20 OCT 2003SOLAR ORBITER MEETING1 Optical Design Activities at RAL Kevin Middleton Optical 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 2003SOLAR ORBITER MEETING2 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 2003SOLAR ORBITER MEETING3 RAL Baseline Design We are defining a baseline design which we will use for thermal and mechanical design: Wavelength:58-63nm & nm Overall length:~1m Resolution1 arcsecond spatial 60nm, 100nm Throughputaim for x2 improvement on CDS Field of View10 arcmin minimum Detector2048 x 10um pixel

20 OCT 2003SOLAR ORBITER MEETING4 Outline Optical Layout

20 OCT 2003SOLAR ORBITER MEETING5 Current Baseline Performance Wavelength:58-63nm & nm Overall length:~1m ResolutionSpatial:1.1 arcsecond average 0.8 arcsecond best 1.2 arcsecond worst Spectral8.1nm average (with 1arcsecond slit width) 7.1nm best 9.3 nm worst Throughputx1.7 wrt CDS (viewing extended source at 62.97nm) (50mm x 50mm entrance aperture) Field of View20 arcmin (0.6 arcsecond / pixel) Detector2048 x 10um pixel

20 OCT 2003SOLAR ORBITER MEETING6 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 2003SOLAR ORBITER MEETING7 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)

20 OCT 2003SOLAR ORBITER MEETING8 Tolerances Diffraction limited depth of focus=+/- 2*lambda*f/no^2 Telescope ~ f/10 Lambda ~ 50nm Depth of focus = +/- 10um Surface form Lambda/4 ~50nm  lambda/2 surface ~ 50nm