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A scanning infrared image converter is described in which the line scanning is performed by sampling of the signals from a one-dimensional array of identical detectors, thus eliminating the need for a fast mechanical line scanning device. Gallium-doped silicon acting as an extrinsic photoconductor at an operating temperature of 4°K has been chosen as a detector material. A temperature resolution of 0.1-0.2°C at a speed of 50 frames/s is obtained with the apparatus. This limitation of the resolution can be ascribed to errors in the gain adjustment of the preamplifiers, the noise equivalent temperature difference of the detectors being much lower than the experimental temperature resolution value.

A new thermographic apparatus is described. Present infrared techniques have been employed together with a novel optical scanner and a calibrated electronic digital readout system to produce a fast scanning radiometer capable of reading black-body temperatures at the rate of 15000 values per second. The range covered is 27.8-37.4 degrees C in 0.2 deg C steps, or in simultaneous multiple isothermal increments of 1 deg C. The scanning time is 1 s for a field of view 37 cm*30 cm with a spatial resolution of 3 mm. The scanner is fixed focus with a depth of field of about +or-5 cm. The recording error due to mirror variations is less than 0.2 deg C and the noise equivalent temperature less still. A stability of 0.2 deg C has been achieved. The application of this instrument to the assessment of static thermal patterns and dynamic variations is discussed with particular reference to its potential value in medicine.

A wide-band detector for the 1.0 to 1.6 mm atmospheric transmission window has been developed for astronomical observations at the McDonald Observatory 2.7 m optical telescope. For observations of continuum astronomical sources, the relevant figure of merit is the « Noise Equivalent Temperature » or δ Trms. The present δ Trms = 0.25 K for a 1 s observation. The astronomical objects which have been observed so far include the sun, moon, Venus, Jupiter, 3C 273 and the galactic center. With the present detector sensitivity, a 1 mm source of 0.7 flux units would give a signal to noise of one for a 3 h observation at the NRAO 11 m telescope. The detector uses a point contact Josephson junction, with a niobium point against tin. The junction is mounted coaxially in a multimode 5 mm diameter cylindrical cavity which is coupled by a cone to a 5 mm oversize circular wave guide leading up the neck of the dewar. The wide-band mode of operation is used, in which the incident continuum radiation from an astronomical source causes a depression of the junction critical current. The junction is biased with a 20 Ω source resistance, and the change in bias voltage due to the change in the junction critical current is measured. Two modes are used to chop the 1 mm radiation incident on the junction. For bright astronomical sources such as the sun and the moon, a total power chopper at the entrance of the wave-guide alternately opens and closes the radiometer entrance. For faint sources, a differential chopper chops between the source and adjacent sky.

Progress made toward the development of pyroelectric/integrated circuit thermal imaging area arrays and their associated address and sense circuits is described. The processing techniques and steps required to form two- dimensional arrays of thin film triglycine sulfate detectors on field-effect integrated circuit substrates are reviewed. The approach to providing the required high degree of thermal isolation between the polycrystalline detectors and the silicon portion of the circuit is to etch away the silicon underlying the detectors. A second pyroelectric imaging array consisting of a thin permanently poled single crystal section of TGS positioned above the integrated circuit substrate is also described. In this arrangement the resulting air gap provides the thermal isolation and contacts to the array detectors are made by means of vacuum deposited microfinger springs. The relative merits of X-Y addressed versus bucket brigade pyroelectric arrays are discussed. An analysis of the performance capabilities of an X-Y addressed polycrystalline TGS array indicates that a system noise equivalent temperature difference of 0.42C at 10 frames/second should be achievable in an array consisting of 10-micrometer thick detectors 4 mils on a side and spaced on 8-mil centers.

In this technical memorandum a set of equations is developed which permits one to calculate acquisition, classification and identification ranges for ship targets when viewed by an airborne forward looking infrared (FLIR) imaging device. Inputs to the model are the average dimensions and aspect angle of the target, the average ship-to-background temperature difference, the surface air temperature and relative humidity, and the nominal resolution, noise equivalent temperature difference and altitude of the FLIR. Novel features of the model are the use of square picture elements (pixels) to establish criteria for acquisition, classification and identification and the relating of pixel size to the minimum resolvable temperature difference of the FLIR.

An infrared hot-electron transistor with a thin (300 AA) InGaAs base layer is constructed. The transistor structure increases the detectivity of a state-of-the art quantum well infrared photoconductor (QWIP) by a factor of two at 77 K, provides a photovoltage gain of 9.7 and a power gain of 3.2, reduces the noise equivalent temperature difference of a detector array by a factor of 36, and can be used for quasi-photovoltaic operation. Using the transistor structure as an analytical tool, the photoelectron transport properties of a QWIP can be extracted, based on which a quantitative theory for the photoconductive gain can be established. >

Silicon Schottky barrier diode arrays, operating in a high sensitivity storage mode, provide the basis for a new class of IR imaging sensor. A Pd on p-Si retina which has a wavelength dependent quantum efficiency from 1 to 3.5 µm is described, This device has a noise equivalent temperature of .17K against a 300K background. The operating temperature is 120K and retina nonuniformities cause negligible reduction in sensitivity.

The pyroelectric detector is a new radiation detector that employs the temperature sensitivity of electrostatic polarization as the sensing principle. Electrically, the detector behaves as a capacitance on which a charge appears when thermally irradiated. This detector has a number of features that make its use attractive for thermal imaging. It does not require cooling, and no biasing voltage is needed. Being electrically capacitative, the noise decreases with frequency, and consequently it has a useful signal/noise ratio at frequencies far above that corresponding to its thermal time constant. Also, these characteristics suppress 1/f type amplifier noise and permit good performance at very low frequencies. A new thermal imaging device or thermograph has been developed to exploit these properties. This is a scanning radiometer that scans a 10 degrees x 10 degrees field in 30 sec with a 0.1 degrees x 0.1 degrees instantaneous element, thus giving 10,000 picture elements. It uses a 7.6-cm diam germanium objective lens and has a noise equivalent temperature of 0.1 degrees C. The thermal image is presented as either a black to white tonal picture or a color picture on Polaroid film. Examples of its use for nondestructive testing purposes are given.