ASO-S is a mission proposed for the 25th solar maximum by the Chinese solar community. The scientific objectives are to study the relationships among solar magnetic field, solar flares, and coronal mass ejections (CMEs). ASO-S consists of three payloads: Full-disk Magnetograph (FMG), Lyman-alpha Solar Telescope (LST), and Hard X-ray Imager (HXI), to measure solar magnetic field, to observe CMEs and solar flares, respectively. ASO-S is now under the phase-B studies. This paper makes a brief introduction to the mission.
The waveplate made of Polyvinyl Alcohol (PVA) plastic film has several advantages compared with that of birefringent crystal in visible region, such as its lower cost and insensitivity to temperature and incidence angle. What are the performances when they are used in the near infrared spectral region? In this paper, we provide some experimental results of infrared PVA waveplates. To do this, we make some samples and measure their polarization characteristics at several aspects. Firstly, we measure the performance of these PVA waveplates by precise instruments in laboratory. Secondly, we put the waveplates into a Stokes polarimeter to observe the solar magnetic field at near infrared line FeI1.56μm. By use of this polarimeter mounted on the vertical spectrograph of 2m McMath telescope at Kitt Peak, the two-dimensional Stokes parameters, I, Q, U, and V, of a sunspot were observed. From the results of laboratory and observation, we get the conclusion that PVA waveplate has the fair polarization performance to be used to observe the solar magnetic fields in the near infrared spectral region. By these experiments, we provide a design of an achromatic waveplate in infrared region, which consists of five-element, to illustrate the PVA waveplate is the best choice to it.
A new Stokes polarimeter for high accuracy measurement of solar magnetic field is being developed by National Astronomical Observatories, Chinese Academy of Sciences (NAOC). This instrument will be installed in the Space Solar Telescope (SST), which has a one-meter primary mirror, and a two-dimensional spectrograph with 8-channel birefringent filter. In order to minimize the crosstalk in linear polarization from the circular polarization, a novel optical assembly has been selected. This design consists of a quarter retarder, a rotatable polarizer, and a half retarder. The half retarder will rotate with the polarizer by an angle of half quantity of the rotating angle of the polarizer. In this paper, we will introduce this polarimeter and discuss the achromatic performance of the polarization elements in the polarimeter. We will focus on comparing the orientation and retardation of different kind of achromatic waveplate in profiles and give which is the best one for SST polarimeter. In addition, we will show the calculation crosstalk value of this polarimeter at designed wavelength.
KEYWORDS: Polarimetry, Magnetism, Near infrared, Infrared radiation, Spectrographs, Telescopes, Solar processes, Free electron lasers, Optical components, Infrared search and track
FeI 1.56 micrometers Zeeman-sensitive lines are very important and potential to measure the magnetic field of the deepest layer of the solar photosphere. The new generation polarimeter is designed and manufactured in this wavelength range. By use of the polarimeter mounted on the vertical spectrograph of the 2m solar telescope at Kitt Peak, we can observe the Stokes I, Q, U, Vv parameters simultaneously. The paper presents the introduction of the near infrared polarimeter and the polarmetry of a sunspot group.
A one-meter Space Solar Telescope (SST) is being developed in Beijing Astronomical Observatory. This paper introduces its polarimeter that can get a polarimetric accuracy of 10-4. By the optical design of this polarimeter we succeed in reducing the crosstalk between incident circular and linear polarization light when the polarimeter is installed in front of a birefringent filter. In this article, we select Mueller Matrix to describe the polarization characteristics of optical elements, and compare three kinds of design of polarimeter. From the error analysis we determine the orientation and retardation tolerance of the optical elements in order to control the instrumental polarization less than 10-4. As a result of this analysis, we demonstrate the polarimeter that utilizes a rotatable polarizer and a half waveplate, which has a rotary angle of half quantity of polarizer's, is the best design for minimizing the circular crosstalk and thus is the choice for the SST Polarimeter.
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