Patent Document ID: 8441532
Application ID: 12391585
Patent Status: 1

Claim One:
1. A method of measuring a shape of a specular reflective surface, the method comprising: positioning a specular reflective surface to be measured at a measurement plane; positioning a target having a surface on which a pattern is displayed adjacent to and facing the specular reflective surface; positioning a recording device at an imaging plane adjacent to and facing the specular reflective surface to receive a reflection on the specular reflective surface of the pattern on the target; recording an image of the reflection at the imaging plane with the recording device; determining positions of a plurality of points on the specular reflective surface relative to the measurement plane; determining a first relation between feature positions on the image of the reflection and feature positions on the pattern; and determining the shape of the specular reflective surface from a second relation involving a surface profile of the specular reflective surface and the first relation using the positions of the plurality of points as an initial condition; wherein the second relation in one dimension has the form: ⅆ z ⅆ x = u ⁢ ⁢ x - t ⁡ ( u ) + z 1 + u 2 ⁢ ( t ⁡ ( u ) - z ) 2 + x 2 + x + u ⁡ ( t ⁡ ( u ) - z ) wherein z is the surface profile in a direction perpendicular to the measurement plane, dz/dx is the derivative of the surface profile, x is a direction parallel to the measurement plane, α=ArcTan(u) is the angle between a vector in the direction of the reflected light and the measurement plane, t(u) is the first relation and u = z p - z x p - x ; where (xp,zp) is a location of a center of projection of the reflection onto the imaging plane.