Abstract: Detector apparatus includes a diffraction grating (11) having a period such that the incidence of coherent point-source radiation upon it produces a number of spaced self-images of the grating behind it. A Moire grating (12) is placed to coincide with one of these self-images and a detector array (13-16) is placed behind the Moire grating to detect the resulting interference fringes.

Abstract: A pixel data memory is provided for use with an information display system having a raster scan screen divided into a plurality of pixels each of which represents a separate area of the screen. The memory comprises a multiple-bit memory plane (13) capable of providing a plurality of separate bit locations each of which may correspond to a separate display pixel and arranged to store pixel data in the form of a plurality of multiple-bit words. The memory plane (13) comprises a number of memory chips each capable of storing a separate bit of each of the multiple-bit words. An address generator (10) is operable to generate the addresses of required individual bit locations in the memory plane. A number of separate control circuits (14) are provided, equal to the number of bits in each word. Each control circuit (14) is associated with a separate memory chip and is responsive to a generated address defining a bit location on that chip to access the pixel data identified by the bit at that location.

Abstract: The power supply includes an oscillator (20) which generates a radio-frequency signal amplified by an amplifier (21). The amplified signal is applied to a laser (22) to initiate and maintain a discharge in the laser gaseous active medium. Power control means (24) are provided operable after initiation of the discharge to adjust the power applied to the laser to the value required to operate the laser at maximum efficiency. Automatic gain control means (25) may be provided, responding to the output from a power meter (23).

Abstract: A laser optical cavity extends between two end reflectors (11, 12) and is defined by at least three sections. A number of folding reflectors (14) are provided for directing radiation emerging from one section into the next. An active medium is contained in the sections and excitation means are provided to produce laser action. A rigid support member (10) supports the end reflectors (11, 12) and the folding reflectors (14) around a generally cylindrical surface such that a continuous optical path extends between the end reflectors (11, 12) by way of each folding reflector (14) in turn. At least three of the laser sections extend across a substantial part of the area with the cylinder (10) and each section crosses at least one other section at or near to the axis of said cylinder as viewed along that axis.

Abstract: The apparatus comprises a radiation-sensitive detector (17) and optical means for directing radiation from an observed field of view on to the detector. The optical means includes a rotatable support member (10) rotatable about an axis (11) and carrying a number of reflecting members (12) equally-spaced around it. Each reflecting member (12) is located in a plane parallel to the axis (11) of the support member and each is arranged at the same non-perpendicular angle to a radius of the support member. A pivoted reflecting member (14) is located inside the locus of the plurality of reflecting members (12) and is rotatable about an axis (15) located in a plane perpendicular to that axis (15). In operation radiation from the field of view is reflected by the pivoted reflecting member (14) on to successive ones of the rotating reflecting members (12) and thence on to the detector (17).

Abstract: The apparatus includes alignment means (13, 14) for determining the direction of a sight-line (12) extending from an observer (11) to a display surface (10), projection means (15, 16) for projecting an image of a graticule into the sight-line for movement therewith, and control means (17) operable to cause the display of a movable cursor on the display surface (10) when the sight-line (12) intersects the display surface.

Abstract: An optical element (10) is pivoted for limited rotation about an axis (12). An actuator arm (14) is rotatable by an actuator (13) about an axis (15) and is connected to the optical element by a first link (16). A second link (21) connects the actuator arm (14) to a balance arm (18) which carries a balance mass (20) and is pivoted about an axis (19). The arrangement is such that the line (23) joining the axis (12) of the optical element to the point of connection between the first link (16) and the optical element (10) is always parallel to the line (24) joining the axis (19) of the balance arm (18) to the point of connection between the balance arm and the second link (21).

Abstract: A CRT display system providing a raster pattern, possibly for a flat screen CRT, has an oscillator driving a Line counter. The Line counter drives a Field counter and a Line DAC. The Field counter drives a Field DAC. In response, there are generated signals, representing functions, to be applied to the CRT deflection plates, and whereby there is represented the inverse of any function representing distortion of the raster pattern required to be corrected. At least one further DAC may be provided, comprising one of a pair of interacting DAC's, with one DAC driven by the Line counter, and one DAC driven by the Field counter, the output of said further DAC causing a combined function to be represented by the output of said other DAC. Said other DAC may comprise either the Line DAC, or the Field DAC; or said further DAC of another pair of interacting DAC's.

Abstract: A pulse circuit is provided for switching a grid electrode of an electron beam generator having a cathode electrode at a very high potential relative to ground. The grid electrode is to be switched between two control voltages (+V, -V) of opposite polarity by first and second switching devices (TS1, TS2) each operable to connect one of the control voltages to the grid electrode. A pair of control devices (TC1, TC2) is provided, each associated with a separate one of the switching devices (TS1, TS2) and operable to switch off the associated switching device. A first pulse transformer (TR1, TR2) is provided having a primary winding to which pulses may be applied substantially at ground potential and a secondary winding operating at the potential of the cathode. A pulse amplifier (TA1-TA2, TA3-TA4) is connected between that secondary winding and the primary winding of a second or third pulse transformer (TR2, TR3).

Abstract: The apparatus comprises a sighting unit, such as helmet 10 carrying a cathode-ray tube 11 and a semi-reflecting screen 13 enabling a user to view a display superimposed on an outside scene. The sighting unit carries a detector unit 15 which determines the movements of the helmet 10 without reference to apparatus external to the helmet, and preferably comprising some form of gyroscopic apparatus. The helmet also carries a boresight detector 16 which forms part of correction means operable to correct automatically from time to time for errors in the output of the detector unit.

Abstract: The apparatus permits an external target to be viewed along a sight-line by a sensing device and for the projection of a beam of laser radiation (12) towards the target. The apparatus includes a viewing window (10) transparent to radiation at a wavelength to which the sensing device is sensitive and inclined at an angle to the sight-line. The window (10) has a viewing area through which the target may be viewed and a laser output area through which the laser beam passes. An anti-reflection coating is formed on that surface of the viewing window (10) remote from the target. Optical deflector means (16) are provided for deflecting laser radiation reflected from the other surface of the viewing window in the laser output area into the viewing area of the window for reflection into the field of view of the sensing device.

Abstract: Apparatus for measuring the phase noise content of a microwave signal source (10) includes a microwave cavity (22) resonant at a fixed frequency, signal generating means (23) operable to generate a frequency representing the difference between the source frequency and that of the resonant cavity, and mixing means (20) for combining the outputs of the source and the signal generating means. The output from the resonant cavity (22) is applied to a phase detector (15) together with a portion of the output of the mixing means (20) and the output of the phase detector (15) represents the phase noise content of the output of the microwave source (10). The signal generating means (23) includes a voltage-controlled oscillator the frequency of which is controlled by an output from the phase detector means (15) so as to maintain the output of the mixing means (20) at the resonant frequency of the microwave cavity (22).

Abstract: A transversely-excited waveguide laser made up from the two blocks of electrically-insulating material. One block (1) has three parallel slots (3, 4 and 5) formed in one face, while the other block (2) forms a cover which may be secured to the first block to close the slots. The two outermost slots (4 and 5) each contain a layer (7) of electrically-conductive material to which an electrical conductor (8) is attached to form an electrode, while the dimensions of the center slot (3) are such as to enable it to form a laser cavity which will support waveguide laser action.

Abstract: A dither mechanism comprises a hub (10) arranged to be fixed to a mounting, and a rim (11) coaxial with the hub and to which the ring laser may be attached. A number of radial spokes (12) interconnect the hub (10) and the rim (11), and each has its point of attachment to the rim (11) recessed into the rim in a radial direction. A pair of pegs (32) is associated with at least one spoke and is arranged for insertion into the recesses (15) between the rim and each side of the spoke (12) so as to vary the effective length of the spoke. Drive means (30) are provided for imparting an oscillatory rotational motion to the rim (11) relative to the hub (10) about the axis of the hub.

Abstract: For a semiconductor device including a bipolar transistor, the emitter, a heavily doped base region surrounding the emitter, and base and collector contact regions, (the collector including a buried layer at an epitaxial layer/substrate interface of the semiconductor body), are formed by employing, on the epitaxial layer, layers of first and second resists, each resist layer comprising an impurity barrier, the second resist being attacked by an etchant relatively inactive with the first resist, by first or second photolithographic steps, of a sequence of only three photolithographic steps, forming three apertures in a first resist layer, to expose the subsequent emitter and two contact regions, then before each, or the, remaining photolithographic step of the sequence, providing a second resist layer, and exposing selectively, and coarsely through the second resist, the subsequent emitter, and either the collector contact region by the third photolithographic step, or the base contact region by the second pho

Abstract: A data compression system includes an input store (1) for receiving and storing a plurality of bytes of data from an outside source. Data processing means for processing successive bytes of data from the input store includes circuit means (21-25) operable to check whether a sequence of bytes is identical with a sequence of bytes already processed, output means (27) operable to apply to a transfer medium (12) each byte of data not forming part of such an identical sequence, and an encoder (26) responsive to the identification of such a sequence to apply to the transfer means (12) an identification signal which identifies both the location in the input store of the previous occurrence of the sequence of bytes and the number of bytes in the sequence.

Abstract: A feedback servo positioning system for motor 13 is configured under the control of microprocessor 27 either as a position feedback servo for small displacement demands or an acceleration feedback servo for large displacements. In the latter role, the processor determines an intermediate position (e.g. mid point), accelerating the motor at maximum acceleration rate until the intermediate position is reached, and then calculates the deceleration rate required to stop the motor at the demand position. During deceleration the instantaneous position and velocity are monitored to update the optimum deceleration rate to compensate for variations from the initially computed value due to friction and other measurement errors.

Abstract: Apparatus for determining the position of a point movable throughout a measuring volume relative to a set of reference axes includes a probe member (10) having a probe tip (11) defining the position of the movable point. The measuring probe (10) also has first and second reference points (12, 13) spaced apart from one another and having a fixed known spatial relationship with one another and with the probe tip (11). Means (16) are provided for moving the probe member (10) so that the probe tip may be positioned at any desired point within the measuring volume. At least three distance measuring equipments (15) are provided, located outside the measuring volume at fixed known positions relative to the set of reference axes and each operable to determine the distance between it and each of the reference points (12, 13) on the probe member (10). Calculating means (19) are provided to calculate from said distance measurements the position of the probe tip (11).

Abstract: A direct-current power supply circuit includes a series-connected switch (TR1) and an inducator (L) connected together with a flywheel diode (D) across an input voltage supply (V.sub.s). A transformer (TX) has a primary winding connected to the inductor (L) and the diode (D) by way of a bridge-connected network of switching devices (TR2-TR5). A reservoir capacitor (c) is connected to a secondary winding of the transformer (TX) by way of a full-wave rectifier (DB), and a load (LD) may be connected to the reservoir capacitor (c). Control means (CM) are provided to control the operation of the series-connected switch (TR1) and the network of switching devices (TR2-TR5) so that each cycle of operation transfers an equal amount of charge to the reservoir capacitor (c) regardless of variations in the input voltage (V.sub.s) or load conditions.

Abstract: A CRT display system providing a raster pattern has digital means 30, 31, 32 to drive a DAC 34. In response, there are supplied analogue signals, on a line 37. There are also provided pulse generating means 90 controlled by the digital means, and integrating means comprising two integrators. Each integrator is connected individually to an X deflection plate 14 of the CRT, and comprises an amplifier and a feedback capacitor. One capacitor C2 is charged by negative-going pulses, and the other capacitor C2' is charged by positive-going pulses, until the pulses are removed, when the required ramps are applied to the deflection plates. Then a current flows through a transistor T7, and is controlled by the DAC output on the line 37. Hence, the waveforms applied to the deflection plates cause distortion of the raster pattern otherwise obtained, to be corrected, the DAC output representing a function comprising the inverse of the function representing the distortion.