Abstract: A method for manufacturing optical components having a periodic or quasi-periodic structure such as diffraction gratings, volume holograms or distributed feedback mirrors in optical fibers. An optical medium is subjected to acoustic waves which induce periodic or quasi-periodic changes in the optical properties of the medium, the changes being at least partially retained on removal of the waves. The changes may result from stress associated with the antinodes of an acoustic standing wave, alteratively the stress distribution associated with a travelling acoustic wave in an electro-viscous liquid may be semi-permanently retained by the solidification of the material resulting from the application of an electric field.

Abstract: A broadband electrical signal spectrum analyser comprises a spatial light modulator such as a Bragg cell located within at least one resonant cavity and illuminated by a polychromatic source of light. The signal to be analysed is connected to the Bragg cell. The tuned cavity is arranged to lase the diffracted light to thereby enhance the signal before detection. In one arrangement the cavity is formed by opposed mirrors set at the Bragg angle and one of the mirrors is oscillated through a range of frequencies required by the broadband application. In a second arrangement a plurality of narrow band channels is formed by a fibre optic array. The fibres are arranged such that first ends of the fibres form a linear input array and the second ends form a linear output array. Light at the Bragg angle passes into an appropriate one or more of the output array fibres, passes around the looped fibres to the input array where the light (zero order) is transmitted through the Bragg cell and then back to the fibre loop.

Abstract: A metal vapor apparatus comprising a laser tube within which laser action occurs during operation of the apparatus, and means for applying a liquid metal coolant to the tube.

Abstract: Metal vapor laser apparatus includes an envelope within which is contained electrodes and a plurality of cylindrical copper segments arranged between them. During operation of the laser, bromine and helium buffer gas are arranged to flow through the envelope, causing copper bromide to be produced. When a discharge is established between the electrodes, the copper bromide vaporizes and dissociates to give copper vapor which is then excited to produce a population inversion. Such apparatus is able to operate at relatively low temperatures, in the region of 600.degree. C.

Abstract: Laser apparatus includes a gas filled tube and is arranged to act as a switch to trigger, within the tube itself, a discharge. The power dissipated in the discharge is applied to material which forms, or is to form, a laser amplifying medium, to provide pumping power. Thus, no external switch, such as a thyratron, is required, unlike conventional laser arrangements.

Abstract: Laser apparatus including a relatively long cylindrical cathode within a discharge tube containing a buffer gas at a low pressure of less than 1 Torr. By employing a laser constructed according to the invention, it is possible to achieve a plasma which extends along the length of the cathode, which may be up to one meter long.

Abstract: Laser apparatus includes hydrogen or deuterium buffer gas and dispenser reservoirs which contain a hydride or deuteride as appropriate. As gas molecules from the buffer gas are lost within the discharge tube due to trapping and sputtering processes, hydrogen or deuterium is given off from the surfaces of the reservoirs at a greater rate to maintain the vapor pressure within the discharge tube at a substantially constant level. Thus the laser apparatus may operate in a "sealed-off" mode, that is without requiring that buffer gas be flowed through it.

Abstract: In a laser arrangement, solid or liquid material, at least part of which comprises a laser amplifying medium, is atomized in a gas prior to being applied to a discharge region. In one embodiment of the invention, the gas is combustible and is ignited to produce a flame which provides heating of the material. The invention is particularly applicable to metal vapour lasers.In another embodiment of the invention, the material is atomized in an inert gas and a discharge within a laser discharge tube is used to provide excitation.

Abstract: A discharge tube arrangement, for example, a thyratron, in accordance with the invention has a first electrode arranged co-axially about a second electrode. Thus, in a thyratron, the anode may surround the cathode or vice versa. The envelope may be tubular having an aperture at its center. The discharge tube arrangement is constructed such that it is capable of being added to another such arrangement. A plurality of such arrangements may be added together to produce, for example, a thyratron capable of large current conduction.

Abstract: Laser apparatus includes an outer envelope which contains a plurality of laser discharge tubes. Each of the laser discharge tubes includes copper pieces which, when vaporised, acts as a laser amplifying medium. Each of the laser discharge tubes is of the maximum volume compatible with good efficiency which, when combined with the output power of the other tubes, enables a very high power output to be achieved compared with previously known tubes.

Abstract: A laser arrangement includes electron beam apparatus comprising a plurality of electrodes, each of which having an aperture therethrough. The apertures are aligned along the longitudinal axis of an envelope which surrounds them and contains gas. The electrodes are electrically connected such that, of an adjacent pair, one is at a lower potential than the other. An electron beam is produced between the first electrode and an adjacent electrode, and is accelerated along the axis through the apertures, the electron current increasing in magnitude. The electron beam produced is used to provide pumping powder to the gas contained within the envelope such that it acts as a laser amplifying medium.

Abstract: Apparatus for forming an electron beam sheet includes a cathode member having a slot in a front surface thereof, a grid electrode and the anode of a thyratron. When it is desired to trigger the thyratron into conduction, a suitably large potential difference is applied between the cathode member and the grid, resulting in an electron beam sheet being produced extensive of a slot formed in the front surface of the cathode member. This produces ionisation and a main discharge current is established between the main anode and cathode of the thyratron.

Abstract: Laser apparatus includes a ceramic tube within which is contained a gas and a cylindrical cathode having a plurality of holes therethrough. An anode is located along the axis of the tube. During operation of the apparatus, a large potential difference is applied between the anode and cathode, causing a plurality of electron beams to be formed extensive of the holes. Vapor is emitted from the electron bombarded cylindrical rod and becomes excited, and laser action occurs.

Abstract: Discharge tube apparatus includes an outer containing vessel and a structure comprising for example five metal cylinders located co-axially within it. Each of the metal cylinders includes projecting spacers on its outer surface which serve to space it from adjacent ones. Such a structure is thermally insulating and may be arranged to enable a large temperature difference to be maintained between the interior of the discharge tube and the outer containing vessel. In other embodiments, a plurality of structures are included disposed along the axis of the tube. Also, dispenser segments for dispensing part of the active medium of a metal vapor laser may be included and arranged to shield vulnerable surfaces in the tube from direct exposure to the discharge.

Abstract: A metal vapor discharge tube includes cylindrical dispenser blocks of sintered tungsten which are porous and support metal whose vapor is to form at least part of the active medium of the tube. Thus, the dispenser blocks retain the metal, holding it in position when in its solid and liquid states. Heat shields serve to retain heat within the envelope of the discharge tube and uniformly heat the cylinders.

Abstract: Laser apparatus comprising a discharge vessel of thermally insulating material and a protective metal layer disposed on the inner surface of the discharge vessel. During operation of the laser apparatus, copper powder is vaporised to form at least part of the laser active medium. Because of the protective metal layer the discharge vessel wall is prevented from damage due to its contents.

Abstract: A thyratron comprises an anode and control grids between which is located a double layer screen grid. Thermionic cathode material is inserted in an aperture in the part of the screen grid furthest from the anode, and in operation this is heated to the required temperature by hot plasma which surrounds it, thus eliminating the need for a cathode heater.

Abstract: A gas discharge device includes an anode, an enclosure member having an aperture therein and substantially enclosing a volume of a gas filling, and a mechanism for injecting electrons into the volume of gas filling to produce ionization of the gas filling within the volume so that during operation of the device, the enclosure member and the ionization within the enclosure member constitute a cathode, and a conduction path is established between the interior of such cathode and the anode through the aperture of the enclosure member.

Abstract: The present invention provides apparatus for forming electron beams, which may be advantageously employed in many applications, for example in display devices or thyratrons. A cathode member has a hole in its front surface. All the surfaces of the cathode member, except for the wall and base of the holes, are covered in an electrically insulating material such as glass. The cathode member and an anode member are contained within an envelope which also contains a gas filling. On application of a suitably high voltage between the cathode and anode members an electron beam is formed extensive in a direction away from the hole. The anode member may be located behind the front surface of the cathode member, and an electron beam still forms in front of the front surface.

Abstract: Conventional discharge tubes comprise electrodes within a separate containing vessel. The electrodes are joined to an external circuit by electrical conductors which pass through the vessel wall via an insulated side arm. Such a construction has disadvantages in that careful manufacture is required and it is also difficult to produce a desired distribution of the active medium in a laser and maintain a stable optimum temperature. In an attempt to reduce these problems the invention provides a discharge vessel which comprises electrical conductors and insulators arranged alternately so that a separate discharge vessel is not required. Since the discharge vessel is partially thermally conducting, temperature control is facilitated by its fast response to stabilizing controls, heat being supplied from an external source.