Abstract:
Incident infrared radiation of a particular polarity is sensed by a set of Niobium Trisulfide (NbS 3 ) crystal fibers which are fixed in parallel upon a substrate. In order to detect unpolarized or variously polarized infrared radiation, plural substrates, each having associated therewith its own such set of parallel fibers, can be coplanarly arrayed whereby different angles are described by different sets of parallel fibers; for instance, 0-degree, 45-degree, 90-degree and 135-degree angles can each be described by one or more sets of parallel fibers within a given array. The crystalline fibrous Niobium Trisulfide material is not a semiconductor material but rather is a “charge density wave” material having special attributes. The invention thus offers more economical operability at much higher temperatures when compared with conventional infrared-photosensitive materials, and is especially suitable for detecting midwavelength infrared radiation.

Description:
STATEMENT OF GOVERNMENT INTEREST 
     The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor. 
     BACKGROUND OF THE INVENTION 
     The present invention relates to methods, apparatuses and compositions pertaining to infrared radiation detection, more particularly to the photon detection of infrared radiation such as associated with thermal emissions. 
     The electromagnetic spectrum has conventionally been divided into approximate regions according to wavelength. The visible region, approximately in the range between 400 nm and 700 nm, corresponds to electromagnetic radiation to which the human eye is sensitive (visible light). The regions of successively shorter wavelengths than the visible region are ultraviolet, x-rays and gamma rays. The regions of successively longer wavelengths than the visible region are the near infrared, infrared and radio waves. 
     The near infrared region (NJR) approximately encompasses the 700 nm to 1 μm range. The infrared region approximately encompasses the 1 μm to 100 μm range. The infrared region is approximately subdivided into: short wave infrared (SWIR), having wavelengths approximately between 1 μm and 3 μm; midwave infrared (MWIR), having wavelengths approximately between 3 μm and 5 μm; and, long wave infrared (LWIR), having wavelengths longer than about 8 μm and up to about 100 μm. The region between MWIR and LWIR is conventionally disregarded due to strong atmospheric absorption. Radio waves have wavelengths longer than about 100 μm. 
     An electromagnetic radiation detector (also referred to as a photodetector, or an electromagnetic radiation sensor, or an electro-optic detector or sensor) is a device which absorbs electromagnetic radiation and gives rise to an electrical output signal that, generally speaking, is proportional to the irradiance (the intensity of the incident electromagnetic radiation). Depending on the type of detector, the output signal will be either a voltage or a current. In comparison with thermal detectors, photon detectors are characterized by a higher speed of response. Current semiconductor photon detectors having long wavelength limits in the ultraviolet, visible or near infrared (up to 2-3 μm) operate uncooled at room temperature (300 degrees kelvin, or 300 K). At longer, midwavelength infrared (MWIR) limits (up to 4-5 μm), cooling to dry ice temperature (195 K) is required. For detectors operating in the long wavelength infrared (LWIR) 8-12 μm range, cooling to liquid nitrogen temperature (77 K) is essential. 
     Because all bodies at temperatures greater than absolute zero radiate in the infrared radiation region, infrared radiation detection has been of importance in military applications. By employing infrared radiation detection (e.g., via infrared “seekers”), warm targets can be detected in the dark by virtue of their own infrared radiation, thus obviating the need to illuminate such targets in order to render them visible. Warm bodies emit infrared radiation, and bodies which absorb infrared radiation are warmed. It is incorrect, however, to call infrared radiation “heat radiation,” because the radiation itself is not “heat.” 
     Higher operating temperature has been a goal of infrared detection development for the last few decades. Direct bandgap alloy semiconductor-materials such as HgCdTe replaced extrinsic germanium and silicon devices for LWIR applications because they could operate under ambient background flux conditions at 80 K. It has been thought that, theoretically at least, if 12 μm detectors could operate at 80 K, then 5 μm detector operation at 180 K should be possible. 
     At MWIR wavelengths, InSb has remained the infrared detector of choice for many applications. InSb has a spectral cutoff at 5.5 μm at 80 K, but its bandgap of 0.22 eV narrows as the temperature increases, extending its spectral response into the water vapor band between 5.5 and 7.5 μm, and also resulting in a very rapid increase in thermally generated noise. InSb detectors cannot operate effectively above about 145 K, and are seldom used above 100 K. Within the past decade HgCdTe and InAsSb photoconductive and photodiode technology has matured in the MWIR spectral band so that operation at 180 K, using thermoelectric coolers as well as mechanical coolers at 120 K, has been possible. The spectral response of thermoelectric cooled HgCdTe detector has a cutoff of 5 μm at 180 K. 
     State-of-the-art performance is often desired in the realm of infrared radiation detection; in general; in order to be optimal, infrared radiation detection requires use of very high quality material. InSb and HgCdTe are both very mature for use in the NWIR spectral region. InSb is an equally sensitive alternative to HgCdTe for MWIR applications. InSb is easier to produce at high quality than HgCdTe, and has found a niche in the marketplace as a cost-effective alternative for high-sensitivity MWIR applications that require good, corrected uniformity. See, e.g., J. L. Miller,  Principles of Infrared Technology—A Practical Guide to the State - of - the - Art , Van Nostrand Reinhold, John Wiley &amp; Sons, Inc., New York, 1994, incorporated herein by reference; see, especially, pages 370-431. 
     The availability of photovoltaic HgCdTe and InSb infrared image detectors continues to expand rapidly as the technology has matured and entered a transition to production for both commercial and military applications. Detector costs for staring array formats, however, continue to limit the market demand. Although a seeker containing these arrays represents a small percentage of the weight of a missile system, it represents a large percentage of the cost—up to 50% or more; see, e.g., aforementioned book by J. L. Miller entitled  Principles of Infrared Technology—A Practical Guide to the State - of - the - Art . Although a missile seeker could, therefore, conceivably be produced for only tens of thousands of dollars, in reality missile seeker development is still expensive and can run from tens to hundreds of millions of dollars. 
     SUMMARY OF THE INVENTION 
     In view of the foregoing, it is an object of the present invention to provide method and apparatus for effectuating midwavelength infrared radiation photon detection. 
     It is another object of the present invention to provide a high caliber composition for optimally effectuating midwavelength infrared (MWIR) radiation photon detection. 
     It is a further object of this invention to provide apparatus, including such high caliber composition, for optimally effectuating midwavelength infrared radiation photon detection. 
     It is another object of this invention to effectuate midwavelength infrared radiation detection at relatively high temperatures (e.g., room temperature), so that such detection does not require cooling or only requires relatively moderate cooling. 
     A further object of this invention is to effectuate midwavelength infrared radiation photon detection of both polarized and unpolarized radiation. 
     Another object of this invention is to effectuate midwavelength infrared radiation photon detection efficiently and economically. 
     According to many embodiments of the present invention, these objects are achieved by providing fibers of Niobium Trisulfide (NbS 3 ) and an insulative substrate. The NbS 3  fibers form a single layer of approximately parallel sensing segments resting on an electrically insulating quartz (or other insulating material) substrate. According to some embodiments of this invention, an assembly includes NbS 3  fibers (along with their corresponding insulative substrates) which are arranged in four types of fiber orientations (viz., 0 degrees, 45 degrees, 90 degrees and 135 degrees) as part of an extended focal plane array; this inventive assembly permits the detection of polarized and unpolarized infrared light (radiation); that is, the array permits infrared detection of plural polarizations of infrared radiation. 
     The present invention provides an infrared electro-optic charge-density-wave conducting material, viz., Niobium Trisulfide (NbS 3 ), in crystalline fibrous form, for use in association with midwavelength infrared radiation photon detection. The present invention also provides a device for infrared radiation detection, the device comprising NbS 3  and a substrate. For use in association with photon detection of midwavelength infrared radiation, the inventive combination includes an approximately parallel, fibrous configuration of NbS 3  situated atop an insulative (nonconductive) substrate. According to typical such inventive embodiments, charge-density-wave fibers of NbS 3  are provided for an uncooled detector in the 3-5 μm infrared wavelength range. 
     This invention provides a midwavelength infrared radiation photon detector and a methodology for midwavelength infrared radiation photon detection. A typical infrared detector according to this invention comprises the combination of plural Niobium Trisulfide crystalline fibers and an insulative substrate. The insulative substrate has an approximately flat substrative surface. The Niobium Trisulfide fibers are adjoinedly disposed in approximately parallel fashion on the substrative surface. The detector is positionable relative to incident infrared radiation so that the substrative surface is approximately orthogonally facing the incident infrared radiation. A typical infrared detection method according to this invention comprises positioning such an inventive device relative to incident infrared radiation so that the substrative surface is approximately orthogonally facing the incident infrared radiation. 
     According to many inventive embodiments, an uncooled polarized radiation photon detector is intended for utilization in focal plane arrays for the purpose of sensing polarized thermal emissions. Frequently according to such embodiments, this invention provides a detector with thin fibers of NbS 3  lying in parallel on a rectangular noninsulative (e.g., quartz) substrate, and with thin strips of electrically conductive metallic (e.g. tin) films coupling the fibers to leads for connection to external circuitry. 
     According to many embodiments of the present invention, the inventive midwavelength infrared detector includes pre-grown parallel thin, flat, narrow crystalline fibers of NbS 3  charge-density-wave conductors resting flatwise on a rectangular quartz substrate on which thin strips of evaporated tin films electrically couple the ends of the fibers to leads for connection to external circuitry. The inventive NbS 3  electrical conductors have an energy gap of about 0.3 eV for temperatures below 355 K, enabling sensing in the 3-5 μm wavelength range. The flat fibers sense the radiation of an emitting object through the excitation of unpaired charge carriers by means of infrared photons breaking up paired charges. The inventors have made a prototypical embodiment of the present invention&#39;s infrared detector which demonstrates the efficacy thereof. 
     The present invention can be used individually to detect the presence of infrared radiation, or can be used in arrays to provide additional information such as spatial resolution (e.g., for an imager or spectrometer). The inventive arrays can include like or unlike inventive detectors. A particularly noteworthy latter kind of inventive array comprises plural detectors characterized by varying NbS 3  fiber orientations. In this regard, a preferred embodiment of the present invention provides a combination of plural midwavelength infrared detectors, such combination including at least one set of four detectors, wherein the detectors of a given set have parallel fibers oriented at 0°, 45°, 90° and 135° for use in a focal plane array. In other words, the combination of plural detectors includes: at least one square region having fibers oriented at 0°; at least one square region having fibers oriented at 45°; at least one square region having fibers oriented at 90°; and, at least one square region having fibers oriented at 135°. According to many such inventive embodiments, a plurality of the inventive uncooled detectors, including at least one set of four of the inventive uncooled detectors wherein the parallel fibers are oriented at the four different orientations (0 degrees, 45 degrees, 90 degrees and 135 degrees), enables the development of a focal plane array for detection not only of polarized infrared radiation, but also of unpolarized infrared radiation. Such arrays may be used in lightweight weapon seekers which are suitable for advanced target recognition, decoy discrimination and clutter rejection. 
     By way of explanation, normally the waves of a beam (ray) of radiation (light) are disorderly; that is, although each wave vibrates in a direction perpendicular to its path, there is no favored orientation or direction of such vibrations. Such light beams are referred to as “unpolarized.” However, when all of the waves in a light beam vibrate in parallel planes and in the same perpendicular direction, such light beams are referred to as “polarized” (e.g., “linearly polarized,” as distinguished from “circularly polarized” or “elliptically polarized”). These well-known scientific principles concerning polarized and unpolarized electromagnetic radiation are applicable to the present invention. A single inventive infrared detector will normally be photosensitive only to those components of infrared radiation beams which are polarized in comportment with the particular configuration of its parallel Niobium Trisulfide fibers; in other words, that detector will sense only the portions of the infrared radiation which are polarized insofar as being characterized by waves which vibrate in planes which are parallel to each other and in identical perpendicular directions which are parallel to the parallelly arranged Niobium Trisulfide fibers. On the other hand, an array of infrared detectors according to this invention will include at least four detectors corresponding to at least four orientations of the parallelly distributed Niobium Trisulfide fibers. Each detector of the array will be photosensitive to infrared radiation which is polarized in agreement with the Niobium Trisulfide fiber parallelness specific thereto. However, with the assistance of apparatus such as including a processor, information can be obtained according to this invention as to other, “in-between” directions of infrared waves, based on infrared wave data pertaining to the actual fibrous orientations. In fact, a complete or nearly complete representation of the “unpolarized” infrared light beam can be achieved in accordance with inventive practice of detector arrays. 
     Advantageously, the present invention can afford moderately cooled or uncooled infrared detection. The present invention succeeds in reducing or eliminating the requirement of cooling. Hence, infrared seeker packaging will be more lightweight and compact with lower power consumption. Furthermore, seeker packaging according to this invention will be much less costly, because NbS 3 —a detector material other than a semiconductor material—is implemented. Moreover, system reliability will be improved. 
     The present invention features, inter alia, the nonsemiconducting charge-density-wave crystalline fibrous material NbS 3 , which possesses an energy gap of about 0.3 eV for temperatures below 355 K. Although the crystalline fibrous material NbS 3  is known generally, it has never been used or known to be useful in any infrared detection applications. In the context of any manner of infrared radiation detection (including but not limited to midwavelength infrared radiation detection), the present invention&#39;s mere use of NbS 3  in any photosensitive capacity (e.g., as a photoconductive material), in and of itself, represents a significant, unique and previously unknown improvement in the art. The energy gap in InSb is smaller at 0.18 eV at 300 K, whereas the gap can be tailored in the ternary alloys HgCdTe and InAsSb for use at longer wavelengths. The much more robust energy gap in NbS 3  greatly reduces the dark current noise, which rapidly increases above 80 K in the semiconductors, making the semiconductor materials practically useless for IR detection much above 80 K. 
     HgCdTe, InAsSb and InSb can detect through either of two processes, viz., the photoconductive semiconductor mode of varying conduction with illumination intensity, or the photovoltaic (photodiode) mode wherein the voltage across the detector is generated from the incident radiation. In the photoconductive mode, these detectors are characterized by moderate to high detectivity and relatively low frequency response. On the other hand, similar photoexcitation properties, but faster response times are observed in thin-film high temperature superconductors; see R. Sobolewski, “Ultrafast Dynamics of Nonequilibrium Quasiparticles in High Temperature Superconductors,” in  Proceedings of SPIE , Vol. 3481, Jul. 20-24, 1998, pp 480-491, incorporated herein by reference. These superconducting materials are being considered for detection, since their critical temperatures T C &gt;90 K exceed the best temperatures for cooling of InSb and HgCdTe. 
     Other studies of these superconducting materials have indicated, however, that the photoeffect must occur at lower temperatures in the 10 K-30 K range; see M. G. Forrester and J. Talvacchio, “Photon Detection by High Temperature Superconducting Films: Fundamental Limits,”  Physica C , Vol. 162-164, pp 391-392 (1989), incorporated herein by reference. At higher temperatures, the generation-recombination (g-r) noise would limit the detectors. That is, in the absence of incident radiation, there would be an equilibrium density of quasiparticles due to thermal excitation. Fluctuations in their generation rate from breakup of Cooper pairs, and their recombination into Cooper pairs, would constitute noise in the readout. 
     Generally speaking, charge density wave (CDW) materials are analogous to superconductive materials, particularly insofar as being characterized by a kind of “condensation” effect wherein under certain circumstances electrons tend to behave collectively (but do not behave so in the presence of a magnetic field). In this regard, the charge density wave material NbS 3  has certain properties similar to those of superconductors. In the CDW material NbS 3 , the much larger energy gap of 0.3 eV leads to a much smaller thermal generation rate and a lower g-r noise level. In fact, the g-r noise for NbS 3  is smaller than the level in any of the semiconductors with smaller energy gaps of &lt;0.22 eV. Thus, since the spectral detectivity or specific sensitivity is inversely proportional to the square root of the g-r noise, NbS 3  is the superior material of choice, even at temperatures colder than 300 K. 
     NbS 3  is only one member of a series of CDW materials. See the following references, each of which is incorporated herein by reference: P. J. Sarman, R. D. Bardo and R. Chen, “Charge Density Wave Materials,” in  FY 98  NSWC Carderock Division Research Digest , Naval Surface Warfare Center, Carderock Division, CARDEROCKDIV-99/CT01, Mar. 1999, pp 73-75; P. J. Sarman, R. D. Bardo and R. Chen, “Charge Density Wave Materials,” in  FY 99  NSWC Carderock Division Research Digest , Naval Sea Systems Command, Naval Surface Warfare Center, Carderock Division, CARDEROCKDIV-00/CT01, March 2000, pp 48-50. Also notable is R. D. Bardo, P. Sarman and R. E. Thorne, “Infrared (2.5 μm to 13.5 μm) Reflectance Measurements and Calculations of the Peierls Gap Energy in NbSe 3 ,” accepted for publication in  Phys. Rev. B . Nevertheless, NbS 3  has, by far, the highest critical temperature of 355 K. 
     Moreover, single, high-quality fibrous NbS 3  crystals are easily and inexpensively grown in a three-zone infrared furnace at temperatures of 650° C. NbS 3  crystals of any length up to 1 cm may be routinely grown, enabling the design of detectors up to 1 cm 2 . As illustrated in FIG. 1 herein, the reflectance measurements performed by the present inventors (also the authors of the aforementioned articles by Sarman and Bardo, each article entitled “Charge Density Wave Martials”) on these NbS 3  crystals confirm their high quality and the existence of the energy gap in the 3-5 μm wavelength range. 
    
    
     Other objects, advantages and features of this invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In order that the present invention may be clearly understood, it will now be described, by way of example, with reference to the accompanying drawings, wherein like numbers indicate the same or similar components, and wherein: 
     FIG. 1 is a graphical representation, in terms of percentage reflectance versus wavelength (μm), of a reflectance comparison between Niobium Trisulfide (NbS 3 ) and Niobium Triselenide (NbSe 3 ). 
     FIG. 2 is a schematic diagram of an embodiment of an infrared detection system in accordance with the present invention. Especially shown is a diagrammatic perspective view of the transverse geometry of an embodiment of an uncooled NbS 3  CDW fiber detector in accordance with the present invention. Also illustrated, inter alia, are an external circuit and leads, wherein the leads connect the inventive detector to the external circuit. 
     FIG. 3, FIG.  4  and FIG. 5 are each a diagrammatic top plan view of an embodiment of a focal plane array in accordance with the present invention, each rectangle of the focal plane representing an inventive detector such as shown in FIG.  2 . The focal plane array of rectangular detectors includes four orientational kinds of detectors having fibers oriented at 0°, 45°, 90° and 135°, respectively. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to FIG. 1, the reflectance spectra of two charge density wave (CDW) conductors, viz., NbS 3  (T C =355 K) and NbSe 3  (T C =145 K), were compared by the joint inventors; see aforementioned articles by Sarman et al. each entitled “Charge Density Wave Materials.” The NbS 3  crystals were newly grown by the joint inventors in an infrared furnace; the NbSe 3  crystals were previously grown. The joint inventors performed infrared reflectance measurements on the NbS 3  crystals and the NbSe 3  crystals. 
     As distinguished from NbSe 3 , the Peierls energy gap (2Δ) for NbS 3  exists at 300 K, resulting in the much higher room temperature reflectance of about 70 percent near wavelength λ=4.1 μm. Unfortunately, the presence of a strong absorption for CO 2  at 4.3 μm prevents a precise determination of 2Δ, although at 4.1 μm, 2Δ=0.3 eV. This value and the calculated value of 2Δ/k B T C =10 gives critical temperature T C =348 K, which is close to the accepted value of 355 K obtained by other researchers. To the present inventors, these results suggested the possible usefulness of good crystals of NbS 3  which can be readily grown and produced in quantity. 
     Reference is now made to FIG. 2, which shows the overall arrangement of the inventive charge density wave (CDW) infrared detector  10  and the required external circuit  12 . Inventive infrared detector  10  includes insulative substrate  14  and NbS 3  crystal fibers  16 . The insulative substrate  14  is made of an electrically nonconductive (insulative) material such as quartz, corundum, germanium, glass, plastic, ceramic (e.g., porcelain) or composite. Because of its usually robust quality, a material such as quartz may be a preferred composition for substrate  14 , which can be opaque, translucent or transparent. Substrate  14 , at least substantially flat or planar and of arbitrary thickness, supports the discretely and approximately coplanarly arranged CDW fibers  16 . 
     In terms of functionality, it is critical to this invention that the fibers  16  be arranged discretely and approximately parallelly with respect to each other. In order to sustain fibers  16  in this manner, a substrate  14  (upon which the fibers  16  are laid) is a preferred component of the housing means for holding fibers  16  in place. Fibers  16  will typically be rather frangible; because of their fragility, use of a substrate  16  will generally represent the most practical inventive technique for holding or helping to hold fibers  16  in position. The protectiveness of the housing may be especially important if, in application, inventive device  10  is expected to be subjected to strong external forces such as the “g”-forces associated with rocketry. 
     According to typical inventive practice, each of the fibers  16  is up to 1 cm in length, 50-100 μm (microns) in width, and 5-10 μm in thickness; nevertheless, smaller or larger dimensions of fibers  16  are possible in accordance with inventive principles. In view of the wavelengths characterizing MWIR radiation, fiber  16  lengths of 1 cm or less will normally suffice for inventive practice. Generally, the width of a fiber  16  will be roughly ten times its thickness. CDW fibers  16  are flat, or tape-like, or at least substantially so. Each NbS 3  crystal fiber  16  essentially represents a single or integral strand of crystalline NbS 3 . A cross-sectional view of a representative NbS 3  fiber  16  would reveal a basically rectangular peripheral shape, with surface irregularities perhaps on the order of one micron (1 μm) or less in height. 
     As pertains to a particular inventive detector  10 , neither spacing of the fibers  16 , nor exact parallel alignment of the fibers  16 , is critical to inventive practice. The fibers  16  can be spaced equidistantly (uniformly) or nonequidistantly (nonuniformly). The fibers  16  can be spaced relatively closely or relative distantly, or some combination thereof. Nor is it important whether the fibers  16  are of uniform thickness within a given detector  10 . However, regardless of the spacing therebetween in a given detector  10 , it is critical that the fibers  16  not touch each other. In particular, the fibers  16  must be distributed in a physically separated manner with respect to each other, in order that they be distributed in an electrically separated manner with respect to each other; that is, in an electrical sense, each fiber  16  must be insulated or isolated from every other fiber  16 . Furthermore, it is critical that each NbS 3  fiber  16 , at both ends thereof, touch the highly conductive contacts  18 . 
     Moreover, the number of fibers  16  in a particular infrared detector  10  may be an important consideration in practicing this invention. A good inventive “rule of thumb” is that there should be at least ten fibers per cm 2  of substrate  14  area, such as described by a 1 cm by 1 cm substrate  14 . Since the NbS 3  crystal fibers  16  will generally be characterized by surface defects (irregularities, peaks and valleys, or a “hilly terrain”), a greater number of fibers  16  will better serve to average out such anomalies associated with the shapes of fibers  16 . Such anomalies in the fiber  16  shape may have decreasing significance with increasing infrared wavelength. In the light of this disclosure, it will be apparent to the ordinarily skilled artisan that detector  10  can be inventively practiced using any of diverse configurations, in terms of dimensions and distances, of the fibers  16  encompassed by a detector  10 . 
     The pre-grown NbS 3  crystal fibers  16  can be placed upon (e.g., singly laid down on top of) the substrate  14  with their flat surfaces parallel to the planar top (upper) surface  15  of substrate  14 . Fibers  16  are contiguous with (e.g., resting upon) top surface  15  of substrate  14 , fibers  16  thereby describing an imaginary plane which is closely parallel to top surface  15 . Evaporation of tin (or perhaps preferably another, even more highly electrically conductive metal material such as copper, aluminum, gold, silver or chromium) onto the ends or extremities of the fibers  16  can form the metallic contacts  18 , which bondingly secure the fibers  16  and lead wires  20  to the substrate  14 . A flat transparent sapphire window  21  can be sandwiched onto the NbS 3  crystal fibers  16  and high conductivity contacts  18  for protection. Window  21  is next to or adjacent to substrative surface  15  so as to contact or be proximate fibers  16 , fibers  16  thereby being situated between substrative surface  15  and window  21 . Window  21  is made of a material which is both electrically nonconductive and transparent to infrared radiation, such as quartz, diamond (film), germanium, glass, plastic (e.g., polyethylene), ceramic or composite; material such as germanium or polyethylene may be preferable as having superior transparency characteristics as pertains to infrared radiation. Metallic contacts  18  can also be used for their adhering effect to secure window  21  to substrate  14 . There are various ways of coupling the fibers  16 , lead wires  20  and window  21  with the substrate  14 . 
     For instance, an adhesive (e.g., glue) can be used for adhering fibers  16 , lead wires  20  and/or window  21  to the substrate  14 . As another example, solid metallic contacts  18  can be attached to substrate  14  so as to be situated over the ends or extremities of fibers  16 , thereby holding fibers  16  in position. As a further alternative, metallic contacts  18  can be provided in to the form of indium film which is disposed upon substrate  14  and over the ends or extremities of fibers  16 . The perimeter of substrate  14  can be provided with slots for engagement with the ends or extremities of fibers  16 . Window  21  can be congruent or coextensive with substrate  14 , or can be slightly shorter than substrate  14  so as to be compatibly situated between metallic contacts  18 ; window  21  can serve merely as a transparent protective covering, or can serve the additional purpose or purposes of holding down fibers  16  and/or securing fibers  16  with respect to substrate  14 . In the light of this disclosure, various other approaches to coupling fibers  16 , lead wires  20  and window  21  with substrate  14  will be apparent to the ordinarily skilled artisan. For instance, for such purposes, fastening means such as that which includes clamps, clasps, screws, bolts, etc. can be implemented according to this invention, but preferably in such a way as to minimize weight. 
     Lead wires  20  connect inventive detector  10  to the external electronic circuitry  12 . According to typical inventive embodiments, circuitry  12  will be situated behind substrate  14  (i.e., below the imaginary plane defined by substrate  14 ). Since the inventive CDW detector  10  photo-response is similar to that relating to photoconductor detection, the associated circuitry  12  is also similar. The incident radiation  22  may be perpendicular to the direction in which the current is measured. 
     The present invention can operate in photoconductive mode (such as described herein with reference to FIG. 2) or photovoltaic (photodiode) mode. That is, detection of the photosignal  28  (the increase in current when detector  10  is exposed to infrared radiation) will be made by observation of a change in either current, or voltage, developed across the load resistor  24  in series with the inventive infrared detector  10 . In accordance with most embodiments of the present invention, practice in photoconductive mode (such as described herein with reference to FIG. 2) will be preferred instead of practice in photovoltaic mode; this is so not only because the state of the art in general seems to be such that photoconductive detectors are favored over photovoltaic detectors, but also because, specifically as regards the present invention, the Niobium Trisulfide fibrous crystals seem to be more conducive to, or lend themselves more effectively to, practice in photoconductive mode. Nevertheless, in the light of this disclosure, the ordinarily skilled artisan will be capable of practicing the present invention in either photoconductive mode or photovoltaic mode. For instance, effectuation of photovoltaic mode would be illustrated similarly as illustrated in FIG. 2 (which pertains to photoconductive mode), with at least one notable difference involving utilization of a kind of voltmeter means or photodiode means (instead of a voltage biasing means  20 ) which is connected to power supply  42 . 
     When the load resistance greatly exceeds the detector resistance R d , the observed photovoltage change ΔV L  across the load is essentially the open circuit value, ΔV L =I R d , where I is the increase in current above the “dark current” caused by the ever-present thermal excitation of quasiparticle charges. Generation of current I, which is proportional to the photo-excited charges, involves the application of a bias voltage  26  (the source of which is power supply  42 ) across inventive detector  10 . This voltage must be on the order of 0.1 to 0.2 eV, which are less than the gap energy of 0.3 eV for NbS 3 . These values will convert the conductivity modulation to an electrical signal  28  voltage or current. 
     A typical infrared detection system  40  according to this invention includes infrared detector  10 , external circuitry  12  and other components. In inventive practice, a power supply  42  will usually be required to be in connection with circuitry  12 . Furthermore, according to conventional infrared detection practice, there are certain known apparatuses and techniques which are utilized for processing an electrical signal (or photosignal) which is produced or given forth by an infrared detector and its associated circuitry. Typical embodiments of the present invention will implement similar apparatuses and techniques. For example, still referring to FIG. 2, generally according to this invention, a preamplifier (also referred to as a preliminary amplifier)  44  will be used for extracting the useful signals  28  from detector  10  and its accompanying circuitry  12 . Basically, preamplifier  44  is an amplifier which serves to boost or synchronize the signal  28  output so that signal  28  can be further processed, and to do so without significant degradation of the signal-to-noise ratio of infrared detection system  40 . Preamplifier  44  receives a (typically low level) signal  28  and amplifies it so that it can become the input for additional amplifier circuitry such as depicted by amplifier  46 . At some point, a total output signal  28  received from amplifier circuitry (such as depicted in FIG. 2 by amplifier  46 ) is processed by computer processing means (such as depicted in FIG. 2 by computer  48 ). Then, the information from computer  48  is comprehensibly displayed visually on a monitor or other device, such as depicted in FIG. 2 by display  50 . 
     With reference to FIG.  3  through FIG. 5, the parallel fibers  16  of NbS 3  are oriented at a 0° angle, a 45° angle, a 90° angle and a 135° angle, relative to the substrate  14  parallel edges  18 , to form four basic orientational types of inventive detectors  10 , viz., detector  10   0 , detector  10   45 , detector  10   90  and detector  10   135 , respectively. In each detector  10 , the fibers  16  are non-touching (electrically separate) vis-a-vis&#39; each other. The fibers  16  for each of detectors  10   0  and  10   90  are about equal in length, while the fibers  16  for each of detectors  10   45  and  10   135  vary in length. Each detector  10  is rectangular in shape and is individually “wired,” having associated therewith its own external circuitry  12  (not shown in FIG.  3  through FIG. 5) such as shown in FIG.  2 . Also, each detector  10  in array  30  will typically have associated therewith its own preamplification means and amplification means such as preamplifier  44  and amplifier  46 , respectively, shown in FIG.  2 . However, it may be preferable that a single data acquisition and processing unit—such as including a single processing means (e.g., computer  48  shown in FIG. 2) and a single display means (e.g., display  50  shown in FIG.  2 )—be used in association with array  30 . 
     For each detector  10 , the corresponding circuitry  12  will normally be below plane (i.e., below the imaginary plane defined by the detector&#39;s substrate). These detectors  10   0 ,  10   45 ,  10   90  and  10   135 , respectively characterized by the four various (forty-five degree incremental) orientations of fibers  16 , are then assembled into the complete focal plane array  30  for polarized and unpolarized radiation detection and discrimination. In other words, a single detector  10  will be adapted or adaptable to sensing infrared radiation characterized by a single polarization; in contrast, an array  30  of detectors  10  will be adapted or adaptable to sensing infrared radiation characterized by plural polarizations. Such array  30  collections of the four orientational types of detector  10  elements will be inventively practicable, on an individual detector  10  basis, in accordance with the basic architecture and bias control such as illustrated in FIG.  2 . 
     In order to constitute a complete inventive array  30 , it is necessary to include at least one detector  10  of each fiber  16  orientational type in a given array  30 &#39;s multi-orientational scheme. For instance, an array  30  characterized by four different fiber  16  orientations, in forty-five degree increments, should have at least one zero-degree detector  10   0 , at least one forty-five degree detector  10   45 , at least one ninety-degree detector  10   90  and at least one one-hundred-thirty-five-degree detector  10   135 . FIG.  4  and FIG. 5 exemplify two possible inventive array  30  configurations having the minimum four detectors  10 . FIG. 3 exemplifies a possible inventive array  30  having more than four detectors  10  (To be exact, fifteen detectors  10  are shown in FIG.  3 ). Although the performance of array  30  would, in general, tend to improve with increasing numbers of detectors  10 , such benefit may be counterbalanced against the greater costs and complexities associated with greater numbers of detectors  10 . Diverse array  30  arrangements, in terms of rows and columns of detectors  10 , are possible in inventive practice—such as comparatively demonstrated by the two-by-two four-detector arrangement of FIG.  4  and the one-by-four four-detector arrangement of FIG.  5 . 
     As shown in FIG.  3  through FIG. 5, each detector  10  has an approximately rectangular shape. Whether used singly or in combination with other detectors  10  in an array  30 , diverse detector  10  shapes are possible consistent with inventive principles; nevertheless, from a practicality (e.g., economic) standpoint, in the vast majority of inventive applications it will be preferred that the detector or detectors  10  be rectangularly shaped. A square detector  10  shape is depicted in FIG.  3  and FIG. 4. A non-square rectangular detector  10  shape is depicted in FIG.  5 . When used in the context of array  30 , a square rectangular detector  10  shape, vis-a-vis&#39; a non-square rectangular shape, may be advantageous in terms of the overall manufacturing costs associated with array  30 . 
     In accordance with the present invention, detector  10  sizes of 5 μm or larger and array  30  sizes of 1024×1024 may ultimately be feasible with grown crystals  16  of 5 μm or greater lengths. However, such a large array  30  would primarily serve the purpose of employing a large field of view, which usually is not necessary with a seeker unless it is performing additional functions such as surveillance. Within a given array  30 , it is generally preferable (but not necessary) that every detector  10  in such array  30  be characterized by about the same size and shape. 
     Within a given array  30 , it is essential that the fibers  16  be variously oriented among the plural detectors  10 ; however, in terms of each detector  10  as compared to the others, it is not important whether the fibers  16  be similar (equivalent) or dissimilar (nonequivalent) in terms of number, spacing or fiber  16  thickness. Usually, in inventive practice, the minimum orientational requirement is that at least a first detector  10  have a fiber  16  orientation which can be considered to be zero degrees, at least a second detector  10  have a fiber  16  orientation which can be considered to be forty-five degrees, at least a third detector  10  have a fiber  16  orientation which can be considered to be ninety degrees, and at least a fourth detector  10  have a fiber  16  orientation which can be considered to be one hundred thirty-five degrees. Although it is inventively possible to provide an array  30  having just two-detectors  10  (e.g., in ninety degree orientational increments) or just three detectors  10  (e.g., in sixty degree orientational increments), it is generally preferred inventive practice to provide an array  30  having at least four detectors  10  (e.g., in forty-five degree orientational increments). Four is the preferred number of detectors  10  for many embodiments of array  30 . Providing more than four detectors  10  may afford additional benefits, but may not be worth the additional costs in view of the great precision which can be achieved using computer processing in association with an array  30  having four detectors  10 . 
     Some inventive embodiments may provide more than four fiber  16  orientations. For example, an inventive array  30  can include at least eight detectors  10 , wherein: at least a first detector  10  has a fiber  16  orientation of 0 degrees; at least a second detector  10  has a fiber  16  orientation of 22.5 degrees; at least a third detector  10  has a fiber  16  orientation of 45 degrees; at least a fourth detector has a fiber orientation of 67.5 degrees; at least a fifth detector has  10  has a fiber  16  orientation of 90 degrees; at least a sixth detector  10  has a fiber orientation of 112.5 degrees; at least a seventh detector  10  has a fiber  16  orientation of 135 degrees; and, at least an eighth detector  10  has a fiber  16  orientation of 157.5 degrees. In the light of this disclosure, it will be apparent to the ordinarily skilled artisan that inventive practice of array  30  lends itself to any of multifarious numbers, orientations, shapes, configurations, sizes and/or arrangements of the detectors  10  within an array  30 , and of the array  30  itself. 
     An inventive array  30  typically comprises at least two inventive devices  10  such that the corresponding substrates  14  are generally adjacent to each other, and their respective substrative surfaces  15  approximately lie in the same geometric plane. The devices  10  can be integrated into a single array  30  unit in any of various ways. In the light of this disclosure, various techniques for constructing an array  30  of devices  10  will be apparent to the ordinarily skilled artisan. According to frequent inventive practice, each device  10  will include it own fibers  16  and substrate  14 , and the separate devices  10  will be united to form a single array  30  unit. To such end, for instance, the individual substrates  14  can be joined with each other, and/or can each be coupled with a foundational or base structure  60 , such as shown in FIG.  4 . According to less typical inventive practice, the plural devices  10  will share the same comprehensive substrate  14   C  having a comprehensive substrative surface  15   C , such as shown in FIG. 4, whereby each substrate  14  (each of which has its own substrative surface  15 ) represents a portion or section of comprehensive substrate  14   C ; comprehensive substrate  14   C  can be included in, incorporated into or essentially function as a foundational/base structure  60 , as well. 
     Other embodiments of this invention will be apparent to those skilled in the art from a consideration of this specification or practice of the invention disclosed herein. Various omissions, modifications and changes to the principles described may be made by one skilled in the art without departing from the true scope and spirit of the invention which is indicated by the following claims.