Wavefront measuring apparatus and wavefront measuring method

A wavefront measuring apparatus for measuring a wavefront of light passing through a test optical system, said wavefront measuring apparatus comprising:

• a light source;
• a reference light path in which a reference member for producing reference light is disposed;
• a test light path in which said test optical system is disposed;
• and
• a plano-convex optical member disposed in said test light path in such a manner that a plane surface thereof faces toward said test optical system, said plano-convex optical member having a wall thickness approximately equal to a radius of curvature of a convex surface thereof;
• wherein an optical path length of said test light path and that of said reference light path are approximately equal to each other, and the following condition (2) is satisfied:
• L<2×nopt×d (2)
• where:
• L denotes a coherence length of said light source;
• d denotes a wall thickness of said plano-convex optical member;
• and nopt denotes a refractive index of said plano-convex optical member.

A wavefront measuring method for measuring a wavefront of light passing through a test optical system by using a measuring optical system having a light source, a reference light path in which a reference member for producing reference light is disposed, and a test light path in which said test optical system is disposed,

• wherein a plano-convex optical member is disposed in said test light path in such a manner that a plane surface thereof faces toward said test optical system, said plano-convex optical member having a wall thickness approximately equal to a radius of curvature of a convex surface thereof,
• an optical path length of said test light path and that of said reference light path are made approximately equal to each other, and
• the following condition (2) is satisfied:
• L<2×nopt×d (2)
• where:
• L denotes a coherence length of said light source;
• d denotes a wall thickness of said plano-convex optical member;
• and nopt denotes a refractive index of said plano-convex optical member.