1. Field of the Invention
The present invention relates to an aberration measurement system and an aberration measurement method.
2. Description of the Related Art
There is a demand for a highly precise measurement of a polarization aberration and a nonpolarization aberration of an optical element (test object). The polarization aberration is an aberrational component that is caused by birefringence and depends upon the polarization, and the nonpolarization aberration is a component that does not depend upon the polarization. In general, the interferometric measurement is usually used for the measurement of the nonpolarization aberration of the test object. On the other hand, Japanese Patent No. 3,209,390 proposes use of circularly polarized light for illumination light so as to measure the polarization aberration of the test object. Other prior art include Japanese Patent Laid-Open No. 2-116732.
However, even if the circularly polarized light is used as proposed in Japanese Patent No. 3,209,390, the retardation of the test object cannot be measured near an (integer+½)-th wavelength due to drops of the interference contrast (visibility). In addition, when the polarization aberration is expressed by the retardation and the principal axis direction, the quantitative understanding becomes difficult.