Real-Time Interferometric Testing Of Weak Aspheric Surfaces

With the development of optical manufacturing, precise mechanical fabrication and computer-aided designment and alignment, the condition of the production and the application of aspheres have been highly improved. But the disadvantages of manufacturing and testing of aspheric components restrict their widely use in optical system. In this paper, basing the technology of non-null testing of weak paraboloid, we first ascertain the resolution of the video sensor by computation, and further make sure the measurement range of the ZYGO interferometer for non-null testing of aspheres. The Zernike coefficients are computed, the ideal wavefront aberration is calculated by importing the math model of the asphere. The weak paraboloid is measured directly using ZYGO interferometer, its real surface error is obtained by wavefront fitting and subtracting between the testing result and the computing result. In the non-null configuration, the test wavefront does not retrace itself, and it follows a different return path through the transmission sphere. So the measurement will contain aberrations from the interferometer optics additional to the test part itself. Combining the absolute measurement in the technique, the paraboloid is then under more accurate test. The precision of the measurement is further improved, and the better experimental result is achieved. Incidenting the parallel beam onto the paraboloid, the reliability of the technique is verified by the self-collimated way using a small sphere at the confocal position, the surface's precision is gained.