow Ge-Sb-S sulfide glass with capability to transmit the long-wavelength infrared (LWIR) photons as well as to possess highly dispersive refractive indexes over the LWIR spectral range, we have compositionally adjusted ternary Ge-Sb-S glass prior to tuning quaternary Ge-X-Sb-S (X = Ga, Bi, In or Sn) glass. Among the constituent atoms of ternary Ge-Sb-S glass, Ge content turned out to exert the strongest influence not only on thermal and mechanical properties but also on infrared transmission edge. Specifically, glass transition temperature and Vickers hardness tended to be directly proportional to Ge content, but infrared transmission edge was blue-shifted upon increase of Ge content, simultaneously producing an additional multiphonon absorption peak at ~ 9 µm. As such, Ge-Sb-S glass containing Ge atoms less than ~ 15 at% was considered to feature applicability in LWIR range, which on the other hand suffers from relatively poor thermal and mechanical properties. In our experimental attempts on quaternary sulfide glasses performed to mitigate such deteriorations, presence of relatively small amount of Ga appeared to be most effective among the elements employed in this study as the fourth constituent. Moreover, only Ga atoms improved thermal stability with significantly increasing crystallization temperature. Quaternary Ge-Ga-Sb-S glass compositionally optimized in this study was then verified to be much more dispersive than typical Se-based chalcogenide glasses in the LWIR region.

Modeling high-peak-power few-cycle field waveform generation by optical parametric amplification in the long-wavelength infrared.

Extended coupled-wave analysis of optical parametric chirped-pulse amplification (OPCPA) reveals regimes whereby high-peak-power few-cycle pulses can be generated in the long-wavelength infrared (LWIR) spectral range. Broadband OPCPA in suitable nonlinear crystals pumped at around 2 μm and seeded either through the signal or the idler input is shown to enable the generation of high-power field waveforms with pulse widths shorter than two field cycles within the entire LWIR range.

Electrically tunable infrared filter based on the liquid crystal Fabry-Perot structure for spectral imaging detection.

An electrically tunable infrared (IR) filter based on the liquid crystal (LC) Fabry-Perot (FP) key structure, which works in the wavelength range from 5.5 to 12μm, is designed and fabricated successfully. Both planar reflective mirrors with a very high reflectivity of ∼95%, which are shaped by depositing a layer of aluminum (Al) film over one side of a double-sided polished zinc selenide wafer, are coupled into a dual-mirror FP cavity. The LC materials are filled into the FP cavity with a thickness of ∼7.5 μm for constructing the LC-FP filter, which is a typical type of sandwich architecture. The top and bottom mirrors of the FP cavity are further coated by an alignment layer with a thickness of ∼100 nm over Al film. The formed alignment layer is rubbed strongly to shape relatively deep V-grooves to anchor LC molecules effectively. Common optical tests show some particular properties; for instance, the existing three transmission peaks in the measured wavelength range, the minimum full width at half-maximum being ∼120 nm, and the maximum adjustment extent of the imaging wavelength being ∼500 nm through applying the voltage driving signal with a root mean square (RMS) value ranging from 0 to ∼19.8 V. The experiment results are consistent with the simulation, according to our model setup. The spectral images obtained in the long-wavelength IR range, through the LC-FP device driven by the voltage signal with a different RMS value, demonstrates the prospect of the realization of smart spectral imaging and further integrating the LC-FP filter with IR focal plane arrays. The developed LC-FP filters show some advantages, such as electrically tunable imaging wavelength, very high structural and photoelectronic response stability, small size and low power consumption, and a very high filling factor of more than 95% compared with common MEMS-FP spectral imaging approaches.

Directional emittance of dry and moist paper

Abstract The directional emittance of dry and moist paper and board samples was measured in two wavelength ranges; the mid-wavelength infrared (MWIR) range and the long-wavelength infrared (LWIR) range. The influence of pulp type, pulp drying, pulp refining, fibre orientation, additives, coating, and observation angle on the emittance of dry paper was examined. The influence of sample moisture and observation angle on the emittance of moist samples was also investigated. The emittance in the LWIR range was higher than the MWIR emittance. The emittance varied with pulp type, especially for TMP, which had a significantly lower emittance compared to the samples made of chemical pulp. The impact of different properties, such as pulp type, refining or coating, was much smaller in the LWIR range than in the MWIR range. Observation angle was found to significantly impact the emittance at angles larger than 60° from the normal direction in the MWIR range, and angles larger than 70° in the LWIR range. The emittance increased with increasing moisture ratio. This increase was most pronounced at low absolute moisture ratios, where an addition of an already small amount of water could impart a large change in emittance. It was found that the emittance and sample moisture could be correlated well using a linear combination of the emittance of dry paper and pure water.

Low-Frequency Noise Characteristics of HgCdTe Infrared Photodiodes Operating at High Temperatures

We present experimental results of 1/f noise characterization in n+/p mercury-vacancy-doped photodiodes. The 1/f noise was measured as a function of temperature and diode bias voltage for different photodiode configurations. We have investigated the 1/f noise of devices with various geometries and structures, in different spectral bands, and produced using different growth processes. Contrasting 1/f noise behavior was observed in mid-wavelength infrared range (MWIR) and long-wavelength infrared range (LWIR) devices. The results indicate that the 1/f noise in MWIR photodiodes is proportional to the diode area, which implies the presence of a previously unreported noise-generating mechanism occurring in bulk material. The 1/f noise in the LWIR photodiodes was found to be independent of diode geometry, indicating the presence of a diffusion current modulation at specific points of the junction.

Photoluminescence and photoresponse from InSb/InAs-based quantum dot structures

InSb-based quantum dots grown by metal-organic vapor-phase epitaxy (MOVPE) on InAs substrates are studied for use as the active material in interband photon detectors. Long-wavelength infrared (LWIR) photoluminescence is demonstrated with peak emission at 8.5 µm and photoresponse, interpreted to originate from type-II interband transitions in a p-i-n photodiode, was measured up to 6 µm, both at 80 K. The possibilities and benefits of operation in the LWIR range (8-12 µm) are discussed and the results suggest that InSb-based quantum dot structures can be suitable candidates for photon detection in the LWIR regime.

Doping dependence of minority carrier lifetime in long-wave Sb-based type II superlattice infrared detector materials

Theoretical modeling and experimental evidence show that the dark currents of antimonide (Sb)-based Type-II Superlattice (T2SL) detectors sensitive to long-wavelength infrared (LWIR) radiation are limited by the minority carrier lifetimes associated with the Shockley Read-Hall (SRH) generation-recombination process. Despite the low minority carrier lifetimes, the present photodiode dark current performance is achieved by increasing the background doping density of the absorber layers to NA ∼ 2×1016 cm−3. This paper will discuss the measured minority carrier lifetimes of T2SL LWIR detectors with various background doping densities. To make comparisons, we designed several T2SL absorber layers sensitive in the LWIR range and p-type doped up to various densities. We find the minority carrier lifetimes are dominated by the SRH generation-recombination process. By analyzing minority carrier lifetime data as a function of excess carrier densities, we estimate SRH lifetimes and actual ionized acceptor densities of the absorber layers. The data are compared with the measured impurity doping densities of the detectors. In addition, we predict the type of flaws responsible for the SRH recombination process and narrow down the flaw energy level relative to the Fermi energy.

Three-color broadband asymmetric quantum well infrared photodetectors in long wavelength infrared range (LWIR)

A theoretical investigation of a GaAs/AlGaAs-material-system-based four quantum well infrared detector structures consisting of ten periods of three asymmetric quantum well units are presented. Each quantum well in the units is sensitive to wavelengths of 8.75, 10, and 11.75 μm, respectively. The effect of the barrier thicknesses on the responsivity spectra is discussed with respect to barrier transmissions under negative and positive bias voltages. Each detector structure shows voltage-tunable broadband and multicolor features in 8–12-μm long wavelength infrared range (LWIR).

Broadband staircase quantum well infrared photodetector: working in long wavelength infrared range (LWIR)

AbstractWe present a theoretical investigation of a staircase‐like quantum well infrared photodetector (QWIP). It detects wavelength between 7.6 μm and 13.5 μm range at an applied electric field of F = 1.9x104 V/cm at 77 K. The dark current density was found to be around 2x10–7 A/cm2 at operating bias, which is lower than the conventional QWIPs in the literature. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Overview of antimonide based III-V semiconductor epitaxial layers and their applications at the center for quantum devices

The properties of Sb-based III-V semiconductor compounds for optoelectronic applications in the mid-wavelength infrared (MWIR) and long-wavelength infrared (LWIR) range were reviewed. The growths of the Sb-based binary, ternary and quaternary were studied by molecular beam epitaxy (MBE) and metalorganic chemical vapor deposition (MOCVD). The structural, optical and electrical characterizations were carried out. Focal plane array, photoconductors and photodiodes were fabricated for the MWIR and LWIR range. Doublehetero structure (DH), multi-quantum well (MQW) and strained superlattice (SSL) lasers in the 3–5 μ m range were fabricated. InAs-GaSb type-II superlattices were designed, grown and fabricated into photodetectors for the MWIR and LWIR range.

QUANTUM WELL INFRARED PHOTOCONDUCTORS IN INFRARED DETECTORS TECHNOLOGY

Investigations of the performance of quantum well infrared photodetectors (QWIPs) as compared to other types of semiconductor infrared (IR) detectors are presented. In comparative studies both photon and thermal detectors are considered. More attention is paid to photon detectors and between them we can distinguish: HgCdTe photodiodes, InSb photodiodes, Schottky barrier photoemissive detectors, and doped silicon detectors. Special attention has been paid to competitive technologies in long wavelength IR (LWIR) and very LWIR (VLWIR) spectral ranges with emphasis on the material properties, device structure, and their impact on FPA performance. The potential performance of different materials as infrared detectors is examined utilizing the α/G ratio, where α is the absorption coefficient and G is the thermal generation. From the discussion results, LWIR QWIP cannot compete with HgCdTe photodiode as the single device especially at higher temperature operation(> 70 K) due to fundamental limitations associated with intersubband transitions. However, the advantage of HgCdTe is less distinct in the temperature range below 50 K due to problems involved in the HgCdTe material (p-type doping, Shockley–Read recombination, trap-assisted tunneling, surface and interface instabilities). Even though the QWIP is a photoconductor, several its properties such as high impedance, fast response time, long integration time, and low power consumption, well comply with requirements for large FPAs fabrication. Due to the high material quality at low temperature, QWIP has potential advantages over HgCdTe for VLWIR FPA applications in terms of the array size, uniformity, yield and cost of the systems. Both HgCdTe photodiodes and quantum well infrared photodetectors offer multicolor capability in the MWIR and LWIR range. Powerful possibilities of QWIP technology are connected with VLWIR FPA applications and with multicolor detection. QWIP FPAs combine the advantages of PtSi Schottky barrier arrays (high uniformity, high yield, radiation hardness, large arrays, lower cost) with the advantages of HgCdTe (high quantum efficiency and long wavelength response).

On the amounts of lead contained in some silver coins

Porous silicon Fabry-Pérot (PS-FP) filters operating in the long wavelength infrared (LWIR) range are demonstrated and studied. Porous silicon (PS) offers many advantages for such filters, including improved optical and mechanical properties compared to other LWIR filter materials, and the ability to modulate porosity to form multilayer structures that are compatible with conventional semiconductor technologies. This work discusses the optical and the mechanical characterizations of what are the first MEMS-based suspended PS-FP filters operating in the LWIR range. Methods developed to model and characterize PS-FP filters are discussed, with characterization a challenge for such porous structures considering their low refractive index and low Young’s modulus. The transmittance measurements show that introducing notches at the four corners of the top mirror minimizes the bowing of the top mirror significantly. The stress measurements of attached films show that the lattice mismatch at the PS/silicon interface is likely the key factor controlling the stress in multilayer PS thin films. The micromachining techniques developed to form a resonance cavity within PS-FP filters can also be tuned to reduce the stress mismatch and the absorption loss in the LWIR range. This study shows exciting promise for the use of micromachined PS-based filters for LWIR operation.