Abstract: Alignment apparatus including a source of coherent radiation mounted in a reference location and arranged to provide an output beam extending along a reference axis, a laser light reflector mounted at a location sought to be aligned with respect to the reference location and/or the reference axis, a laser light scatterer arranged to receive reflected laser light from the reflector and to produce a speckle pattern and a detector arranged to sense the speckle pattern produced by the laser light scatterer in response to incident reflected laser light, whereby variations in the speckle pattern indicate changes in relative orientation between the reference location and the laser light reflector.

Abstract: A method for producing stimulated emission of radiation in the X-ray region comprising the steps of: selecting as an active medium a system having the following properties; two energy levels separated by an energy difference .DELTA.E corresponding to radiation of frequency .omega..sub.t in the X-ray region such that a transition from the upper to the lower of the two levels by one-photon emission is weakly allowed or strictly forbidden, one of the two levels having a nearly degenerate partner level optically coupled thereto such that a transistion therebetween by one-photon emission has a high probability; providing a resonator containing such an active medium; subjecting the active medium in the resonator to stimulating radiation at a frequency .omega..sub.1 that is preferably, substantially equal to the frequency of the optical coupling between the nearly degenerate levels but much smaller than the frequency .omega..sub.