We describe the design and first calibration tests of an imaging polarimeter based on Liquid Crystal Variable Retarders (LCVRs), for the study of the solar K-corona. This K-polarimeter (KPol) is part of the visible light path of the UltraViolet and Visible-light Coronal Imager (UVCI) of the Sounding-rocket Coronagraphic Experiment (SCORE). SCORE/UVCI is an externally occulted, off-axis Gregorian telescope, optimized for the narrow-band (i.e., λ/▵λ ~10) imaging of the HeII, λ 30.4 nm and HI λ 121.6 nm coronal emission. We present some preliminary results of the application of LCVR plates to measurements of linear polarized radiation. LCVR plates replace mechanically rotating retarders with electro-optical devices, without no moving parts. LCVR are variable waveplates, in which the change of the retardance is induced by a variable applied voltage. The retardance of a LCVR is a function of the wavelength. KPol observations of the visible coronal continuum of the Sun (K-corona) will be made over the 450-600 nm wavelength band. We have studied the LCVR's properties in this bandpass. We tested a LCVR plate assembled in a linear polarization rotator configuration to measure the polarization plane rotation of input radiation as a function of wavelength. We estimated the LCVR's chromatic response in the KPol wavelength bandpass. The preliminary results show reasonable achromatic behaviour at high regimes of the driving voltage, Vd (i.e., Vd>3 volt).
A new concept CCD camera is currently under development at the XUVLab of the Department of Astronomy and Space Science of the University of Florence. This CCD camera is the proposed detector for the space- and ground-based solar corona observations. This camera will be the detector for the polarimetric channels of the UVC coronagraph of the HERSCHEL rocket mission to observe the solar corona in an optical broadband. The ground-based application consists in a UVC prototype for coronagraphic measurements from Earth in the visible range. Within this project, a CCD camera with innovative features has been produced: the camera controller allows the fine tuning of all the parameters related to charge transfer and CCD readout, i.e., the use of virtually any CCD sensor, and it implements the new concept of high level of versatility, easy management, TCP/IP remote control and display.
A new concept CCD camera is currently under development at the XUVLab of the Department of Astronomy and Space Science of the University of Florence. This CCD camera is the proposed detector for the broadband visible light polarimetric channels of the UVCI coronagraph of HERSCHEL and of Solar Orbiter space missions. The main features of this camera are a high level of versatility and a fast pixel that will satisfy the requirements of both the space missions. Within this project, a versatile CCD controller has been produced with interesting and innovative features: it allows the selection of all the parameters related to charge transfer and CCD readout and therefore it allows the use of virtually any CCD sensor. The software interface is LabVIEW 6i based and it will allow both local and remote control and display.
A new concept CCD camera is currently being realized at the XUV Lab of the Department of Astronomy and Space Science of the University of Florence. The main features we aim to get are a high level of versatility and a fast pixel rate. Within this project, a versatile CCD sequencer has been realized with interesting and innovative features. Based on a microcontroller and complex programmable logic devices (CPLD), it allows the selection of all the parameters related to charge transfer and CCD readout (number, duration and overlapping of serial and parallel transfer clocks, number of output nodes, pixel transfer rate) and therefore it allows the use of virtually any CCD sensor. Comparing to a common DSP-based sequencer, it is immune to jitter noise and it can also reach pixel rates greater than 40 MHz. The software interface is LabVIEW 6i based and it will allow both local or remote control and display. Furthermore, it will be possible to remote debug the system and to upgrade the LabVIEW interface itself and also the microcontroller resident program and the CPLD implemented schemes.
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