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| technical:description [2025/02/12 09:39] – etienne | technical:description [2025/03/24 17:36] (current) – [(14) Spectral cameras] etienne |
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| ===== THEMIS technical description ===== | ===== THEMIS technical description ===== |
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| THEMIS is a versatile 92cm effective apperture Ritchey-Chrétien optical solar telescope that can be used in daylight for solar or bright objects observations, or at night for fainter objects. THEMIS handle the (extremely) wide range of available light energy flux through a dedicated light distribution detailed below. \\ | THEMIS is a versatile 92cm effective aperture Ritchey-Chrétien optical solar telescope that can be used in daylight for solar or bright objects observations, or at night for fainter objects. THEMIS handle the (extremely) wide range of available light energy flux through a dedicated light distribution detailed below. \\ |
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| Overall, the working characteristics of THEMIS are the following: | Overall, the working characteristics of THEMIS are the following: |
| * 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 apperture: 92 cm | * Effective aperture: 92 cm |
| * Effective focal length: ~57m | * Effective focal length: ~57m |
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| <html> <a href="https://www.themis.iac.es/lib/exe/fetch.php?media=results:gallery:schema:themis_optpath_functionaldiagram.jpg"><img src="https://www.themis.iac.es/lib/exe/fetch.php?media=results:gallery:schema:themis_optpath_functionaldiagram.jpg" style="width:90%; height: auto;"></a></html> | <html> <a href="https://www.themis.iac.es/lib/exe/fetch.php?media=results:gallery:schema:themis_optpath_functionaldiagram2.jpg"><img src="https://www.themis.iac.es/lib/exe/fetch.php?media=results:gallery:schema:themis_optpath_functionaldiagram2.jpg" style="width:90%; height: auto;"></a></html> |
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| ==== (2) Full-Sun guider ==== | ==== (2) Full-Sun guider ==== |
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| 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 green continuum 540nm photosphere filter, and a ZWO ASI 178 mono (2kx3k) CMOS camera.The full-sun guider image is always available in the control room of THEMIS. Please note that given the location of the entrance pupil and depending on the telescope/dome relative positions, this guider may be momentarily obscured by the dome edge(for less than 30 seconds in any circumstance). \\ | 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/dome relative positions, this guider may be momentarily obscured by the dome edge(for less than 30 seconds in any circumstance). <html><font color="#ff9900"> Camera settings can be changed by the user in the control room. Acquisition is left to the needs and appreciation of the user. </font></html>\\ |
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| <html><font color="#0000ff"> The image from this camera is an available data product </font></html> [[observation:data#Full-sun guider images| (cf. THEMIS data products)]]. | <html><font color="#0000ff"> The image from this camera is an available data product </font></html> [[observation:data#Full-sun guider images| (cf. THEMIS data products)]]. |
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| ==== (7) Beam splitters at F2 ==== | ==== (7) Beam splitters ==== |
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| THEMIS has currently no unique solution for a feeding a context camera in all the possible situations of flux. This is why, just ahead of the F2 optical focus, a translation stage is present with diverse beam-splitting options. <html><font color="#ff9900"> THEMIS observer shall decide on the adequate option. The choice correspond to the relative % of light flux that feeds the context camera or the spectrograph. We recommend the user to choose one configuration for the whole run, as for now the amount of refocusing and adjusting the flux on the camera after a change is not precisely known.</font></html> A cartoon of the different option is presented on the right. | THEMIS has currently several solutions for a feeding the broadband imaging (BBI) camera depending on the possible situations of incoming light flux. This is why, ahead of the F2 optical focus, a translation stage is present with diverse beam-splitting options. <html><font color="#ff9900"> THEMIS observer shall decide on the adequate option. The choice correspond to the relative % of light flux that feeds the BBI camera or the spectrograph. We recommend the user to choose one configuration for the whole run, as for now the amount of refocusing and adjusting the flux on the camera after a change is not precisely known.</font></html> A cartoon of the different option is presented on the right. |
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| * Passthrough/Hole: 100% light transmitted to spectrograph; 0% reflected to context camera (no context camera data). This option is for planetary and stellar spectropolarimetry requesting 100% of the flux to the spectrograph. Obviously there is then no light on the context camera, hence no context camera data. However, there is light on the slit-jaw camera with a mirror decker slit, providing a low quality image of the field,and showing the slit position. \\ | * Passthrough/Hole: 100% light transmitted to spectrograph; 0% reflected to BBI camera. This option is mainly designed for planetary and stellar spectropolarimetry requesting 100% of the flux to the spectrograph. Obviously there is then no light on the BBI camera, hence no broadband imaging data. However, there is light on the slit-jaw camera with a mirror decker slit, providing a lower quality image of the field, and showing the slit position. \\ |
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| * Plain lambda/10 mirror: 0% light transmitted to spectrograph (no slit-jaw and spectrograph data); 0% reflected to context camera.This option is suitable for pure imaging program of (preferably) faint objects, e.g. planets, stars. It is also an engineering mode for tuning the adaptive optics NCP abberations. \\ | * Plain lambda/10 mirror: 0% light transmitted to spectrograph (no slit-jaw and spectrograph data); 100% reflected to the BBI camera. This option is suitable for pure imaging program of (preferably) faint objects, e.g. planets, stars. It is also an engineering mode for tuning the adaptive optics for non-common path abberations (NCPA). \\ |
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| * Custom wideband beamsplitter (BS): 80% light transmitted to spectrograph ; 20% reflected to context camera. This option allows the context camera to run in parallel with the spectrograph, providing a high quality field image together with the spectropolarimetric analysis. The ratio 20/80 has been chosen because the 2nd surface coating of the BS plate shall provoke a (displaced) 2nd image in the range 0.5 to 1%. A ratio of 20 to 40 % of reflection with the first surface is thus requested to safely ignore this issue, so that the flux of the first surface reflexion remains significantly larger than the second one. \\ | * Custom wideband beamsplitter (BS): 80% light transmitted to spectrograph ; 20% reflected to BBI camera. This option allows the BBI camera to run in parallel with the spectrograph, providing a high quality field image together with the spectroscopic/spectropolarimetric analysis. The ratio 20/80 has been chosen because the 2nd surface coating of the BS plate shall provoke a (displaced) 2nd image in the range 0.5 to 1%. A ratio of 20 to 40 % of reflection with the first surface is thus requested to safely ignore this issue, so that the flux of the first surface reflection remains significantly larger than the second one. \\ |
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| * Wideband Film : 80% light transmitted to spectrograph ; 20% reflected to context camera. This option is offered as a backup in the case the BS would not work properly; Films have no 2nd image and a much larger transmitted fraction, the reflected 4% is largely enough to feed the context camera. However they have a poor optical quality and cannot be used for tuning the AO for NCP aberrations. | * Wideband Film : 96% light transmitted to spectrograph ; 4% reflected to BBI camera. This option is offered as a backup in the case the beamsplitter would not work properly. Films have no 2nd image and a much larger transmitted fraction, the reflected 4% is largely enough to feed the BBI camera. However they have a poor optical quality and cannot be used for tuning the AO for NCP aberrations. |
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| | Cartoon of the beam splitting options. |
| | <html> <a href="https://www.themis.iac.es/lib/exe/fetch.php?media=results:gallery:schema:beamsplitteroptions.jpg"><img src="https://www.themis.iac.es/lib/exe/fetch.php?media=results:gallery:schema:beamsplitteroptions.jpg" style="width:90%; height: auto;"></a></html> \\ |
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| ==== (8-9) Context camera and context camera filter ==== | ==== (8-9) Broadband Imaging (BBI) filter & camera ==== |
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| If illuminated, the context camera offers a high-resolution image of THEMIS with a square field-of-view of about ~55"x55" in the red continuum. A red filter, with a ~10nm passband centered around 630 nm is placed upstream of the camera. | If illuminated, the BBI camera offers a broadband high-resolution image with a square field-of-view of about ~55"x55". A broadband red filter, with a ~3nm passband centred around 656 nm is placed upstream of the camera. THEMIS BBI camera thus currently provides images or the red visible continuum. |
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| The context 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/second) that are ideal for post image reconstruction. | 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/second) that are ideal for post image reconstruction. <html><font color="#ff9900"> Camera acquisition settings can be changed by the user in the THEMIS control room. Acquisition is left to the needs and appreciation of the user. </font></html>\\ |
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| <html><font color="#0000ff"> The red continuum images from this camera are an available data product. Post-observation image processing methods & routines (Knox-Thompson reconstruction method) are available </font></html> [[observation:data#context camera| (cf. THEMIS data products)]]. | <html><font color="#0000ff"> The red continuum images from the BBI camera are an available data product. Post-observation image processing methods & routines (Knox-Thompson reconstruction method) are available </font></html> [[observation:data#Broadband images (BBI) | (cf. THEMIS data products)]]. |
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| | Views of the BBI camera and its broadband filter. \\ |
| <html> <a href="https://www.themis.iac.es/lib/exe/fetch.php?media=results:gallery:schema:beamsplitteroptions.jpg"><img src="https://www.themis.iac.es/lib/exe/fetch.php?media=results:gallery:schema:beamsplitteroptions.jpg" style="width:90%; height: auto;"></a></html> \\ | <html> <a href="https://www.themis.iac.es/lib/exe/fetch.php?media=results:gallery:instrumentation:bbicamera.jpg"><img src="https://www.themis.iac.es/lib/exe/fetch.php?media=results:gallery:instrumentation:bbicamera.jpg" style="width:90%; height: auto;"></a></html> \\ |
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| When polarimetric observations are performed, because of the latter need of a dual beam polarimetric output, the field of view must be reduced to 2'x 1' (along the slit length). <html><font color="#ff9900"> The orientation of the slit relatively to the field of view can be modified. Typical solar observation permits to put the slit align with the solar north or parallel to the solar equator. </font></html> | When polarimetric observations are performed, because of the latter need of a dual beam polarimetric output, the field of view must be reduced to 2'x 1' (along the slit length). <html><font color="#ff9900"> The orientation of the slit relatively to the field of view can be modified. Typical solar observation permits to put the slit align with the solar north or parallel to the solar equator. </font></html> |
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| ==== (11-12) Slit-jaw filters & camera === | ==== (11-12) Slit-jaw filter & camera === |
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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. |
| 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 field of view is 2'x2', while it is reduced to 2'x1' when polarimetric analysis are carried. | 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 field of view is 2'x2', while it is reduced to 2'x1' when polarimetric analysis are carried. |
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| <html><font color="#0000ff"> The green-light continuum images from the slit-jaw camera are an available data product. </font></html> [[observation:data#context camera| (cf. THEMIS data products)]] | <html><font color="#0000ff"> The green-light continuum images from the slit-jaw camera are an available data product. </font></html> [[observation:data# Slit-jaw context images| (cf. THEMIS data products)]] |
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| <html> <a href="https://www.themis.iac.es/lib/exe/fetch.php?media=:call22:f2_slit_conf.png"><img src="https://www.themis.iac.es/lib/exe/fetch.php?media=:call22:f2_slit_conf.png" style="width:90%; height: auto;"></a></html> \\ | |
| Cartoon of the spectrograph entrance slit options. \\ | Cartoon of the spectrograph entrance slit options. \\ |
| | <html> <a href="https://www.themis.iac.es/lib/exe/fetch.php?media=:call22:f2_slit_conf.png"><img src="https://www.themis.iac.es/lib/exe/fetch.php?media=:call22:f2_slit_conf.png" style="width:90%; height: auto;"></a></html> \\ |
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| The THEMIS spectrograph is an essential block of the THEMIS instrumentation that enable the formation of the solar spectrum and its detailed analysis. | The THEMIS spectrograph is an essential block of the THEMIS instrumentation that enable the formation of the solar spectrum and its detailed analysis. |
| MTR2 is the advanced version of the original MulTi-Ray spectrograph of THEMIS. MTR2 enables the production of high-spectral resolution spectrograms simultaneously in different wavelengths. This enables the study of different physical properties of the distinct layers of the solar atmosphere. | MTR2 is the advanced version of the original MulTi-Ray spectrograph of THEMIS. MTR2 enables the production of high-spectral resolution spectrographs simultaneously in different wavelengths. This enables the study of different physical properties of the distinct layers of the solar atmosphere. |
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| <html><font color="#ff9900"> Numerous user options are available here concerning the choice of the combination of spectral lines. </font></html> | <html><font color="#ff9900"> Numerous user options are available here concerning the choice of the combination of spectral lines. </font></html> |
| ==== (14) Spectral cameras ==== | ==== (14) Spectral cameras ==== |
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| At the exit of the spectrograph, several cameras are placed so that to record simultaneous spectrograms (lambda,y) in different wavebands. The spectrograms have a typical spectral range of 6-7 Å (0.6-0.7 nm) depending of the wavelength. The spatial direction has an extend of 1' when performing polarised observations, 2' otherwise. When performing polarimetric observations, two spectrograms are fitted on the camera field-of-view, each including the opposite polarimetric state (e.g. I+V and I-V Stokes). | At the exit of the spectrograph, several cameras are placed so that to record spectral images (lambda,y) simultaneously in different wavebands. The spectrographic images have a typical spectral range of 6-7 Å (0.6-0.7 nm) depending of the wavelength. The spatial direction has an extend of 1' when performing polarised observations, 2' otherwise. When performing polarimetric observations, two spectrographs are fitted on the camera field-of-view, each including the opposite polarimetric state (e.g. I+V and I-V Stokes). |
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| <html><font color="#0000ff"> The spectrographic images from the spectral cameras are the main data product of THEMIS MTR2 spectrograph observation mode. </font></html> [[observation:data#context camera| (cf. THEMIS data products)]] | <html><font color="#0000ff"> The spectrographic images from the spectral cameras are the main data product of THEMIS MTR2 spectrograph observation mode. </font></html> [[observation:data#context camera| (cf. THEMIS data products)]] |
