20 OCT 2003 SOLAR ORBITER MEETING 1
Optical Design Activities at RAL
Kevin MiddletonOptical Systems Group
Space Science & Technology Dep’t.Rutherford Appleton Laboratory
Brief overview of:
Design Options
Some ROM optical tolerances
Manufacturing / alignment considerations
Possible next steps
20 OCT 2003 SOLAR ORBITER MEETING 2
Design Options
• Two designs proposed:– Normal incidence: Off-axis parabola & TVLS grating– Grazing incidence: Wolter type telescope
• We are concentrating on analysing and developing Roger Thomas’s normal incidence design
• The reasons for starting with this design, as opposed to grazing incidence are:– Simpler geometry– Easier alignment– Rastering can be performed by primary
• Potential disadvantages are:– Thermal control more difficult– Requires multi-layer coating if 17-22nm waveband required
• If analysis shows that the normal incidence design cannot be made to work, given the thermal loads, the alternative grazing incidence design can be investigated
20 OCT 2003 SOLAR ORBITER MEETING 3
RAL Baseline Design
• We are defining a baseline design which we will use for thermal and mechanical design:
• Wavelength: 58-63nm & 97.5-103.5nm• Overall length: ~1m• Resolution 1 arcsecond spatial• 5nm @ 60nm, 65nm @ 100nm• Throughput aim for x2 improvement on CDS• Field of View 10 arcmin minimum• Detector 2048 x 10um pixel
20 OCT 2003 SOLAR ORBITER MEETING 5
Current Baseline Performance
• Wavelength: 58-63nm & 97.5-103.5nm• Overall length: ~1m• Resolution Spatial: 1.1 arcsecond average• 0.8 arcsecond best• 1.2 arcsecond worst• Spectral 8.1nm average (with
1arcsecond slit width)• 7.1nm best• 9.3 nm worst• Throughput x1.7 wrt CDS (viewing extended source at
62.97nm)• (50mm x 50mm entrance aperture)• Field of View 20 arcmin (0.6 arcsecond / pixel)• Detector 2048 x 10um pixel
20 OCT 2003 SOLAR ORBITER MEETING 6
Trade-Offs
• Work ongoing to define baseline design.• Can trade-off:
– Spatial resolution against field of view– Spectral against spatial resolution (for fixed angular slit width)– Bandwidth against spectral resolution– Throughput (entrance aperture size) against spatial and spectral
resolution
• Aim to get as close as possible to desired baseline performance and then freeze design for a period, to allow mechanical and thermal analysis
20 OCT 2003 SOLAR ORBITER MEETING 7
Resolution
• Defining what we mean by spot size at the detector is not straightforward
• I have chosen to take the 80% enslitted energy diameter in either the spatial or spectral direction as my measure of spot size
• This calculation accounts for:– Diffraction effects in image space at the exit pupil– Geometric aberrations
• The calculation does not account for:– Diffraction effects at the slit
• (But more limited full diffraction calculations show that this is an acceptable assumption for initial analysis)
• Spatial Resolution = sqrt(spot size^2 + pixel size^2)• Spectral Resolution = sqrt(spot size^2 + pixel size^2 + slit
width at det^2)
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