Optics Glossary

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Introduction

This information offered in these pages is a compilation of technical data of crystal and glass materials that has been gathered over many years experience of working with them. Notes, tables and formulae are included which have proved to be useful on countless occasions, and are collected together here as a convenient resource.

The information can never be comprehensive, only the most common categories are offered and some pieces of data always elude and must be assumed never to have been researched. More esoteric data is better obtained from original scientific publications.

Values quoted are expressed in SI units, except where alternative units are in common usage.

Figures quoted are in the main derived from published data. Although careful cross checking of conflicting data has been extensive, no responsibility for the accuracy of the figures is accepted by Crystran Ltd.
 

Crystal Growth

We have many years of experience in manufacturing a wide range of crystals using Stockbarger melt-grown techniques in custom-built furnaces. This is supplemented with special purchase of other stock crystal as ingot to offer a comprehensive range of crystals and crystal products for UV, IR and scintillation applications.
 

Optics Manufacture

Crystal materials can be supplied in a number of different forms, as raw boules, cut and shaped blanks, and polished optics. Thus we maintain cutting and polishing shops for the production of components to customer specifications.

The skills of the Crystran people and our investment programme into increasingly sophisticated equipment enables us to work to high standards. Surface qualities of up to Lambda/40 at 10.6µm and parallelism of better than 1 minute of arc can be achieved depending on material type, and method of working. Double sided and conventional polishing techniques coupled with computerised interferometry and other test equipment ensures that specifications are met.

Polish Specfication

Specifying a polishing standard needs to be approached with caution to establish what is necessary for a particular requirement. Costs escalate rapidly the more exacting the specification and particularly if combinations of requirements are involved. For instance ultra-flatness can often be achieved at the expense of a good cosmetic finish and the reverse holds true. Good flatness and parallelism in thin windows is only possible when double-sided polishing techniques are the appropriate manufacturing method. These are just a few of the factors that need to be considered and you will find that our technical staff will always be willing to discuss and advise on these matters.
 

Hot-forged Optics

We use a quick and cost effective method for the production of silver chloride and silver bromide optics, by the use of a hot-forging technique. Lenses and windows are in regular production, and the technique is particularly appropriate for spectroscopic mini-cell windows where the surface has a small depression to accommodate liquid films. The quality achievable by this technique, although inferior to conventional polishing, is more than adequate for a wide range of infra- red applications.

In the course of our hot-forging operations, a considerable stock of tooling has been assembled. Dies are the containing vessel for the press and control the diameter of the optics. Tools are the polished plates and can be flat (for windows) or radii (for lenses). Flats and radii can be combined for plano-convex lenses.
 

By designing around current stock of equipment, tooling charges for small runs of windows or lenses can be avoided. Similarly for non-standard diameters which can be easily edged down from these sizes. Although incurring some tooling charges, the acquisition of new radius tools for existing die diameters is a more cost effective solution than setting up for a completely new set.