Transcript High performance microchannel plate detectors for UV/visible Astronomy Dr. O.H.W. Siegmund Space Sciences Laboratory, U.C.

High performance microchannel
plate detectors for UV/visible
Astronomy
Dr. O.H.W. Siegmund
Space Sciences Laboratory, U.C. Berkeley
Work funded by NASA grants, NAG5-8667, NAG5-11547, NAG-9149
Space Sciences Lab, UC Berkeley, CA, USA
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Advanced MCP Sensors for Astrophysics
Existing Detectors
High QE alkali halide cathodes (CsI, KBr) with ~50%QE covering 10nm - 185nm
MCP’s with 12µm to 6µm pores, background 0. 2 events cm-2 sec-1
Cross-delay line readouts with 15µm resolution, 90 x 20mm, 65mm formats
COS 2 x 90mm x 10mm XDL detector
GALEX 65mmsealed tube XDL detector
Space Sciences Lab, UC Berkeley, CA, USA
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Advanced MCP Sensors for Astrophysics
COS FUV Detector and Electronics
Space Sciences Lab, UC Berkeley, CA, USA
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Advanced MCP Sensors for Astrophysics
COS FUV Detector QE
CsI cathodes on FUV02 flight detector compared with COS spec
Segment B
Segment A
0.5
0.6
Requirements
QE post miniscrub2
Requirements
QE post miniscrub2
0.4
Quantum Efficiancy
Quantum Efficiency
0.5
0.4
0.3
0.3
0.2
0.2
0.1
0.1
0
1100
1200
1300
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1500
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1700
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1100
1800
WAVELENGTH (Å)
Space Sciences Lab, UC Berkeley, CA, USA
4
1200
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WAVELENGTH (Å)
1700
1800
Advanced MCP Sensors for Astrophysics
COS Detector Event Rate Performance
COS FUV local and global count rate performance
is better than FUSE, and exceeds specs.
Global count rate throughput
Gain and PHD vs. Localized Input Rate
(Single 25µm x 500µm Slit)
Digital Event Counter (cps)
2
Relative Gain
1.8
Relative Gain
Relative PH width
1.6
100000
1.4
1.2
80000
60000
40000
1
20000
0.8
0.6
0
0.1
1
10
100
0
Microchannel Pore Input Rate (cps)
Space Sciences Lab, UC Berkeley, CA, USA
50000
100000
150000
Fast Event Counter (cps)
5
200000
250000
X FWHM(µm)
Advanced MCP Sensors for Astrophysics
COS Detector Resolution
COS detector co-added image of 10µm pinholes on 500µm centers & 25µm x 500µm
slits 200µm apart. Pixels are 6µm x 25µm or ~15,000 x 400 format per segment.
CO S FUV01 Segment A - Pinhole Resolution vs. X
100
80
COS FUV detector resolution
is ~20µm x 30µm FWHM
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40
20
0
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6000
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10000
12000
14000
X centroid (pxl)
Space Sciences Lab, UC Berkeley, CA, USA
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16000
Advanced MCP Sensors for Astrophysics
Developing Detector Prospects
Raw flat field image
Shows MCP multi
-fibers, but after
thermal correction
and division data
looks statistical (with
~4400 cnts/resel we
get S/N ~60:1).
Using FPSPLIT with 4 co-added images each with 60:1 S/N we get S/N of
~100:1 which is in close accord with photon statistics. For analysis see memo
by Wilkinson/Penton/Vallerga/McPhate.
Space Sciences Lab, UC Berkeley, CA, USA
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Photocathode Development
GaAs Photocathodes on windows, & Diamond Photocathodes on Silicon & Si MCP’s
Polycrystalline boron doped diamond, band gap - 5.47 eV (227 nm) - Solar blind.
Hydrogenated diamond is air stable (<10% drop in 18 hours) and is very robust.
GaAs QE up to 50% in the red now possible, low background ≈10 events/sec @-20°C
Time response <1ns, for Interferometry, Lidar,Molecular fluorescence.
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Diamond coated Silicon MCP
Cs activated
QDE
0.1
#2
#1
#5
#8
21201
Si MCP
20801
20501
0.01
0.001
0
500
Pre-hydrogenated values
1000
Wavelength (Å)
GaAs photocathode UV efficiency
Space Sciences Lab, UC Berkeley, CA, USA
1500
2000
Diamond Photocathodes on Silicon and Si MCP’s
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GaN Photocathodes
opaque
semitransparent
Fig.1. Measured quantum efficiency of CsI on MCP’s,
CsTe semitransparent (NIST) on MgF2 window and CsTe
semitransparent (GALEX) on thick UV silica windows.
Space Sciences Lab, UC Berkeley, CA, USA
Fig.2. Measured QE of GaN samples on sapphire
(300µm) after cesiation, for semitransparent
(corrected for substrate transmission) & opaque modes
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Silicon MCP Developments
Silicon MCP’s
Hexagonal pore Si MCP with
~7µm pores, >75% open area
Silicon MCP’s are made by photo-lithographic methods
Photolithographic etch process - very uniform pore pattern
No multifiber boundaries & array distortions of glass MCP’s
Large substrate sizes (100mm) OK, with small pores (5µm)
High temperature tolerance - CVD and “hot” processes OK
UHV compatible, low background (No radioactivity)
Development in collaboration with Nanosciences.
Typical Silicon microchannel plates in test program
25mm diameter (75mm currently feasible)
40:1 to 60:1 L/D (>100:1 possible)
7µm pore size, hexagonal and square pore
~2° bias and 8° bias, resistances ~GΩ, to <100MΩ possible
Working on processing techniques to improve uniformity
Techniques for gain & QE enhancement under investigation
8cm Si MCP on
100mm substrate
Space Sciences Lab, UC Berkeley, CA, USA
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Silicon MCP Performance Characteristics
Gain & PHD very similar to glass MCP’s, stacks of Si MCP’s (4) with gain up to 10
QE is similar to good bare glass MCP’s (COS, EUVE, 12/10/6µm)
The background rate is lower (0.02 events cm-2 sec-1) than any glass MCP
Gain and response uniformity are reasonably good. No “hex” modulation!
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0.2
12/10µm COS
Si MCP
Bare glass
Si Hex MCP
0.15
QDE
6µm pore MCP
0.1
0.05
0
200
400
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1200
1400
Wavelength (Å)
QDE for Si & bare glass MCP’s vs Wavelength
Space Sciences Lab, UC Berkeley, CA, USA
Contrast enhanced image of the fixed pattern response
to a Hg vapor lamp with a stack of 4 Si MCP’s. ~14mm
area, 107 counts, ~50µm resolution XDL.
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Cross strip anode readout
32mm x 32mm XS anode, 0.5mm period
Cross strip is a multi-layer cross finger layout.
Fingers have ~0.5mm period on ceramic.
Charge spread over 3-5 strips per axis,
Event position is derived from charge centroid.
Can encode multiple simultaneous events.
Fast event propagation (few ns).
Anodes up to 32 x 32mm have been made
Signals are routed to anode backside by hermetic vias
Packaging can be compact with amp on anode backside
Overall processing speed should support >> MHz rates
Compact and robust (900°C).
Bottom fingers
Space Sciences Lab, UC Berkeley, CA, USA
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Cross Strip Anode Electronics Chain
Basic encoding sequence
Small, low power ASIC encoding with sparsification
reduces data throughput requirements
Cross strip anode position encoding electronics
test-bed system. All signals amplified and
digitized. Can choose up to 12 bits per signal.
Space Sciences Lab, UC Berkeley, CA, USA
Anode backside showing the external
board where preamplifier chips are mounted.
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Cross Strip Anode Readout
Outstanding Spatial Resolution/Linearity
~7µm pores are resolved, <3 µm electronic resolution with 10 bit encoding electronics
Image linearity is ~1µm level and shows pore misalignments and multi-fiber boundaries
Gain required is <4 x 105, allows higher local event rates than normal readouts
Lower gain means longer overall MCP lifetime due to reduced charge extraction.
Small zone of a single 12µm 160:1
L/D MCP at 2x105 gain showing
apparent displacement of pore images
at multifiber boundaries
Flood image of 12µm pore MCP pair at 4 x 106
Gain, ≈1mm square area.
Space Sciences Lab, UC Berkeley, CA, USA
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Resolution of Cross Strip MCP Sensors
Gain 1.3 x 106
Air force mask on
6µm pore MCP pair
with cross strip readout
Space Sciences Lab, UC Berkeley, CA, USA
Air force mask on
Single 6µm pore
MCP optical image
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Advanced MCP Sensors for Astrophysics
GALEX Early Observations
60mm XDL detectors with CsI and CsTe photocathodes, Launched 6/03
M101
M83
Near-UV Channel
Space Sciences Lab, UC Berkeley, CA, USA
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M51 – Whirlpool Galaxy
Comparison
GALEX Early Data
Ultraviolet
GALEX
Space Sciences Lab, UC Berkeley, CA, USA
Visible
DSS
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Near Infrared
2MASS
M31 Andromeda
Space Sciences Lab, UC Berkeley, CA, USA
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