A method for reducing the coherent noise, by a factor of two, in dynamic interferometry measurements is presented. Reducing coherent noise is particularly important in "on-machine" metrology applications where residual noise can be polished into the surface under test. Both theory and experimental measurements are discussed.
Changes in the shape of large lens elements due to the influences of gravity are important to consider in the fabrication, testing and assembly of optical systems. Tried and proven methods used for mounting large mirrors to minimize the effects of gravity are typically not applicable to large transmissive lens elements, due to the simple requirement that the clear aperture of a lens must remain free of mechanical obstructions. Precautions must be taken to ensure that an element's surfaces are correctly fabricated and then maintained when assembled into the final system. The amount of distortion caused by the weight of a particular lens element is dependent on a number of factors including: size, aspect ratio, shape, material, and the support on which it rests. Examples of the effects of these factors are modeled using Finite Element Analysis and demonstrated through interferometric testing. Attention is given to the mounting of lens elements within a system and simulating "real-world" conditions. These "real-world" conditions can produce results that are different from what was expected if only ideal cases have been considered. The work presented will aid the designer, fabricator, and metrologist to identify what optical elements and mounting conditions may be problematic and to minimize their effects.
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