The wavefront aberration analysis and testing accuracy evaluation for the large aberration aspheric system based on the best fit sphere - art. no. 68342V

fIn the measurement of aspheric surfaces, the vertex sphere and the best fit sphere are often used as reference sphere to calculate the non-null compensation deviation. In traditional interferometry, the detected wavefront is equal to twice of the deviation; but it is true only in the null condition or with a certain tolerance in the near null condition. In the non-null condition, when reference spherical wavefront (the best fit sphere in this paper) incidences to the aspheric surface, the rays will not return in the same path but deviate certain angles which cause normal longitudinal aberration. If the normal longitudinal aberration is small enough, for example, much smaller than one wavelength, the wavefront aberration can be equalized to twice of the deviation between the aspheric surface and the reference sphere. However, if the normal longitudinal aberration can not be negligible, the wavefront aberration should not be equalized to twice of the deviation. In this paper, the distribution of the deviation between the aspheric surface and the reference sphere is modeled, and the relationship between the wavefront aberration and the normal longitudinal aberration is discussed. Two paraboloids, one with small asphericity and the other large, are analyzed respectively to compare the different result when whether considering the influence of the normal longitudinal aberration. Computer simulation is also carried out in optical tracing software.