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Nuovi rivelatori e tecniche nell’astrofisica dell’UV

Nuovi rivelatori e tecniche nell’astrofisica dell’UV. Emanuele Pace Dipartimento di Astronomia e Scienza dello Spazio Università di Firenze. UV astronomy. Most of the emission of hot thermal processes occuring in a wide variety of astrophysical enviroments peak in the UV.

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Nuovi rivelatori e tecniche nell’astrofisica dell’UV

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  1. Nuovi rivelatori e tecniche nell’astrofisica dell’UV Emanuele Pace Dipartimento di Astronomia e Scienza dello Spazio Università di Firenze

  2. UV astronomy Most of the emission of hot thermal processes occuring in a wide variety of astrophysical enviroments peak in the UV. UV spectroscopic and imaging capabilities are a fundamental tool to study plasmas at temperatures in the 3,000-300,000 K range. Electronic transitions of the most abundant molecules in the universe (H2, CO, OH, CS, CO2+, CO2) are in the UV.

  3. UV eyes IUE, HST, GALEX, FUSE, …

  4. World Space Observatory/UV

  5. WSO-UV Payload • HIRDES: R  55000 echelle spectrographs: • UVES (178-320nm) • VUVES (102-180nm) • LSS: 102- 320 nm,R~1500–2500 long slit (1x75 arcsec) spectrograph • FCU: 3 imaging cameras • FUV : scale=0.20 “/px; FoV= 6.6x6.6 arcmin2 • NUV : scale=0.03 “/px; FoV= 1.0x1.0 arcmin2 • UVO : scale=0.07 “/px; FoV= 4.6x4.6 arcmin2

  6. NUV Camera on axisOptical Bench  1000 mm Telescope Focal Plane 5 mm Aspherical Mirror M2 Pick Up Mirror Image (MCP) 40 mm Spherical Mirror M1 500 mm S. Shore, E. Pace

  7. NUV Camera Data/ Requirements

  8. Proposed operating mode • High resolution NUV imaging • Slitless multi-object spectroscopy • Slitless multi-object polarimetry • Slitless multi-object spectro-polarimetry

  9. Wollaston Detector Dispersive element filter Conceptual scheme Advantage of Wollaston: two fields in one image BUT! The material must be carefully selected The refraction index of MgF2 is not constant Calibration is an issue: filters, prism and detector must be carefully selected and calibrated

  10. NUV Spectra on MCP Grating 60 linee/mm R=100 Grating 90 linee/mm R=100 All fields Orders -1,0,+1

  11. Il futuro

  12. Output Signal from an optical system S  B A W T h Telescope aperture  large primary mirror  spatial resolution Detector high sensitivity  high quantum efficiency  high S/N

  13. Stellar imager

  14. Large space telescopes

  15. Technological issues for large area space optics • Weight • a conventional 3 m  lens or mirror is too heavy (> 1000 kg) for any reasonable spacecraft • Ultra-lightweight optics required • Surface quality • A sufficient optical surface quality must be guaranteed after launch and under orbital condition • Active surface control possibly needed • Deployment • 3 m is about the maximum diameter possible with available launchers (2.5 m for Shuttle) • In orbit mechanical deployment necessary

  16. Space mirrors’ areal density

  17. Concept of thin glass active mirrors Mass~ 5 Kg/m2

  18. ALC : Advanced Light Collectors • Feasibility study of deployable and active large mirrors • Consortium: CNR-INOA, INAF-Arcetri, CGS • ESA contract • Submitted proposal for producing a demonstrator

  19. NASA conceptual study: OWL Deployable Schmidt camera During deployment Packaged in the spacecraft

  20. Deployable large mirrors Primary mirror: Ø≤ 8 m

  21. Deployment system

  22. Trusses support structure (CFRP) Stiffening ribs (CFRP) Primary mirror: deployment kinematics EMC actuators for each petal: front and back sides

  23. Propulsion System Deployment kinematics and mechanisms Primary Mirror Secondary Mirror Power System Baffle Telescope design

  24. I rivelatori

  25. Ideal UV detector for space Very low noise Radiation hardness REQUESTS High sensitivity Large area Solar blindness Chemical inertness

  26. Charge Coupled Devices (CCD) CCD di EIT/SOHO

  27. UV CCD Quantum yield improves the detector sensitivity Ne =Eg(eV) / 3.65 eV DQE =Neh

  28. Backside CCD • Back illumination • Wafer thinning • Ion implantation • Laser annealing

  29. UV CCD Quantum yield improves the detector sensitivity Ne =Eg(eV) / 3.65 eV DQE =Neh

  30. CCD – spectral response Courtesy of L. Poletto et al., Università di Padova

  31. d-doping JPL/USA – California Institute of Technology A boron thin layer is deposited on the back surface through molecular beam epitaxy (MBE)

  32. d-doped CCD – spectral response S. Nikzad et al, 2003

  33. Micro-Channel Plates (MCP)

  34. GALEX

  35. FUSE

  36. Photocathodes

  37. CMOS - APS

  38. Limits of CMOS - APS • Still high Readout noise • Low quantum efficiency (< 50%) • Low filling factor (circa 50%) • Limited dynamic range (12-bits in analog mode) • Spectral range centered on the visible Ref. N. Waltham, RAL, UK

  39. CMOS APS back illuminated @ RAL

  40. Wide bandgap materials: Diamond Appealing materials for XUV photon detection. The main properties are hereafter summarized : • Eg = 5.5 eV  dark current < 1 pA  visible rejection (ratio 10-7)  high XUV sensitivity • Highly radiation hard • Chemical inert • Mechanically robust • High electric charge mobility = fast response time • Low dielectric constant = low capacitance

  41. Diamond detectors in Italy • Università di Firenze (E. Pace) • Univ. di Roma Tor Vergata (M. Marinelli) • Università di Reggio Calabria (G. Messina) • INAF–Osservatorio di Catania (S. Scuderi)

  42. MATERIAL PROPERTY IMAGER PROBLEM SYSTEM SOLUTION SYSTEM PENALTY Back support Difficult to thin Severe cleanliness Requirements Low young's modulus Cooling Dark current Power hungry Small band gap More optics Visible light response Heavy Reactive surface Phosphor, coating Unstable UV response Vibration problems Weak Bonding Shielding Bulk radiation damage Magnetic torque on spacecraft Hybrid Why diamond? Higher performances No cooling Less optics & no filters No coatings No radiation shielding Mechanical hardness Low power Light system Long durability Clean environment SPACE SYSTEM IMPROVEMENT

  43. hν hν Coplanar geometry Transverse geometry Diamond photoconductors

  44. Interdigitated electrodes Diamond layer Detector technology

  45. We started from…

  46. Dark current

  47. Response time

  48. pCVD E. Pace et al., Diam. Rel. Mater. 9 (2000) 987-993. 100 E = 2.8 V/mm UV/VIS > 108 10 1 0,1 External quantum efficiency 0,01 1E-3 1E-4 1E-5 1E-6 1E-7 1E-8 Wavelength (nm) 200 400 600 800 1000 Electro-optical performance R = I/Pott

  49. pCVD scCVD Quantum efficiency

  50. [1] [2] Comparison [1] Naletto, Pace et al, 1994 [2] Wilhelm et al.,1995

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