Focal Plane Detector Research Articles

Timing Calibration of the Follow-up X-Ray Telescope On Board the Einstein Probe Satellite

Abstract The Follow-up X-ray Telescope (FXT) is one of the main scientific instruments on board the Einstein Probe astronomical satellite, which was launched in 2024 January. FXT consists of two Wolter I type nested telescopes (FXT-A and FXT-B) with a focal length of 1600 mm. The focal plane detector employs a PNCCD with 384 × 384 pixels. The timing mode of FXT serves as the primary operating mode for fast X-ray timing observations. To evaluate and validate the timing performance of FXT prior to launch, a comprehensive timing calibration was performed at the 100 m X-ray test facility. By simulating various periodic Crab-like profiles using the Grid Controlled X-ray Tube (GCXT) in conjunction with a pulsar simulation module, it was verified that the relative time accuracy of FXT exceeds 5 × 10−9. Furthermore, employing GCXT with a voltage pulse generation module enabled the determination of the time resolutions for FXT-A and FXT-B, recorded as 45.6 ± 2.7 μs and 47.1 ± 2.8 μs, respectively. An absolute timing calibration for FXT-B was carried out using the GCXT and a time interval analyzer, revealing a measured time delay of 3.9 ± 2.1 μs for FXT-B.

Ground testing and calibration of focal plane detector flight model on board the first pathfinder of CATCH

Ground testing and calibration of focal plane detector flight model on board the first pathfinder of CATCH

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.

Characterization of newly developed large area SiC sensors for the NUMEN experiment

Characterization of newly developed large area SiC sensors for the NUMEN experiment

Toward the Discovery of New Elements: Production of Livermorium (Z=116) with ^{50}Ti.

The ^{244}Pu(^{50}Ti,xn)^{294-x}Lv reaction was investigated at Lawrence Berkeley National Laboratory's 88-Inch Cyclotron. The experiment was aimed at the production of a superheavy element with Z≥114 by irradiating an actinide target with a beam heavier than ^{48}Ca. Produced Lv ions were separated from the unwanted beam and nuclear reaction products using the Berkeley Gas-filled Separator and implanted into a newly commissioned focal-plane detector system. Two decay chains were observed and assigned to the decay of ^{290}Lv. The production cross section was measured to be σ_{prod}=0.44(_{-0.28}^{+0.58}) pb at a center-of-target center-of-mass energy of 220(3)MeV. This represents the first published measurement of the production of a superheavy element near the "island of stability," with a beam of ^{50}Ti and is an essential precursor in the pursuit of searching for new elements beyond Z=118.

Research on a miniature Mattauch-Herzog mass spectrometer designed for space exploration

Research on a miniature Mattauch-Herzog mass spectrometer designed for space exploration

Remote detection of polluted gases based on thermal infrared spectral imaging in the field

Remote detection of polluted gases based on thermal infrared spectral imaging in the field

Precision Manufacturing in China of Replication Mandrels for Ni-Based Monolithic Wolter-I X-ray Mirror Mandrels

The X-ray satellite “Einstein Probe” of the Chinese Academy of Sciences (CAS) was successfully launched on 9 January 2024 at 15:03 Beijing Time from the Xichang Satellite Launch Center in China with a “Long March-2C” rocket. The Einstein Probe is equipped with two scientific X-ray telescopes. One is the Wide-field X-ray Telescope (WXT), which uses lobster-eye optics. The other is the Follow-up X-ray Telescope (FXT), a Wolter-I type telescope. These telescopes are designed to study the universe for high-energy X-rays associated with transient high-energy phenomena. The FXT consists of two modules based on 54 thin X-ray Wolter-I grazing incidence Ni-replicated mirrors produced by the Italian Media Lario company, as contributions from the European Space Agency and the Max Planck Institute for Extraterrestrial Physics (MPE), which also provided the focal-plane detectors. Meanwhile, the Institute of High Energy Physics (IHEP), together with the Harbin Institute of Technology and Xi’an Institute of Optics and Precision Mechanics, has also completed the development and production of the structural and thermal model (STM), qualification model (QM) and flight model (FM) of FXT mirrors for the Einstein Probe (EP) satellites for demonstration purposes. This paper introduces the precision manufacturing adopted in China of Wolter-I X-ray mirror mandrels similar to those used for the EP-FXT payload. Moreover, the adopted electroformed nickel replication process, based on a chemical nickel–phosphorus alloy, is reported. The final results show that the surface of the produced mandrels after demolding and the internal surface of the mirrors have been super polished to the roughness level better than 0.3 nm RMS and the surface accuracy is better than 0.2 μm, and the mirror angular resolution for single mirror shells may be as good as 17.3 arcsec HPD (Half Power Diameter), 198 arcsec W90 (90% Energy Width) @1.49 keV (Al-K line). These results demonstrate the reliability and advancement of the process. As the first efficient X-ray-focusing optics manufacturing chain established in China, we successfully developed the first focusing mirror prototype that could be used for future X-ray satellite payloads.

Spectral Performance of the Follow-up X-Ray Telescope on Board the EP Satellite

The Follow-up X-ray Telescope (FXT) is one of the two main scientific instruments on board the Einstein Probe astronomical satellite, which was launched in 2024 January. FXT focuses on the energy range of 0.3–10 keV and mainly conducts follow-up observations of transients and burst sources. It consists of two units of completely independent optical system and detector system (FXT-A and FXT-B). The focal plane detector adopts PNCCD provided by Max Planck Institute for Extraterrestrial Physics. FXT was designed to have three operating modes with different integration times and readout schemes, namely full-frame mode, partial-window mode and timing mode. We conducted a detailed calibration for PNCCD at the Institute of High Energy Physics before launch. Our results demonstrate that both FXT-A and FXT-B exhibit excellent spectral performance. The energy resolution (Full Width at Half Maximum) of FXT-A and FXT-B are both better than 85 eV at 1.487 keV. We determined a mean equivalent noise charge around 2.8 e− for FXT-A and FXT-B in three operating modes at −90°C ± 0.5°C, except for a few noisy pixels in full-frame mode. In addition, we measured the relation of charge transfer inefficiency as function of photon energy and confirmed the ability to detect photons in the energy range of 0.3–10 keV. These calibration results have been ingested into the initial version of calibration database and applied to the analysis of scientific data acquired by FXT.

Multifunctional plasmonic metamaterial absorber in the middle infrared range for polarization detection

Multifunctional plasmonic metamaterial absorber in the middle infrared range for polarization detection

Reducing non-effective pixel rate and nonuniformity in AlGaN solar-blind UV focal plane detectors by controlled curvature

A 1600 × 1280 small pixel photodetector was successfully fabricated to verify the controlled curvature of the focal plane array improving the non-effective pixel rate and non-uniformity of the detector. The stress strain generated during epitaxial growth was reduced by growing a 2 μm thick AlN stress correction layer on the backside of the AlGaN/sapphire system substrate. Compared with the material without an AlN stress correction layer on the backside, material curvature reduced from 7.252 μm to 2.740 μm over a length of 0.5 cm. The non-effective pixel rate and the non-uniformity of a focal plane array have been reduced. A process was proposed to reduce the impact of misalignment generated by the flip-chip interconnection process. A solar-blind UV focal plane array was hybridized with a readout integrated circuit using an unsymmetrical flip-chip interconnection process. There is no significant change in peak spectral response, nonuniformity, non-effective pixel rate, or responsivity.

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.

Scanning-assisted focal plane-detection system for a sector-field mass spectrometer - Part-I: Simulation and data processing

Scanning-assisted focal plane-detection system for a sector-field mass spectrometer - Part-I: Simulation and data processing

Radiation tolerance test and performance verification of pnCCD at high temperatures for future satellite mission HiZ-GUNDAM

Radiation tolerance test and performance verification of pnCCD at high temperatures for future satellite mission HiZ-GUNDAM

Autofocusing in digital holography based on an adaptive genetic algorithm

In digital holography (DH), determining the reconstruction distance is critical to the quality of the reconstructed image. However, traditional focal plane detection methods require considerable time investment to reconstruct and evaluate holograms at multiple distances. To address this inefficiency, this paper proposes a fast and accurate autofocusing method based on an adaptive genetic algorithm. This method only needs to find several reconstruction distances in the search area as an initial population, and then adaptively optimize the reconstruction distance through iteration to determine the optimal focal plane in the search area. In addition, an off-axis digital holographic optical system was used to capture the holograms of the USAF resolution test target and the coin. The simulation and experimental results indicated that, compared with the traditional autofocusing, the proposed method can reduce the computation time by about 70% and improve the focal plane accuracy by up to 0.5 mm.

Development of pixelated silicon detector for AMS study

Development of pixelated silicon detector for AMS study

Thermalization of Mesh Reinforced Ultra-Thin Al-Coated Plastic Films: A Parametric Study Applied to the Athena X-IFU Instrument.

The X-ray Integral Field Unit (X-IFU) is one of the two focal plane detectors of Athena, a large-class high energy astrophysics space mission approved by ESA in the Cosmic Vision 2015-2025 Science Program. The X-IFU consists of a large array of transition edge sensor micro-calorimeters that operate at ~100 mK inside a sophisticated cryostat. To prevent molecular contamination and to minimize photon shot noise on the sensitive X-IFU cryogenic detector array, a set of thermal filters (THFs) operating at different temperatures are needed. Since contamination already occurs below 300 K, the outer and more exposed THF must be kept at a higher temperature. To meet the low energy effective area requirements, the THFs are to be made of a thin polyimide film (45 nm) coated in aluminum (30 nm) and supported by a metallic mesh. Due to the small thickness and the low thermal conductance of the material, the membranes are prone to developing a radial temperature gradient due to radiative coupling with the environment. Considering the fragility of the membrane and the high reflectivity in IR energy domain, temperature measurements are difficult. In this work, a parametric numerical study is performed to retrieve the radial temperature profile of the larger and outer THF of the Athena X-IFU using a Finite Element Model approach. The effects on the radial temperature profile of different design parameters and boundary conditions are considered: (i) the mesh design and material, (ii) the plating material, (iii) the addition of a thick Y-cross applied over the mesh, (iv) an active heating heat flux injected on the center and (v) a Joule heating of the mesh. The outcomes of this study have guided the choice of the baseline strategy for the heating of the Athena X-IFU THFs, fulfilling the stringent thermal specifications of the instrument.

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.

Non-uniformity correction algorithm for DoFP adapted to integration time variations.

Division of the focal plane (DoFP) polarization detector is a pivotal technology in real-time polarization detection. This technology integrates a micropolarization array (MPA) onto the conventional focal plane, introducing a more intricate non-uniformity than traditional focal plane detectors. Current non-uniformity correction algorithms for DoFP are difficult to adapt to changes in integration time and perform poorly in low-polarization scenarios. Analyzing the characteristics of DoFP, formulating a pixel response model, and introducing an adaptive non-uniformity correction algorithm tailored for varying integration time. The DoFP analysis vectors are decomposed into average polarization response and unit analysis vectors for correction separately to improve the performance of the correction algorithm in different polarization scenarios. The performance of modern correction algorithms was tested and evaluated using standard uniform images, and the proposed method outperformed existing algorithms in terms of polarization measurement accuracy under the root mean square error (RMSE) metric. Moreover, in natural scene images, our proposed algorithm shows favorable visual effects and distinguishes itself from its superior stability amid changes in the integration time.

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.