Abstract: An apparatus and method for measuring the density of a low density medium ch as air by measuring the absorption of radioactivity decay particles such as alpha particles in the air. The apparatus includes a source of alpha particles from which the alpha particles are directed to the air sample to be measured. An alpha particle detector is spaced from the source by a path distance which traverses the air sample. The detector is located at an operating point which corresponds to the path distance where one half of the emitted alpha particles are detected. A control system employs a double sideband, suppressed carrier waveform generator which supplies a double sideband, suppressed carrier as a reference signal and supplies a double sideband, suppressed carrier waveform that is modulated by the detection signal.

Abstract: A method and apparatus exploiting the discovery that the crosscorrelation of constantly spaced rows of the matrices representing certain pulse codes sum to zero. In a ranging system, such as a radar, pulses are coded according to the rows of a such a matrix, transmitted sequentially and each return processed sequentially through a filter matched to one of the coded pulses. (A different preselected filter is used for each return.) The sequence of filters is chosen so that for returns for a given range interval, each filter is matched to the returning pulse, resulting in outputs from the filters representing auto-correlations of the returned pulses. These outputs are time delayed added coherently to form the compressed pulse, and annunciated as a target hit. Should the filters and returns be mismatched, as with ambiguous stationary clutter returns, the outputs of the filters are cross-correlations which, according to said discovery, sum to zero.

Abstract: A laser system employing thulium and holmium in a trivalent state. The quantum levels of interest in the thulium and holmium are coupled so that one pumping photo absorbed by the thulium results in two photons emitted by the holmium, making for an unusually efficient laser system. The lower level is sufficiently depopulated at room temperature to allow laser operation without cryogenics. In preferred embodiments, the laser pump can be a laser diode, itself especially efficient, and whose output frequency is closely matched in photon energy to the thulium quantum state of interest, thus lending additional efficiency to the overall system. The thulium and the holmium exist in an yttrium-aluminum garnet crystal as lattice replacements for yttrium.

Abstract: An apparatus and method for producing films of silicon nitride whose index of refraction varies continuously with film depth by preselected amounts between n=3.9 and n=1.99. This is done by producing an amorphous film of silicon nitride, Si.sub.1-x N.sub.x, of pre-selected stoichiometry between x=0 and x=0.57. In a vacuum-chamber, a target substrate is exposed to vaporized silicon while being simultaneously bombarded with an ion beam of relatively high kinetic energy, ionized, nitrogen particles. The nitrogen embeds in the silicon film deposited on the substrate to form amorphous silicon nitride, the stoichiometry of which depends on the intensity of the ion beam. Instruments measure during the deposition the relative rate of arrival at the target for silicon and nitrogen, and, with pre-generated calibration data for the apparatus, enable an operator to selectively control the film's stoichiometry by controlling the ion beam's intensity response to the measured rate of silicon deposition.

Abstract: An apparatus and method for pumping a gas laser, wherein a field emitter is sed to emit electrons into the gas to effect laser pumping. The low energy electrons emitted by field emitters, and the fine controllability of electron energy permitted by field emitters, enables one to effect population inversion of the laser gas, without ionizing the gas, or causing electrical breakdown.

Abstract: Distributed amplifiers in integrated circuit form wherein dielectric matel and electrically conductive material combine to form field emitter cathodes, grids, and anodes in a module forming one or more amplifier cells embedded in a matrix of reactive impedances that form companion stripline-like transmission lines in a vacuum or sufficiently low pressure gas such that electrons remain unscattered during travel over trajectories from cathode to anode in a cell.

Abstract: A method and apparatus for discharging electric charge accumulated on an object tht expels an electrically conductive gas flow, such as a jet engine, a rocket, or a helicopter or aircraft with an internal combustion engine. The system has an electrical shield surrounding a portion of the gas flow, and an electrode for imposing an electric potential in the shielded gas flow. A servo controller measures the accumulated charge at a point on the object and creates a control signal responsive to the rate at which charge is accumulating. The servo controller imposes an electric potential on the electrode, and hence the gas flow, of an amount and polarity determined by the rate and polarity of charge accumulation. In so doing, the electrode accelerates charges of opposite polarity in the conductive gas away from the object, and deaccelerates like charges towards the object, where they tend to cancel accumulated charges, thus discharging the object.

Abstract: An FET device especially useful in common gate amplifier circuits used as amplifiers of microwave and millimeter wave signals. The device has a diamond film layer constituting the device's channel. Device geometry is selected so that, in a common gate amplifier circuit, device input and output are impedance matched to avoid phase cancellation between input and output. In one embodiment a boron nitride layer is disposed heteroepitaxially with the diamond channel and separating the channel from the gate. In another embodiment plural such devices are yoked together integrally source to drain in such a manner that charge carriers entering the second and subsequent stages do so at maximum velocity without the need to accelerate from zero or low velocity. The resulting device has a higher power handling capacity, upper frequency range, and dynamic range.

Abstract: A Field Effect Transistor (FET) device especially useful in common gate amplifiers of signals in the microwave to millimeter range. The device's input and output are impedence matched to preclude phase cancellation and form a traveling wave amplifier capable of high voltage operation. The channel is formed of gallium arsenide separated from the gate by a layer of aluminum arsenide heteroepitaxial with gallium arsenide layer. The channel is bounded by heavily doped regions which act as inherent sources and drains, and limit electric field strength to avoid sluggish response of heavy mass carriers. The gates are formed by etching trenches in a semi-insulating gallium arsenide layer on the opposite side of the aluminum arsenide layer from the channel, using the aluminum arsenide as an etch stop, oxidizing the exposed aluminum arsenide, and epitaxially growing gallium arsenide to narrow the trench.

Abstract: Distributed amplifiers in integrated circuit form wherein dielectric material and electrically conductive material combine to form field emitter cathodes, grids, and anodes in a module forming one or more amplifier cells embedded in a matrix of reactive impedances that form companion stripline-like transmission lines in a vacuum or sufficiently low pressure gas such that electrons remain unscattered during travel over trajectories from cathode to anode in a cell.

Abstract: (F.sub.2.sup.+).sub.A color centers can be produced in additively-colored KI:Li or RbI:Li crystals provided that the material is colored in a nitrogen-free atmosphere. Copious (F.sub.2.sup.+).sub.A centers are produced in lithium-doped KI:Li or RbI:Li crystals using a procedure in which the crystals are grown, additively colored, and annealed in an argon ambient; and optically excited at successively-lower temperatures with a light of a wavelength readily absorbed by the crystal situated in a vacuum.

Abstract: An apparatus and method for locating the vertical axis of symmetry of a sace of horizontal circular cross-section. The apparatus has a plumb structure that establishes a vertical line of sight, and a horizontal translating structure that preselectedly locates the plumb in the two horizontal dimensions. The plumb has at least three arms whose ends are constrained to lie on a circular perimeter which, because the arms are fixed to the plumb, is horizontally disposed. The translating structure and the arms are manipulated so that the end of the arms touch the surface, constraining the line of sight to be colinear with the axis of symmetry. A laser can make the axis visible. The apparatus and method are useable to locate the focal axis and focus of a parabolic antenna.

Abstract: A method for producing desired changes in a beam of coherent light radiating at .lambda..sub.1, comprising the steps of (a) splitting a beam of coherent light radiating at .lambda..sub.1, correcting one of the beams to achieve a desired wavefront and recombining this beam with the first, where a record medium (I) is placed such that the beams are separated by an angle determined by Bragg's law and the line spacing of the interference pattern formed by the two beams; (b) developing the first medium such that a diffraction grating of spacing d.sub.1 is recorded in a material, specifically sensitive to .lambda..sub.1, which will become the master; (c) illuminating the master with a second wavelength, .lambda..sub.2, selected by choice of a second medium which possesses very high diffraction efficiency. The second beam is split into two parts. The first is directed to the master. This diffracted order is recombined with the second beam.

Abstract: A semiconductor device useable as an electromagnetic isolator. The device has a semiconductor substrate epitaxial with a layer of metal, the latter deposited so as to generate a residual magnetic flux. A waveguiding structure is disposed transverse to the flux effective to cause electromagnetic signals propagating in the waveguiding structure to be attenuated a different amount depending on the direction of propagation. The waveguiding structure is preferably a seminconductor layer deposited epitaxially with the substrate in a channel in the metal.

Abstract: Disclosed as a beamforming system, particularly useful for seismic exploration or undersea surveillance, in which data processing of the system is done optically. Sensor outputs are subjected to plural sets of time delays, and the system beams formed optically. Four embodiments are presented of the optical processing hardware.

Abstract: Disclosed are two modifications of the Tank-Hopfield circuit, each of which enables the deconvolution of a signal in the presence of noise. In each embodiment, the Tank-Hopfield circuit is modified so that the equation for total circuit energy reduces to one term representing convolution and another information theoretic (or Shannon) entropy. Thus, in finding its global minimum energy state, each modified circuit inherently identifies an optimal estimate of a deconvoluted input signal without noise.

Abstract: A method and apparatus exploiting the discovery that the cross-correlation of rows of Frank or P4 matrices of a given spacing sum to zero. In a ranging system, such as a radar, pulses are coded according to the rows of a Frank or P4 matrix, transmitted sequentially and each return processed sequentially through a filter matched to one of the coded pulses. (A different preselected filter is used for each return.) The sequence of filters is chosen so that for returns for a given range interval, each filter is matched to the returning pulse, resulting in outputs from the filters representing auto-correlations of the returned pulses. These outputs are time delayed added coherently to form the compressed pulse, and annunciated as a target hit. Should the filters and returns be mismatched, as with ambiguous stationary clutter returns, the outputs of the filters are cross-correlations which, according to said discovery, sum to zero.

Abstract: A method of identifying the presence, and amount, of elemental constituents in a material. The method uses an apparatus known for use in measuring extended x-ray absorption fine structure, and adapts it to the measurement of x-ray appearance potential in a manner to yield both qualitative and quantitative information about the elemental constituents of the material. The source of x-rays can be a synchrotron, which, because of its high power output, increases the speed and sensitivity of the measurements, permitting the use of less sensitive x-ray detectors to yield statistically significant data.

Abstract: An Inverse Synthetic Aperture Radar (ISAR) imaging system provides an image of an incoming aircraft for the purpose of deciding which retaliatory tactic, if any, will be employed. By estimating change rates in attitude about one or more of the roll, pitch, and yaw axes, for an aircraft on a course toward the search radar, estimates of rate of change provide information from which a reliable ISAR image may be prepared. A more identifiable target and relief from ambiguity about the apparent intentions of the incoming aircraft are the result.

Abstract: This invention reduces the weight and bulk of shipboard-mounted microwave antenna systems by achieving horizontally and vertically polarized radar return signals without the need for a rotary joint.