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Processes
Manufacturing Processes
Our process starts with crystals and glasses bought in from all over the world. We obtain calcite, our principal material, from South Africa, Mexico, Brasil and India. Natural quartz comes from Madagascar, while synthetic quartz and magnesium fluoride are grown for us in the U.S.A. Laser glasses come from the UK and Germany.
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Quality and Orientation
We examine the material for inclusions, striae and absence of strain, using a cw laser in dark conditions, to ensure that it meets our stringent quality requirements. One of the most critical tasks is to establish the optic axis. While crystals like calcite cleave along well-defined planes that are inclined at very precise angles to the axis, others such as natural quartz crystals have no such property. To find the axis in these, we use an immersion tank with proprietary index matched fluid. When the quartz is immersed it 'disappears' and a probe laser beam can find the axis using crossed polarizers and the familiar 'Maltese cross' interference pattern. Synthetic crystals are inspection polished to find the axis, again between crossed polarizers, and an accurate reference surface is established.
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Manufacture - Cutting & Grinding
The first stage of the component manufacturing process, after establishing the reference surface, is to cut and grind to shape, using a high speed diamond saw and conventional carborundum/aluminium oxide grinding powders. Angles accurate to 2 seconds of arc can be established by means of high power autocollimators and certified master angles.
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Manufacture - Polishing & Assembly
Once the prisms/windows/plates are ground to size, they are optically polished on pitch laps. For interferometric quality surfaces, we have constructed our own Draper (ca 1864) style polishing machines to achieve flatness to lambda/20 routinely. Even soft surfaces such as calcite can be polished to lambda/8 over a complete 25mm aperture. For polarizer manufacture, having tested for surface figure and angular accuracy, individual prisms are paired off and assembled using a proprietary cement, while maintaining through deviations to specification.
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Optical Contact
Our speciality is optical contacting - a technique of bonding two optical surfaces together without recourse to cement. This bonding process requires that the two surfaces are perfectly flat and very clean. When brought together, they form a molecular bond that binds them in place. UV transmitting polarizers, such as Rochons and Wollastons in both quartz and magnesium fluoride rely on this bonding method between the two prisms to provide transmission down to the low wavelength cut-off of the material. This results in a component that will transmit down to 190nm for synthetic quartz and to 120nm for magnesium fluoride. High power quartz depolarizers and Fresnel rhomb pairs are similarly bonded.
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Specials
Like most small companies who want to keep ahead, we maintain our position as the UK's leading manufacturer of polarizing components by keeping in close touch with university researchers and industrial product development scientists so that we can work with them on new product development. Since we design and make all our products 'from scratch', we are uniquely placed to collaborate in the development of specials. Informed answers to technical questions and strict company confidentiality are our watchwords, so that new customers can have every confidence in us. We can provide an unrivalled design and consultancy service for new requirements, and can design and make special-to-type components with competitive pricing (especially for OEMs) and delivery.
For more information, see our brief Tutorial on polarization and birefringence to enable you to understand how the various polarizing and depolarizing components work.
Sketches by Suzanne Koetser
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