Randomness describes one inherent property of self-assembled metamaterials and greatly limits the practical applications of metamaterials based on bottom-up techniques,such as the microsphere lithography technique.Her...Randomness describes one inherent property of self-assembled metamaterials and greatly limits the practical applications of metamaterials based on bottom-up techniques,such as the microsphere lithography technique.Herein,by subtly utilizing the randomness in long-range disorder metasurfaces,we demonstrate a high-performance one-shot full-Stokes polarimeter in the visible waveband.The long-range disorder metasurfaces,i.e.,chiral shells,were realized by depositing Ag on the self-assembled microsphere monolayer comprised of many micro-domains of random lattice directions and areas.The distinct optical anisotropy and chirality in different micro-domains can result in distinct photo-currents to the photodetector array placed underneath upon the injection of polarized lights.Through establishing the mapping relationship S=f[/]between the detected photo-currents/and the states of polarization(SoP)S with the convolutional neural network(CNN)algorithm,we realize a high-precision full-Stokes polarimeter in the waveband ranging from 500 to 650 nm,and the minimum mean square errors(MSEs)can reach about 0.37%(S_(1)),0.33%(S_(2)),and 0.19%(S_(3))at 566 nm.The average MSEs in the investigated waveband are 0.49%(S_(1)),0.45%(S_(2)),and 0.31%(S_(3)),respectively.We have systematically investigated the macro-and micro-optical properties of chiral shells,the optical randomness of chiral shells in different domains,the reference SoP number,the exposure time and pixel number of the CCD,as well as the reliability and stability of the system.展开更多
Full-Stokes polarimeters can detect the polarization states of light,which is critical for the next-generation optical and optoelectronic systems.Traditional full-Stokes polarimeters are either based on bulky optical ...Full-Stokes polarimeters can detect the polarization states of light,which is critical for the next-generation optical and optoelectronic systems.Traditional full-Stokes polarimeters are either based on bulky optical systems or complex metasurface structures,which cause the system complexity with unessential energy loss.Recently,filterless on-chip full-Stokes polarimeters have been demonstrated by using optical anisotropic materials which are able to detect the circularly polarized light.Nevertheless,those on-chip full-Stokes polarimeters have either the limited detection wavelength range or relatively poor device performance that need to be further improved.Here,we report the high performance broadband full-Stokes polarimeters based on rhenium disulfide(ReS_(2)).While the anisotropic structure of the ReS_(2)introduces the in-plane optical anisotropy for linearly polarized light(LP)detection,Schottky contacts formed by the ReS_(2)-Au could break the symmetry,which can detect circularly polarized(CP)light.By building a proper model,all four Stokes parameters can be extracted by using the ReS_(2)nanobelt device.The device delivers a photoresponsivity of 181 A/W,a detectivity of 6.8×10^(10)Jones and can sense the four Stokes parameters of incident light within a wide range of wavelength from 565-800 nm with reasonable average errors.We believe our study provides an alternative strategy to develop high performance broadband on-chip full-Stokes polarimeters.展开更多
This work analyzes the annual fluctuation of the observation data of the Mingantu Solar radio Telescope(MST)in S,C and X bands.It is found that the data vary with local air temperature as the logarithmic attenuation o...This work analyzes the annual fluctuation of the observation data of the Mingantu Solar radio Telescope(MST)in S,C and X bands.It is found that the data vary with local air temperature as the logarithmic attenuation of equipment increases with temperature and frequency.A simplified and effective calibration method is proposed,which is used to calibrate the MST data in 2018-2020,while the correction coefficients are calculated from data in 2018-2019.For S,C and X bands,the root mean square errors of one polarization are 2.7,5.7 and 20 sfu,and the relative errors are 4%,6%and 8%respectively.The calibration of MUSER and SBRS spectra is also performed.The relative errors of MUSER at 1700 MHz,SBRS at 2800 MHz,3050 MHz and 3350 MHz are 8%,8%,11%and 10%respectively.We found that several factors may affect the calibration accuracy,especially at X-band.The method is expected to work for other radio telescopes with similar design.展开更多
Polarimetry plays an important role in the measurement of solar magnetic fields. We devel- oped a high-sensitivity and high-accuracy polarimeter （HHP） based on nematic liquid crystal variable retarders （LCVRs）, wh...Polarimetry plays an important role in the measurement of solar magnetic fields. We devel- oped a high-sensitivity and high-accuracy polarimeter （HHP） based on nematic liquid crystal variable retarders （LCVRs）, which has a compact setup and no mechanical moving parts. The system design and calibration methods are discussed in detail. The azimuth error of the transmission axis of the polarizer as well as the fast axes of the two LCVRs and the quarter-wave plate were determined using dedicated procedures. Linearly and circularly polarized light were employed to evaluate the performance of the HHP. The experimental results indicate that a polarimetric sensitivity of better than 5.7 × 10-3 can be achieved by using a single short-exposure image, while an accuracy on the order of 10-5 can be reached by using a large number of short-exposure images. This makes the HHP a high-performance system that can be used with a ground-based solar telescope for high-precision solar magnetic field investigations.展开更多
The very low frequency(VLF)regime below 30 MHz in the electromagnetic spectrum has presently been drawing global attention in radio astronomical research due to its potentially significant science outcomes exploring m...The very low frequency(VLF)regime below 30 MHz in the electromagnetic spectrum has presently been drawing global attention in radio astronomical research due to its potentially significant science outcomes exploring many unknown extragalactic sources,transients,and so on.However,the nontransparency of the Earth’s ionosphere,ionospheric distortion and artificial radio frequency interference(RFI)have made it difficult to detect the VLF celestial radio emission with ground-based instruments.A straightforward solution to overcome these problems is a space-based VLF radio telescope,just like the VLF radio instruments onboard the Chang’E-4 spacecraft.But building such a space telescope would be inevitably costly and technically challenging.The alternative approach would be then a ground-based VLF radio telescope.Particularly,in the period of post 2020 when the solar and terrestrial ionospheric activities are expected to be in a’calm’state,it will provide us a good chance to perform VLF ground-based radio observations.Anticipating such an opportunity,we built an agile VLF radio spectrum explorer co-located with the currently operational Mingantu Spectra Radio Heliograph(MUSER).The instrument includes four antennas operating in the VLF frequency range 1-70 MHz.Along with them,we employ an eight-channel analog and digital receivers to amplify,digitize and process the radio signals received by the antennas.We present in the paper this VLF radio spectrum explorer and the instrument will be useful for celestial studies of VLF radio emissions.展开更多
POLAR is a compact space-borne detector initially designed to measure the polarization of hard X-rays emitted from Gamma-Ray Bursts in the energy range 50–500 ke V.This instrument was launched successfully onboard th...POLAR is a compact space-borne detector initially designed to measure the polarization of hard X-rays emitted from Gamma-Ray Bursts in the energy range 50–500 ke V.This instrument was launched successfully onboard the Chinese space laboratory Tiangong-2(TG-2) on 2016 September 15.After being switched on a few days later,tens of gigabytes of raw detection data were produced in-orbit by POLAR and transferred to the ground every day.Before the launch date,a full pipeline and related software were designed and developed for the purpose of quickly pre-processing all the raw data from POLAR,which include both science data and engineering data,then to generate the high level scientific data products that are suitable for later science analysis.This pipeline has been successfully applied for use by the POLAR Science Data Center in the Institute of High Energy Physics(IHEP) after POLAR was launched and switched on.A detailed introduction to the pipeline and some of the core relevant algorithms are presented in this paper.展开更多
We report the design concept and performance of a compact,lightweight and economical imaging polarimeter,the Triple Range Imager and POLarimeter(TRIPOL),capable of simultaneous optical imagery and polarimetry.TRIPOL s...We report the design concept and performance of a compact,lightweight and economical imaging polarimeter,the Triple Range Imager and POLarimeter(TRIPOL),capable of simultaneous optical imagery and polarimetry.TRIPOL splits the beam in wavelengths from 400 to 830 nm into g′-,r′-and i′-bands with two dichroic mirrors,and measures polarization with an achromatic half-waveplate and a wire grid polarizer.The simultaneity makes TRIPOL a useful tool for small telescopes for the photometry and polarimetry of time variable and wavelength dependent phenomena.TRIPOL is designed for a Cassegrain telescope with an aperture of^1 m.This paper presents the engineering considerations of TRIPOL and compares the expected with observed performance.Using the Lulin 1-m telescope and 100 seconds of integration,the limiting magnitudes are g′~19.0 mag,r′~18.5 mag and i′~18.0 mag with a signal-to-noise ratio of 10,in agreement with design expectation.The instrumental polarization is measured to be^0.3%in the three bands.Two applications,one to the star-forming cloud IC 5146 and the other to the young variable GM Cep,are presented as demonstrations.展开更多
A new method of single sample polarization filtering is proposed. The algorithm is fast and suitable for the polarization processing of stationary or nonstationary polarized disturbed signals with one or more independ...A new method of single sample polarization filtering is proposed. The algorithm is fast and suitable for the polarization processing of stationary or nonstationary polarized disturbed signals with one or more independent disturbances. A ground wave polarimetric radar with the ability of radio disturbance suppression is then introduced. Some numerical results demonstrate the effectiveness of single sample polarization filtering method for ground wave polarimetric radar.展开更多
Polarimetry plays an important role in investigating physical properties for celestial objects. We present a polarimeter named YFPOL for the Cassegrain focus of the Lijiang 2.4 m Telescope(LJT) of Yunnan Observatories...Polarimetry plays an important role in investigating physical properties for celestial objects. We present a polarimeter named YFPOL for the Cassegrain focus of the Lijiang 2.4 m Telescope(LJT) of Yunnan Observatories, Chinese Academy of Sciences. YFPOL is a traditional single-beam polarimeter with a rotating polarizer. As the focal-reducer instrument Yunnan Faint Object Spectrograph and Camera(YFOSC) is always positioned on the Cassegrain focal plane of LJT, we develop two sets of ultra-thin(thickness <12 mm) polarizer rotation control systems with wireless charging and control functions, which are suitable for mounting on the two front-wheels of YFOSC. One set is used as the polarimetric calibration unit, and the other is for the polarimetric modulation unit. Both of the polarizers have an ultra-high contrast ratio of 1,000,000:1 in the optical band. We investigate the instrumental polarization characteristics(IPCs) in the full field of view that is transferred from YFOSC. Furthermore, we identify that the IPCs change when the Cassegrain axis rotates. The spurious polarization from the IPCs can be effectively minimized by flat-fielding using the unpolarized domeflat, when the Cassegrain rotation angle is the same or nearest to that of the polarization observation. We develop a quasiautomatic pipeline for YFPOL and its effectiveness has been verified by tests of the polarimetric observation with blazar S5 0716+714. The calibration is performed by observing the zero-polarized and highly-polarized standard stars. We successfully reach high precision polarization in the 7’ field of view, and the systematic uncertainty is below 0.8% for a V = 11.68 target with a 10 s exposure. The instrument polarization angle offset is 2°. 6. YFPOL is not only a simple polarimeter, but also a spectropolarimeter with grisms that can be considered in the future.展开更多
The polarization characteristics of an astronomical telescope is an important factor that affects polarimetry accuracy. Polarization modeling is an essential means to achieve high precision and efficient polarization ...The polarization characteristics of an astronomical telescope is an important factor that affects polarimetry accuracy. Polarization modeling is an essential means to achieve high precision and efficient polarization measurement of the telescope, especially for the alt-azimuth mount telescope. At present, the polarization model for the telescope(i.e., the physical parametric model) is mainly constructed using the polarization parameters of each optical element. In this paper, an artificial neural network(ANN) is used to model the polarization characteristics of the telescope. The ANN model between the physical parametric model residual and the pointing direction of the telescope is obtained, which reduces the model deviation caused by the incompleteness of the physical parametric model. Compared with the physical parametric model, the model fitting and predictive accuracy of the New Vacuum Solar Telescope(NVST) is improved after adopting the ANN model. After using the ANN model, the polarization cross-talk from I to Q, U, and V can be reduced from 0.011 to 0.007, and the crosstalk among Q, U, and V can be reduced from 0.047 to 0.020, which effectively improves the polarization measurement accuracy of the telescope.展开更多
The J-TEXT three-wave polarimeter-interferometer system(POLARIS),which measures timespace distribution of electron density and current density,has been optimized with both the optical system and the equilibrium recons...The J-TEXT three-wave polarimeter-interferometer system(POLARIS),which measures timespace distribution of electron density and current density,has been optimized with both the optical system and the equilibrium reconstruction method.The phase resolution of a Faraday rotation angle has been improved from 0.1 to 0.06 degree in chords from–0.18 to 0.18 m(plasma minor radius),and the sawtooth oscillation behavior has been detected by Faraday rotation angle measurement.By combining the POLARIS measured data and the equilibrium and fitting code(EFIT),an upgraded equilibrium reconstruction method has been developed,which provides a more accurate temporal and spatial distribution of current density and electron density.By means of the optimized POLARIS and improved equilibrium reconstruction,variations of profiles with increasing density have been carried out,under both Ohmic and electron cyclotron resonance heating discharges.展开更多
PolarLight is a space-borne X-ray polarimeter that measures the X-ray polarization via electron tracking in an ionization chamber.It is a collimated instrument and thus suffers from the background on the whole detecto...PolarLight is a space-borne X-ray polarimeter that measures the X-ray polarization via electron tracking in an ionization chamber.It is a collimated instrument and thus suffers from the background on the whole detector plane.The majority of background events are induced by high energy charged particles and show ionization morphologies distinct from those produced by X-rays of interest.Comparing on-source and off-source observations,we find that the two datasets display different distributions on image properties.The boundaries between the source and background distributions are obtained and can be used for background discrimination.Such a means can remove over 70%of the background events measured with PolarLight.This approaches the theoretical upper limit of the background fraction that is removable and justifies its effectiveness.For observations with the Crab nebula,the background contamination decreases from 25%to 8%after discrimination,indicative of a polarimetric sensitivity of around 0.2 Crab for PolarLight.This work also provides insights into future X-ray polarimetric telescopes.展开更多
In-depth studies of solar flares emissions and energy releases include analyses of polarization data. Polarization gives clear information about mechanisms and processes leading to electron acceleration and photon pro...In-depth studies of solar flares emissions and energy releases include analyses of polarization data. Polarization gives clear information about mechanisms and processes leading to electron acceleration and photon production. Despite of many past attempts, the key energy range of hard X-rays was only rarely explored and results were inconclusive. To large extend it was due to greater instrumental complications. Currently several novel polarimeters are either to be employed or under constructions for both balloon and satellite based observations. The novel hard X-ray polarimeter POLAR is an instrument developed by a collaboration between Switzerland, China and Poland. It is primarily designed for high accuracy polarization measurements from the prompt photon emissions of the gamma-ray bursts. The satellite orientation and instrument pointing direction make it also capable for precise measurements of polarization in solar flares. The instrument should fly in near future onboard of the Chinese Space Station TG2.展开更多
This study presents an electronics system for cosmic X-ray polarization detection(CXPD).The CXPD was designed as a high-sensitivity soft X-ray polarimeter with a measurement energy range of 2-10 keV carried by a CubeS...This study presents an electronics system for cosmic X-ray polarization detection(CXPD).The CXPD was designed as a high-sensitivity soft X-ray polarimeter with a measurement energy range of 2-10 keV carried by a CubeSat.A stable and functionally complete electronics system under power and space constraints is a key challenge.The complete CXPD electronics system(CXPDES)comprises hardware and firmware.CXPDES adopts a three-layer electronic board structure based on functionality and available space.Two gas pixel detectors(GPDs)were placed on the top layer board,and CXPDES provided the GPDs with voltages up to-4000 V.Each GPD signal was digitized,compressed,encoded,and stored before being transmitted to the ground.The CXPDES provided stable and high-speed communication based on a scheme that separated command and data transmission,and it supports the CXPDES in-orbit upgrade.In addition,environmental monitors,silicon photomultiplier(SiPM)triggers,power management,GPDs configuration,and mode switches were included in the overall operating logic of the CXPDES.The results obtained by testing the CXPDES showed that it satisfied all the requirements of CXPD.The CXPDES provides design experience and technological readiness for future large-area X-ray polarimetry missions.展开更多
The Advanced Space-based Solar Observatory(ASO-S) mission aims to explore the two most spectacular eruptions on the Sun: solar flares and coronal mass ejections(CMEs), and their magnetism.For the study of CMEs, the pa...The Advanced Space-based Solar Observatory(ASO-S) mission aims to explore the two most spectacular eruptions on the Sun: solar flares and coronal mass ejections(CMEs), and their magnetism.For the study of CMEs, the payload Lyman-alpha Solar Telescope(LST) has been proposed. It includes a traditional white-light coronagraph and a Lyman-alpha coronagraph which opens a new window to CME observations. Polarization measurements taken by white-light coronagraphs are crucial for deriving fundamental physical parameters of CMEs. To make such measurements, there are two options for a Stokes polarimeter which have been applied by existing white-light coronagraphs for space missions. One uses a single or triple linear polarizer, the other involves both a half-wave plate and a linear polarizer. We find that the former option is subject to less uncertainty in the derived Stokes vector propagating from detector noise.The latter option involves two plates which are prone to internal reflections and may have a reduced transmission factor. Therefore, the former option is adopted as our Stokes polarimeter scheme for LST. Based on the parameters of the intended linear polarizer(s) colorPol provided by CODIXX and the half-wave plate 2-APW-L2-012 C by Altechna, it is further shown that the imperfect maximum transmittance of the polarizer significantly increases the variance amplification of Stokes vector by at least about 50% when compared with the ideal case. The relative errors of Stokes vector caused by the imperfection of colorPol polarizer and the uncertainty due to the polarizer assembly in the telescope are estimated to be about 5%. Among the considered parameters, we find that the dominant error comes from the uncertainty in the maximum transmittance of the polarizer.展开更多
In this paper, we present a simple Stokes parameter measurement method for a rotating quarter-wave plate polarimeter. This method is used to construct a model to describe the principle of how the magnitudes of errors ...In this paper, we present a simple Stokes parameter measurement method for a rotating quarter-wave plate polarimeter. This method is used to construct a model to describe the principle of how the magnitudes of errors influence the deviation of the output light Stokes parameter, on the basis of accuracy analysis of the retardance error of the quarter-wave plate, the misalignment of the analyzing polarizer, and the phase shift of the measured signals, which will help us to determine the magnitudes of these errors and then to acquire the correct results of Stokes parameters. The method is validated by the experiments on left-handed circularly polarized and linear horizontal polarization beams. With the improved method, the maximum measurement deviations of Stokes parameters for these two different polarized states are reduced from 2.72% to 2.68%, and from 3.83% to 1.06% respectively. Our results demonstrate that the proposed method can be used as a promising approach to Stokes parameter measurement for a rotating quarter-wave plate polarimeter.展开更多
In this work,we report a method of removing scattering induced retardance in polarization sensitive fnll field optical coherence tomography(PS-FFOCT).First,the Mueller matrix that describes its operation is derived.Th...In this work,we report a method of removing scattering induced retardance in polarization sensitive fnll field optical coherence tomography(PS-FFOCT).First,the Mueller matrix that describes its operation is derived.The thickness invariant retardance induced by the scattering of collagenous fiber bundles is then used to find the accurate values of the birefringence of the layers that consist collagenous fibers.Finally,the initial en face birefringent images of in vitro beef tendon samples are presented to demonstrate the capability of our method.展开更多
The magnetic field is one of the most important parameters in solar physics,and a polarimeter is the key device to measure the solar magnetic field.Liquid crystals based Stokes polarimeter is a novel technology,and wi...The magnetic field is one of the most important parameters in solar physics,and a polarimeter is the key device to measure the solar magnetic field.Liquid crystals based Stokes polarimeter is a novel technology,and will be applied for magnetic field measurement in the first space-based solar observatory satellite developed by China,Advanced Space-based Solar Observatory.However,the liquid crystals based Stokes polarimeter in space is not a mature technology.Therefore,it is of great scientific significance to study the control method and characteristics of the device.The retardation produced by a liquid crystal variable retarder is sensitive to the temperature,and the retardation changes 0.09°per 0.10℃.The error in polarization measurement caused by this change is 0.016,which affects the accuracy of magnetic field measurement.In order to ensure the stability of its performance,this paper proposes a high-precision temperature control system for liquid crystals based Stokes polarimeter in space.In order to optimize the structure design and temperature control system,the temperature field of liquid crystals based Stokes polarimeter is analyzed by the finite element method,and the influence of light on the temperature field of the liquid crystal variable retarder is analyzed theoretically.By analyzing the principle of highprecision temperature measurement in space,a high-precision temperature measurement circuit based on integrated operational amplifier,programmable amplifier and 12 bit A/D is designed,and a high-precision space temperature control system is developed by applying the integral separation PI temperature control algorithm and PWM driving heating films.The experimental results show that the effect of temperature control is accurate and stable,whenever the liquid crystals based Stokes polarimeter is either in the air or vacuum.The temperature stability is within±0.0150℃,which demonstrates greatly improved stability for the liquid crystals based Stokes polarimeter.展开更多
基金supported by the National Natural Science Foundation of China(Nos.11604227,62175222,and 62105369)the International Visiting Program for Excellent Young Scholars of SCU(No.20181504)+3 种基金the International Science and Technology Innovation Cooperation of Sichuan Province(No.21GJHZ0230)the China Postdoctoral Science Foundation(No.W03019023601004373)the Natural Science Foundation of Hunan Province(No.2025JJ40065)the Basic Research Program of National Major Project of China(No.JG2023273)。
文摘Randomness describes one inherent property of self-assembled metamaterials and greatly limits the practical applications of metamaterials based on bottom-up techniques,such as the microsphere lithography technique.Herein,by subtly utilizing the randomness in long-range disorder metasurfaces,we demonstrate a high-performance one-shot full-Stokes polarimeter in the visible waveband.The long-range disorder metasurfaces,i.e.,chiral shells,were realized by depositing Ag on the self-assembled microsphere monolayer comprised of many micro-domains of random lattice directions and areas.The distinct optical anisotropy and chirality in different micro-domains can result in distinct photo-currents to the photodetector array placed underneath upon the injection of polarized lights.Through establishing the mapping relationship S=f[/]between the detected photo-currents/and the states of polarization(SoP)S with the convolutional neural network(CNN)algorithm,we realize a high-precision full-Stokes polarimeter in the waveband ranging from 500 to 650 nm,and the minimum mean square errors(MSEs)can reach about 0.37%(S_(1)),0.33%(S_(2)),and 0.19%(S_(3))at 566 nm.The average MSEs in the investigated waveband are 0.49%(S_(1)),0.45%(S_(2)),and 0.31%(S_(3)),respectively.We have systematically investigated the macro-and micro-optical properties of chiral shells,the optical randomness of chiral shells in different domains,the reference SoP number,the exposure time and pixel number of the CCD,as well as the reliability and stability of the system.
基金the support from the National Key Research and Development Program of China(2022YFB2803900 and 2018YFA0704403)NSFC(62074064)。
文摘Full-Stokes polarimeters can detect the polarization states of light,which is critical for the next-generation optical and optoelectronic systems.Traditional full-Stokes polarimeters are either based on bulky optical systems or complex metasurface structures,which cause the system complexity with unessential energy loss.Recently,filterless on-chip full-Stokes polarimeters have been demonstrated by using optical anisotropic materials which are able to detect the circularly polarized light.Nevertheless,those on-chip full-Stokes polarimeters have either the limited detection wavelength range or relatively poor device performance that need to be further improved.Here,we report the high performance broadband full-Stokes polarimeters based on rhenium disulfide(ReS_(2)).While the anisotropic structure of the ReS_(2)introduces the in-plane optical anisotropy for linearly polarized light(LP)detection,Schottky contacts formed by the ReS_(2)-Au could break the symmetry,which can detect circularly polarized(CP)light.By building a proper model,all four Stokes parameters can be extracted by using the ReS_(2)nanobelt device.The device delivers a photoresponsivity of 181 A/W,a detectivity of 6.8×10^(10)Jones and can sense the four Stokes parameters of incident light within a wide range of wavelength from 565-800 nm with reasonable average errors.We believe our study provides an alternative strategy to develop high performance broadband on-chip full-Stokes polarimeters.
基金supported by NSFC(Grant Nos.11433006,11661161015,11790301,11790305,11973057,11773043,11941003 and 2018YFA0404602)the MOST grant(2014FY120300)。
文摘This work analyzes the annual fluctuation of the observation data of the Mingantu Solar radio Telescope(MST)in S,C and X bands.It is found that the data vary with local air temperature as the logarithmic attenuation of equipment increases with temperature and frequency.A simplified and effective calibration method is proposed,which is used to calibrate the MST data in 2018-2020,while the correction coefficients are calculated from data in 2018-2019.For S,C and X bands,the root mean square errors of one polarization are 2.7,5.7 and 20 sfu,and the relative errors are 4%,6%and 8%respectively.The calibration of MUSER and SBRS spectra is also performed.The relative errors of MUSER at 1700 MHz,SBRS at 2800 MHz,3050 MHz and 3350 MHz are 8%,8%,11%and 10%respectively.We found that several factors may affect the calibration accuracy,especially at X-band.The method is expected to work for other radio telescopes with similar design.
基金funded by the National Natural Science Foundation of China(NSFC,Grant Nos.11661161011,11433007,11220101001,11328302,11373005 and 11303064)the Opening Project of Key Laboratory of Astronomical Optics&Technology,Nanjing Institute of Astronomical Optics&Technology,Chinese Academy of Sciences(CASKLAOT-KF201606)+4 种基金the“Strategic Priority Research Program”of the Chinese Academy of Sciences(Grant No.XDA04075200)the special fund for astronomy of CAS(2015–2016)the special funding for Young Researcher of Nanjing Institute of Astronomical Optics&Technologythe International Partnership Program of the Chinese Academy of Sciences(Grant No.114A32KYSB20160018)the Mt.Cuba Astronomical Foundation
文摘Polarimetry plays an important role in the measurement of solar magnetic fields. We devel- oped a high-sensitivity and high-accuracy polarimeter （HHP） based on nematic liquid crystal variable retarders （LCVRs）, which has a compact setup and no mechanical moving parts. The system design and calibration methods are discussed in detail. The azimuth error of the transmission axis of the polarizer as well as the fast axes of the two LCVRs and the quarter-wave plate were determined using dedicated procedures. Linearly and circularly polarized light were employed to evaluate the performance of the HHP. The experimental results indicate that a polarimetric sensitivity of better than 5.7 × 10-3 can be achieved by using a single short-exposure image, while an accuracy on the order of 10-5 can be reached by using a large number of short-exposure images. This makes the HHP a high-performance system that can be used with a ground-based solar telescope for high-precision solar magnetic field investigations.
基金funded by the National Natural Science Foundation of China(NSFC,Nos.11573043,11790305,11433006)National Key R&D 278 Program of China(2018YFA0404602)+1 种基金the CE4 mission of the Chinese Lunar Exploration Program:the Netherlands-China Low Frequency Explorer(NCLE)Chinese Academy of Sciences(CAS)Strategic Priority Research Program(XDA15020200)。
文摘The very low frequency(VLF)regime below 30 MHz in the electromagnetic spectrum has presently been drawing global attention in radio astronomical research due to its potentially significant science outcomes exploring many unknown extragalactic sources,transients,and so on.However,the nontransparency of the Earth’s ionosphere,ionospheric distortion and artificial radio frequency interference(RFI)have made it difficult to detect the VLF celestial radio emission with ground-based instruments.A straightforward solution to overcome these problems is a space-based VLF radio telescope,just like the VLF radio instruments onboard the Chang’E-4 spacecraft.But building such a space telescope would be inevitably costly and technically challenging.The alternative approach would be then a ground-based VLF radio telescope.Particularly,in the period of post 2020 when the solar and terrestrial ionospheric activities are expected to be in a’calm’state,it will provide us a good chance to perform VLF ground-based radio observations.Anticipating such an opportunity,we built an agile VLF radio spectrum explorer co-located with the currently operational Mingantu Spectra Radio Heliograph(MUSER).The instrument includes four antennas operating in the VLF frequency range 1-70 MHz.Along with them,we employ an eight-channel analog and digital receivers to amplify,digitize and process the radio signals received by the antennas.We present in the paper this VLF radio spectrum explorer and the instrument will be useful for celestial studies of VLF radio emissions.
基金financial support from the Joint Research Fund in Astronomy under a cooperative agreement between the National Natural Science Foundation of China and the Chinese Academy of Sciences (Grant No. U1631242)the National Natural Science Foundation of China (Grant Nos. 11503028 and 11403028)+1 种基金the Strategic Priority Research Program of the Chinese Academy of Sciences (XDB23040400)the National Basic Research Program (973 Program) of China (2014CB845800)
文摘POLAR is a compact space-borne detector initially designed to measure the polarization of hard X-rays emitted from Gamma-Ray Bursts in the energy range 50–500 ke V.This instrument was launched successfully onboard the Chinese space laboratory Tiangong-2(TG-2) on 2016 September 15.After being switched on a few days later,tens of gigabytes of raw detection data were produced in-orbit by POLAR and transferred to the ground every day.Before the launch date,a full pipeline and related software were designed and developed for the purpose of quickly pre-processing all the raw data from POLAR,which include both science data and engineering data,then to generate the high level scientific data products that are suitable for later science analysis.This pipeline has been successfully applied for use by the POLAR Science Data Center in the Institute of High Energy Physics(IHEP) after POLAR was launched and switched on.A detailed introduction to the pipeline and some of the core relevant algorithms are presented in this paper.
基金supported by Grant-in-Aid for Science Research from the Ministry of Education,Culture,Sports and Technology of Japan
文摘We report the design concept and performance of a compact,lightweight and economical imaging polarimeter,the Triple Range Imager and POLarimeter(TRIPOL),capable of simultaneous optical imagery and polarimetry.TRIPOL splits the beam in wavelengths from 400 to 830 nm into g′-,r′-and i′-bands with two dichroic mirrors,and measures polarization with an achromatic half-waveplate and a wire grid polarizer.The simultaneity makes TRIPOL a useful tool for small telescopes for the photometry and polarimetry of time variable and wavelength dependent phenomena.TRIPOL is designed for a Cassegrain telescope with an aperture of^1 m.This paper presents the engineering considerations of TRIPOL and compares the expected with observed performance.Using the Lulin 1-m telescope and 100 seconds of integration,the limiting magnitudes are g′~19.0 mag,r′~18.5 mag and i′~18.0 mag with a signal-to-noise ratio of 10,in agreement with design expectation.The instrumental polarization is measured to be^0.3%in the three bands.Two applications,one to the star-forming cloud IC 5146 and the other to the young variable GM Cep,are presented as demonstrations.
文摘A new method of single sample polarization filtering is proposed. The algorithm is fast and suitable for the polarization processing of stationary or nonstationary polarized disturbed signals with one or more independent disturbances. A ground wave polarimetric radar with the ability of radio disturbance suppression is then introduced. Some numerical results demonstrate the effectiveness of single sample polarization filtering method for ground wave polarimetric radar.
基金supported by the National Key R&D Program of China with No.2021YFA1600404the National Natural Science Foundation of China (NSFC, Grant Nos. 11991051, 11573067, 11673062,11527804, U1931206 and 11873091)+3 种基金the CAS “Light of West China” Programthe Yunnan Province Basic Research Plan with No. 2019FA001the China Manned Space Project with No. CMS-CSST-2021-A06funded by Yunnan Province,Chinese Academy of Sciences and NSFC。
文摘Polarimetry plays an important role in investigating physical properties for celestial objects. We present a polarimeter named YFPOL for the Cassegrain focus of the Lijiang 2.4 m Telescope(LJT) of Yunnan Observatories, Chinese Academy of Sciences. YFPOL is a traditional single-beam polarimeter with a rotating polarizer. As the focal-reducer instrument Yunnan Faint Object Spectrograph and Camera(YFOSC) is always positioned on the Cassegrain focal plane of LJT, we develop two sets of ultra-thin(thickness <12 mm) polarizer rotation control systems with wireless charging and control functions, which are suitable for mounting on the two front-wheels of YFOSC. One set is used as the polarimetric calibration unit, and the other is for the polarimetric modulation unit. Both of the polarizers have an ultra-high contrast ratio of 1,000,000:1 in the optical band. We investigate the instrumental polarization characteristics(IPCs) in the full field of view that is transferred from YFOSC. Furthermore, we identify that the IPCs change when the Cassegrain axis rotates. The spurious polarization from the IPCs can be effectively minimized by flat-fielding using the unpolarized domeflat, when the Cassegrain rotation angle is the same or nearest to that of the polarization observation. We develop a quasiautomatic pipeline for YFPOL and its effectiveness has been verified by tests of the polarimetric observation with blazar S5 0716+714. The calibration is performed by observing the zero-polarized and highly-polarized standard stars. We successfully reach high precision polarization in the 7’ field of view, and the systematic uncertainty is below 0.8% for a V = 11.68 target with a 10 s exposure. The instrument polarization angle offset is 2°. 6. YFPOL is not only a simple polarimeter, but also a spectropolarimeter with grisms that can be considered in the future.
基金supported by the National Natural Science Foundation of China(Grant Nos.11833010,11773069,11773072,11873091 and 12073077)Key Research and Development Project of Yunnan Province(202003AD150019)+1 种基金Yunnan Province Basic Research Plan(2019FA001)the CAS‘Light of West China’Program(Y9XB015001)。
文摘The polarization characteristics of an astronomical telescope is an important factor that affects polarimetry accuracy. Polarization modeling is an essential means to achieve high precision and efficient polarization measurement of the telescope, especially for the alt-azimuth mount telescope. At present, the polarization model for the telescope(i.e., the physical parametric model) is mainly constructed using the polarization parameters of each optical element. In this paper, an artificial neural network(ANN) is used to model the polarization characteristics of the telescope. The ANN model between the physical parametric model residual and the pointing direction of the telescope is obtained, which reduces the model deviation caused by the incompleteness of the physical parametric model. Compared with the physical parametric model, the model fitting and predictive accuracy of the New Vacuum Solar Telescope(NVST) is improved after adopting the ANN model. After using the ANN model, the polarization cross-talk from I to Q, U, and V can be reduced from 0.011 to 0.007, and the crosstalk among Q, U, and V can be reduced from 0.047 to 0.020, which effectively improves the polarization measurement accuracy of the telescope.
基金the National MCF Energy R&D Program of China(No.2018YFE0310300)National Natural Science Foundation of China(Nos.11905080 and 51821005)。
文摘The J-TEXT three-wave polarimeter-interferometer system(POLARIS),which measures timespace distribution of electron density and current density,has been optimized with both the optical system and the equilibrium reconstruction method.The phase resolution of a Faraday rotation angle has been improved from 0.1 to 0.06 degree in chords from–0.18 to 0.18 m(plasma minor radius),and the sawtooth oscillation behavior has been detected by Faraday rotation angle measurement.By combining the POLARIS measured data and the equilibrium and fitting code(EFIT),an upgraded equilibrium reconstruction method has been developed,which provides a more accurate temporal and spatial distribution of current density and electron density.By means of the optimized POLARIS and improved equilibrium reconstruction,variations of profiles with increasing density have been carried out,under both Ohmic and electron cyclotron resonance heating discharges.
基金funding support from the National Natural Science Foundation of China(Grant Nos.11633003,12025301 and 11821303)the CAS Strategic Priority Program on Space Science(Grant No.XDA15020501-02)the National Key R&D Project(Grant Nos.2018YFA0404502 and 2016YFA040080X)。
文摘PolarLight is a space-borne X-ray polarimeter that measures the X-ray polarization via electron tracking in an ionization chamber.It is a collimated instrument and thus suffers from the background on the whole detector plane.The majority of background events are induced by high energy charged particles and show ionization morphologies distinct from those produced by X-rays of interest.Comparing on-source and off-source observations,we find that the two datasets display different distributions on image properties.The boundaries between the source and background distributions are obtained and can be used for background discrimination.Such a means can remove over 70%of the background events measured with PolarLight.This approaches the theoretical upper limit of the background fraction that is removable and justifies its effectiveness.For observations with the Crab nebula,the background contamination decreases from 25%to 8%after discrimination,indicative of a polarimetric sensitivity of around 0.2 Crab for PolarLight.This work also provides insights into future X-ray polarimetric telescopes.
文摘In-depth studies of solar flares emissions and energy releases include analyses of polarization data. Polarization gives clear information about mechanisms and processes leading to electron acceleration and photon production. Despite of many past attempts, the key energy range of hard X-rays was only rarely explored and results were inconclusive. To large extend it was due to greater instrumental complications. Currently several novel polarimeters are either to be employed or under constructions for both balloon and satellite based observations. The novel hard X-ray polarimeter POLAR is an instrument developed by a collaboration between Switzerland, China and Poland. It is primarily designed for high accuracy polarization measurements from the prompt photon emissions of the gamma-ray bursts. The satellite orientation and instrument pointing direction make it also capable for precise measurements of polarization in solar flares. The instrument should fly in near future onboard of the Chinese Space Station TG2.
基金supported by the National Natural Science Foundation of China (Nos.11875146,U1932143)National Key Research and Development Program of China (No.2020YFE0202002)。
文摘This study presents an electronics system for cosmic X-ray polarization detection(CXPD).The CXPD was designed as a high-sensitivity soft X-ray polarimeter with a measurement energy range of 2-10 keV carried by a CubeSat.A stable and functionally complete electronics system under power and space constraints is a key challenge.The complete CXPD electronics system(CXPDES)comprises hardware and firmware.CXPDES adopts a three-layer electronic board structure based on functionality and available space.Two gas pixel detectors(GPDs)were placed on the top layer board,and CXPDES provided the GPDs with voltages up to-4000 V.Each GPD signal was digitized,compressed,encoded,and stored before being transmitted to the ground.The CXPDES provided stable and high-speed communication based on a scheme that separated command and data transmission,and it supports the CXPDES in-orbit upgrade.In addition,environmental monitors,silicon photomultiplier(SiPM)triggers,power management,GPDs configuration,and mode switches were included in the overall operating logic of the CXPDES.The results obtained by testing the CXPDES showed that it satisfied all the requirements of CXPD.The CXPDES provides design experience and technological readiness for future large-area X-ray polarimetry missions.
基金supported by NSFC (Grant Nos. 11522328, 11473070, 11427803 and U1731241)CAS Strategic Pioneer Program on Space Science (Grant Nos. XDA15010600, XDA15052200, XDA15320103 and XDA15320301)the National Key Research and Development Program of China (2018YFA0404202)
文摘The Advanced Space-based Solar Observatory(ASO-S) mission aims to explore the two most spectacular eruptions on the Sun: solar flares and coronal mass ejections(CMEs), and their magnetism.For the study of CMEs, the payload Lyman-alpha Solar Telescope(LST) has been proposed. It includes a traditional white-light coronagraph and a Lyman-alpha coronagraph which opens a new window to CME observations. Polarization measurements taken by white-light coronagraphs are crucial for deriving fundamental physical parameters of CMEs. To make such measurements, there are two options for a Stokes polarimeter which have been applied by existing white-light coronagraphs for space missions. One uses a single or triple linear polarizer, the other involves both a half-wave plate and a linear polarizer. We find that the former option is subject to less uncertainty in the derived Stokes vector propagating from detector noise.The latter option involves two plates which are prone to internal reflections and may have a reduced transmission factor. Therefore, the former option is adopted as our Stokes polarimeter scheme for LST. Based on the parameters of the intended linear polarizer(s) colorPol provided by CODIXX and the half-wave plate 2-APW-L2-012 C by Altechna, it is further shown that the imperfect maximum transmittance of the polarizer significantly increases the variance amplification of Stokes vector by at least about 50% when compared with the ideal case. The relative errors of Stokes vector caused by the imperfection of colorPol polarizer and the uncertainty due to the polarizer assembly in the telescope are estimated to be about 5%. Among the considered parameters, we find that the dominant error comes from the uncertainty in the maximum transmittance of the polarizer.
基金Project supported by the National High Technology Research and Development Program of China(Grant No.2015AA123702)the National Natural Science Foundation of China(Grant No.61505222)
文摘In this paper, we present a simple Stokes parameter measurement method for a rotating quarter-wave plate polarimeter. This method is used to construct a model to describe the principle of how the magnitudes of errors influence the deviation of the output light Stokes parameter, on the basis of accuracy analysis of the retardance error of the quarter-wave plate, the misalignment of the analyzing polarizer, and the phase shift of the measured signals, which will help us to determine the magnitudes of these errors and then to acquire the correct results of Stokes parameters. The method is validated by the experiments on left-handed circularly polarized and linear horizontal polarization beams. With the improved method, the maximum measurement deviations of Stokes parameters for these two different polarized states are reduced from 2.72% to 2.68%, and from 3.83% to 1.06% respectively. Our results demonstrate that the proposed method can be used as a promising approach to Stokes parameter measurement for a rotating quarter-wave plate polarimeter.
基金This research was supported by the Fundamental Research Funds for the Central Universities(30920010003)the Natural Science Foundation of China(NSFC)(61275198,60978069).
文摘In this work,we report a method of removing scattering induced retardance in polarization sensitive fnll field optical coherence tomography(PS-FFOCT).First,the Mueller matrix that describes its operation is derived.The thickness invariant retardance induced by the scattering of collagenous fiber bundles is then used to find the accurate values of the birefringence of the layers that consist collagenous fibers.Finally,the initial en face birefringent images of in vitro beef tendon samples are presented to demonstrate the capability of our method.
基金the National Natural Science Foundation of China(Grant Nos.11427803,11427901 and 11773040)the Strategic Pioneer Program on Space Science,Chinese Academy of Sciences(CAS)(XDA04061002 and XDA15010800)the Public Technology Service Center,National Astronomical Observatories of CAS(829011V01)。
文摘The magnetic field is one of the most important parameters in solar physics,and a polarimeter is the key device to measure the solar magnetic field.Liquid crystals based Stokes polarimeter is a novel technology,and will be applied for magnetic field measurement in the first space-based solar observatory satellite developed by China,Advanced Space-based Solar Observatory.However,the liquid crystals based Stokes polarimeter in space is not a mature technology.Therefore,it is of great scientific significance to study the control method and characteristics of the device.The retardation produced by a liquid crystal variable retarder is sensitive to the temperature,and the retardation changes 0.09°per 0.10℃.The error in polarization measurement caused by this change is 0.016,which affects the accuracy of magnetic field measurement.In order to ensure the stability of its performance,this paper proposes a high-precision temperature control system for liquid crystals based Stokes polarimeter in space.In order to optimize the structure design and temperature control system,the temperature field of liquid crystals based Stokes polarimeter is analyzed by the finite element method,and the influence of light on the temperature field of the liquid crystal variable retarder is analyzed theoretically.By analyzing the principle of highprecision temperature measurement in space,a high-precision temperature measurement circuit based on integrated operational amplifier,programmable amplifier and 12 bit A/D is designed,and a high-precision space temperature control system is developed by applying the integral separation PI temperature control algorithm and PWM driving heating films.The experimental results show that the effect of temperature control is accurate and stable,whenever the liquid crystals based Stokes polarimeter is either in the air or vacuum.The temperature stability is within±0.0150℃,which demonstrates greatly improved stability for the liquid crystals based Stokes polarimeter.
