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| technical:description [2026/03/05 21:30] – [(3) First optical focus instrumentation, F1] etienne | technical:description [2026/03/17 15:57] (current) – etienne | ||
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| Overall, the working characteristics of THEMIS are the following: | Overall, the working characteristics of THEMIS are the following: | ||
| * Observational electromagnetic spectrum range: 400-1100 nm | * Observational electromagnetic spectrum range: 400-1100 nm | ||
| - | * Imaging field-of-view : ~2’x2’; square shaped | + | * Imaging field-of-view : ~2’x2’ square shaped |
| * Overall focal ratio : f/62 | * Overall focal ratio : f/62 | ||
| * Effective aperture: 92 cm | * Effective aperture: 92 cm | ||
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| ==== (2) Full-Sun guider ==== | ==== (2) Full-Sun guider ==== | ||
| - | A full-sun guider has been setup on the telescope outer ring of the heat protection, near the 1m entrance plate. It uses a 45/500 mm objective, an Herschel prism, a neutral filter, a broadband (10 nm) green continuum 540nm photosphere filter (Baader Planetarium GmbH), and a ZWO ASI 178 mono (2000x3000 pixel²) CMOS camera. The full-sun guider image is always available in the control room of THEMIS. The full-Sun guider images are not meant for pure scientific analysis. Please note that given the location of the entrance pupil and depending on the telescope/ | + | A full-sun guider has been setup on the telescope outer ring of the heat protection, near the 1m entrance plate. It uses a 45/500 mm objective, an Herschel prism, a neutral filter, a broadband (10 nm) green continuum 540nm photosphere filter (Baader Planetarium GmbH), and a ZWO ASI 178 mono (2000x3000 pixel²) CMOS camera. The full-sun guider image is always available in the control room of THEMIS. The full-Sun guider images are not meant for pure scientific analysis. Please note that given the location of the entrance pupil and depending on the telescope/ |
| < | < | ||
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| The original fundamental //raison d' | The original fundamental //raison d' | ||
| - | Maintaining THEMIS excellent polarimetric sensitivity has been one of the main challenge of the upgrade of THEMIS and the development of [[tao |THEMIS adpative optics (TAO)]]. The original optical design of THEMIS was composed of a double beam, each of them carrying the opposite polarisation state and having its own optical path. This design was not compatible with the existence of an AO in which the wavefront correction requires an unique light beam. The inclusion of TAO has thus required the complete redisign of THEMIS optical path as well as polarisation analysis instrumentation. | + | Maintaining THEMIS excellent polarimetric sensitivity has been one of the main challenge of the upgrade of THEMIS and the development of [[technical:tao |THEMIS adpative optics (TAO)]]. The original optical design of THEMIS was composed of a double beam, each of them carrying the opposite polarisation state and having its own optical path. This design was not compatible with the existence of an AO in which the wavefront correction requires an unique light beam. The inclusion of TAO has thus required the complete redisign of THEMIS optical path as well as polarisation analysis instrumentation. |
| As of today, a Full-Stokes analyzer (An4) is located at F1, producing superposed dual-beam polarimetry with beam exchange. The analyser is composed of double Savart plates. The first Savart plates generate the dual beam, each of them carrying opposite polarisation state, e.g. I±S, with S the Stokes polarization parameter. The second Savart plates then superimpose both beams, each of them in a polarisation state that is orthogonal to each other. Both beams then do behave as one, differing only by their linear polarization state. | As of today, a Full-Stokes analyzer (An4) is located at F1, producing superposed dual-beam polarimetry with beam exchange. The analyser is composed of double Savart plates. The first Savart plates generate the dual beam, each of them carrying opposite polarisation state, e.g. I±S, with S the Stokes polarization parameter. The second Savart plates then superimpose both beams, each of them in a polarisation state that is orthogonal to each other. Both beams then do behave as one, differing only by their linear polarization state. | ||
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| Thanks to THEMIS “polarization friendly” new optical path (geometry of the elevation axis, field rotator, coatings), polarizer output can travel through the telescope and reach the spectrograph cameras “minimally perturbed”. Latter, just ahead of each of the spectral cameras, a Wollaston prism splitter separates the superimposed beam into complementary Stokes components to form the spectral focal plane. | Thanks to THEMIS “polarization friendly” new optical path (geometry of the elevation axis, field rotator, coatings), polarizer output can travel through the telescope and reach the spectrograph cameras “minimally perturbed”. Latter, just ahead of each of the spectral cameras, a Wollaston prism splitter separates the superimposed beam into complementary Stokes components to form the spectral focal plane. | ||
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| - | Polarimetric analyser : < | + | < |
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| ==== (8-9) Broadband Imaging (BBI) filter & camera ==== | ==== (8-9) Broadband Imaging (BBI) filter & camera ==== | ||
| - | If illuminated, | + | If illuminated, |
| THEMIS BBI camera is currently a 2000 x 2000 pixels Andor Zyla camera. This camera relies on the scientific CMOS technology (active-pixel sensor). This offers a high quality image of a subset of the THEMIS field-of-view with a very fast read-out, enabling the capture of a burst of images capture (up to 40 images/ | THEMIS BBI camera is currently a 2000 x 2000 pixels Andor Zyla camera. This camera relies on the scientific CMOS technology (active-pixel sensor). This offers a high quality image of a subset of the THEMIS field-of-view with a very fast read-out, enabling the capture of a burst of images capture (up to 40 images/ | ||
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| If the slit-jaw slit configuration has been chosen at F2, the light not entering the spectrograph is captured by the slit-jaw camera. Slit-jaw images offers the context images of the spectrograph slit and allows a precise knowledge of the localisation of the slit. | If the slit-jaw slit configuration has been chosen at F2, the light not entering the spectrograph is captured by the slit-jaw camera. Slit-jaw images offers the context images of the spectrograph slit and allows a precise knowledge of the localisation of the slit. | ||
| - | As almost all the remaining 15 watts of radiative power are then directed toward the camera, filters shall be place upstream of the camera to reduce the light flux. Presently a green continuum filter at XXX nm, with a 10 nm passband is used. | + | As almost all the remaining 15 watts of radiative power are then directed toward the camera, filters shall be place upstream of the camera to reduce the light flux. Presently a green continuum filter at 540 nm, with a 10 nm passband is used. |
| The slit-jaw camera is currently a ZWO ASI 178MM camera capturing the F2 field-of-view on a 3000x2000 pixels array. It's a CMOS camera. Without polarimetry, | The slit-jaw camera is currently a ZWO ASI 178MM camera capturing the F2 field-of-view on a 3000x2000 pixels array. It's a CMOS camera. Without polarimetry, | ||
