Download Diapositiva 1 - Astronomy and Astrophysics Section

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
SBAWTh
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