Non-contact interference optical system for measuring the length of a moving surface with a large N.A. collector optical system

摘要

An optical device for measuring the length of a surface that has an undulating specular appearance. The device includes a beam delivery unit that superimposes a pair of laser beams onto a moving surface for producing an interference pattern having straight-line fringes on it and a light collector assembly that captures radiation reflected from different parts along the surface and directs the radiation to a detector. One particular beam delivery unit creates two interfering beams by using refracting prisms to intercept and redirect half of an elliptically shaped laser beam leaving the other half as the second beam. The collector assembly can have a variety of configurations and acts like a bucket collecting as much of the reflected radiation as possible. In order to accomplish this, the numerical aperture in the object space of the collector assembly is made greater than 0.5. In one embodiment, the collector assembly includes a plano-convex lens to collect narrow to moderate angle radiation, and the combination of a concave annular reflector and a partially reflective convex surface of the plano-convex lens to collect the moderate to wide angle radiation reflected from the moving surface to be measured. In other embodiments, Fresnel, aspheric or high refractive index lenses are used to collect the radiation reflected from the surface.