Mechanism for measuring nanosecond time differences between luminous events using streak camer

Oertel, G. K.

Williams, M. D.

English

NASA Technical Reports Server

REPLY TO 
ATTNOF GP 
TO z 
SUBJECT s 
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION 
WASHINGTON. D.C. 20546 
USI/Scientific SC Technical Information Division 
Attention: Miss Winnie M e  Morgan J 
GP/Office of Assistant General 
Counsel for Patent Matters 
Announcement of NASA-Owned 
U,S, Patents in STAR 
In accordance with the procedures contained in the Code GP 
to Code US1 memorandum on this subject, dated June 8, 1970, 
the attached NASA-owned U , S .  patent is being forwarded for 
abstracting and announcement in NASA STAR, 
The following information is provided: 
U,S, Patent No. 
Corporate Source 
Supplementary 
Corporate Source * 
NASA Patent Case No,: A-0 
Gaybe Parker 
Enclosure: 
Copy of Patent 
I 
(NASA CR OR TRRX OR AD NUMBER) NASA-HQ 
https://ntrs.nasa.gov/search.jsp?R=19710014500 2020-03-17T03:04:42+00:00Z
8 6. K. OERTEL. ETAL 
MEASUREMENT OF T I M E  D I F F E R E N C E S  BETWEEN LUMINOUS EVENTS 
Filed April 13, 1966 
FIG. 1 
13 4 
. 
BY 
INVENTORS 
atente e 
It is therefore an object of this invention to measure 
extremely short time differences between several luminous 
Another object of this invention is to provide an in- 
~ ~ ~ ~ b ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ e ~ ~ ~ ~ ~ ~ ~  5 expensive and reliable method and apparatus for accu- 
rately measuring extremely short time differences between 
several luminous events. 
In accomplishing these and other objects this invention 
employs fiber optics (light pipes) to transmit the light 
from the luminous events to an image converter streak 
camera. There is one light pipe for each monitored 
luminous event with one of its ends near to and pointed 
A mechanism for measuring nanosecond time differ- in the direction of the luminous event. The other ends 
ences between luminous events utilizing a streak camera. of the 1k1lt Pipes are arranged in a linear array to form 
Light pipes transmit the light from the events to the 15 a luminous slit for the image converter streak camera 
streak camera and display them in a linear array for to photograph. The light transmitted from each of the 
photographing. The events are photographed by the streak luminous events to the camera is a point source of light 
camera and the events appearing in the form of streaks that is photographed as a streak. The beginning of the 
on the film are compared to determine the time differences streak represents the time that the luminous event oc- 
of the events. 20 curred and the length of the photograph in units of 
time is known. Consequently, if a large number of these 
streaks appear side-by-side on a photograph, the time dif- 
The invention described herein was made by employees ferences between the different luminous events can be 
of the 'United States Government and may be manufac- determined. 
tured and used by or for the Government for govern- 25 Other objects and advantages of this invention will 
mental purposes without the payment of any royalties further become apparent hereinafter and in the drawings, 
thereon or therefor. in which: 
This invention relates generally to measuring and more FIG. 1 is a block diagram of the invention; 
specifically concerns a method and apparatus for meas- FIG. 2 is 0 drawing of a typical photograph taken by 
uring extremely short time differences between luminous 30 an image converter streak camera of several luminous 
events. events; and 
Ssmetimes it is desired that a set of luminous events FIG. 3 is a schematic drawing showing how the lumi- 
occur as close to the same time as possible. For example, 
suppose there exists an electrical storage system consisting In describing the preferred embodiment of the inven- 
of several hundred charged capacitors with each capacitor 35 tion illustrated in the drawings, specific terminology Will 
connected in series with a spark gap and with the resulting be resorted to for the sake of clarity. However, it is not 
series circuits connected in parallel. Suppose that this intended to be limited to the specific terms So selected, 
electrical storage system is connected across a load and and it is to be understood that each specific term includes 
it is desired to pass maximum .&ctrical energy through all technical equivalents which operate in a similar man- 
the load. Then it is desirable that all spark gaps fire 40 ner to accomplish a similar Purpose. 
as close to the same time as possible. Obviously, the spark Turning now to the specific embodiment of the inven- 
gaps cannot be fired simultaneously: there will always be tion selected for illustration in the drawings, the num- 
a time interval (jitter) between the time the first spark ber 41 in FIG. 1 is a block which represents the lumi- 
gap fires and the time the last spark gap fires. If this nous events the time differences of which are to be meas- 
time interval is to be made as short as possible, to supply 45 ured. They can be any set of luminous events which 
the most possible electrical energy to the load, it becomes occur within a few nanoseconds of each other. Each lu ' 
necessary to measure the time differences between the nous event is monitored by one end of a light pipe 
firing of the different spark gaps. Then adjustments can which consists of a bundle of optical fibers. The o 
be made in the system to minimize these time differences. ends of the light pipes 12 terminate in a linear array at  
Since a spark gap Produces light when it fires, the Problem 80 an image converter streak camera 13. The front optics 
is to measure the time differences between the occurrences of camera 13 is oriented such that the linear array 
of a set of luminous events. of light pipe 12 ends are focused on the 
Previously there has been no suitable device available oi the image converter tube in camera 
3,392,403 
BETWEEN ~ ~ ~ O ~ S  EVENTS ~ E A S U ~ ~ ~ N ~  OF TIME ~ ~ ~ ~ ~ ~ N ~ E ~  events. 
by ahe Administrator of the ~ ~ t i ~ ~ ~ l  
Aeronautics and Space Administration 
Filed Apr. 13, 1966, Sei-. No. 542,713 
6 Claims. (Cl. 346-107) 
nous events are monitored. 
for measuring extremely short (in the nanosecond range) luminous events 11 occur, light is transmitted through 
time differences between the occurrences of a set of 55 light pipes 12 to form a straight line of point light 
luminous events. Individual phototubes or pickup loops sources at the linear array of the light pipe 12 ends. could be placed near the luminous events, and the signals 
be compared to determine the time differences between 60 graphed by 
the occurrences of the luminous events. However, such 
a technique is tedious, extremely costly for a large num- 
ber of events, and not very accurate in the nanosecond 
range. 
be simultaneously recorded on as many oscilloscope 
riels as there are events. Then the photographs could 
These point light are swept across the phosphor 
of the image converter tube in camera 13 and photo- 
I3 as streaks* is a drawing 
of a typical Photograph taken by Camera 13 of ~ ~ v e r a l  
luminous events 11. Each steak 14 in the Photograph 
is a picture of one of the luminous events 11. Camera 
13 sweeps the luminous events 11 at a known constant 
3,392, 
3 
rate from right to left on the photograph. Thus, the 
streaks 14 all start at different points on the righthand 
end of the photograph. The times at  which the streaks 
14 start represent the times at  which the luminous events 
11 occur. Therefore, by making measurements of the 5 
lengths of streaks 14 one can determine the time dif- 
ferences between the luminous events 11 which caused 
these streaks. 
To photograph the luminous events 11, it is necessary 
that camera 13 be turned “on” slightly before the light 
from luminous events 11 reaches the camera. To do this a 
trigger generator I§ is provided which produces a pulss 
when an input is applied to its input terminal 16. The 
pulse from trigger generator B5 is applied through a time 
delay 18 to a camera trigger 19 which produces a pulse to 15 
turn “on” camera 13. Time delay 18, although shown as a 
separate block, is actually part of camera trigger 19 and 
is variable by the proper setting of dials. The lengths 
of connections to (electrical o r  optical) and from camera 
trigger 19 plus a fixed amount of delay inherent in camera 20 
trigger 19 determine the minimum value of delay 18. 
The pulse from trigger generator 1.5 is also applied 
through another time delay 17 to the luminous events 
11 to cause them to be triggered. To be assured that 
the camera 13 is turned “on” prior to the time that lumi- 25 
nous events 81 reach camera 13 it is necessary that the 
time delay 18 be shorter than the sum of the time delay 
19 and the delay caused by light pipes 12. Consequently, 
when an input is applied to input terminal 16, camera 13 
iq first turned “on” and then luminous events 11 begin 30 
to occur shortly thereafter. These events are photographed 
as streaks 14 in FIG. 2, providing a means by which the 
differences in the occurrence of these luminous events 
can be determined. 
There are image converter streak cameras commer- 35 
cially available that can be used as camera 13. These 
commercially available cameras will permit streak speeds 
up to 250 cm./psec. Consequently, time differences below 
one nanosecond can be measured between luminous events 
1H. Even though camera 13 is disclosed as an image 40 
converter streak camera, it is obvious that other streak 
cameras could be used. If the input to camera trigger 
19 is a light pulse, then a commercially available trig- 
ger generator, consisting of a photoelectric detector and 
a time delay network can be used as camera trigger 19. 
Trigger unit 19 also accepts a suitable electrical signal 45 
directly. 
Turning now to FIG. 3 there is shown a specific exam- 
ple of the type of luminous events 11 that this invention 
is capable of measuring. This example consists of a bank 
of capacitors 21. Only three of these capacitors 21 are 50 
shown; however, in the application of this invention 
as many as 200 or more of the capacitors could be pres- 
ent. Connected in series with each one of these capacitors 
21 is a hemispherical switch 22. The resulting series cir- 
cuits are each connected in parallel with a load 23. In 55 
operation, the capacitors 21 are charged by some means, 
not shown, so that the upper part of the capacitar is at 
a high potential. Then upon application of a voltage at  
input terminal 16 trigger generator 15 produces a pulse 
which is applied to the upper electrodes of switches 22. 60 
This produces a great potential difference between the 
electrodes of switches 22 which causes conduction be- 
tween them. The capacitors 21 then discharge through 
switches 22 and the load 23. It is desirable that all of 
the switches 22 become conductive simultaneously. That 65 
is, that there be as little jitter between the switches 
as possible. At the time each of the switches 22 begins 
to conduct, it produces light; therefore, if the time dif- 
ferences between the onset of lights can be determined 
then the jitter between the different switches 22 can be 70 
determined. This is the purpose of this invention. One 
end of each of the light pipes 2 is directed into the 
area between the electrodes of a switch 22. Thus, when 
the switch begins to conduct, it produces light which is 
transmitted through a light pipe 12 to the image converter 75 
403 
4 
streak camera 13. And as described before, the image 
converter streak camera 13 produces a streak 14 such as 
any one of those shown in FIG. 2. Hence, a streak 14 is 
photographed €or each switch 22 which provides sufficient 
information to determine when each switch fires relative 
to all other switches. 
The advantages of this invention are simplicity, lower 
cost, greater ease of operation, high time resolution with 
considerably smaller sources of errors, and larger possi- 
ble number cf events which can be recorded simultane- 
ously. 
It is to be understood that the form of the invention 
herewith shown and described is to be taken as a preferred 
embodiment. Various changes may be made in the shape, 
size and arrangement of parts. For example, equivalent 
elements may be substituted for those illustrated and de- 
scribed herein; parts may be reversed; and certain fea- 
tures of the invention may be utilized independently of 
the use of other features, all without departing from the 
spirit or scope of the invention as defined in the following 
claims. 
What is claimed as new and desired to be secured by 
Letters Patent of the United States is: 
1. A method for measuring extremely short time dif- 
ferences between several luminous events comprising the 
steps of: transmitting the light from each luminous event 
to a streak camera; arranging the light sources from all 
the several luminous events in a straixght line to be photo- 
graphed by said streak camera; and photographing said 
light from all the said several luminous events by said 
streak camera whereby the photograph of the several 
luminous events are streaks from which the time differ- 
ences between the occurrences of the different luminous 
events can be determined. 
2. Apparatus for measuring extremely short time dif- 
ferences between several luminous events comprising: (a)  
streak camera means which photographs a line of several 
point sources of light as streaks that appear side-by-side 
on a photograph whose length is known in terms of time; 
a light pipe for each of said several luminous events with 
one end of each light pipe near its respective luminous 
event and with the other ends of said light pipes arranged 
in a linear array at  said camera means to be photo- 
graphed by said camera means; and means for turning 
on said camera prior to the occurrence of the first lumi- 
nous event whereby said camera photographs said several 
luminous events as streaks that appear side-by-side on 
a photograph from which the time differences between 
the occurrences of the several luminous events can be 
determined. 
3. Apparatus for measuring extremely short time dif- 
ferences between several luminous events according to 
claim 2 wherein said several luminous events are several 
spark gaps and said one end of each light pipe is pointed 
in the direction of the space between the two electrodes 
of its respective spark gap. 
4. Apparatus for measuring extremely short time dif- 
ferences between several luminous events according to 
claim 2 wherein said means for turning on said camera 
immediately prior to the occurrence of the first luminous 
event comprises: (a)  first time delay means; (b) second 
time delay means such that the sum of time delay of 
the second time delay means and the time delay caused 
by said light pipes is slightly greater than the time delay 
caused by said first time delay means; and means for 
simultaneously applying a pulse through said first and 
second time delay means to said image converter streak 
camera to turn it on and to said luminous events to initiate 
them. 
5. Apparatus for measuring extremely short time dif- 
ferences between several luminous events comprising: a 
light pipe for each of said luminous events with its one 
end near and pointed in the direction of the luminous 
event and with its other end arranged in a linear array 
with all other light pipes; and (a)  streak camera means 
for photographing the light emitted by said linear array 
3,392,403 
References Cite 
UNITED STATES PATENTS 
5 
as streaks that appear side-by-side on the photograph 
whose length in units of time is known whereby the time 
differences between the occurrences of the several lumi- 
nous events can be determined from said photographs. 2,967,664 1/1961 Ress _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _  178-6 
6. Apparatus for measuring extremely short time dif- 5 2,9933195 7/1961 Grow -------------- 346-1°7 
ferences between several luminous events according to 299999420 9/1961 Buck ---------------- g5-11 
claim 5 wherein means are provided for turning on said 
streak camera means prior to the occurrence of the first 
luminous event. 
WILKINSoNy Primary 
E. C. SIMMONS, Assistant Examiner. 


Measurement of time differences between luminous events Patent

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