Abstract: Stimulated Raman scattering (SRS) at kHz pulse repetition rates is substantially improved with a laser configuration in which the Raman oscillator mirrors within the laser resonator are removed and the laser mirrors are used for both the laser and the Raman (Stokes) resonators. This sharing of the laser resonator by the Raman oscillator has increased the average power and stability of the first and second Stokes wavelengths, has reduced optical wear on the mirrors, and has resulted in a substantially simplified resonator design.

Abstract: A broadband (8-18 GHz) radomed horn antenna system comprises a conical horn having broadband slots on the inner surface and a radome having a frusto-conical side wall and a spherically shaped transverse wall inserted into the horn. The radome wall is thin relative to operating wavelength. The radome side wall fits snugly against the inner surface of the horn wall so that transverse wall is proximate to the horn feed port with its convex side facing toward the horn aperture. The cylindrical feed guide contains a higher order hybrid mode suppressor which maintains a substantially uniform radiation pattern over the operating band with an acceptable insertion loss.

Abstract: The sensitivity of a buried electrostatically charged cable transducer, such as an electret cable, to mechanical disturbances caused by men, vehicles and the like moving on the surface of the ground is greatly improved by disposing the cable loosely in a coextensive rigid hollow member such as a tube. The inside dimension of the tube is larger than the outside diameter of the cable, the cable being supported on the inner surface of the tube at longitudinally randomly spaced points. The cable is thus free to move radially relative to the tube in response to pressure waves or vibrations propagating through the ground and incident on the exterior of the tube so as to bend, twist, compress and/or otherwise stress the cable and generate corresponding electrical signals between the inner and outer conductors of the cable.

Abstract: Broadband (8-18 GHz) operation of a horn antenna with broadband corrugations is achieved by provision of dissipative TM.sub.11 mode suppressor means in the input waveguide feed to the horn. For a conical horn the input feed waveguide is circular and the mode suppressor means comprises a pair of axially extending diametrically spaced conductive wires or rods supported within the waveguide in dielectric foam, or alternatively, a cylindrical resistance card similarly supported coaxially with the waveguide. For a square corrugated horn of this type, the input waveguide is square and the mode suppressor means comprises a pair of parallel spaced axially extending resistance cards located in the planes of the magnetic field nulls in the waveguide.

Abstract: An improved low-cost line transducer comprises a pair of electret covered conductors twisted about each other to form longitudinal helices and mechanically coupled to a medium that transmits mechanical forces transversely of the conductors. A change in the conductor-electret spacing caused by the mechanical disturbance generates an electrical signal between the conductors which is detected and processed by appropriate circuitry for indicating the occurrence of the disturbance. This simplified line transducer has improved sensitivity to the low frequency disturbances because of the non-symmetrical relation of the two conductors throughout their length. Undesired hum and noise picked up by the unshielded line is reduced or eliminated by appropriate circuits in the signal processor.

Abstract: An adjustable two-axis lockable vibration resistant mirror mount assembly with an accuracy of approximately two arc seconds features separately adjustable inner and outer coaxial gimbals having locks which clamp the gimbals in the adjusted position without altering that position. An adjusting screw for each gimbal is mounted on the frame and abuts the respective gimbal offset from its pivotal axis. Diagonally opposed pairs of U-shaped locking clips mounted on the outer gimbal straddle bosses on adjacent parts of the frame and inner gimbal, respectively, and are moved tightly against the bosses in directions parallel to the respective gimbal axes by locking screws to secure the gimbals in relatively fixed positions. After locking, the adjusting screws may be removed from the assembly. The center of the reflective mirror surface lies at the intersection of mutually perpendicular pivot axes with the normal to the mirror surface at its center substantially perpendicular to the pivot axes.

Abstract: An active ultrasonic perimeter intrusion detection system comprises an elongated flexible electret tape capable of being stored on and deployed from a reel or the like and connectable when deployed to a signal generator operating at ultrasonic frequencies and to a receiver having a signal processing and alarm capability. The tape comprises an electret layer sandwiched between relatively fixed and movable conductive strips and lies flat on a surface adjacent to the area to be protected such as the walls or ceiling of a room or the perimeter of a ground area. The movable stip produces a substantially undirectional ultrasonic beam outwardly from the tape and along its length so as to illuminate objects that cross over the tape. This causes a reflection of the ultrasonic signal and doppler shifting of its frequency which is detected by the tape, the output of which passes to the receiver for indicating the intrusion.

Abstract: An optical tracking system for aircraft and the like which measures positional variations of a portion of a laser transmitter pulse train or beam returned from a tracked object to derive error signals for energizing the tracking servo mechanism. In particular, the system detects such beam position change by measuring variations in energy received by a quadrant-segmented photo sensor relative to the sensor axis of symmetry. Compensation for scintillation (variation with time of the spatial intensity distribution) of the return beam due to change in the index of refraction of the atmosphere is achieved, in accordance with the invention, by focusing the return beam to a small diameter and passing it through a diffusing medium such as opal glass or a fiber optic bundle. The energy in the output beam from this medium is homogeneous and substantially invariant with time so that tracking error due to scintillation is eliminated.

Abstract: A system for identifying and locating objects of known chemical composition and discriminating against a background having a different chemical composition comprises a source of radiation for illuminating the object and the background and a receiver responsive solely to the fluorescent radiation from the object. The receiver comprises a filter which passes radiation from the object and a photodetector array which receives the filter output and produces an output containing the coordinates of the location of the received signal or signals on the array. This location information is applied to utilization apparatus which may comprise a marking mechanism which marks the location of the object on the background or automatic tracking apparatus which tracks the object of interest or counter apparatus which identifies the quantity of such objects that are illuminated.The invention also comprehends the method of deriving position data by causing a known substance to fluoresce at wavelengths (centered at .lambda..sub.

Abstract: A wideband analog photorecorder comprises a transparent Bragg cell as an acousto-optic transducer and a pulsed laser positioned to sequentially illuminate a moving recording medium (photographic film) through the cell. The acousto-optic cell is energized by an input electrical signal and the resultant acoustical wave passing through the cell diffracts the "strobelike" output beam from the laser so as to expose the film one line at a time with the optical analog of the signal. The pulse repetition frequency of the laser is synchronized with the velocity of acoustic wave propagation in the Bragg cell so as to expose a new signal segment in the cell with each laser pulse and thereby form one recorded line on the film. The Bragg cell utilizes an optically transparent medium, such as lithium niobate, as an acoustic wave carrier to provide optical resolution through diffraction of the laser beam.

Abstract: A phase locked loop circuit for a controlled oscillator employs a digital phase detector and maintains phase lock between trains of reference (R) pulses and controlled (C) pulses derived from the oscillator. Acquisition of a state of phase lock is aided by delaying or advancing the C-pulse relative to the next occurring R-pulse when the frequency of the C-pulses is higher or lower, respectively, than the R-pulse frequency. A frequency divider connected to the oscillator output is reset once during each cycle to produce C-pulses as an input to the phase detector and the R-pulse input to the phase detector is applied from a reference pulse source through a delay circuit. Logic elements responsive to the two phase detector inputs determine the relative frequencies of the latter and control operation of the frequency divider to either delay or advance the production of the C-pulse relative to the R-pulse without interrupting operation of the R-pulse source.

Abstract: A log-periodic longitudinal slot antenna array comprises a dimensionally linearly tapered ridged waveguide having top and bottom walls, either forming part of a metallic ground plane and in which longitudinally elongated and spaced slots are formed. The long axis of each slot is parallel to the longitudinal component of the magnetic field in the waveguide and the slots have dimensions and inter-slot spacings which decrease in increments of a predetermined ratio .tau. in a direction toward the smaller end of the tapered waveguide. The antenna produces a fan-shaped beam with its narrow radiation pattern lying in the E-plane of the waveguide when fed at either the large or small end of the waveguide or both, the boresight axes of the resultant independent beams being different for the two feed points. For bi-directional radiation, a similar array of slots is formed in both the top and bottom walls of the waveguide either or both of which optionally may comprise extended ground planes.

Abstract: A simplified hydrophone array for use in a towed marine streamer for seismic undersea exploration comprises a longitudinal series of electrically separate sensor sections comprising radially spaced coaxial inner and outer conductors and a plurality of longitudinally extending electret cables tightly fitted in the annular space between the conductors. Each cable has a conductive lead wire insulated by an electret covering, such as electrostatically charged tetrafluoroethylene (Teflon); an electrical signal between inner and outer conductors and across the electret is produced by acoustic energy transmitted to the outer conductor. The outer conductors are electrically insulated from each other and the inner conductor is longitudinally continuous throughout the length of the array and thus is common to all sections.

Abstract: A modular wall system comprises a plurality of wall modules in end to end relation, each module having a spring loaded ceiling channel engaging the ceiling and a floor channel frictionally or mechanically engaging the floor. The ceiling channel has a shallow upwardly opening longitudinally extending channel-shaped adapter plate on its top adapted to engage a strip secured to the underside of a ceiling tile support hanger for stabilizing and aligning the module. The ceiling and floor channels have sides formed with longitudinal grooves adapted to be engaged by a suitable dolly for contracting or expanding the ceiling channel away from or toward the ceiling to enable each module to be maneuvered into and out of position in the line of the wall.

Abstract: An adaptive gain control for a signal processor of an intrusion detection system comprises a circuit which utilizes the weighted summation of selected characteristics of sensed signals for producing optimum control of the gain of the circuit for discriminating between target and non-target signals more effectively. The parameters of signal envelope, envelope amplitude variance and signal frequency obtained from a processor such as that described in U.S. Pat. No. 3,696,369 are fed to a summing amplifier through resistors having weighted values calculated from previously recorded seismic signals obtained from several previously identified sites which, taken as a group, are representative of the type or types of sites in which the detection system is to be installed.

Abstract: This fence protection system comprises an elongated electret cable for sensing vibrations on a fence and an electronic processing circuit connected to the cable for discriminating against spurious signals such as those caused by raindrops on the fence and nuisance signals produced by stick dragging on the fence. This circuit comprises a charge amplifier connected directly to the cable transducer and series connected burst width and interburst discriminators in conjunction with parallel connected pulse counter and integrator means feeding an alarm mechanism through an OR gate; signals produced by an intruder climbing or cutting the fence are distinguished from spurious raindrop and stick dragging signals and produce and alarm.

Abstract: A shutter and beam expander for diverting the output of a high power laser into an absorption body comprises a onepiece metallic structure having a convex spherically shaped portion adapted to be moved into the beam path for simultaneously reflecting and expanding the beam into energy absorption material.