Radiant energy – Invisible radiant energy responsive electric signalling – Infrared responsive
Reexamination Certificate
2001-07-26
2003-09-23
Hannaher, Constantine (Department: 2878)
Radiant energy
Invisible radiant energy responsive electric signalling
Infrared responsive
Reexamination Certificate
active
06624416
ABSTRACT:
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 &mgr;m range. The infrared region approximately encompasses the 1 &mgr;m to 100 &mgr;m range. The infrared region is approximately subdivided into: short wave infrared (SWIR), having wavelengths approximately between 1 &mgr;m and 3 &mgr;m; midwave infrared (MWIR), having wavelengths approximately between 3 &mgr;m and 5 &mgr;m; and, long wave infrared (LWIR), having wavelengths longer than about 8 &mgr;m and up to about 100 &mgr;m. The region between MWIR and LWIR is conventionally disregarded due to strong atmospheric absorption. Radio waves have wavelengths longer than about 100 &mgr;m.
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 &mgr;m) operate uncooled at room temperature (300 degrees kelvin, or 300 K). At longer, midwavelength infrared (MWIR) limits (up to 4-5 &mgr;m), cooling to dry ice temperature (195 K) is required. For detectors operating in the long wavelength infrared (LWIR) 8-12 &mgr;m 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 &mgr;m detectors could operate at 80 K, then 5 &mgr;m 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 &mgr;m 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 &mgr;m, 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 &mgr;m 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 & 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 pres
Bardo Richard D.
Sarman Peter J.
Hannaher Constantine
Kaiser Howard
The United States of America as represented by the Secretary of
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