Design of a Lyman-αdetector and imager for SMESE-LYOTFirst SMESE workshop: Coronal mass ejections...
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Optical design: At these wavelengths (121.5 nm) it is possible to use Al-MgF 2 high-reflectivity mirrors and interference filters. We suggest a simple design consisting of an off-axis Gregorian telescope with a medium-band entrance filter (e.g., Acton Research 122 N) selecting the Lyman-α line and a narrower Lyman-α filter (Acton Research 122 XN) before the detector. U. Schühle, L. Teriaca Design of a Lyman-α detector and imager for SMESE-LYOT Abstract Abstract We describe the development and first performance results of a new camera for the LYOT instrumentation at the Lyman-α wavelength. The development consists of an Intensified Active Pixel Sensor (IAPS) system and the electronic image read-out and data acquisition system. Based on the efficiency of this detector we present the calculated radiometric budget and performance of a telescope (imager) operating at the H I Lyman-α line. The telescope, a filtergraph imager, yields very high count rates with a spectral purity above 90%, allowing monochromatic imaging of the lower transition region at unprecedented temporal resolution. The Imager The Imager Table 1: Expected throughput and performances of different combinations of detectors and filters for the Lyman-α telescope under quiet-Sun and active region radiances. The forth column indicates the number of photons arriving at one pixel per second assuming an aperture size of 3 cm diameter. The seventh column indicates the total number of detected photons. The eighth column reports the percentage of the signal from wavelengths larger than 130 nm. The last column shows the percentage of the signal that is coming from the 115 – 130 nm range after removing the Lyman-α contribution. This is mainly due to emission lines such as the C III multiplet around 117.5 nm, Si III 120.65 nm, O V 121.83 nm and N V 123.88 nm and 124.28 nm. Spectral response of the instrument for the combination of two filters and a KBr-coated MCP-Detector (red). The use of a APS- detector without intensifier sensible to visible light requires an additional filter to reduce the continuum above 130 nm (green). MPI für Sonnensystemforschung, 37191 Katlenburg-Lindau, Germany A Lyman-α telescope design with two mirrors, two filters and a IAPS camera 122N Ly-α Filter 122XN Ly-α Filter Target phot pix −1 s −1 Lumogen coated CCD KBr MCP + APS Detected Phot pix −1 s −1 λ > 130 nm % Nearby spectrum 115 – 130 nm % X X X QS 371 X 43 4.7 2.5 X X X AR 1053 X 122 2.1 6.5 X X QS 7276 X 464 0.7 2.7 X X AR 11173 X 1351 0.7 6.9 The Detector The Detector First SMESE workshop: Coronal mass ejections and flares: new insights with the SMESE project at the Institut d’Astrophysique de Paris, 10. – 12. March 2008 built at MPS: BB electronics STAR-1000 sensor 1024 x 1024 pixel format 14 bit ADC electronics USB interface for PC operation PC-based user I/F for image acquisition (IDL-based) Breadboard unit of the SMESE camera Design of the Intensified APS camera The SMESE-EM1 unit: delivered and tested Intensifier with selective KBr coating Images at 121.6nm with old coating and fresh KBr coating The intensifier and the APS sensor are mated with fiber optic coupling plates. The image size can be adapted by a fiber optic taper if needed. Detector facilities at MPS: Detector photocathode evaporation chamber (left), and VUV characterization chamber (right) Camera design: We baseline an APS detector, that is mated with a micro-channel plate intensifier coated with KBr to increase efficiency around 121 nm and reduce the efficiency above 160 nm. The sensor will be mated with the intensifier by a fiber-optic block with a phosphor screen. Radiometric Performance : • MCP + APS camera: The combined effects of the mirrors reflectivity drop-off below 120 nm and of the detector blindness above 160 nm act like an additional Lyman-α filter providing high throughput and spectral purity. • Alternatively, if a classical Lumogen-coated CCD is used instead, at least one additional medium- band filter is required to reduce the contribution of the long wavelength (λ > 130 nm) spectrum. However, the additional filter and the lower quantum efficiency at Lyman-α would produce an order- of-magnitude reduction of the final throughput. The main goal is to suppress the very strong long-wavelength continuum. This can be achieved by using a solar-blind detector. A metal coating on the phosphor anode makes the detector visible-blind and, thus, no additional blocking filter is needed. The combination of MCP intensifiers with an imaging APS sensor adds many important advantages and flexibilities: the intensifier can be made sensitive in a certain spectral range by selection of the photocathode material, by switching the high voltage of the MCP, the intensifier can be used as an electronic shutter, the size of the focal plane, and thus the image scale of the optical system, gets independent of the imaging chip size, as it can be adapted by the optical magnification of the coupling system, the intensifier can be made visible-blind without additional filter, the amplification of the intensifier, given by the high voltage of the intensifier and the phosphor conversion factor, can be used to adjust the dynamic range of the camera, i. e., the signal strength to the full well capacity of the sensor, it allows the image sensor to operate in current accumulation mode or in single-photon counting mode. In photon counting mode the signal can be discriminated against the dark noise. This allows the operation at room temperatures (without the need for cooling the sensor). Conclusions: Conclusions:
Transcript of Design of a Lyman-αdetector and imager for SMESE-LYOTFirst SMESE workshop: Coronal mass ejections...
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Optical design: At these wavelengths (121.5 nm) it is possible to use Al-MgF2 high-reflectivity mirrors and interference filters. We suggest a simple design consisting of an off-axis Gregorian telescope with a medium-band entrance filter (e.g., Acton Research 122 N) selecting the Lyman-α line and a narrower Lyman-α filter (Acton Research 122 XN) before the detector.
U. Schühle, L. Teriaca
Design of a Lyman-α detector and imager for SMESE-LYOT
AbstractAbstractWe describe the development and first performance results of a new camera for the LYOT instrumentation at the Lyman-α wavelength. The development consists of an Intensified Active Pixel Sensor (IAPS) system and the electronic image read-out and data acquisition system. Based on the efficiency of this detector we present the calculated radiometric budget and performance of a telescope (imager) operating at the H I Lyman-α line. The telescope, a filtergraph imager, yields very high count rates with a spectral purity above 90%, allowing monochromatic imaging of the lower transition region at unprecedented temporal resolution.
The ImagerThe Imager
Table 1: Expected throughput and performances of different combinations of detectors and filters for the Lyman-α telescope under quiet-Sun and active region radiances. The forth column indicates the number of photons arriving at one pixel per second assuming an aperture size of 3 cm diameter. The seventh column indicates the total number of detected photons. The eighth column reports the percentage of the signal from wavelengths larger than 130 nm. The last column shows the percentage of the signal that is coming from the 115 – 130 nm range after removing the Lyman-α contribution. This is mainly due to emission lines such as the C III multipletaround 117.5 nm, Si III 120.65 nm, O V 121.83 nm and N V 123.88 nm and 124.28 nm.
Spectral response of the instrument for the combination of two filters and a KBr-coated MCP-Detector (red). The use of a APS-detector without intensifier sensible to visible light requires an additional filter to reduce the continuum above 130 nm (green).
MPI für Sonnensystemforschung, 37191 Katlenburg-Lindau, Germany
A Lyman-α telescope design with two mirrors, two filters and a IAPS camera
122N Ly-αFilter
122XN Ly-αFilter
Target photpix−1 s−1Lumogen
coated CCD
KBr MCP +
APS
DetectedPhot pix−1 s−1
λ > 130 nm%
Nearby spectrum115 – 130 nm
%
X X X QS 371 X 43 4.7 2.5
X X X AR 1053 X 122 2.1 6.5
X X QS 7276 X 464 0.7 2.7
X X AR 11173 X 1351 0.7 6.9
The DetectorThe Detector
First SMESE workshop: Coronal mass ejections and flares: new insights with the SMESE project at the Institut d’Astrophysique de Paris, 10. – 12. March 2008
built at MPS: BB electronics
STAR-1000 sensor 1024 x 1024 pixel format
14 bit ADC electronics
USB interface for PC operation
PC-based user I/F for image acquisition (IDL-based)
Breadboard unit of the SMESE camera
Design of the Intensified
APS camera
The SMESE-EM1 unit: delivered and tested
Intensifier with selective KBr coating Images at 121.6nm with old coating and fresh KBr coating
The intensifier and the APS sensor are mated with fiber optic coupling plates. The image size can be adapted by a fiber optic taper if needed.
Detector facilities at MPS:
Detector photocathode evaporation
chamber (left),
and VUV characterization chamber (right)
Camera design: We baseline an APS detector, that is mated with a micro-channel plate intensifier coated with KBr to increase efficiency around 121 nm and reduce the efficiency above 160 nm. The sensor will be mated with the intensifier by a fiber-optic block with a phosphor screen.
Radiometric Performance:
• MCP + APS camera: The combined effects of the mirrors reflectivity drop-off below 120 nm and of the detector blindness above 160 nm act like an additional Lyman-α filter providing high throughput and spectral purity.
• Alternatively, if a classical Lumogen-coated CCD is used instead, at least one additional medium-band filter is required to reduce the contribution of the long wavelength (λ > 130 nm) spectrum. However, the additional filter and the lower quantum efficiency at Lyman-α would produce an order-of-magnitude reduction of the final throughput.
The main goal is to suppress the very strong long-wavelength continuum. This can be achieved by using a solar-blind detector. A metal coating on the phosphor anode makes the detector visible-blind and, thus, no additional blocking filter is needed.
The combination of MCP intensifiers with an imaging APS sensor adds many important advantages and flexibilities:
the intensifier can be made sensitive in a certain spectral range by selection of the photocathode material,
by switching the high voltage of the MCP, the intensifier can be used as an electronic shutter,
the size of the focal plane, and thus the image scale of the optical system, gets independent of the imaging chip size, as it can be adapted by the optical magnification of the coupling system,
the intensifier can be made visible-blind without additional filter,
the amplification of the intensifier, given by the high voltage of the intensifier and the phosphor conversion factor, can be used to adjust the dynamic range of the camera, i. e., the signal strength to the full well capacity of the sensor,
it allows the image sensor to operate in current accumulation mode or in single-photon counting mode. In photon counting mode the signal can be discriminated against the dark noise. This allows the operation at room temperatures (without the need for cooling the sensor).
Conclusions:Conclusions:
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