Polarization-sensitive Detectors Research Articles

Photon noise correlations in millimeter-wave telescopes.

Many modern millimeter and submillimeter ("mm-wave") telescopes for astronomy are deploying more detectors by increasing the detector pixel density and, with the rise of lithographed detector architectures and high-throughput readout techniques, it is becoming increasingly practical to overfill the focal plane. However, when the pixel pitch p p i x is small compared to the product of the wavelength λ and the focal ratio F, or p p i x ≲1.2F λ, the Bose term of the photon noise correlates between neighboring detector pixels due to the Hanbury Brown and Twiss (HBT) effect. When this HBT effect is non-negligible, the array-averaged sensitivity scales with the detector count N det less favorably than the uncorrelated limit of Ndet-1/2. In this paper, we present a general prescription to calculate this HBT correlation based on a quantum optics formalism and extend it to polarization-sensitive detectors. We then estimate the impact of HBT correlations on the sensitivity of a model mm-wave telescope and discuss the implications for a focal plane design.

Polarization-Sensitive Detector Based on MoTe2/WTe2 Heterojunction for Broadband Optoelectronic Imaging.

Polarization-sensitive detectors have significant applications in modern communication and information processing. In this study. We present a polarization-sensitive detector based on a MoTe2/WTe2 heterojunction, where WTe2 forms a favorable bandgap structure with MoTe2 after forming the heterojunction. This enhances the carrier separation efficiency and photoelectric response. We successfully achieved wide spectral detection ranging from visible to near-infrared light. Specifically, under zero bias, our photodetector exhibits a responsivity (R) of 0.6 A/W and a detectivity (D*) of 3.6 × 1013 Jones for 635 nm laser illumination. Moreover, the photoswitching ratio can approach approximately 6.3 × 105. Importantly, the polarization sensitivity can reach 3.5 (5.2) at 635 (1310) nm polarized light at zero bias. This study both unveils potential for utilizing MoTe2/WTe2 heterojunctions as polarization-sensitive detectors and provides novel insights for developing high-performance optoelectronic devices.

Emission of coherent spin waves from a helimagnetic layer embedded within a ferromagnetic matrix

We have studied the Schlömann emission of exchange spin waves by a microwave driven helimagnetic layer containing integer and half-integer numbers of turns into surrounding semi-infinite ferromagnetic media. Analytical expressions of the emitted spin-wave’s amplitude and phase are obtained in closed form. For the case of a half-integer number of turns, we propose a method for applying the driving magnetic field so that the emission has an asymmetric (nonreciprocal) character, controlled by the polarization of the driving magnetic field. Our results can be used both in the design of polarization-sensitive magnonic detectors of microwaves and in using microwaves to characterize the microscopic configuration of non-collinear magnetic materials.

Polarization-sensitive UV detector based on a double-layer subwavelength grating of Al and ZnO

Polarization-sensitive detectors are of great importance in the fields of remote sensing and imaging, environmental monitoring, and medical diagnosis. The surface plasmon effect can the enable polarization sensitivity of photodetectors through metallic gratings. However, limited by the precision of the nano-fabrication process, it is difficult to fabricate an ultraviolet (UV) polarization-sensitive detector integrated with sub-wavelength metal gratings and the polarization extinction ratio is relatively low. In this paper, an Al–ZnO composite double-layer grating structure was designed. The ZnO active layer and the Al layer were both fabricated into same-sized grating structures. Through this design, the slit width could be enlarged to some degree, while the response to 90° polarized light remained low. It is beneficial to realize a high polarization ratio and to spare the need for rigid fabrication accuracy. In addition, the influence of the structural parameters of the grating on the performance of the detector was studied by simulation. It was found that the resonance wavelength can be adjusted by changing the slit width and grating height, respectively. This provides a useful means for polarization-sensitive detection in different wavelength ranges. The polarization extinction ratio of the detector with a double-layer composite grating can reach 52 in the UV band (365 nm). This provides a good alternative to replace the traditional framework relying on the combination of polarizers and detectors. Moreover, it is a promising structure for high-density integrated photodetectors and imaging chips in the future.

Ultrafast carrier dynamic anisotropy of single crystal rhenium disulfide flake based on transient absorption spectroscopy

In recent years, rhenium disulfide (ReS2) has attracted much attention in polarization dependent photonic applications due to its anisotropic optoelectronic response. To reveal the anisotropic response mechanisms, single crystal layered ReS2 flake with lateral size of about 10 μm is obtained using mechanical exfoliation method, and the ultrafast carrier dynamics of an individual flake is studied using transient absorption microscopy. The excited carrier concentration of layered ReS2 flake exhibits obvious polarization dependence of the pump light, which is caused by the anisotropic linear absorption and electron mobility rates in different orientations. These results could provide more references for the application of ReS2 in polarization sensitive detectors and optoelectronic devices.

The Gas Pixel Detectors for the Imaging X-Ray Polarimetry Explorer mission

On December 9th 2021, the Imaging X-ray Polarimetry Explorer (IXPE) was launched aboard a Falcon 9 to its equatorial low Earth orbit, where it began scientific observations on January 11th 2022. Equipped with three identical telescopes – each providing simultaneous polarimetric, spatial, spectroscopic and temporal information – IXPE will measure, for the first time in the soft X-ray band, the polarization of tens of celestial objects of different classes: supernova remnants, pulsars and pulsar wind nebulae, magnetars, active galactic nuclei and accreting black holes.Here I will describe the design and construction of the innovative polarization-sensitive gaseous detectors mounted in the focal plane of the IXPE telescopes, as well as report on the first scientific results of the mission.

In-plane optical anisotropy of quasi-one-dimensional layered semiconductor Nb<sub>4</sub>P<sub>2</sub>S<sub>21</sub> single crystal

Transition-metal phosphorous chalcogenide <i>M</i>PS (<i>M</i> = transition metal), an emerging type of two-dimensional (2D) van der Waals material with the unique optical and opto-electronic properties, has received much attention. The quasi-one-dimensional chain structure of Nb<sub>4</sub>P<sub>2</sub>S<sub>21</sub> will possess the strong anisotropic optical and photoelectric properties. Therefore, the single crystal and low-dimensional materials of Nb<sub>4</sub>P<sub>2</sub>S<sub>21</sub> have potential applications in new polarization controllers, polarization-sensitive photoelectronic detectors, etc. However, there is still a lack of research on the anisotropic optical properties of the high-quality Nb<sub>4</sub>P<sub>2</sub>S<sub>21</sub> single crystals. Herein, the millimeter-sized Nb<sub>4</sub>P<sub>2</sub>S<sub>21</sub> single crystals are successfully prepared by the chemical vapor transport method. The chemical composition, the crystal structure and the anisotropic optical properties of the Nb<sub>4</sub>P<sub>2</sub>S<sub>21</sub> single crystals are carefully analyzed. The energy dispersive X-ray spectroscopy results show that the element distribution is uniform and the element ratio is close to the stoichiometric ratio. The X-ray diffraction and the transmission electron microscopy results show a good crystallinity. The absorption spectra shows that the optical band gap of the Nb<sub>4</sub>P<sub>2</sub>S<sub>21</sub> single crystal is 1.8 eV. Interestingly, the Nb<sub>4</sub>P<sub>2</sub>S<sub>21</sub> single crystal can be mechanically exfoliated to obtain few-layer material. The thickness-dependent Raman spectra show that the Raman vibration peaks of bulk and few-layer Nb<sub>4</sub>P<sub>2</sub>S<sub>21</sub> each have only a weak shift, indicating a weak interlayer interaction in the Nb<sub>4</sub>P<sub>2</sub>S<sub>21</sub> single crystal. In order to make an in-depth study of the optical properties of Nb<sub>4</sub>P<sub>2</sub>S<sub>21</sub> single crystals, the polarized-dependent Raman spectra and the femtosecond transient absorption (TA) spectra by using pump pulses and probe pulses with a wavelength of 400 nm and a wavelength range of 500–700 nm are recorded. Importantly, the polarized-dependent Raman scattering spectra with the angle-dependent measurements reveal that the intensity of Raman peak at 202 cm<sup>–1</sup> and at 489 cm<sup>–1</sup> show a 2-fold symmetry and a 4-fold symmetry in the parallel and vertical polarization configurations, respectively. Moreover, the results of ultrafast carrier dynamics with the in-plane rotation angles of Nb<sub>4</sub>P<sub>2</sub>S<sub>21</sub> single crystals in the parallel polarization configurations, clearly indicate that both the hot carrier number and the relaxation rate after photoexcitation have the in-plane anisotropic properties. These results are useful in understanding the in-plane anisotropic optical properties of Nb<sub>4</sub>P<sub>2</sub>S<sub>21</sub> single crystal, which can further promote their applications in the low-dimensional angle-dependent optoelectronics.

Template-confined growth of copper halides micro-wire arrays for highly polarization-sensitive deep-ultraviolet photodetectors with a polarization sensitivity of 4.45

Polarization-sensitive detectors operating in the deep-ultraviolet (DUV) region have been favored for their great meaning in the field of biological tissue morphology, image display systems and sensors. The advantages of intrinsic DUV light absorption, low-symmetry crystal structure and morphology anisotropy make Cs3Cu2I5 micro-wire arrays the perfect choice for polarization-sensitive DUV photodetection. In this work, we demonstrate a polarization-sensitive DUV photodetector developed from the Cs3Cu2I5 micro-wire arrays, which were prepared by a microchannel-confined crystallization strategy, and the optical and optoelectronic anisotropy of Cs3Cu2I5 micro-wire arrays with adjustable sizes were systematically investigated. Owing to the high crystallinity and good carrier transportation ability of the Cs3Cu2I5 micro-wires, the photodetector exhibits a large responsivity of ∼ 23.6 A/W and a fast response speed of 2.9/370.7 μs. Based on the intrinsic anisotropy of the asymmetric structure and external morphology anisotropy of the Cs3Cu2I5 micro-wires, the photodetector exhibits an ultra-high polarization sensitivity of 4.45. Moreover, the photodetector can keep nearly the identical capability even after 40 days exposure in the open air. This work reveals the potential of Cs3Cu2I5 as environmentally-friendly and stable candidates for polarization-sensitive DUV photodetectors, opening up possibilities for developing polarized DUV imaging technology.

Polarization Sensitive Photodetectors Based on Two-Dimensional WSe2.

In this work we show the possibility of imparting polarization-sensitive properties to two-dimensional films of graphene-like semiconductors, using WSe2 as an example, by the application of ordered silver triangular nanoprisms. In addition, such nanoprisms made it possible to increase the optical sensitivity of optical detectors created on two-dimensional films by a factor of five due to surface plasmon resonance. The peculiarities of the surface plasmon resonance were shown by theoretical modeling, and the optimal conditions of its occurrence were determined. This article demonstrates an effective approach to creating spectrally selective, polarization-sensitive detectors based on two-dimensional graphene-like semiconductors.

New Antenna for Detecting Polarization States of Terahertz

The polarization measurement of terahertz (THz) waves is indispensable in THz time-domain spectroscopy (THz-TDS) applications to detect material properties. The rapid development of accurate THz wave polarization-sensitive detectors will greatly promote THz-TDS applications. A new type of photoconductive antenna array detector is proposed in this paper. The antenna is composed of two vertical 1*2 arrays, which respectively detect the orthogonal component of the terahertz pulse in any direction, while quickly and accurately detecting the polarized THz waves. Rotating the detector to measure the THz electric field at different angles shows the reliability of the detector for THz wave polarization measurement. Its polarization detection accuracy is 0.2°. At the same time, we use the response matrix to analyze the symmetry of the antenna array.

The IXPE instrument calibration equipment

The Imaging X-ray Polarimetry Explorer is a mission dedicated to the measurement of X-ray polarization from tens of astrophysical sources belonging to different classes. Expected to be launched at the end of 2021, the payload comprises three mirrors and three focal plane imaging polarimeters, the latter being designed and built in Italy. While calibration is always an essential phase in the development of high-energy space missions, for IXPE it has been particularly extensive both to calibrate the response to polarization, which is peculiar to IXPE, and to achieve a statistical uncertainty below the expected sensitivity. In this paper we present the calibration equipment that was designed and built at INAF-IAPS in Rome, Italy, for the calibration of the polarization-sensitive focal plane detectors on-board IXPE. Equipment includes calibration sources, both polarized and unpolarized, stages to align and move the beam, test detectors and their mechanical assembly. While all these equipments were designed to fit the specific needs of the IXPE Instrument calibration, their versatility could also be used in the future for other projects.

Two-Dimensional Guanidine-Based Hybrid Perovskites with Strong Dichroism for Multiwavelength Polarization-Sensitive Detection.

Two-dimensional (2D) organic-inorganic hybrid perovskites, benefiting from their natural anisotropy of quantum-well motifs and optical properties, have shown remarkable polarization-dependent responses superior to the 3D counterparts. Here, for the first time, multiwavelength polarization-sensitive detectors were fabricated by using single crystals of a guanidine-based 2D hybrid perovskite, (BA)2 (GA)Pb2 I7 (where BA+ is n-butylammonium and GA+ is guanidium). Its unique 2D quantum-well structure results in strong crystallographic-dependence of optical absorption. Strikingly, our crystal-based photodetector exhibits a prominent photocurrent dichroic ratio (Imax /Imin ) of ∼2.2 at 520 nm, higher than the typical 2D inorganic materials (GeSe, ∼1.09, PdSe2 , ∼1.8). In addition, notable dichroic ratios of 1.29 and 1.23 at 405 nm and 637 nm are also created for the multiwavelength polarized-light detection. The prominent detecting performances, including low dark current (1.6×10-11 A), considerable on/off ratio (∼2×103 ), high photodetectivity (∼3.3×1011 Jones) and responsivity (∼12.01 mA W-1 ), make (BA)2 (GA)Pb2 I7 a promising candidate for polarized-light detection. This work sheds light on the rational engineering of new 2D hybrid perovskites for the high-performance optoelectronic device applications.

Initial Tests and Characterization of the Readout Electronics for the IXPE Mission

Due to be launched in late 2021, the imaging X-ray polarimetry explorer (IXPE) is a NASA Small Explorer mission designed to perform polarization measurements in the 2–8-keV band, complemented with imaging, spectroscopy, and timing capabilities. At the heart of the focal plane, there are a set of three polarization-sensitive gas pixel detectors, each based on a custom-integrated circuit acting as a charge-collecting anode, with their readout electronics. We designed an integrated test equipment based on the VMEbus protocol to characterize the performance of such detectors, debug the IXPE readout electronics, and perform stable data acquisitions to study the whole system. The test campaign was conducted to validate the readout processor against the mission requirements in more demanding conditions than the worst case foreseen for in-orbit operations. The test showed that the device under test could sustain an event rate with a 5.9-keV source, nearly twice the worst case of 300 Hz at 3 keV, with a dead time down to 1.1 ms. Additionally, we performed various scans in the readout electronics parameter space to optimize its performance in observing celestial sources. The success of the test campaign proved the robustness and reliability of the system in these conditions, legitimating its adoption for the IXPE mission.

Simulating instrumental systematics of Cosmic Microwave Background experiments with s4cmb

The observation of cosmic microwave background (CMB) anisotropies is one of the key probes of physical cosmology. The weak nature of this signal has driven the construction of increasingly complex and sensitive experiments observing the sky at multiple frequencies with thousands of polarization sensitive detectors. Given the high sensitivity of such experiments, instrumental systematic effects can become the limiting factor towards the full scientific exploitation of their data. In this paper we present s4cmb (Systematics for CMB), a Python package designed to simulate raw data streams in time domain of modern CMB experiments based on bolometric technology, and to inject in these realistic instrumental systematics effects. The aim of the package is to help assessing the contamination due to instrumental systematic effects on real data, to guide the design of future instruments, as well as to increase the realism of simulated data sets required in the development of accurate data analysis methods.

Actively tunable polarization-sensitive multiband absorber based on graphene* *Project supported by the National Natural Science Foundation of China (Grant Nos. 11804178 and 11274188) and the Natural Science Foundation of Shandong Province, China (Grant No. ZR2018BA027).

We design an actively tunable polarization-sensitive multiband absorber in the mid-infrared region, which consists of stacked graphene multilayers separated by dielectric layers on a metal mirror. Benefiting from the anisotropic structure, the absorber has dual absorption bands with almost perfect absorption at different wavelengths under the x and y polarizations. Analyzing the electric field amplitude distributions and the surface currents, we find that the absorption peaks under the same polarization are excited in the graphene layers independently. Therefore, more absorption bands can be achieved by increasing the graphene layers. Adjusting the Fermi energy of the graphene layers, the working wavelengths of the polarization-sensitive multiband absorbers can be tuned actively, and thus achieving a wide band regulation range. Besides, the peak number and the peak strength of the multiband absorber can be actively controlled by the polarization angle as well. We also propose a method to design an actively tunable polarization-sensitive multiband absorber, which may have potential applications in mid-infrared devices, such as polarization-sensitive filters and detectors.

Low-temperature growth of high-quality a-plane GaN epitaxial films on lattice-matched LaAlO3 substrates

Nonpolar GaN demonstrates a significant potential for application in the field of light-emitting diodes, polarization sensitive detectors, etc. However, the achievement of the high-quality nonpolar GaN epitaxial films still faces significant challenges. In this study, the high-quality nonpolar a-plane GaN epitaxial films have been obtained on the lattice-matched LaAlO3(100) substrates through the low-temperature pulsed laser deposition. The ~500 nm-thick nonpolar a-plane epitaxial films grown at 450 °C exhibit small full-width at half-maximum (FWHM) of 0.15° and 0.20° for GaN(11–20) and GaN(10–11) for the X-ray rocking curves, respectively, and very smooth surface with a root-mean-square roughness of 1.2 nm. In addition, sharp and abrupt GaN/LaAlO3 hetero-interfaces are observed. The developed GaN epitaxial films present strong potential of application in the field of UV detection and curing in the near future.

Magnetic-induced PL modulation of InGaN/GaN MQWs by a CoFeB ferromagnetic cap layer

III-nitride semiconductors show wide applications in general illumination, displays, visible-light communication, power electronics and so on. Until recently, it has been rather hard to experimentally realize magnetic modulation or coupling due to the lack of magnetism in GaN-based semiconductors. Here, we have fabricated the nonpolar a-plane InGaN/GaN MQWs capped by ferromagnetic CoFeB thin film. After magnetizing a CoFeB cap layer under a low magnetic field of 100 mT, the peak PL wavelength of nonpolar a-plane InGaN/GaN MQWs has a red shift from 460 to 475 nm, while its PL polarization degree shows an effective enhancement from 29% to 41% by increasing the CoFeB thickness. The magnetic-induced carrier redistribution has played a great role on the PL modulation of nonpolar InGaN/GaN MQW active region. Therefore, our proposed method exhibits a great potential to develop the highly polarized light emitters, optical polarization modulation, polarization-sensitive detectors, magnetic-optical modulation and coupling sensing in future multi-field applications.

Superconducting Ti/TiN Thin Films for mm-Wave Absorption

Polarization-sensitive detectors at 120–500 GHz are required for the observation of the cosmic microwave background radiation. In this paper, superconducting thin films based on Ti/TiN bilayers are developed to be integrated as electromagnetic wave absorbers in suspended cooled silicon bolometers. The critical temperature (Tc) is tuned in the range of 600–800 mK through the superconductivity proximity effect between Ti and TiN to optimize the absorption of the incident power while minimizing the heat capacity of the system at low temperature. Ti/TiN bilayer samples are fabricated on silicon with two different thicknesses (100/5 and 300/5 nm). Electrical characterizations at low temperature have been performed and revealed the effect of thermal annealing (20–250 °C) on residual stress, Tc, critical magnetic field (Hc) and resistance above Tc. A physical characterization by X-ray photoelectron spectroscopy provides evidences of oxidized states which may explain these effects.

A high-resolution combined scanning laser and widefield polarizing microscope for imaging at temperatures from 4 K to 300 K.

Polarized light microscopy, as a contrast-enhancing technique for optically anisotropic materials, is a method well suited for the investigation of a wide variety of effects in solid-state physics, as, for example, birefringence in crystals or the magneto-optical Kerr effect (MOKE). We present a microscopy setup that combines a widefield microscope and a confocal scanning laser microscope with polarization-sensitive detectors. By using a high numerical aperture objective, a spatial resolution of about 240 nm at a wavelength of 405 nm is achieved. The sample is mounted on a 4He continuous flow cryostat providing a temperature range between 4 K and 300 K, and electromagnets are used to apply magnetic fields of up to 800 mT with variable in-plane orientation and 20 mT with out-of-plane orientation. Typical applications of the polarizing microscope are the imaging of the in-plane and out-of-plane magnetization via the longitudinal and polar MOKE, imaging of magnetic flux structures in superconductors covered with a magneto-optical indicator film via the Faraday effect, or imaging of structural features, such as twin-walls in tetragonal SrTiO3. The scanning laser microscope furthermore offers the possibility to gain local information on electric transport properties of a sample by detecting the beam-induced voltage change across a current-biased sample. This combination of magnetic, structural, and electric imaging capabilities makes the microscope a viable tool for research in the fields of oxide electronics, spintronics, magnetism, and superconductivity.

Planckintermediate results

Measurements of flux density are described for five planets, Mars, Jupiter, Saturn, Uranus, and Neptune, across the sixPlanckHigh Frequency Instrument frequency bands (100–857 GHz) and these are then compared with models and existing data. In our analysis, we have also included estimates of the brightness of Jupiter and Saturn at the three frequencies of thePlanckLow Frequency Instrument (30, 44, and 70 GHz). The results provide constraints on the intrinsic brightness and the brightness time-variability of these planets. The majority of the planet flux density estimates are limited by systematic errors, but still yield better than 1% measurements in many cases. Applying data fromPlanckHFI, theWilkinsonMicrowave Anisotropy Probe (WMAP), and the Atacama Cosmology Telescope (ACT) to a model that incorporates contributions from Saturn’s rings to the planet’s total flux density suggests a best fit value for the spectral index of Saturn’s ring system ofβring= 2.30 ± 0.03 over the 30–1000 GHz frequency range. Estimates of the polarization amplitude of the planets have also been made in the four bands that have polarization-sensitive detectors (100–353 GHz); this analysis provides a 95% confidence level upper limit on Mars’s polarization of 1.8, 1.7, 1.2, and 1.7% at 100, 143, 217, and 353 GHz, respectively. The average ratio between thePlanck-HFI measurements and the adopted model predictions for all five planets (excluding Jupiter observations for 353 GHz) is 1.004, 1.002, 1.021, and 1.033 for 100, 143, 217, and 353 GHz, respectively. Model predictions for planet thermodynamic temperatures are therefore consistent with the absolute calibration ofPlanck-HFI detectors at about the three-percent level. We compare our measurements with published results from recent cosmic microwave background experiments. In particular, we observe that the flux densities measured byPlanckHFI and WMAP agree to within 2%. These results allow experiments operating in the mm-wavelength range to cross-calibrate againstPlanckand improve models of radiative transport used in planetary science.