Detector array and method

A detector array and method are disclosed in which plural sets of electrode elements are provided with each set comprising a plurality of linear extending parallel electrodes. The sets of electrode elements are disposed at an angle (preferably orthogonal) with respect to one another so that the individual elements intersect and overlap individual elements of the other sets. Electrical insulation is provided between the overlapping elements. The thus configured detector array is exposed to a source of charged particles which in accordance with one embodiment comprise electrons derived from a microchannel array plate exposed to photons. Amplifier and discriminator means are provided for each individual electrode element. Detection means is provided to sense pulses on individual electrode elements in the sets, with coincidence of pulses on individual intersecting electrode elements being indicative of charged particle impact at the intersection of the elements. Electronic readout means are provided to provide an indication of coincident events and the location where the charged particle or particles impacted. Display means are provided for generating appropriate displays representative of the intensity and location of charged particles impacting on the detector array.

BACKGROUND OF THE INVENTION 
This invention pertains to a detector array and method for detecting 
charged particles and in accordance with one embodiment pertains to such a 
detector array and method for use with microchannel array plates for 
photon counting. 
One of the important applications of charged particle detector arrays has 
been in connection with detector arrays for photon counting. In the prior 
art, instruments for photometric studies such as at ultraviolet and x-ray 
wavelengths have been either photographic or photoelectric. Photographic 
instruments, employing film as the detection system, have the great 
advantage of an image-storing capability. It is therefore possible to use 
this type of instrument to record a very large amount of data with a 
single exposure. However, the sensitivity of photographic film is 
considerably lower than that of a photoelectric detector and the quantum 
efficiency is typically less than a photoelectric detector. Further 
disadvantages include the fact that the photographic film response is 
non-linear as a function of the incident energy, and since the output 
signal is not electrical in character the photographic film must be 
recovered, thus inhibiting to some extent its use on orbiting satellites. 
Photoelectric instruments, on the other hand, are more sensitive and have a 
greater stability of response and provide a linear output as a function of 
the incident energy. However, since most photoelectric detectors do not 
have image-recording capabilities, the data must be readout sequentially, 
point-by-point. Consequently, the overall speed of the system is quite 
low. 
The development of the channel electron multiplier and its miniaturization 
into the microchannel array plate have been important developments in the 
field of photometrics, combining the advantages of both the photographic 
and the photoelectric detection systems. The microchannel array plate can 
be operated as an image-intensifier and has the potential of being 
developed to yield signal outputs superior to those of conventional 
photomultipliers. In particular, the microchannel array plate has a 
photo-counting capability and a negligible dark count rate. These devices 
can operate stably and efficiently at extreme ultraviolet (EUV) and soft 
x-ray wavelengths in a windowless configuration or can be installed with a 
photocathode in a sealed tube for use at ultraviolet and visible 
wavelengths. 
The readout systems generally employed with microchannel array plates in 
the prior art have been a visible-light phospor coupled to either a 
vidicon tube or photographic film. In this arrangement, the detected 
photon is converted to a pulse of electrons in the microchannels; these 
electrons are accelerated towards the phospor and reconverted to visible 
photons, which are detected by either the vidicon photocathode or the 
photographic emulsion. Although the microchannel array plate can provide a 
gain on the order of 10.sup.7, this system is cumbersome and has all the 
inherent disadvantages of either the photographic plate or the vidicon 
tube. 
In order to exploit the full sensitivity, dynamic range and photometric 
stability of the microchannel array plate, it is necessary to employ 
pulse-counting readout systems working directly at the output of the 
plate. Some examples of pulse-counting systems to readout spatial 
information from microchannel array plates have been described in the 
prior art, but have been designed to employ a limited number of 
amplifiers, two for a one-dimensional array and four for a two-dimensional 
array, and have consequently been limited in terms of dynamic range and 
spatial resolution. This is especially the case for applications at high 
signal levels such as from laboratory EUV and soft x-ray sources or from 
telescopes for solar studies at EUV and soft x-ray wavelengths. There have 
been suggestions of a multielement anode array in the prior art, such as 
in "The Multianode Photomultiplier", by Catchpole and Johnson, Pub. 
Astron. Soc. Pacific, volume 84, February 1972, pages 134-136. This 
article discloses a detector array for use with a microchannel array plate 
in which a two-dimensional array of individual anode elements (10.times.10 
anode array) is provided. Individual amplifier and electronic means appear 
to be contemplated for each of the individual anode elements. That article 
further indicates that an alternative readout possibility was 
contemplated, in which a resistive strip anode was utilized, which is made 
to act as a voltage divider. Comparison of the pulses at the channel plate 
and at one end of the resistive anode would enable the position of the 
pulse to be calculated electronically. This article acknowledges that such 
a system would have limitations in the maximum pulse rate could handle. 
Another version of such a resistive anode readout system for a detector 
array is described in an article by G.M. Lawrence and E.J. Stone, "Rev. 
Sci. Instrum. 46, 432" (1975). Such systems have a limited dynamic range 
and have pincushion distortion inherent in the system. 
In applicants' copending application Ser. No. , filed June 8, 1976 and 
entitled "ONE-DIMENSIONAL PHOTON-COUNTING DETECTOR ARRAY", there is 
disclosed and claimed a one-dimensional detector array system having good 
spatial resolution and dynamic range. In that system, the output of a 
microchannel array plate is proximity focused on a detector array 
comprising a plurality of parallel, linearly extended anode elements. 
Individual amplifier and discriminator means are provided for each of the 
anode elements. 
OBJECTS AND SUMMARY OF THE INVENTION 
It is an object of this invention to provide a system and method for 
providing a two-dimensional detector array having good spatial resolution 
and dynamic range. 
It is a more specific object for this invention to provide such a system 
and method in which a large number of picture elements are provided 
without requiring separate amplifier and discriminator means for each 
picture element. 
It is a further object of this invention to provide such a system and 
method in which a plurality of sets of electrode elements are provided, 
with each set having a plurality of individual electrode elements. The 
sets of electrode elements intersect and overlap each other to form, e.g. 
rows and columns, with coincident detection means provided for detecting a 
simultaneous event in a row and column. 
It is a further object of this invention in accordance with a specific 
embodiment to provide a two-dimensional coincidence detector array in 
association with a channel electron multiplier proximity focused thereon 
to provide a two-dimensional photon-counting detector array. 
Briefly, in accordance with one embodiment of the invention, a charged 
particle detector array is provided for use with a two-dimensional source 
of charged particles. An electrode array is provided adjacent to the 
two-dimensional source with the charged particles being imaged upon the 
electrode array. The electrode array comprises a plurality of sets of 
electrode elements, each set in turn comprising a plurality of individual 
electrode elements. Each of the sets of electrode elements are oriented at 
predetermined angles (preferably orthogonally) with respect to each other 
so that individual elements of each set intersect and overlap individual 
elements of the other sets to form a charged particle counting zone in the 
vicinity of overlapped elements. Electrical insulating means insulates the 
intersecting and overlapping elements from each other. Amplifier and 
discriminator means are connected to each individual linearly extending 
electrode element for generating output pulses in response to charged 
particle impacts thereon. Coincidence detection means is provided for 
detecting approximately coincident output pulses from an amplifier and 
discriminator means in each set of electrode elements, the occurrence of 
which is indicative of charged particles impinging in the charged particle 
counting zone at the intersection of the respective elements with respect 
to which the coincident output pulses appear.

DETAILED DESCRIPTION 
Turning now to FIGS. 1 and 2, there is illustrated in schematic form one 
embodiment of a two-dimensional electrode array in accordance with this 
invention. In FIG. 1 a two-dimensional electrode array 11 is shown in 
proximity focus to the output face of a microchannel array plate 12. In 
response to incident photons, the microchannel array plate 12 (being 
provided with suitable accelerating potential and biasing potentials) 
generates electrons and multiplies these electrons, with the output of the 
microchannel array plate 12 being proximity focused on the electrode 
assembly 11. The microchannel array plate 12 in FIG. 1 is illustrated as 
being a single microchannel array plate having curved microchannels 
therein (only one microchannel is illustrated in FIG. 1). Alternatively, a 
microchannel array of two or more plates having straight microchannels but 
being arranged in a chevron relationship can be utilized. As known to 
those skilled in this art, the curved microchannels in the microchannel 
array plate or alternatively the chevron arrangement of microchannels into 
adjacent plates, serves to inhibit ion feedback which could otherwise lead 
to instability in operation of the microchannel array plate. 
The two-dimensional electrode array 11 comprises an insulating substrate 13 
which may for example be a quartz substrate. The top surface of the 
substrate 13 should be reasonably flat, and in accordance with a 
particular embodiment has been polished flat to better than 2 microns. 
Upon the top surface of the substrate 13 a first set of electrodes is 
deposited, such as by evaporation or sputtering techniques. This first set 
of electrodes can consist of a great many linearly extending parallel 
electrodes; four electrodes 14, 15, 16 and 17 are illustrated in FIGS. 1 
and 2. As a typical example of the dimensions involved, this first set of 
electrodes 14-17 can be 25 microns in width, 1.6 millimeters in length, 
and set on 50 micron centers. 
Thereafter, the first set of electrodes 14-17 is covered with an insulating 
layer, such as an evaporated quartz film which can be, for example, 2500 A 
thick. This insulating layer is illustrated in the drawings by reference 
numeral 18. A second set of electrodes is then deposited on top of the 
insulating quartz film, such as by evaporation or sputtering. Of course a 
large number of these electrodes may be provided, with there being three 
electrodes 19, 20, and 21 illustrated in FIGS. 1 and 2. As illustrated in 
the drawings, the second set of electrodes 19-21 are all parallel with 
each other and linearly extending, but are oriented at an angle 
(preferably right angles) with respect to the first set of electrodes 
14-17. Therefore, individual electrode elements intersect and overlap each 
other to form charged particle counting zones or picture elements (pixels) 
at their intersection and overlapping. In fabricating the electrode 
assembly, following the deposition of the second set of electrodes 19-21, 
photomasking can be applied to protect the upper electrodes 19-21, with 
the quartz insulating film or layer 18 in the spaces between the upper 
electrodes then being etched away such as by plasma discharge to expose 
the lower electrodes as shown in FIG. 2. Thus, there results a matrix-like 
array with one set of electrodes 14-17 being parallel to one another and 
extending in one direction, and a second set of electrodes 19-21 being 
electrically insulated from the first and running in another direction so 
as to form intersecting overlapping zones with the first set of 
electrodes. Each of these overlapping zones, identified by reference 
numeral 22 in FIG. 2, is a charged particle counting zone or picture 
element (pixel). 
With this kind of electrode arrangement, the output charge from the 
microchannel array plate 12 falls on the charged particle counting zones 
22 or picture elements, with the incident output charge being divided 
between the two overlapping electrodes at that picture element. In 
accordance with a specific embodiment of the invention, the uppermost 
electrodes 19-21 were 15 microns in width, 1.6 millimeters in length, and 
set on 50 micron centers. By making the uppermost electrodes of a narrower 
width than the bottommost electrodes, the exposed areas of the two sets of 
electrodes for any given picture element 22 are approximately equal, so 
that the output charge from the microchannel array plate falls in 
approximately equal amounts on both of the electrodes, i.e. electrode 16 
and electrode 19 in FIG. 2. 
As will be hereinafter described, individual amplifier and discriminator 
means are provided for each electrode element in each set. If two sets of 
electrode elements are used, they can be referred to as row and column 
electrode elements, or anodes in the case of the specific arrangement 
shown in FIGS. 1 and 2. Since the output charge from the microchannel 
array plate (or any other two dimensional source of charged particles) is 
divided between the row and column electrodes at the intersection where 
the event occurs, the spatial location of the event can be identified by 
the coincident arrival of pulses on the appropriate row and column anodes. 
It is possible with this kind of method and system for a detector array to 
obtain photometric information from (N.times.M) pixels using only (N+M) 
amplifier and discriminator circuits. In accordance with a specific 
embodiment of the invention, a detector array was constructed in which two 
sets of electrode elements are provided with each set comprising 32 
individual elements. Therefore, a detector array having 1024 picture 
elements resulted. 
Although FIGS. 1 and 2 illustrate the principles of this invention as 
applied to a coincidence detection electrode array in which two sets of 
electrode elements are provided, the principles of the invention are 
equally applicable to detector array systems in which three superimposed, 
intersecting and overlapping sets of electrode elements are provided as 
well as even four or more. If three sets of overlapping electrodes are 
provided, then the coincident arrival of pulses on all three superimposed 
overlapping electrodes is utilized as indicative of charged particle 
impact at the intersection of the three electrode elements, and so forth. 
For best results for a detector array in accordance with this invention, 
the overlapping and intersecting electrodes are configured so that an 
approximately equal surface area of each of the overlapping electrodes is 
exposed to the charged particle source at the pixel. One way to achieve 
this as described in connection with FIGS. 1 and 2 is to very the widths 
of the electrode elements in the various sets. Thus in FIG. 2 the 
uppermost electrode set has individual electrode elements which are of a 
more narrow width than the lower electrode elements. Other ways to achieve 
this approximately equal surface area of the electrode elements exposed to 
the charged particle source at the pixels are shown in FIGS. 3 and 4. In 
FIG. 3, a plurality of lower electrodes 23, 24, 25 and 26 are shown with a 
plurality of upper electrodes 27, 28, 29 and 30 disposed at an angle 
thereto and overlapping the bottom electrodes. Each of the upper electrode 
elements 27-30 has a linearly extending aperture 27a-30a formed therein so 
that the lower electrode is exposed through the aperture. With this 
configuration the width of the lower electrode, the width of the upper 
electrode, and the aperture width in the upper electrode are configured so 
that an approximately equal surface area of upper and lower electrode are 
exposed to the source charged particles at each charged particle counting 
zone or picture element 39. 
FIG. 4 is similar to FIG. 3 and illustrates an alternative arrangement for 
configuring the sets of electrodes so that approximately equal surface 
areas of electrodes in the different sets are exposed to the source of 
charged particles. In FIG. 4 the first set of electrodes is provided which 
comprises a plurality of electrode elements 31, 32, 33 and 34. A second 
set of electrodes 35, 36, 37 and 38 are provided and are disposed as an 
angle (preferably right angles) with respect to the first set of 
electrodes so that they overlap the first set of electrodes. Of course, 
electrical insulation is provided underneath the second set of electrodes 
so that they are electrically insulated from the first set of electrodes. 
Apertures or windows are formed in the upper set of electrodes 35-38 at 
locations along these electrodes where they overlap the first set of 
electrodes 31-34. Thus of the electrodes shown in FIG. 4 the electrode 35 
has apertures 35a-35d formed therein to expose portions of the underlying 
electrodes 31-34, and so forth. The width of the individual elements in 
the first and second sets of electrodes together with the dimensions of 
the apertures formed in the upper set of electrodes are controlled in 
order to provide an approximately equal surface area of the bottom and top 
electrodes at each of the charged particle counting zones or picture 
elements 40. 
Turning now to FIG. 5, there is shown in block diagram form suitable 
electronic circuitry for use with the coincidence two-dimensional detector 
array of this invention in accordance with one embodiment thereof. In FIG. 
5, there is schematically shown the use of two chevron arranged 
microchannel array plates 41 and 42 with the output of microchannel array 
plate 42 being proximity focused on a detector array 43. The detector 
array 43 is constructed in accordance with the principles of this 
invention to have plural sets of electrodes with each set of electrode 
elements comprising a plurality of the linearly extending parallel 
individual electrode elements. In accordance with the specific embodiments 
schematically illustrated in FIG. 5, two sets of approximately orthogonal 
electrode elements are provided, with there being 32 electrode elements in 
each set. A matrix-like array thus results having 32 .times. 32 = 1024 
charged particle counting zones or picture elements. A suitable high 
voltage power supply 44 is provided for the accelerating and biasing 
potentials on the microchannel array plates 41 and 42 and on the detector 
array 43. 
Since in accordance with the embodiment shown in FIG. 5 only two sets of 
electrode elements are utilized, we can refer to one set of electrode 
elements as row anodes and the other set of electrode elements as column 
anodes. 
A separate charge sensitive amplifier is provided connected to each of the 
32 row anodes and to each of the 32 column anodes. Thus, a total of 64 
charge sensitive amplifiers are provided. In FIG. 5, only two of the 
amplifiers for the column anodes are illustrated, these being amplifiers 
46 and 47. Similarly, only two of the amplifiers for the row anodes are 
shown, these being illustrated in FIG. 5 as amplifiers 48 and 49. A 
discriminator and one-shot circuit is provided connected to each of the 
charge sensitive amplifiers. Thus, a total of 64 discriminator and 
one-shot circuits are provided, with four of these indicated by reference 
numerals 51, 52, 53 and 54 being illustrated in FIG. 5. The purpose of the 
discriminator and one-shot circuit is to eliminate any erroneous output 
indication caused by noise pulses which might be due to cross coupling 
between adjacent electrodes in the anode array. Suitable specific circuits 
for the charge amplifiers and for the discriminator and one-shot circuits 
are known, and one example of suitable specific circuits is set forth in 
"One-Dimensional Photon-Counting Detector Array For Use At EUV And Soft 
X-ray Wavelengths", by J.G. Timothy and R.L. Bybee, Applied Optics, volume 
14, pages 1632-1644, July 1975, hereby incorporated by reference. The 
charge sensitive amplifiers integrate and amplify the charges on the 
respective anode elements and may, for example, provide an output pulse on 
the order of one volt where the input charge to the anode is on the order 
of 10.sup.-12 C (equivalent to a gain of 6.3 .times. 10.sup.6 in the 
microchannel array plate). Each of the discriminator and one-shot circuits 
are in accordance with a preferred embodiment a level discriminator and 
one-shot multivibrator circuit which generates a logic pulse compatible 
with the data handling circuits provided. For example, one embodiment of 
discriminator and one-shot circuit in accordance with the invention 
generated a 10 volt logic pulse, 300 nsec in width. Preferably, the 
discriminator threshold is adjustable, a typical adjustment range being 8 
.times. 10.sup.-13 C (5 .times. 10.sup.6 electron/pulse) to 1.1 .times. 
10.sup.-11 C (7 .times. 10.sup.7 electron/pulse). A threshold adjustment 
control 56 is schematically illustrated in FIG. 5. 
In operation, the digital pulse data from the 32 column amplifiers and the 
32 row amplifiers and discriminator circuits are fed to two 
32-line-to-5-line binary encoders 57 and 58. These two encoders generate 
two 5-bit binary address words which are fed to a 10-bit parallel load 
address counter 59 in addition to row and column event pulses which are 
fed to a coincident detection circuit 61. The coincident detection circuit 
61 also receives a COINCIDENCE ENABLE signal from shutter logic 62 which 
is in turn under control of memory control and timing logic circuitry 63. 
The shutter logic 62 permits the selection of a variety of integration 
times, which as an example can range from 0.25 seconds to 4096 seconds. 
If a row and a column pulse occurred approximately in coincidence (say 
within 150 nsec of each other) the coincidence detection circuit 61 
generates an event pulse which, in turn, causes the memory control and 
timing logic 63 to initiate the storage cycle of a 10-bit by 1024 word 
random access memory (RAM) 64. In this cycle, the 10-bit location address 
word is first loaded into the memory address register of RAM 64. The data 
stored in the address register are then read into a data output shift 
register 67 and loaded into the external register 66 which is a 10-bit 
accumulate register. This register 66 is then incremented by one event 
under control of the memory control and timing logic 63 and loaded back 
into memory of the RAM 64. In accordance with a specific embodiment of the 
invention, the total cycle time of the coincidence-detection and 
memory-address circuit is 1.mu., allowing a total count rate of 10.sup.6 
counts per second to be determined with this detector array. 
FIG. 6 is a block circuit diagram of display electronics for use with the 
detector electronics shown in FIG. 5. A timing generator and control logic 
circuit 68 provides signals which are labeled EXTERNAL READ COMMAND, 
EXTERNAL READ CLOCK, and EXTERNAL SHUTTER CONTROL. These signals control 
the memory control and timing logic circuit 63 and the shutter logic 62. 
The display electronics of FIG. 6 includes a data input shift register 69 
into which the serial data from data output shift register 67 of the 
detector electronics in FIG. 5 is connected. An additional 1024 .times. 10 
bit random access memory (RAM) 71 is provided as part of the display 
electronics. This RAM 71 stores the data to allow refresh of the display 
circuits and to produce a serial biphase output which can be coupled to an 
on-line digital computer. This is achieved through a computer interface 
shift register 72 and biphase converter 73. 
A display word select switches circuit 74 is provided along with an address 
register 76 forming inputs to address comparison logic 77. The address 
comparison logic 77 loads into a parallel load binary down counter 78 
under control of a display clock 79 a signal indicative of the accumulated 
count in the particular words selected by display words select switches 
74. This is coupled through a BCD up counter 81 to suitable selected words 
intensity display 82 which displays the accumulated count (intensity) of 
the particular word or picture elements selected by the switches 74. 
The display system illustrated in FIG. 6, in addition to displaying in 
digital format the count in any selected address in the memory, also 
includes provision for displaying the intensity in all 1024 pixels in 
analog format on a CRT or plotter. Thus a binary address register 83 is 
coupled to the RAM 71 with an address d/a converter 84 provided to 
generate an address input to analog display control circuits 85. An 
intensity d/a converter 86 is coupled to the RAM 71 and provides an input 
to the analog display control circuit 85 indicative of the count for the 
respective pixels. The analog display control circuits 85 generate 
horizontal and vertical outputs as well as a Z-axis output which can be 
coupled to a CRT and/or a plotter for displaying the intensities in all 
1024 pixels in analog format. 
Turning now to FIG. 7, there is shown an embodiment of the invention in 
which a linear extended electrode array can be formed by "unfolding" a 32 
.times. 32 matrix array. FIG. 7 illustrates the basic concept of forming 
such a linear extended array. In FIg. 7 the 32 X electrode elements of one 
set X1-X32, are arranged in two rows. The two rows are parallel and each 
of the 16 elements in each row is arranged end-to-end but separated by a 
small space. The 32 electrode elements of the other set, Y1-Y32, are then 
convoluted to cross back and forth across all of the X electrodes of the 
first set. The intersection of each of the Y electrodes with each of the X 
electrodes is a pixel, thus resulting in a linear extended array of 2 by 
512 pixels utilizing a total of only 64 electrode elements, with 
corresponding 64 amplifiers and discriminators. 
Such two-dimensional coincidence arrays in an extended linear format as 
shown in FIG. 7 can, of course, be arranged in many different ways. Such 
linear extended formats are ideally suited for use in high efficiency 
spectrometers for faint object spectroscopy. The format of the array can 
be exactly matched to the dispersion characteristics of the diffraction 
grating utilized, and in addition, spectra of source and background can be 
recorded simultaneously. The pixels can be formed so that the individual 
elements of each electrode set have approximately the same electrode area 
exposed to the source of charged particles, either by tailoring the 
dimensions of the respective sets of electrodes or by providing apertures 
or windows as schematically illustrated before in connection with FIGS. 3 
and 4. 
Turning now to FIG. 8, there is shown in schematic cross-sectional side 
view one particular example of the coincident electrode detector 
arrangement of this invention utilized with a microchannel array plate in 
a sealed "wafer" tube. Microchannel array plates are constructed from a 
semiconducting glass which has a work function of about 5 eV. An uncoated 
microchannel array plate can thus be used as an efficient photomultiplier 
only at EUV wavelengths in the range 300 to 1250 A. The wavelength range 
can, however, be extended in a number of ways. First, a microchannel array 
plate can be coated with an opaque MgF.sub.2 cathode at the input of the 
microchannel to produce a high efficiency open structure detector for soft 
x-ray in the wavelength range from 20 to 300 A. Second, it is possible to 
integrate the microchannel array plate and anode array with either an 
opaque photocathode, or with a semi-transparent photocathode in proximity 
focus at the input of the microchannels, in a sealed tube for use at 
ultra-violet and visible wavelengths. 
Referring now to FIG. 8, thereis shown one example of a "wafer" tube 
utilizing a photocathode. A glass window 87 overlies a photocathode 88 
which is placed at the entry face of a microchannel array plate 89. A 
ceramic sidewall spacer 91 spaces the various elements with respect to 
each other and connecting electrodes 92 and 93 are provided to make 
electrical contact with the photocathode and microchannel array plate for 
applying the proper biasing potentials thereto. An anode array 94 is 
provided in proximity focus to the output face of the microchannel array 
plate 89. An insulating spacer 96 may be provided to accurately space the 
output face of the microchannel array plate with respect to the anode 
array. The anode array 94 is conveniently situated on top of a multilayer 
ceramic substrate 97 with there being provided conducting electrodes 98 
for contacting the ceramic substrate to provide proper biasing and 
accelerating potentials for electrons generated in the microchannel array 
plate. Electrical connections to the detector array may be made through 
connecting pins 98 on the bottom of the multilayer ceramic substrate 97 
with connecting paths such as path 99 formed through the ceramic substrate 
and contacting the individual electrode elements. This is thus one 
construction which advantageously utilizes the detector array of the 
present invention to provide a relatively large number of picture elements 
without the necessity of separate amplifiers for each picture element. 
Although the invention has been shown and described with reference to 
specific embodiments, various modifications can of course be made by those 
skilled in this art without departing from the true spirit and scope of 
the invention.