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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. 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. UV eyes IUE, HST, GALEX, FUSE, … World Space Observatory/UV 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 NUV Camera on axis Optical Bench 1000 mm Telescope Focal Plane 5 mm Pick Up Mirror Aspherical Mirror M2 Image (MCP) 40 mm Spherical Mirror M1 500 mm S. Shore, E. Pace NUV Camera Data/ Requirements Pixel Size (micron) 20 Detector Format pixel 2000 Detector size (mm) 40 Sampling (arcsec/pixel) 0.03 Scale Factor (arcsec/mm) 1.5 Effective Focal Length (mm) 137510 F/# 81 m 8.1 Field of View (arcmin) 1 Field of View (mm) 5 Wavelength Min (nm) 150 Wavelength Max (nm) 280 Proposed operating mode • High resolution NUV imaging • Slitless multi-object spectroscopy • Slitless multi-object polarimetry • Slitless multi-object spectro-polarimetry Conceptual scheme Wollaston filter Dispersive element Detector 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 NUV Spectra on MCP Grating 60 linee/mm R=100 All fields Orders -1,0,+1 Grating 90 linee/mm R=100 Il futuro Output Signal from an optical system SBAWTh Telescope aperture large primary mirror spatial resolution Detector high sensitivity high quantum efficiency high S/N Stellar imager Large space telescopes 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 Space mirrors’ areal density Technologies Hubble primary Current Developing Membrane mirror Reflective coating Kg/m2 Kg @ 5 m 180 3533 10 196 1 20 1.0E-02 2.0E-01 1.0E-04 2.0E-03 Concept of thin glass active mirrors Mass~ 5 Kg/m2 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 NASA conceptual study: OWL Deployable Schmidt camera During deployment Packaged in the spacecraft Deployable large mirrors Primary mirror: Ø ≤ 8 m Deployment system Primary mirror: deployment kinematics EMC actuators for each petal: front and back sides Trusses support structure (CFRP) Stiffening (CFRP) ribs Telescope design Propulsion System Deployment kinematics and mechanisms Primary Mirror Secondary Mirror Power System Baffle I rivelatori Ideal UV detector for space Radiation hardness REQUESTS High sensitivity Very low noise Large area Solar blindness Chemical inertness CCD di EIT/SOHO Charge Coupled Devices (CCD) UV CCD Quantum yield improves the detector sensitivity Ne = Eg (eV) / 3.65 eV DQE = Neh Backside CCD • • • • Back illumination Wafer thinning Ion implantation Laser annealing UV CCD Quantum yield improves the detector sensitivity Ne = Eg (eV) / 3.65 eV DQE = Neh CCD – spectral response Courtesy of L. Poletto et al., Università di Padova d-doping JPL/USA – California Institute of Technology A boron thin layer is deposited on the back surface through molecular beam epitaxy (MBE) d-doped CCD – spectral response S. Nikzad et al, 2003 Micro-Channel Plates (MCP) GALEX FUSE Photocathodes CMOS - APS 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 CMOS APS back illuminated @ RAL 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 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) Why diamond? Higher performances PROBLEM PROPERTY MATERIAL IMAGER SYSTEM SOLUTION No cooling Back support Difficult to thin No coatings Dark current band gapshielding NoSmall radiation Visible light Mechanical hardness response Reactive surface Weak Bonding Low powerSevere cleanliness Less Lowoptics young's& no filters modulus SYSTEM PENALTY Light system Requirements Cooling More optics Long durability Power hungry Clean environment Heavy Phosphor, coating Unstable UV response Vibration problems Shielding Bulk radiation damage Magnetic SPACE SYSTEM IMPROVEMENT torque on Hybrid spacecraft Diamond photoconductors hν Coplanar geometry hν Transverse geometry Detector technology Interdigitated electrodes Diamond layer We started from… 1,0 Normalized photocurrent 5 V/mm, 160 nm 25 0,6 0,4 0,2 0,0 0 DF844 pl DF838 pl DF736 pl 20 1000 2000 3000 Time (s) Photocurrent Transient 15 -12 8 @160nm (Flux=10 g /s) 3,5x10 -12 3,0x10 10 -12 2,5x10 Photocurrent (A) Dark Current (pA) 0,8 5 -12 2,0x10 -12 1,5x10 -12 1,0x10 -13 5,0x10 0 0,0 0 2 4 6 8 Electric Field (V/cm) 10 12 14 -5,0x10 -13 0 100 200 300 400 500 600 700 Time (s) 800 900 1000 1100 1200 Dark current 200 pCVD 10 100 Current (fA) Current (fA) 5 0 0 -5 -100 scCVD -10 -200 -2,5 -2,0 -1,5 -1,0 -0,5 0,0 0,5 1,0 Electric field (V / m) 1,5 2,0 2,5 -5 -4 -3 -2 -1 0 1 2 Electric Field (V/ m) 3 4 5 Normalized photocurrent (a.u.) Response time 1,0 1,0 0,9 0,9 0,8 0,8 0,7 0,7 0,6 0,6 0,5 0,5 0,4 0,4 0,3 0,3 0,2 0,2 0,1 50 kV/cm 10 kV/cm 0,0 50 kV/cm 10 kV/cm 0,1 0,0 100 150 200 Time (s) 425 450 475 500 525 550 Electro-optical performance I f h E EQE h hG L Pott q R = I/Pott pCVD External quantum efficiency E. Pace et al., Diam. Rel. Mater. 9 (2000) 987-993. 100 10 1 0,1 0,01 1E-3 1E-4 1E-5 1E-6 1E-7 1E-8 E = 2.8 V/m UV/VIS > 108 200 400 600 Wavelength (nm) 800 1000 Quantum efficiency pCVD scCVD 100 EQE (electrons/photon) 10 - EQE (e / ph) 100 1 10 1 0,1 1.2 V / m 5 V/ mm 1 V/ mm 0,01 0,1 140 160 180 200 Wavelength (nm) 220 240 140 160 180 200 Wavelength (nm) 220 240 Comparison ApproxEQE 3 1000 10 2 100 10 1 10 10 0 [1] 101 Y Axis EQE / ph) (e Title -1 0,1 10 -2 0,01 10 -3 1E-3 10 -4 1E-4 10 -5 1E-5 10 EQE CVD Diamond EQE UV enhanced CCD EQE MCP + KBr -6 1E-6 10 -7 1E-7 10 -8 1E-8 10 [1] Naletto, Pace et al, 1994 [2] Wilhelm et al.,1995 100 100 120 120 140 140 160 160 180 180 [2] 200 200 X Axis Title(nm) Wavelength 220 220 240 240 260 260 Minimum detectivity NEP l = 210 nm ; EQE = 300 NEP = 5 x 10-11 erg s-1 cm-2nm-1 Fluxes & Sensitivity NEP = 5 x 10-11 erg s-1 cm-2nm-1 Electronic structures DM17 250 µm (8,4 ± 0,4) µm (52,9 ±0,4) µm (15 ± 1)µm (6,8 ± 5) µm (18 ± 1) µm (54 ± 1) µm (8,4 ± 0,4) µm 650 µm DP129 UV spectral response N-doped diamond Vbias = 50 V Vbias = 500 V N-doped diamond MIS structure -20V @160nm -20V @210nm -12 i-Diam PhotoCurrent (A) 2.0x10 Al p-Diam -12 1.0x10 0.0 0 100 200 300 400 500 600 700 800 Time (s) -50 V PC 160nm -50 V PC 210nm Electric connection PhotoCurrent (A) HPHT Diam Substrate -12 6.0x10 -12 3.0x10 0.0 100 200 300 400 Time (s) 500 600 700 Pixels on MIS structure Proposed devices E. Pace et al., ESA Proceedings, 2001 E. Pace et al., SPIE Proc., 2001 Grounded Mesh Incident radiation Diamond layer Back electrodes Soft-X ray range Response times Transitori @ 10keV (@ 1.37E12 ph/s) Transitori @ 10keV (@ 1.37E12 ph/s) -9 8.0x10 -9 7.0x10 1E-8 rise time 222ms rise time 130 ms rise time 170 ms rise time 222ms rise time 170 ms rise time 130 ms -9 Corrente (nA) Corrente (nA) -9 6.0x10 1E-9 5.0x10 -9 4.0x10 -9 3.0x10 -9 2.0x10 fall time 200ms -9 1.0x10 fall time 200ms 0.0 1E-10 -9 -1.0x10 -10 0 10 20 30 40 50 60 Tempo (s) 70 80 90 100 110 0 20 40 60 Tempo (s) 80 100 Photocurrent (A) Linearity 7,0x10 -9 6,0x10 -9 5,0x10 -9 4,0x10 -9 3,0x10 -9 2,0x10 -9 1,0x10 -9 0,0 0,0 2,0x10 11 4,0x10 11 6,0x10 11 8,0x10 Photon flux (ph/s) 11 1,0x10 12 1,2x10 12 EXAFS spectra Compared to IC detectors 1,5 experimental theoretical 1,0 1,0 k(k) k(k) Diamond 0,5 0,0 IC Diamond 0,5 0,0 -0,5 IC -0,5 4 6 8 -1 k (A ) 10 12 14 16 2 4 6 8 10 12 14 16 18 -1 k (A ) A. De Sio, E. Pace, et al., APL 2008 Conclusion • Photon detection in space is dominated by CCD • Improvements in CCD technology toward: – Low signal detection (L3 CCD) – Mosaics – Miniaturization of the readout electronics • Low UV sensitivity • Alternatives: MCP or CMOS-APS • Search for alternative devices based on wide band gap materials: GaN, SiC, diamante. • R&D shows promising results and technology has been developed. • Testing on board technological satellites