Title: High performance microchannel plate detectors for UV/visible Astronomy
1High 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
2Advanced MCP Sensors for Astrophysics Existing
Detectors
High QE alkali halide cathodes (CsI, KBr) with
50QE covering 10nm - 185nm MCPs 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
3Advanced MCP Sensors for Astrophysics COS FUV
Detector and Electronics
4Advanced MCP Sensors for Astrophysics COS FUV
Detector QE
CsI cathodes on FUV02 flight detector compared
with COS spec
Segment B
Segment A
5Advanced 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
6Advanced 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.
COS FUV detector resolutionis 20µm x 30µm FWHM
7Advanced MCP Sensors for Astrophysics Developing
Detector Prospects
Raw flat field image Shows MCP multi -fibers, but
after thermal correction and division data looks
statistical (with4400 cnts/resel we get S/N
601).
Using FPSPLIT with 4 co-added images each with
601 S/N we get S/N of 1001 which is in close
accord with photon statistics. For analysis see
memoby Wilkinson/Penton/Vallerga/McPhate.
8Photocathode Development
GaAs Photocathodes on windows, Diamond
Photocathodes on Silicon Si MCPs
Polycrystalline boron doped diamond, band gap -
5.47 eV (227 nm) - Solar blind. Hydrogenated
diamond is air stable (lt10 drop in 18 hours) and
is very robust. GaAs QE up to 50 in the red now
possible, low background 10 events/sec
_at_-20C Time response lt1ns, for Interferometry,
Lidar,Molecular fluorescence.
Diamond coated Silicon MCP
Cs activated
Pre-hydrogenated values
GaAs photocathode UV efficiency
Diamond Photocathodes on Silicon and Si MCPs
9GaN Photocathodes
opaque
semitransparent
Fig.2. Measured QE of GaN samples on sapphire
(300µm) after cesiation, for semitransparent (corr
ected for substrate transmission) opaque modes
Fig.1. Measured quantum efficiency of CsI on
MCPs, CsTe semitransparent (NIST) on MgF2
window and CsTe semitransparent (GALEX) on thick
UV silica windows.
10Silicon MCP Developments
- Silicon MCPs
- Silicon MCPs are made by photo-lithographic
methods - Photolithographic etch process - very uniform
pore pattern - No multifiber boundaries array distortions of
glass MCPs - 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)
- 401 to 601 L/D (gt1001 possible)
- 7µm pore size, hexagonal and square pore
- 2 bias and 8 bias, resistances G?, to lt100M?
possible - Working on processing techniques to improve
uniformity - Techniques for gain QE enhancement under
investigation
Hexagonal pore Si MCP with 7µm pores, gt75 open
area
8cm Si MCP on 100mm substrate
11Silicon MCP Performance Characteristics
- Gain PHD very similar to glass MCPs, stacks of
Si MCPs (4) with gain up to 106 - QE is similar to good bare glass MCPs (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!
12/10µm COS
6µm pore MCP
Contrast enhanced image of the fixed pattern
response to a Hg vapor lamp with a stack of 4 Si
MCPs. 14mm area, 107 counts, 50µm resolution
XDL.
QDE for Si bare glass MCPs vs Wavelength
12Cross 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
gtgt MHz rates Compact and robust (900C).
Bottom fingers
13Cross 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.
Anode backside showing the external board where
preamplifier chips are mounted.
14Cross Strip Anode Readout
Outstanding Spatial Resolution/Linearity 7µm
pores are resolved, lt3 µm electronic resolution
with 10 bit encoding electronics Image linearity
is 1µm level and shows pore misalignments and
multi-fiber boundaries Gain required is lt4 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 1601 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.
15Resolution of Cross Strip MCP Sensors
Gain 1.3 x 106
Air force mask on 6µm pore MCP pair with cross
strip readout
Air force mask on Single 6µm pore MCP optical
image
16Advanced MCP Sensors for Astrophysics GALEX
Early Observations
60mm XDL detectors with CsI and CsTe
photocathodes, Launched 6/03
M101
M83
17M51 Whirlpool GalaxyComparison
GALEX Early Data
18M31 Andromeda