Phase modulated ronchi testing of aspheric surfaces
First Claim
1. Apparatus for measuring the shape of aspheric surfaces comprising:
- a coherent light source;
means for expanding the beam of light from the coherent light source;
means for splitting the light from the beam expanding means into two coaxial beams;
means for focusing and directing the two coaxial beams onto the aspheric surface to be measured;
means for adjusting the position the aspheric surface so that the optical axis of the aspheric surface coincides with the optical axis of the focusing means;
means for detecting incident light;
means for tilting one of coaxial beams with respect to the other to create an interference pattern between the coaxial beams; and
means for directing the light reflected from the aspheric surface onto the detector, whereby the interference pattern sensed by the detector gives an indication of the shape of the aspheric surface.
1 Assignment
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Accused Products
Abstract
An apparatus and method for measuring the surface contour of an aspheric optical surface 36. This is accomplished by splitting a single coherent beam of light into two individual beams with one beam tilted with respect to the other. The degree of tilt is adjusted until a single interference fringe is observed. This single fringe is then directed onto the aspheric surface 36 under test by means of a focusing lens 30. By the use of a beam spliter 24 the reflected fringe is then directed onto a multi-element optical detector 40 . The shape of the fringe reflected onto the detector 40 corresponds to the shape of the aspheric surface 36. A phase modulating mirror 26 is then moved to increase or decrease the path length of one of the two interfering beams of light. This results in sweeping the fringe across the entire aspheric surface 36 so that the entire aspheric surface 36 can be measured. The result is an easy to perform measurement of the aspheric surface 36 which is close to diffraction limited. Further, the above invention does not require a laboratory environment.
24 Citations
17 Claims
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1. Apparatus for measuring the shape of aspheric surfaces comprising:
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a coherent light source; means for expanding the beam of light from the coherent light source; means for splitting the light from the beam expanding means into two coaxial beams; means for focusing and directing the two coaxial beams onto the aspheric surface to be measured; means for adjusting the position the aspheric surface so that the optical axis of the aspheric surface coincides with the optical axis of the focusing means; means for detecting incident light; means for tilting one of coaxial beams with respect to the other to create an interference pattern between the coaxial beams; and means for directing the light reflected from the aspheric surface onto the detector, whereby the interference pattern sensed by the detector gives an indication of the shape of the aspheric surface. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13)
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14. Apparatus for measuring aspheric surfaces comprising:
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a laser light source; a beam expander mounted in the light path of the coherent light source for increasing the diameter of the light beam from the coherent light source; a first beam splitter mounted at approximately 45°
angle with respect to the light beam, said first beam splitter transmitting a portion of the light beam emitted from the beam expander and also reflecting a portion of said beam;a fixed mirror mounted in the path of that portion of the light beam that is transmitted through the first beam splitter, said the fixed mirror also being mounted approximately perpendicular so said light transmitted through the first beam splitter, whereupon the transmitted light is reflected from the fixed mirror back to the beam splitter, where the light is again split with a portion being transmitted and a portion being reflected in a direction transverse to the axis of the light emitted from the coherent light source; a second mirror movably mounted approximately perpendicular to the fixed mirror and in the path of the portion of the light from the beam expander that is reflected by the first beam splitter whereupon the light that is reflected by the second mirror is directed back to the beam splitter and a portion of this light is transmitted through the first beam splitter in a direction transverse to the direction of the original coherent light source; a second beam splitter mounted in the path of the two transverse light beams that are reflected from the fixed mirror and from the second mirror, the second beam splitter being mounted perpendicular to the first beam splitter whereupon the light from the two transverse light beams are split, one portion being transitted and a second portion being reflected; a pivotal axis upon which the fixed mirror is mounted whereby the fixed mirror can be tilted at a small angle thereby creating an interference pattern between the two transverse light beams; an interferometer mirror mounted in the path of the light reflected from the second beam splitter; a focusing lens mounted in the path of the two light beams transmitted through the second beam splitter; an aspheric surface mounted in the path of the light transmitted from the focusing lens which reflects this light back toward the focusing lens, the aspheric surface being positioned such that the optical axis of the aspheric surface coincides with the optical axis of the focusing lens; a second lens mounted in the path of the two light beams at a point after these beams have been reflected from the aspheric lens back through the focusing lens and then reflected off the second beam splitter; a detector for detecting the light which is transmitted through the second lens whereby one or more interference fringes can be sensed by the detector and the shape of the detected fringe pattern gives an indication of the shape of the aspheric surface; and means for moving said second mirror whereby the path length of one of the two transverse beams of light is increased or decreased by approximately one wavelength, thereby causing the interference fringe to move across the aspheric surface thus permitting the entire aspheric surface to be measured by the detector.
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15. A method for measuring the shape of aspheric surfaces comprising:
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providing a coherent light source; expanding the beam of light from the coherent light source; splitting the expanded light beam into two coaxial beams; focusing and directing the two coaxial beams onto the aspheric surface to be measured; adjusting the position of the aspheric surface so that the focal point of the aspheric surface coincides with the focal point of the focusing means; tilting one of the two coaxial beams with respect to the other to create an interference pattern between the two coaxial beams; providing a means for detecting light; directing the light reflected from the aspheric surface onto the detector, whereby the interference pattern sensed by the detector gives an indication of the shape of the aspheric surface. - View Dependent Claims (16, 17)
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Specification