Geometric measurement system and method of measuring a geometric characteristic of an object

A system for determining at least one geometric characteristic of an object having at least one surface that passes a substantial amount of light therethrough, the system comprising:

• a light source;
• a wavefront sensor;
• an optical system adapted to deliver light from the light source to a surface to be measured of the object, and to deliver light from the surface to be measured of the object to the wavefront sensor, whereby a portion of the light delivered to the surface to be measured passes through the object to a surface of the object that is not being measured;
• a translator adapted to adjust relative positions of the light source and the surface to be measured such that, at each relative position, the light from the light source is delivered onto a sub-region of the surface to be measured, and light from the sub-region of the surface to be measured is delivered to the wavefront sensor, the translator adjusting the relative positions such that adjacent sub-regions have an overlap portion;
• and
• a processor adapted to stitch together wavefronts measured by the wavefront sensor for different sub-regions of the surface to be measured at the relative positions provided by the translator, including using derivatives of wavefronts in overlap regions, to construct a wavefront of light received from a measurement region of the surface to be measured,
• wherein the optical system includes a spatial filter adapted to block a majority of light from the surface of the object not being measured from reaching the wavefront sensor, and
• wherein the translator is also adapted to adjust a distance between the spatial filter and the surface to be measured of the object.

A method of determining at least one geometric characteristic of an object having a first surface and a second surface, the method comprising:

• (a) adjusting a positional relationship between a first surface of the object and a light source to illuminate a subregion of the first surface of the object, including at least one of:
• rotating the object with respect to the light source, rotating the light source with respect to the object, tilting the object with respect to the light source, and tilting the light source with respect to the object;
• (b) delivering light from the subregion of the first surface of the object to a wavefront sensor;
• (c) determining a wavefront of light received from the subregion of the first surface with a wavefront sensor;
• (d) repeating steps (a) through (c) for a plurality of different subregions spanning a measurement region for the first surface of the object, where adjacent subregions have an overlapping portion;
• (e) stitching together the wavefronts determined in each execution of step (c) including derivatives of the wavefronts in the overlapping portions, to construct a wavefront of light received from the measurement region of the first surface of the object;
• and
• (f) determining at least one shape parameter of the first surface of the object from the constructed wavefront.

A system for determining at least one geometric characteristic of an object, the system comprising:

• a light source;
• a wavefront sensor;
• an optical system adapted to deliver light from the light source to a surface to be measured of the object, and for delivering light from the surface to be measured of the object to the wavefront sensor;
• a translator adapted to adjust relative positions of the light source and the surface to be measured such that, at each relative position, the light from the light source is delivered onto a sub-region of the surface to be measured, and light from the sub-region of the surface to be measured is delivered to the wavefront sensor, the translator adjusting the relative positions such that adjacent sub-regions have an overlap portion, wherein the translator includes one of:
• means for rotating the light source, means for rotating the object, means for tilting the light source, and means for tilting the object;
• and
• a processor adapted to stitch together wavefronts measured by the wavefront sensor for different sub-regions of the surface to be measured at the relative positions provided by the translator, including using derivatives of wavefronts in overlap regions, to construct a wavefront of light received from a measurement region of the surface to be measured.