Focal Plane Array Detector Research Articles

Barley leaf cell-wall responses to the penetration by adapted and nonadapted powdery mildew fungi revealed with the thermal-source based Fourier transform infrared microspectroscopy and focal plane array

Infrared microspectroscopy allows for detailed characterization of functional groups at subcellular levels in plants. In this study, barley leaves were inoculated with Blumeria graminis f. sp. hordei (Bgh, adapted) and B. graminis f. sp. tritici (Bgt, nonadapted). Globar-based transmission Fourier transform infrared (gFTIR) microspectroscopy equipped with an upgraded high-resolution focal plane array (FPA) detector which enabled the rapid acquisition of high magnification imaging with a 3.3-μm × 3.3-μm capacity, was employed to quantitatively analyse the cell wall (CW) modification over individual leaf cells in response to attempted penetration at 24 hours post-inoculation. Univariate and multivariate analyses of gFTIR spectra revealed distinct changes in several CW functional groups upon attempted penetration by Bgt, with significant increases in the integrated areas of cellulose, hemicellulose, methyl-esterified pectins and lipid regions compared to cells without penetration. Notably, neither guaiacyl (G) nor syringyl (S) lignin increased significantly in CWs near Bgt penetration sites relative to nonpenetrating controls, though the G/S ratio was higher than in Bgh-penetrated sites. These findings suggest early and rapid CW modifications occur during the nonhost resistance to Bgt. This study also confirms previous results obtained using synchrotron-based FTIR (sFTIR), demonstrating that both gFTIR and sFTIR are valuable for studying plant CW apposition, with gFTIR being more accessible and rapid for imaging over large areas with compatible quality and resolution to sFTIR.

Advances and Challenges of Single‐Pixel Imaging Based on Deep Learning

AbstractSingle‐pixel imaging technology can capture images at wavelengths outside the reach of conventional focal plane array detectors. However, the limited image quality and lengthy computational times for iterative reconstruction still hinder its practical application. Recently, single‐pixel imaging based on deep learning has attracted a lot of attention due to its exceptional reconstruction quality and fast reconstruction speed. In this review, an overview of the current status, and the latest advancements of deep learning technologies in the field of single‐pixel imaging are provided. Initially, the fundamental principles of single‐pixel imaging and deep learning, followed by a discussion of their integration and associated benefits are presented. Subsequently, a comprehensive review is conducted on the advancements of deep learning in various domains of single‐pixel imaging, covering super‐resolution single‐pixel imaging, single‐pixel imaging through scattering media, photon‐level single‐pixel imaging, optical encryption based on single‐pixel imaging, color single‐pixel imaging, and image‐free sensing. Finally, open challenges and potential solutions are discussed.

Investigation of electron backscattering on silicon drift detectors for the sterile neutrino search with TRISTAN

Sterile neutrinos are hypothetical particles in the minimal extension of the Standard Model of Particle Physics. They could be viable dark matter candidates if they have a mass in the keV range. The Karlsruhe tritium neutrino (KATRIN) experiment, extended with a silicon drift detector focal plane array (TRISTAN), has the potential to search for keV-scale sterile neutrinos by measuring the kinematics of the tritium β-decay. The collaboration targets a sensitivity of 10-6 on the mixing amplitude sin2Θ. For this challenging target, a precise understanding of the detector response is necessary. In this work, we report on the characterization of electron backscattering from the detector surface, which is one of the main effects that influence the shape of the observed energy spectrum. Measurements were performed with a tandem silicon drift detector system and a custom-designed electron source. The measured detector response and backscattering probability are in good agreement with dedicated backscattering simulations using the Geant4 simulation toolkit.

Heterogeneous polarization-integrated medium wave infrared HgCdTe focal plane array detector with pixel-wise Al gratings

Heterogeneous polarization-integrated medium wave infrared HgCdTe focal plane array detector with pixel-wise Al gratings

ATR-FTIR spectroscopic imaging with variable angles of incidence of crude oil deposits formed by flocculant flow

Attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopic imaging is a method for spatially resolved analysis of materials that combines the capabilities of ATR-FTIR spectroscopy with the use of a focal plane array detector. This paper presents the methodological aspects of adapting the ATR accessory with variable single reflection angle to the FTIR spectroscopic imaging method. The use of a variable reflection angle allows the image to be studied at different sample depths. Using examples of BMIMPF6 ionic liquid and crude oil droplets placed on the working surface of an internal reflection element, the characteristics of image acquisition as the angle of reflection is varied are discussed. The possibility of obtaining crude oil deposits directly on the working surface of the internal reflection element under the influence of a flocculant flow (n-heptane, acetone) and their study by ATR-FTIR spectroscopic image was demonstrated. Crude oil deposits were obtained under different formation conditions (flow rates of flocculant) and their spectroscopic images were also obtained at different single reflection angles. This information gives an indication of the composition of the deposit’s functional groups not only at spatial resolution but also at depth.

Multi-color long-wave infrared perfect absorber based on a heavily doped semiconductor that is inverse-designed via machine learning.

Metamaterial perfect absorbers (MPAs) with high absorption, thin thickness, and custom-tailorable spectrum are in great demand in many applications, especially in photoelectric detectors. Presently, infrared (IR) focal plane array detectors based on type-II superlattice (T2SL) still face the challenge of a low absorption coefficient. Moreover, it is still difficult to integrate conventional metal-insulator-metal (MIM) MPA with a T2SL infrared detector, due to the incompatibility of fabrication processes. In addition, the need to achieve custom-tailorable multi-peak absorption in the long-wave infrared band is high, and the design process of an MPA with a complicated geometric shape is time-consuming. To tackle these problems, in this work, we replace the ground metal layer in a conventional MIM MPA with a heavily doped semiconductor (n++), whose growth process is compatible with the fabrication process of T2SL infrared detectors and thus can be integrated with them. Moreover, we set up a deep neural network (DNN) to associate the spectral response of the device with the corresponding structural parameters. In this way, we can quickly inverse design the infrared perfect absorber with multiple absorption peaks using a trained DNN. The designed devices can achieve three perfect absorption peaks in the wavelength range of interest (8 ∼ 13 µm), and the peak absorptivity generally reaches over 90%. Our work provides an effective method for the inverse design of n++IM MPA based on DNN, which is of significant guidance for the study of infrared MPA. Additionally, our work anticipates enhancing the detection performance of infrared detectors through absorption enhancement, indicating substantial application potential in the field of optically modulated infrared detectors.

Staring laser situation awareness technology with wide-FOV and high-angle positioning accuracy based on two-dimensional grating and two-channels

Current and future battlefields face the emerging threat of laser weapon development. Existing laser situation awareness technology cannot provide simultaneous operation of wide field-of-view (FOV) and high angle positioning accuracy. This study introduces a system employing a two-dimensional grating and dual-channel approach that offers high precision in situation awareness about laser wavelengths and angle positioning across a wide FOV. The system consists of two main components: an approximate measurement channel and an accurate measurement channel. The former includes a wide-FOV lens and a focal plane array detector (FPA1), acquiring preliminary angle information of the laser. The latter, comprising a two-dimensional grating, a narrow-FOV lens, and a FPA2, captures the incoming laser’s wavelength and precise azimuth and pitch through the analysis of diffraction spot position and distance. Experimental findings confirm that the accuracies of angle and central wavelength measurements exceed 0.05° and 8 nm, respectively, for a FOV of 120°.

Development of a silicon drift detector array to search for keV-scale sterile neutrinos with the KATRIN experiment

Sterile neutrinos in the keV mass range present a viable candidate for dark matter. They can be detected through single β -decay, where they cause small spectral distortions. The Karlsruhe Tritium Neutrino (KATRIN) experiment aims to search for keV-scale sterile neutrinos with high sensitivity. To achieve this, the KATRIN beamline will be equipped with a novel multi-pixel silicon drift detector focal plane array named TRISTAN. In this study, we present the performance of a TRISTAN detector module, a component of the eventual 9-module system. Our investigation encompasses spectroscopic aspects such as noise performance, energy resolution, linearity, and stability.

Evaluation of flip-chip bonding electrical connectivity for ultra-large array infrared detector.

Flip-chip bonding is a key technology for infrared focal plane array (IRFPA) detectors. Due to the high cost of device preparation, the ultra-large array infrared detector cannot be directly used for the flip-chip bonding experiment, and the connectivity rate cannot be measured. To evaluate the flip-chip bonding process, a test device which has the same interconnecting structure as current IRFPA detectors is proposed. Indium bumps are electrically extracted to test electrodes. Electrical measurements were performed to characterize the connection and adhesion of the indium bumps and to calculate the connectivity rate. The electrical connectivity characteristics of the test devices correspond to the observation results of the indium bump extrusion, effectively detecting the interconnecting anomalies such as disconnection, adhesion, overall misalignment, etc., and verifying the feasibility of the test method. The test device has similar multi-layer components and thermal properties as HgCdTe infrared detector for process evaluation and post-processing experiment. The connectivity rate of the test device is up to 100%, and remains above 99% after thermal recycle experiment. The contact resistance of the interconnecting structure is calculated to be about 31.84 Ω based on the test results.

Fine Pitch Micro Indium Bump Interconnect Flip Chip Bonding

Quantum computing processors, micro LED displays and Focal Plane Array (FPA) imaging and detector devices such as infrared (IR) thermal imaging sensors are seeing higher demand as more practical applications requiring these components are coming into research and development, industrial, military and consumer markets. This paired with higher pixel and Qubit count and interconnect density, on larger and larger chips is driving hybridization and monolithic integration in these technologies. This is showing a marked increase in demand for fine pitch micro bump interconnection flip chip die bonding. However, some critical challenges facing these technologies are; larger component sizes mean higher density interconnections over increasing surface area. Submicron accuracy required to align fine pitch micro interconnect arrays. This together with the challenges facing the materials that are becoming the industry standard for these applications, such as the requirement for the assembled components to remain stable in extreme conditions such as cryogenic application environments. Combined with low loss high strength mechanical/ electrical interconnect requirements on components containing sensitive materials, structures and unmatched coefficient of thermal expansion (CTE) means that processing gases such as formic acid or high temperature reflow bonding can no longer be used to bond these devices. These challenges mean that the industry is fast approaching the limitations of even state-of-the-art die bonders and die bonding methods on the market today. This paper is going to highlight these challenges and the methods used to address them to produce large format, high density IR thermal imaging FPA devices, Quantum processors and micro LED displays using fine pitch micro Indium bump array interconnections that meet today’s industry requirements.

Low-latency equal optical path difference sampling for multi-field VLWIR interference signals

The spaceborne Fourier Transform Spectrometer has been utilized for vertical atmospheric soundings with a HgCdTe infrared focal plane arrays (FPAs) detector. However, the VLWIR FPA Fourier spectrometer system faces the difficulty of poor sensitivity due to the major contribution of the system sampling error. In this work, low-latency data acquisition of multi-field VLWIR interference signals based on VLWIR FPA Fourier spectrometer system is realized with an optimized field programmable gate array (FPGA) timing driver scheme and layout algorithm. This scheme can effectively reduce routing delay and constrain critical timing paths, and thus leads to a significant decrease in the deviation of equal optical path difference sampling time from 10.27μs to 0.10μs. Interferograms and spectrograms are efficiently obtained. Furthermore, the average value of noise equivalent spectral radiance (NESR) in VLWIR FPA Fourier spectrometer system, is reduced by 1.75% by timing optimization. In particular, the decay of the NESR can be as high as 15% for some of the pixels. These results illustrate that the proposed scheme will acquire hyperspectral data accurately with VLWIR FPA and meet the needs of rapid soundings development of the Geostationary Interferometric Infrared Sounder (GIIRS) availing a rapid prediction of the appearance of an extreme weather event.

Finite element analysis of the package structure of HgCdTe infrared focal plane array detector

Reliable material parameters, correct boundary condition settings, and a reasonably simplified numerical model are key to obtain reliable and reasonable analysis results. A new finite element analysis model for the HgCdTe infrared focal plane array detector is presented, which includes the core column. The thermal stress and strain of the new model and current model are analyzed, and their distribution laws are obtained. The results are compared, and the reasons are analyzed, which can provide some references for the simulation of infrared detector package structure.

Ultra-Broadband Ultraviolet-Visible Light-Short Wavelength Infrared InGaAs Focal Plane Arrays via n-InP Contact Layer Removal.

PIN InGaAs short wavelength infrared (SWIR) focal plane array (FPA) detectors have attracted extensive attention due to their high detectivity, high quantum efficiency, room temperature operation, low dark current, and good radiation resistance. Furthermore, InGaAs FPA detectors have wide applications in many fields, such as aviation safety, biomedicine, camouflage recognition, and infrared night vision. Recently, extensive research has been conducted on the extension of the response spectrum from short wavelength infrared (SWIR) to visible light (VIS) through InP substrate removal and reserving the n-InP contact layer. However, there is little research on the absorption of InGaAs detectors in the ultraviolet (UV) band. In this paper, we present an ultra-broadband UV-VIS-SWIR 640 × 512 15 μm InGaAs FPA detector by removing the n-InP contact layer in the active area and reserving the InP contact layer around the pixels for n contact, creating incident light to be directly absorbed by the In0.53Ga0.47As absorption layer. In addition, the optical absorption characteristics of InGaAs infrared detectors with and without an n-InP contact layer are studied theoretically. The test results show that the spectral response is extended to the range of 200-1700 nm. The quantum efficiency is higher than 45% over a broad wavelength range of 300-1650 nm. The operability is up to 99.98%, and the responsivity non-uniformity is 3.28%. The imaging capability of InGaAs FPAs without the n-InP contact layer has also been demonstrated, which proves the feasibility of simultaneous detection for these three bands.

Plasmonic photoconductive terahertz focal-plane array with pixel super-resolution

AbstractImaging systems operating in the terahertz part of the electromagnetic spectrum are attractive due to their ability to penetrate many opaque materials and provide unique spectral signatures of various chemicals. However, the use of terahertz imagers in real-world applications has been limited by the slow speed, large size, high cost and complexity of present systems, largely due to the lack of suitable terahertz focal-plane array detectors. Here we report a terahertz focal-plane array that can directly provide the spatial amplitude and phase distributions, along with the ultrafast temporal and spectral information of an imaged object. It consists of a two-dimensional array of ~0.3 million plasmonic photoconductive nanoantennas optimized to rapidly detect broadband terahertz radiation with a high signal-to-noise ratio. We utilized the multispectral nature of the amplitude and phase data captured by these plasmonic nanoantennas to image different objects, including super-resolved etched patterns in a silicon substrate and defects in battery electrodes. By eliminating the need for raster scanning and spatial terahertz modulation, our terahertz focal-plane array offers more than a 1,000-fold increase in the imaging speed compared with the state of the art and potentially suits a broad range of applications in industrial inspection, security screening and medical diagnosis, among others.

16-channel snapshot multispectral imaging based on integrated Fabry Perot microcavity array

<sec>By designing and fabricating a narrow-band Fabry-Perot multi-beam interference spectroscopic microcavity array, and integrating it with a visible light detector focal plane array, we demonstrate a small compact multispectral imaging detector. The micro-cavity filter array with 4×4 basic repeating units and a total of 2048×2048 pixels is obtained on a quartz substrate by the four-fractal combination lithograph-etching process. Then the micro miniatured multispectral imaging detector is formed by fitting with the detector chip. The depth and precision of the etching will determine the distribution and offset of the central wavelength of the narrowband spectral channel respectively. The results show that the etching rate of reactive ion is (3.6 ± 0.2) Å/s, and the process is stable and controllable. Due to the different etching depths, the basic repeating unit forms 16 different levels of steps, and the process achieves the design expectation well.</sec><sec>The results are obtained as follows: the response spectrum peak of the microcavity array sample varies from 520 to 680 nm, the free spectrum range is 160 nm, the full width at the half-peak is less than 10 nm, the transmittance is about 70%, the relative half-width of the transmittance peak at 590 nm is 1.19%, and the waveform coefficient is 2.78. A 16-channel multispectral camera is constructed by using the optical micro-precision assembly device to realize the precise alignment and the fitting of the micro-cavity filter array and the image sensor. Xenon lamp and monochromator are used as tunable wavelength monochromatic cooperative light source to detect the effect of 16-channel snapshot multispectral imaging on a pixel scale. The results show that the multispectral imaging detector has 16 different narrow-band response spectra. The characteristic spectrum of the target can be clearly distinguished by spectral channel.</sec><sec>When imaging the target with known spectral characteristics, for a certain frame of multi-spectral image, selecting a suitable spectral channel can eliminate the background in the field of view through image subtraction and improve the contrast of the target. In the dark room condition, we take the LED light source with center wavelength varying in a range between 528 and 589 nm as the target (the wavelength coincides with the working wavelength of the spectral channel), and effectively suppress the background through the spectral differential intensity subtraction, which can improve the accuracy and sensitivity of the target capture. The 16-channel snapshot multi-spectral imaging detector based on integrated Fabry-Perot microcavity array has the advantages of small size, high integration and strong environmental adaptability, and is expected to play a role in realizing the real-time detection of weak moving targets, auxiliary diagnosis of skin surface observation, and high dynamic range imaging of target observation under backlight conditions.</sec>

New resolution independent approach to noise estimation in Minimum Noise Fraction denoising of tissues measured with Infrared Imaging

The Minimum Noise Fraction (MNF) was originally developed for remote sensing data denoising. However, due to the hyperspectral character of Infrared (IR) imaging data, MNF is becoming increasingly popular in this field. IR imaging obtains data rich in biochemical information, therefore, it is extensively applied in tissue analysis and classification. It is popular to use different IR objectives of different magnification, which combined with Focal Plane Array (FPA) detector of fixed pixels size, give varying projected pixel sizes and as a result – different spatial resolutions. The MNF method proposed by Green et al. uses a noise correlation matrix that is calculated based on neighboring pixel difference, which heavily depends on the registered image magnification and thus spatial resolution, leading to different denoising efficiencies and signal loss. Here, we presented a new resolution-independent approach to noise matrix estimation (MNF2) based on the 2 sequential scans of the sample. In this way, the data acquisition step is only minimally changed, while offering a uniform denoising step. We decided to test our method on representative breast tissue biopsy, due to its spatial and biochemical heterogeneity. We compared the performance of the new method for data measured using objectives giving different spatial pixel projections: low - 11.4 μm (3.5x), standard - 2.7 μm (15x), and high - 1.1 μm (36x). Results of this study show that conventional MNF for standard and low resolutions produces an altered denoised signal, while MNF2 gives a denoised signal of very good quality. In the case of high resolution data, standard MNF gives reasonable results, likewise proposed MNF2.

Damage Mechanism of HgCdTe Focal Plane Array Detector Irradiated Using Mid-Infrared Pulse Laser

To investigate the damage threshold and mechanism of a mid-infrared HgCdTe focal plane array (FPA) detector, relevant experimental and theoretical studies were conducted. The line damage threshold of a HgCdTe FPA detector may be within the range of 0.59 Jcm−2 to 0.71 Jcm−2. The full frame damage threshold of the detector may be in the range of 0.86 Jcm−2 to 1.17 Jcm−2. Experimental results showed that when the energy density reaches 1.17 Jcm−2, the detector exhibits irreversible full frame damage and is completely unable to image. Based on the finite element method, a three-dimensional model of HgCdTe FPAs detector was established to study the heat transfer mechanism, internal stress, and damage sequence. When HgCdTe melts, we think that the detector is damaged. Under these conditions, the theoretical damage threshold calculated using the detector model is 0.55 Jcm−2. The difference between theoretical and experimental values was analyzed. The relationship between damage threshold and pulse width was also studied. It was found that when the pulse width is less than 1000 ns, the damage threshold characterized by peak power density is inversely proportional to pulse width. This relationship can help us predict the experimental damage threshold of an FPA detector. This model is reasonable and convenient for studying the damage of FPA detectors with a mid-infrared pulse laser. The research content in this article has important reference significance for the damage and protection of HgCdTe FPA detectors.

Shortwave Infrared InGaAs Detectors On-Chip Integrated with Subwavelength Polarization Gratings.

Shortwave infrared polarization imaging can increase the contrast of the target to the background to improve the detection system's recognition ability. The division of focal plane polarization indium gallium arsenide (InGaAs) focal plane array (FPA) detector is the ideal choice due to the advantages of compact structure, real-time imaging, and high stability. However, because of the mismatch between nanostructures and photosensitive pixels as well as the crosstalk among the different polarization directions, the currently reported extinction ratio (ER) of superpixel-polarization-integrated detectors cannot meet the needs of high-quality imaging. In this paper, a 1024 × 4 InGaAs FPA detector on-chip integrated with a linear polarization grating (LPG) was realized and tested. The detector displayed good performance throughout the 0.9-1.7 um band, and the ERs at 1064 nm, 1310 nm and 1550 nm reached up to 22:1, 29:1 and 46:1, respectively. For the crosstalk investigation, the optical simulation of the grating-integrated InGaAs pixel was carried out, and the limitation of the ER was calculated. The result showed that the scattering of incident light in the InP substrate led to the crosstalk. Moreover, the deviation of the actual grating morphology from the designed structure caused a further reduction in the ER.

Intra-block pyramid cross-scale network for thermal radiation effect correction of uncooled infrared images.

Thermal radiation effects can greatly degrade the image quality of uncooled infrared focal plane array detection systems. In this paper, we propose a thermal radiation effect correction network based on intra-block pyramid cross-scale feature extraction and fusion. First, an intra-block pyramid residual attention module is introduced to obtain fine-grained features from long-range IR images by extracting cross-scale local features within the residual block. Second, we propose a cross-scale gated fusion module to efficiently integrate the shallow and abstract features at multiple scales of the encoder and decoder through gated linear units. Finally, to ensure accurate correction of thermal radiation effects, we add double-loss constraints in the spatial-frequency domain and construct a single-input, multi-output network with multiple supervised constraints. The experimental results demonstrate that our proposed method outperforms state-of-the-art correction methods in terms of both visual quality and quantitative evaluation metrics.

Laser-interfered studies in HgCdTe infrared focal plane array detector by high-repetition-rate mid-infrared supercontinuum fiber laser

Laser-interfered studies in HgCdTe infrared focal plane array detector by high-repetition-rate mid-infrared supercontinuum fiber laser