1. PHOTOMULTIPLIER Developments over the last 25 years
Jon Howorth
Photek’s 25th Birthday

2. Out to watch the Solar Eclipse on 11th August 1999
Photek People

3. Upper Atmospheric Lidar for Alomar Observatory, Norway.
Photek designed and built a custom 24 Equal Area Concentric ring anode photomultiplier for Alomar and other Upper Atmospheric Lidars,

4. Lidar Results 1996
Paper published by
D. Rees et al in 1997.

5. NASA Goddard SLR2000
In 1997 NASA Goddard decided to develop a new Satellite Laser Range finding system with low enough power to be eye-safe.
Laser power was set as 130µJoules.

7. Quadrant PMT for SLR 2000
Photek developed a new quadrant anode photomultiplier using 6µm pore MCPs

8. Quadrant PMT in SLR 2000 Housing
The Package looks much bigger than the tube.

10. Plasma Physics
Requires huge dynamic range for fusion diagnostics

11. Ultra Fast PMTs in 2009
3.2 m pore MCP PMT
6 m pore MCP

13. Gain

14. Electron Paths in a Venetian Blind Dynode Structure
Original design by Walter Turk and Alfred Sommer in 1946.
Most electrons striking near the input (A) have a low escape probability.
Electrons striking nearer the exit (B) have a high escape probability.

15. RELATIVE TRANSMISSION
The red curve corresponds to a full dynode. Point A corresponds to x=-50; Point B at the exit corresponds to x=50.
Shorter dynodes (d1 decreasing) appear better, but don’t intercept all the primaries.
Essentially secondary electron gain has to exceed 20 to enable primaries striking near the input (A) to generate an electron shower.

16. Transit Time Spread
Shown for different dynode dimension, as a function of output voltage.
Contrary to the original Turk design, we found best performance with a strong input field.

17. SUMMARY Transit time spread is proportional to size.
DIMENSION
FILL Factor
DQE
DQE2
DQE3
TTS
Microns %
G=10
G=30
G=100
(ps)
100
0.65
0.8
0.9 65 75
0.45
0.72 45 50
0.4
0.5 30 25
0.25
Transit time spread is proportional to size.
Fill Factor and gain both impact on DQE because electrons impacting neat the entrance have a low probability of escaping

18. Laser Machined, Diamond coated Dynode
125µm pitch, 100µm thick, so 40% chance of straight through as measured optically.
Bars are relatively thick, and reduce transmission as well.

19. Time Response of a single Dynode
Best response 159ps FWHM.
Response time reduces as field at input and output is increased

20. Gain/Input Voltage
Typical NEA Diamond with gain peaking at around 1200V.
Assume about 40% optical transmission, and 60% electron optical transmission so secondary electron gain 4 times higher than measured-roughly 30;1

21. Counting Efficiency (DQE)
All sorts of wonderful ideas for the structure of photomultiplier Dynodes. The DQE is rarely quoted.

22. Statistical Analysis of DQE
The MCP remains the best electron multiplier for time resolution and counting efficiency

23. ALD Coated Plates ALD coating gives even longer life than Diamond.
Improves Counting Efficiency.
Lower Voltage for the same gain

24. GOODBYE
I’ve enjoyed these meetings---
Thanks for inviting me!

25. Thank you for listening
Photek Limited
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