U.S. patent number RE35,872 [Application Number 08/633,483] was granted by the patent office on 1998-08-18 for superconducting detector assembly and apparatus utilizing same.
This patent grant is currently assigned to Advanced Fuel Research, Inc.. Invention is credited to Robert M. Carangelo, David B. Fenner.
United States Patent |
RE35,872 |
Fenner , et al. |
August 18, 1998 |
Superconducting detector assembly and apparatus utilizing same
Abstract
An array of superconducting bolometers, assembled with a
superposed interference layer of graduated thickness, provides a
microelectronic detector assembly that discriminates radiation
impinging thereon, as a function of wavelength, and that can be
used for transform spectroscopy, color-imaging, and the like. The
interference coating will preferably be of step-like form, with
each plateau of the structure being of the same spatial extent as
the bolometer with which it is associated.
Inventors: |
Fenner; David B. (Simsbury,
CT), Carangelo; Robert M. (Glastonbury, CT) |
Assignee: |
Advanced Fuel Research, Inc.
(East Hartford, CT)
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Family
ID: |
25544054 |
Appl.
No.: |
08/633,483 |
Filed: |
April 17, 1996 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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Reissue of: |
997457 |
Dec 28, 1992 |
05354989 |
Oct 11, 1994 |
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Current U.S.
Class: |
250/336.2;
250/338.4 |
Current CPC
Class: |
G01J
3/26 (20130101); G01J 5/20 (20130101); G01J
3/2803 (20130101) |
Current International
Class: |
G01J
5/20 (20060101); G01J 003/51 (); H01L 027/146 ();
H01L 039/00 () |
Field of
Search: |
;250/336.2,338.4 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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0223136 |
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May 1987 |
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EP |
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722749 |
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Jan 1955 |
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GB |
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Primary Examiner: Hannaher; Constantine
Attorney, Agent or Firm: Dorman; Ira S.
Government Interests
The United States Government has rights in this invention pursuant
to Contract No. ISI-9160506, awarded by the National Science
Foundation.
Claims
Having thus described the invention, what is claimed is:
1. A transform spectrometer comprising, in combination:
(1) a detector assembly for discriminating as a function of
wavelength, radiation impinging thereon, said detector assembly
comprising:
a plurality of superconductor bolometers arranged as an array and
having substantially contiguous operative surfaces providing at
least one planar irradiation face, all of said bolometers being
responsive to radiation throughout a given range of wavelengths;
and an interference layer superposed upon said irradiation face of
said array with an associated region of said layer in registry with
each of said bolometers, said layer being composed of a material
that produces constructive and destructive optical interference
conditions to periodically modulate, and thereby transmit
selectively as a function of layer thickness, multiple bands of
wavelengths of radiation in said range, said regions differing from
one another in thickness so as to constitute said layer a graded
interference filter, and to thereby provide a plurality of
detectors that differ from one another in their response to
radiation within said given range, each of said detectors
registering a spectral irradiance periodically modulated, thereby
being capable of discriminating a plurality of wavelength
bands;
(2) means for maintaining said detector assembly at cryogenic
temperatures in a range for varying the conductance of said
bolometers;
(3) means for generating electrical currents, said means for
generating being operatively connected to said array; and
(4) electronic data processing means for transforming said
currents, after passage through said bolometers of said array, so
as to produce signals representative of the energy of radiation
caused to impinge upon said irradiation face, discriminated as a
function of wavelength said data processing means functioning to
apply matrix-inversion transform algorithms to said electrical
current, for producing such signals.
2. The spectrometer of claim 1 wherein the thickness of each of
said regions of said interference layer is substantially constant,
and wherein each of said regions is dimensioned and configured to
intercept and filter substantially all of the radiation that
impinges upon said bolometer associated therewith.
3. The spectrometer of claim 2 wherein said layer is of step-like
form.
4. The spectrometer of claim 1 wherein said layer is of uniform
composition throughout.
5. The spectrometer of claim 4 wherein said layer is composed of
silicon.
6. The spectrometer of claim 1 wherein said bolometers are
fabricated from a high-temperature superconducting film.
7. The spectrometer of claim 6 wherein said superconducting film is
composed of a compound having the general formula RBa.sub.2
(Cu,M).sub.3 O.sub.(7-.delta.), in which R designates at least one
of the rare earth elements: yttrium, lanthanum, neodymium,
samarium, europium, gadolinium, dysprosium, lutetium, and holmium,
and in which M is either null or designates at least one of the
transition elements: silver, gold, nickel, aluminum, zinc, cobalt,
iron, palladium and platinum.
8. The spectrometer of claim 6 wherein said film is epitaxial on
the underlying substrate.
9. The spectrometer of claim 6 wherein each of said bolometers
comprises a meanderline element.
10. The spectrometer of claim 1 wherein said range of wavelengths
to which said bolometers are responsive is 1 .mu.m to 1000
.mu.m.
11. The spectrometer of claim 1 further including a substrate that
is at least coextensive with said bolometer array, said
interference layer being disposed outwardly adjacent either said
substrate or said array.
12. The spectrometer of claim 11 wherein said substrate comprises a
silicon wafer.
13. The spectrometer of claim 11 further including a buffer film
interposed between said array and said substrate.
14. The spectrometer of claim 1 wherein said assembly is devoid of
spacing between said irradiation face and said interference
layer.
15. The spectrometer of claim 1 further including means for causing
radiation to impinge upon said irradiation face of said array.
16. The spectrometer of claim 1 wherein said spectrometer further
includes a radiation source for generating spectral radiation
within said given range.
17. The spectrometer of claim 1 wherein said given range of
wavelengths to which said bolometers respond comprises the infrared
region of the spectrum. .Iadd.
18. A transform spectrometer comprising, in combination:
(1) a detector assembly for discriminating, as a function of
wavelength, radiation impinging thereon, said detector assembly
comprising: a plurality of photothermal detector elements arranged
as an array and having substantially contiguous operative surfaces
providing at least one planar irradiation face, all of said
detector elements being responsive to radiation throughout a given
range of wavelengths; and an interference layer superposed upon
said irradiation face of said array with an associated region of
said layer in registry with each of said detector elements, said
layer being composed of a material that produces constructive and
destructive optical interference conditions to periodically
modulate, and thereby transmit selectively as a function of layer
thickness, multiple bands of wavelengths of radiation in said
range, said regions differing from one another in thickness so as
to constitute said layer a graded interference filter, and to
thereby provide a plurality of detectors that differ from one
another in their response to radiation within said given range,
each of said detectors registering a spectral irradiance
periodically modulated, thereby being capable of discriminating a
plurality of wavelength bands;
(2) means for generating electrical currents, said means for
generating being operatively connected to said array; and
(3) electronic data processing means operatively connected for
transforming electrical currents from said means for generating,
after passage through said detector elements of said array, so as
to produce signals representative of the energy of radiation caused
to impinge upon said irradiation face, discriminated as a function
of wavelength, said data processing means functioning to apply
matrix-inversion transform algorithms to said electrical currents,
for producing such signals..Iaddend.
Description
This invention relates to integrated radiation detector assemblies,
and to spectrometers and other apparatus incorporating the
same.
BACKGROUND OF THE INVENTION
Conventional methods of infrared spectroscopy utilize either a
small throughput (IR flux) optical element for dispersion, followed
by a detector or a detector array, or a large throughput, scanning
interferometer followed by a detector. In application of the first
technique, the spectrum is accessed directly in the wavelength and
frequency domain, while in the second the spectrum is measured in
the time domain and then transformed (typically using Fourier
algorithms) by a post-measurement calculation to the wavenumber
domain.
As is known to those skilled in the art, the first method is
relatively simple to implement, but is also of relatively low
sensitivity due to the small amount of light throughput involved;
in addition, long scanning times are required if the spectral range
encompassed is substantial, and the instrument itself must be
fairly large if good resolution is to be had. On the other hand,
methods using scanning interferometers find wide application in
Fourier-transform infrared (FT-IR) spectroscopy and in other
specialized applications (e.g., piezoelectric scanning Fabry-Perot
interferometers), but the instruments employed can be very complex
and expensive, and can lack durability, largely because of their
requirement for high-precision moving optics.
Additional limitations, common to both spectroscopy methods
described, are related to the materials presently available for IR
detectors. Current detector technology is based either upon
photoelectric semiconductor materials, which are of a narrow band
character, or upon broad-band but low-sensitivity photo-thermal
materials, which are of slow response; both kinds of materials are,
in addition, difficult to fabricate into satisfactory arrays.
SUMMARY OF THE INVENTION
Accordingly, it is the broad object of the present invention to
provide a novel detector assembly that is capable of
discriminating, as a function of wavelength, spectral radiation
impinging thereupon.
More specific objects of the invention are to provide such an
assembly which is itself capable of directly accomplishing
transform spectroscopy, and to provide a spectrometer incorporating
the same.
Other specific objects are to provide such an assembly which is
adapted for use in color-imaging applications, and to provide
color-imaging apparatus incorporating the same.
Additional objects of the invention are to provide such a detector
assembly, spectrometer and other apparatus that is small and
compact, durable, incomplex and relatively inexpensive to
construct, and that nevertheless provides outstanding levels of
sensitivity and response speed.
It has now been found that certain of the foregoing and related
objects of the invention are attained by the provision of a
detector assembly comprised of a plurality of superconductor
bolometers arranged as an array, and a superposed anti-reflection
layer functioning as a graded interference filter. The bolometers
have substantially contiguous operative surfaces that provide at
least one planar face for irradiation, and all of them are
responsive to radiation throughout substantially a given range of
wavelengths. The interference layer is superposed upon the
irradiation face of the array, with an associated region in
registry with each of the bolometers; it is composed of a material
that transmits selectively, as a function of its thickness,
multiple bands of wavelengths of radiation in the given range. The
several regions of the interference layer vary in thickness to
thereby provide, in combination with the associated bolometers, a
plurality of detectors that differ from one another in their
radiation wavelength response.
In the preferred embodiments of the invention each region of the
interference layer will be of substantially constant thickness
throughout, and will be dimensioned and configured to intercept and
filter substantially all of the radiation that impinges upon the
associated bolometer. Indeed, certain objects of the invention may
be attained by the provision of a detector assembly that employs
nonsuperconducting photothermal detectors (e.g., bolometers) in
combination with an interference layer of such structure. The layer
will, in any event, advantageously be of step-like form and will
normally be of uniform composition throughout. The bolometers will
most desirably be fabricated from a high temperature
superconducting film that is epitaxial on the underlying substrate,
formed as a meanderline element and responsive to wavelengths in
the range 1 .mu.m to 1000 .mu.m, and most desirably in the infrared
region of the spectrum.
The assembly will generally include a substrate that is at least
coextensive with the bolometer array, in which case the
interference layer may be disposed outwardly adjacent either the
substrate or the bolometer array. Although a submicron air gap may
be present, the assembly will preferably be devoid of spacing
between the irradiation face and the interference layer when those
components are adjacently disposed; a buffer film will usually be
interposed between the array and the substrate, and a passivation
layer may be provided on the face of the array that is opposite to
the substrate.
Other objects of the invention are attained by the provision of a
spectrometer comprising, in combination: a superconductor detector
assembly, as described herein; means for maintaining the assembly
at cryogenic temperatures in a range for varying the conductance of
the bolometers; means, operatively connected to the array, for
generating electrical currents indicative of the conductance of the
bolometers after passage therethrough; and electronic data
processing means for transforming the currents generated so as to
produce signals representative of the energy of radiation caused to
impinge upon the irradiation face, discriminated as a function of
wavelength. Preferred embodiments of the spectrometer will further
include means for causing radiation to impinge upon the irradiation
face of the bolometer array, as well as a radiation source for
generating spectral radiation within the range of intended
operation. The data processing means will most desirably function
to apply matrix-inversion transform algorithms (e.g., Fourier and
bilinear) to the generated electrical currents, for producing the
representative signals.
Additional objects are attained by the provision of a color-imaging
apparatus in which is included a substrate having an irradiation
surface, on which is arranged a multiplicity of the detector
assemblies described. The detector assemblies all include the same
combination of detectors having different response characteristics,
and they are arranged with the bolometers exposed for irradiation
on the substrate surface; typically, each detector assembly will
consist of three different detectors. Additionally included in the
apparatus may be means for causing radiation to impinge upon the
irradiation surface, means operatively connected to the bolometers
for generating electrical currents, and display means operatively
connected for receiving such currents from the means for generating
and the bolometers, and for displaying the spatial distribution of
different wavelength components of the impinging radiation.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a diagrammatic perspective view of a rectilinear detector
assembly embodying the present invention, suitable for use in
transform spectroscopy;
FIG. 2 is a fragmentary, diagrammatic elevational view of the
assembly of FIG. 1;
FIG. 3 is a fragmentary, diagrammatic elevational view showing an
alternative arrangement of the components of the assembly of the
preceding Figures;
FIG. 4 is a view similar to FIGS. 2 and 3, illustrating a further
embodiment of the detector assembly in which no separate substrate
component is employed;
FIG. 5 is a plan view of a bolometer array and associated contact
pads, suitable for use in fabricating the detectors employed in the
assemblies of the invention;
FIG. 6 is a diagrammatic representation of a spectrometer embodying
the present invention; and
FIG. 7 is a diagrammatic perspective view of a panel for
three-color imaging apparatus embodying the invention.
DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS
Turning initially to FIGS. 1 and 2 of the drawings, the detector
assembly illustrated consists of a substrate 10 (e.g., a silicon
wafer), a buffer film 12 (e.g., of yttrium-stabilized zirconia)
deposited thereupon, a bolometer array made of a high-temperature
superconducting film (e.g., YBCO), generally designated by the
numeral 14, and, as a graded interference filter, an interference
layer, generally designated by the numeral 16, superposed upon the
bolometer array. Each of the steps 16a, 16b, 16c and 16d of the
layer 16 overlies and registers with the operative area an
associated bolometer 14a, 14b, 14c and 14d of the array 14, thereby
rendering the bolometers effective to detect different, narrow
interference bands of radiation; the bolometer 14e remains
responsive to a broad range of wavelengths, as being unattenuated
by filtration, and functions as a reference detector.
The detector assembly of FIG. 3 is fabricated from the same
components (omitting however the bolometer 14e), arranged for
backside illumination. Thus, rather than being disposed between the
substrate and the filter, the bolometer array 14' is positioned on
the surface of the substrate 10 (with an interposed buffer layer
12) opposite to that on which the interference layer 16 is
disposed. In the assembly of FIG. 4, the layer 16' serves both as
the substrate for the array 14' and also as the interference
filter.
FIG. 5 shows a series-connected "quad" bolometer array pattern,
fabricated (as by a microlithographic technique) from a single film
of material and carried upon a substrate. Each of the bolometers
14a through 14d consists of a meanderline, to which is connected
suitable electrical contact pads 18.
The spectrometer apparatus of FIG. 6 utilizes a superconductor
detector assembly, generally designated by the numeral 20,
comprised of the components 10, 12, 14 and 16 (not shown), formed
and arranged as hereinabove described with reference to the
preceding Figures. The assembly 20 is supported upon a refrigerated
cryostage mounting block 22, surrounded by cryostat walls 30; an
electrical heater 24 is embedded in the block 22, the power to
which is regulated by the temperature controller (TC) 26 in
response to the cryostage temperature, as measured by the
thermometer 28. The detector assembly 20 is positioned for
illumination by radiation reflected from a focusing mirror 34
through the window 32. A power supply 33 is connected to the
bolometers of the assembly 20. Current passing through the
bolometers from the power supply 33, as affected by their
conductance in response to transmitted radiant energy, generates
electrical signals at the contact pads 18. The signals are in turn
processed by application of transform algorithms in the computer
(PC) 36, passing thereto through a multiplexer (MUX) 40, a
preamplifier (PA) 42, and an analog-to-digital converter (ADC) 44,
all in a conventional manner.
A panel suitable for use in three-color imaging apparatus is
depicted in FIG. 7, and consists of a substrate 50 of semiconductor
material, upon which is deposited a buffer film 52. Numerous
identical detector assemblies are formed upon what is to be the
irradiation surface of the panel, each assembly being composed of
the same triangular array of three detectors 54a, 54b and 54c.
Although not specifically illustrated, it will be appreciated that
a superposed graded interference filter renders each detector of
the assembly responsive to a selected radiation "color" band that
is different from the bands to which the other two detectors
respond; multilayer coatings may be employed in certain instances
to further define the sensitivity of the detectors. A power supply
56 and a video display terminal 58 are operatively connected to the
panel, with the terminal serving of course to display, as a
function of wavelength, the spatial distribution of the components
of the impinging radiation.
Although certain embodiments of the instant detector assembly may
utilize bolometers of a non-superconducting nature, those
fabricated from high-temperature superconducting components, and
particularly from films epitaxially deposited upon the substrate,
are most preferred. In accordance herewith, a film will generally
be deemed to exhibit high-temperature superconducting properties if
it demonstrates a maximum zero-resistance state up to 80K, or
higher. Not only can such detectors afford an extremely broad band
of radiation response, but they are in addition capable of
production as monolithic arrays (i.e., etched into a single film)
by use of known micro-fabrication techniques, making an extensive
detector array possible and integrating effectively with existing
silicon wafer and other microelectronic and thin-film technologies.
These factors in turn make feasible the provision of an on-chip
spectrometer and other microelectronic optical devices, using the
detector assemblies described, with the self-evident benefits that
are attendant thereto.
The superconducting film employed will preferably be of a compound
having the general formula RBa.sub.2 (Cu,M).sub.3
O.sub.(7-.delta.), in which R designates at least one of the rare
earth elements: yttrium, lanthanum, neodymium, samarium, europium,
gadolinium, dysprosium, lutetium, and holmium, and in which M is
either null or designates at least one of the transition elements:
silver, gold, nickel, aluminum, zinc, cobalt, iron, palladium and
platinum. It will be appreciated that the foregoing general formula
implies non-exact stoichiometry, and that most commonly the
superconductor film will be of a yttrium-barium-copper-oxygen
(YBCO) compound.
As will be appreciated by those skilled in the art, a primary
advantage in the use of high temperature superconducting bolometer
devices resides in the exceptional temperature sensitivity that is
afforded when the material is on the edge of its transition into
the superconducting state. Under those conditions the heat
equivalent value of even low-intensity irradiance will raise the
temperature of the superconducting film sufficiently to cause a
measurable change in its resistance, and hence to enable the
generation of an electrical signal that is indicative of the energy
passing to the bolometer. More particularly, these detectors
utilize a photothermal process to cause electrical responses to the
small temperature increases effected by the irradiance. By
maintaining the film temperature near that for the middle of the
resistive transition to the superconducting state, and by use of a
suitable film pattern, a large resistance change will accompany
small irradiances, typically a few .mu.V to a few mV response per
.mu.W of irradiance; thus, spectral sensitivity is very high.
Pulsed laser deposition, or laser ablation, is advantageously used
for synthesizing high-quality thin films of high-temperature
superconductor ceramic oxides. The use of laser ablation to
synthesize films of YBCO on silicon wafer substrates, for example,
is found however to require a metal oxide buffer film, which will
preferably be of a compound selected from the group consisting of
zirconia, yttria, yttria-stabilized zirconia, calcia,
calcia-stabilized zirconia, magnesia, ceria, magnesia-stabilized
zirconia, LaAlO.sub.3, BaTiO.sub.3, SrTiO.sub.3, and solid
solutions of the latter two compounds. The buffer film of metal
oxide should be deposited substantially epitaxially on the
substrate surface, and (as noted above) the ceramic-oxide
superconductor film should be deposited substantially epitaxially
on the buffer film.
The substrate will usually be made of a monocrystalline
semiconductor material, most desirably a silicon wafer or membrane.
It may however be of any suitable alternative material, such as for
example GaAs, SrTiO.sub.3, MgO and yttria-stabilized zirconia. It
will be appreciated that the metal oxide buffer film, interposed
between the superconductor film layer and the substrate, serves to
prevent such chemical reaction therebetween as would tend to
destroy the superconductivity of the superconductor film, or to at
least significantly depress its superconducting transition
temperature. In any event, it is important that any buffer layer
employed serve that function while still allowing the growth of a
highly oriented superconducting film.
Although constituting no part of the instant invention, techniques
are known by which a buffer film and a superconductor film can be
deposited substantially epitaxially upon a semiconductor. In
accordance therewith, the substrate is cleaned, passivated, and
sequentially coated to produce the buffer and superconductor films;
cleaning of the substrate surface may be effected by use of a
spin-etch technique, and film deposition may be carried out by
pulsed laser ablation. A protective layer or cap may also be
provided upon the upper surface of the superconductor film, to
stabilize it and prevent chemical degradation; cap layers may have
the same composition as the buffer films.
Central to the invention is of course the antireflection coating or
interference layer that is superposed upon the array of bolometers,
which provides an interference filter of graded thickness; the
layer may be bonded to the face of the array, or it may simply be
disposed in close proximity to it. Most dielectric materials can be
employed as the interference layer, provided of course that the
material has a finite region of light transmission; standard tables
of materials' transmission regions can therefore be used to assist
in the selection. It is noted however that silicon exhibits nearly
ideal IR-transmission characteristics at 77K, and hence may be
employed to provide a very useful interference filter in the
mid-infrared to far-infrared range. Moreover, the fact that silicon
functions in such a highly effective manner, in combination with
the superconducting films described, makes feasible the detector
assembly shown in FIG. 4. But as a second example, if the spectral
range of interest were from the visible to below 5 .mu.m, ZrO.sub.2
could be used as the interference layer.
Physically, it is important that the bolometer and associated
filter element be of the same spatial extent; in the case of the
stepped layer illustrated, therefore, the areas of the plateaus
should match the effective areas of the associated bolometers, and
should lie in close registration therewith. As will be appreciated,
the optical length through the filter is a function of both the
thickness of the layer and also the index of refraction of the
material used. Therefore the profile of the interference layer
and/or its properties can be varied to achieve the desired result;
e.g., to pass a narrow band of radiation, in the case of a thermal-
or color-imaging device, or to lead to the most useful transforms
for purposes of spectrometry. A careful choice of the grading
scheme can produce strong fringe contrast across the entire
spectral region of interest, and can result in each element of the
detector assembly having a spectral response that is partially or
largely orthogonal to that of the other elements. It is in fact the
extent of orthogonality in the transform that makes it advantageous
in spectroscopy, since that renders the decoding algorithm simple,
reducing the interference from cross terms.
Using a graded interference filter of the character described,
periodic or pseudoperiodic intensity envelopes are generated over
the array of detectors for each wavelength of interest, causing
each of the detectors to register a spectral irradiance
periodically modulated by passage through constructive and
destructive optical interference conditions. The periodic nature of
light encoding simplifies decoding, and involves the multiple
advantage of measuring all wavelengths simultaneously. In addition,
a large throughput of radiation to the detector is achieved, which
enhances both the optical efficiency and also the signal-to-noise
ratio for any given spectral acquisition.
It goes without saying that the level of resolution of a certain
wavelength spectrum will vary in direct relationship to the number
of detectors present in the assembly. Typically, an array of 1000
or more detectors will be employed, arranged as rectilinear,
triangular, or rectangular arrays, or in any other suitable
configuration. The associated mechanical, optical, electronic,
circuitry, and data-processing components and software of any
apparatus utilizing the detector assembly of the invention will of
course be specifically adapted to an intended purpose, and the
design, construction, implementation, and arrangement thereof will
be evident to those skilled in the art. Nevertheless, it might be
pointed out specifically that, in a spectrometer system, electronic
circuitry will be provided to scan the detector array into a memory
unit, where a computational transform would be applied to
reconstruct the spectrum. Although applications involving the
infrared region of the spectrum have been stressed herein, and will
in many instances represent the best mode for carrying out the
present invention, it will be appreciated that the underlying
concepts will often be equally as applicable to other spectral
regions.
Thus, it can be seen that the present invention provides a novel
detector assembly that is capable of discriminating, as a function
of wavelength, spectral radiation impinging thereupon, and that is
suitable for use in apparatus for transform spectroscopy,
color-imaging, and the like. The detectors are wavelength
programmable to afford great flexibility of application, and the
assembly and apparatus of the invention may be very small and
highly compact, durable, incomplex, and relatively inexpensive to
construct, while affording outstanding levels of sensitivity and
speed of response.
* * * * *