Abstract: An X-ray examination apparatus includes an X-ray filter with a plurality of filter elements for locally attenuating the X-ray beam. The X-ray absorptivity of each filter element is controlled by the amount of X-ray absorbing liquid with which the filter element is filled. The filling of filter elements is controlled by a voltage. The X-ray absorbing liquid contains a suspension of very small X-ray absorbing particles.

Abstract: In the PCVD method glass is deposited in layers on the inner wall of a glass tube by heating the tube to a temperature between 1100.degree. and 1300.degree. C., by passing a reactive gas mixture through the glass tube from a gas inlet side at a pressure between 1 and 30 hPa, by forming a plasma in the interior of the glass tube, and by reciprocating the plasma between two reversal points. After a quantity of glass corresponding to the desired fiber optical construction has been deposited, the tube is collapsed to form a solid preform from which optical fiber are draw. The range of nonconstant deposition geometry at the preform entrance, (i.e. on the gas inlet side), is reduced by interrupting the reciprocating movement of the plasma at the reversal point on the gas inlet side.

Abstract: In the manufacture of preforms for optical fibres, the materials of the core (.alpha.) and of the light-conducting cladding layer (.beta..sub.1) are previously deposited from the gaseous phase. Deposition time is here considerably reduced in that only the materials of the core (.alpha.) and a part of the light-conducting cladding layer (.beta..sub.1) are deposited from the gaseous phase and the remaining light-conducting cladding material (.beta..sub.2 +.beta..sub.3) is supplied as pre-formed tubes of cladding material.

Abstract: A substrate (35) is coated by using starting materials which are supplied in the form of clusters (28). The clusters are disintegrated into their molecular or atomic constituents, and the constituents are deposited on the substrate in the form of compact layers (34). In this manner it is attained that the layers have a defined structure and do not exhibit inclusions in the form of foreign molecules.

Abstract: Optical fibres whose refractive index profiles show specific peripheral and/or radial and/or axial optical modulation structures are manufactured according to the PCVD method, in which such method parameters are varied which influence:(a) the uniformity of the material transport to the inner wall of the tube and/or the deposition yields of the glass over the tube circumference and/or(b) the axial position of the local deposition zone with respect to the reactor producing the plasma.

Abstract: In an optical fiber based on silicon dioxide with fluorine doping which determines its refractive index profile, at least in the light transmitting core a substance is added that increases the thermal expansion coefficient. The added substance is uniformly distributed at least in the light transmitting core, and reduces the influence of the drawing force F.sub.Z (during drawing of the preform) on the Rayleigh scattering .alpha..sub.R and the wavelength-independent "c term" losses. Even at high fluorine dopant concentrations, low Rayleigh scattering losses in the range of the material-intrinsic losses pure for silicon dioxide are achieved. The OH-contamination level is also further reduced, and cracks in the collapsed preforms are largely avoided.

Abstract: In the PCVD method glass layers are deposited on the inner wall of a glass tube by heating the tube to a temperature between 1100.degree. and 1300.degree. C., passing a reactive gas mixture at a pressure between 1 and 30 hPa through the glass tube, and moving back and forth inside the glass tube a plasma. After the glass layers are deposited, the glass tube is collapsed to produce a solid preform from which optical fibers are drawn. The regions of nonconstant deposition geometry at the ends of the preform (taper) are reduced by moving the plasma in the area of at least one reversal point nonlinearly with time and/or by changing the longitudinal extent of the plasma as a function of time. The length of the ramp is chosen to ensure an effective reduction of the end taper.

Abstract: The inside of a tube of an electrically insulating material is coated with a layer of electrically insulating material by reactive deposition of the coating material from a gas mixture which is passed through the tube. The tube is heated and the deposition is activated by a plasma produced by microwaves. The plasma reciprocates in the tube. Energy consumption is reduced by heating the tube to the reaction temperature at least partly by the energy supplied by the plasma to the tube wall. Thermal losses of the tube are reflected back to the tube wall by a heat reflecting element.