To measure transmission wave fronts without using a reflecting mirror such as a return spherical mirror by using an aplanatic lens.
In an aplanatic lens 12, an object of measurements, incident spherical waves 109 are internally converted into a predetermined wave front by a first surface (R1 surface) 102 and are internally transmitted, and a second surface (R2 surface) 103 is created so as to have the function of a return mirror. In other words, the curvature of the R2 surface is determined by the wavelength of a measuring light beam, the refractive index of the glass material of a aplanatic lens 12, each curvature of the R1 surface 102 and a Fizeau surface, etc. By utilizing these characteristics, a measuring light beam emitted from the Fizeau surface 101 is transmitted through the R1 surface 102, reflected by the R2 surface 103, transmitted through the R1 surface 102 again, the returned to the Fizeau surface 101 at the same angle as that in the emission. By using these characteristics and correcting data on the shape of the R2 surface 103 and data on spherical aberration which occurs in the aplanatic lens 12, it becomes possible to evaluate transmission wave fronts by spherical waves without using a return mirror.
YAMAMOTO TAKAHIRO
ICHIKAWA HAJIME
