The first part of this article gave the background to modes and resonators and the advantages of transverse mode selection. Part 2 gives a review of methods of mode-selection and discusses a wide variety of resonators with emphasis on the experimental results obtained from them. Unstable resonators show particular promise for mode selection of solid state lasers.
The application of ion beam techniques to surface machining and the surface properties of glass is discussed. Particular reference is made to the feasibility of this work with commercially available apparatus. Also included is a brief review of the relevant theory, and some experimental results. Ion beam processing can not only achieve a surface finish but can also improve surface polish.
The optics group at Reading is relatively new, but is all ready making a name for itself in the optics world. This article introduces the work being done by the optics group and explains its history and structure. Perhaps, the most important aspect is the work on optical systems design—a field in which Professor Hopkins name is well-known.
A simple technique is described for the inspection of the interior of smooth or polished cylinders. The technique may be described purely in terms of geometric optics and either a laser or a white-light source can be used. The point source of light is arranged to be coaxial with the cylinder and at a short distance from one end of it. The light emerging from the source is reflected by the walls of the cylinder in a controlled fashion, and is collected on a photographic film or viewing screen on the far side of the cylinder from the source. Minor deviations from parallelism of the cylinder walls are thereby greatly magnified and may easily be measured using the formulae given in the text.
This method can be used by unskilled soldiers to take reflectographs of gun barrels for inspection, and for following the working life of a particular barrel. The technique can be further refined by replacing the screen by a cylindrical one.
A moiré fringe technique has been developed for measuring strains which arise from welding. A grating is etched onto the sample and, after straining, is compared with a mismatch of the original grating. The pitch of the moiré fringes produced gives a measure of the strain.
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