The design of an interferometer workstation for the testing of large concave and convex spherical optics is presented. The workstation handles optical components and mounts up to 425 mm in diameter with mass of up to 40 kg with 6 axes of adjustment. A unique method for the implementation of focus, roll and pitch was used allowing for extremely precise adjustment. The completed system includes transmission spheres with f-numbers from f/1.6 to f/0.82 incorporating reference surface diameters of up to 306 mm and surface accuracies of better than 63 nm PVr. The design challenges and resulting solutions are discussed. System performance results are presented.
As a step toward the Large-Aperture Mirror Array, the LAMA telescope consortium is planning the construction of a prototype telescope. Intended as a test bed for the required technologies, the LAMA Prototype Telescope (LPT) would be a coherent array of six 6.15-m liquid mirrors. Like the LAMA telescope, each telescope would be provided with tracking optics, path-length equalization, phase tracking and adaptive systems. The beam combiner, consisting of six concave adaptive mirrors, would have the Fizeau geometry enabling wide-field interferometric imaging. In order to facilitate construction, testing and operation, the LPT wil be located at or near a developed astronomical site in the continental United States. While the primary purpose of the facility is to develop and prove the LAMA telescope concept and technologies, it will also be a powerful instrument for scientific research. With a light-collecting area equivalent to that of a 15-m telescope, the LPT would be capable of interferometric imaging with the resolution of a 20-m telescope. The telescope would be provided with an infrared imaging camera. This paper describes the telescope design and discusses the main technical challenges that must be faced.
The ISO standard for optical drawing specification (ISO 10110) includes a part on surface form tolerances (figure error). Standardization of this specification provides a succinct and readily understood nomenclature which will be useful in industry, especially as it is intended to unify visual and digital evaluation. It is a peculiar standard in that it does not control surface form directly, but controls it by its effect in a particular test, interferometric comparison with a 'perfect' reference. The application of this standard to digital interferometry is discussed, including a review of the mechanics of this standard and some examples. ISO 10110-5 is vague on some points and these are discussed. These issues include spatial frequency sampling, specific algorithms for calculating some of these tolerances, measurement accuracy concerns, aspherics and guidelines for determining if digital interferometry is required.
In typical interferometric testing the part under test is measured against a reference standard. The measured result is the difference between the errors in the test and reference surfaces plus any addition errors introduced by the interferometer. For accurate qualification of the reference surface it is necessary to employ a technique that can measure the part absolutely. This paper examines an existing technique for absolute testing of spherical surfaces which produces a map of the entire surface. The capabilities of this technique, error sources, and experimental data will be examined.
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