A thermionic diode detector for the far infra-red

81 Pages·03.704 MB·English

by  Jackson, Charles Murfin

A THERMIONIC DIODE DETECTOR FOR THE FAR INFRA-RED
by
Charles Murfin Jackson
Submitted in partial fulfilment
of the requirements for the degree of
MASTER OF SCIENCE
UNIVERSITY OF WESTERN ONTARIO
LONDON
1950
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UMI Number: EC54044
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Approved for the Department of Physics
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This research was made possible by the financial
assistance of the Department of Veterans1 Affairs and a
bursary from the National Research Council. The writer
wishes to thank these organizations for their aid.
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ACKNOWLEDGMENTS
I wish to express my appreciation to
Dr. R. C. Dearie, F.R.S.G., ray research professor, for
his guidance and co-operation, and to Dr. A. D. Misener,
Head of the Physics Department, for use of departmental
facilities.
My sincere thanks to the staff of the Physics
Department for their helpful suggestions.
I am indebted to Dr. K. V. Hunten for his super­
vision during the construction of the evacuation system by
Mr. Turner, Mr. Searle and myself.
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CONTENTS
Page
Acknowledgment s ........................................................................ iv
Tables .......................................................................................... vi
Illustrations ........................................................................... vii
Abstract ................................................................... v iii
Suramary ................ ix
Introduction ................................................................ 1
Chapter I - Theoretical Minimum Detectable Power
of a Thermionic Diode ......... 4
Chapter I I - Construction of Diodes................... 11
Chapter III - Evacuation and Sealing off of the
Diodes ...................................... 17
Chapter 17 - ft Continuously Evacuated Diode ............. 20
Chapter V - Sources of Infra-red Energy and
Energy Filters ............................ 28
Appendix I - (l) Relation between plate current
and galvanometer current ........... 30
(2) Detection in Changes of Filament
Supply Voltage ............................... 31
Appendix II - Richardson's Equation ............................ 33
Appendix III - Evacuation Systems and Equipment .... 37
Appendix 17 - Infra-red Windows and Getters ....... 4&
Bibliography................................................................................ t&
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TABLES
Page
Diode Characteristics ...................................., ............................ 21
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ILLUSTRATIONS
Page
Figure 1. Sensitivities of Detectors ............. v iii
Figure 2, Radiation Spectra ..................................................... 3
Figure 3. Atmospheric Absorption .............................. 3
Figure 4. Diode Sensitivity Curve ............. 10
Figure 5. Diode Infra-red Detector ................. 12
Figure 6. Tubes Constructed ............. 13
Figure 7. Sealing-off Equipment .............. 14
Figure 8. Continuously Evacuated Diode ........................................ 15
Figure 9. Evacuation of Diode ................... 18
Figure 10. Characteristic Curves of Diode .................................... 21
Figure 11. Curve of Power Detectable with Tungsten................... 22
Figure 12. Circuit of Diode ............ 25
Figure 13. Layout of Equipment .......................... 27
Figure 14. Energy Distribution of Hernst Glower................. 28
Figure 15. Sniperscope Window ................ 29
Figure 16, Evacuation of Diode ........... 37
Figure 17. Detection of Leaks ............... 41
Figure 18. Ionization Gauge ................ 41
Figure 19. McLeod Gauge ........... 43
Figure 20. Heating Oven .......................................................................... 44
Figure 21. Regulated Power Supply .............. 45
Figure 22, Trahemission of KC1 and KBr Crystals ...................... 46
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ABSTRACT
In recent years, there has been an increasing interest shown in
receivers for infra-red detection. In 1939, E. D. Wilson patented
a receiver by which infra-red energy is detected as a change in satur­
ation plate current of a diode. If a diode cathode, from which
saturation plate current is drawn, is subjected to infra-red energy,
its temperature is raised and the plate current increases according
5 — h.
to Richardson*s Equation, I - AT e T
Theoretical considerations Indicate that a diode, using a
Cs-CsO-Ag cathode surface, has a maximum sensitivity of 2.34 x 10"^
watts per unit bandwidth^. This value is comparable to the sensi­
tivities of known infra-red detectors (see Fig. l). This fact,
coupled with the diode*s ruggedness and mobility, justifies an inves­
tigation of its properties, when used as an infra-red detector.
Experimental work carried out on a diode using a tungsten wire
emitter led to the conclusion that a diode from which saturation cur­
rent was being drawn could be used to detect radiant energy.
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THERMOCOUPLE OR BOLOMETER
P k -5----------------
PHOTOCONPUCTJVE CELL TIME CONSTANT
»2i-\5EC0NOS
AARREEAA — I MM
Cs~0-----
PHOTOCELL
S
T
T Cs-Sto------
A
photomultipler
W
ONE PHOTON
x $r
\ each
\
SECONDS
H (r RADIO
/A
PRESENT ATTAINABLE THRESHOLD FOR
DETECTION OF ELECTROMAGNETIC RADIATION AS
A FUNCTION OF WAVELENGTH. BLACK-BODY
EMISSION AT 300* K IS ALSO SHOWN.
Figure 1
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