System and method for in-situ particle contamination measurement using shadowgrams

A method for measuring particle contamination on an optical surface comprising:

• illuminating a detector with light provided by a non-coherent light source, the light traveling through a path that includes the optical surface;
• identifying shadows on the detector, the shadows being indicative of particle contamination of the optical surface;
• and
• estimating a particle contamination level for the optical surface based on contrast levels of the shadows identified on the detector,
• wherein the optical surface is a first of a plurality of optical surfaces and wherein the detector is illuminated with light from the non-coherent light source traveling through a path that includes the plurality of optical surfaces, the method further comprising changing a position of the non-coherent light source to distinguish shadows caused by particle contamination on the first of the optical surfaces from shadows caused by particle contamination on other optical surfaces of the plurality, and
• wherein the shadows on the detector are comprised of a first set of shadows indicative of particle contamination on the first of the optical surfaces, and a second set of shadows indicative of particle contamination on a second of the optical surfaces,
• wherein changing the position of the non-coherent light source changes a position of the first set of shadows to a first changed position on the detector and changes a position of the second set of shadows to a second changed position on the detector, and
• wherein the method further comprises:
• identifying the first and second changed positions to distinguish the first set of shadows from the second set of shadows;
• estimating a particle contamination level for the first of the optical surfaces based on contrast levels of shadows of the first set;
• and
• estimating a particle contamination level for the second of the optical surfaces based on contrast levels of shadows of the second set.

A method for measuring particle contamination on an optical surface comprising:

• illuminating a detector with light provided by a non-coherent light source, the light traveling through a path that includes the optical surface;
• identifying shadows on the detector, the shadows being indicative of particle contamination of the optical surface;
• and
• estimating a particle contamination level for the optical surface based on contrast levels of the shadows identified on the detector,
• wherein shadows of greater contrast levels on the detector are indicative of larger size particles than shadows of lesser contrast levels, and wherein estimating the particle contamination level for the optical surface further comprises:
• comparing the contrast level of shadows on the detector with contrast levels in a calibration file to determine particle sizes associated with the shadows;
• and
• determining an average particle contamination level for the optical surface based on a number of particles within predetermined ranges of sizes.

A method of identifying defects on optical surfaces comprising:

• illuminating a detector with light provided by a non-coherent light source, the light traveling through a path that includes the optical surfaces;
• identifying shadows on the detector, the shadows being indicative of defects in the optical surfaces;
• and
• moving the non-coherent light source to distinguish different sets of shadows, wherein a first set of shadows is indicative of defects on a first of the optical surfaces and a second set of shadows is indicative of defects on a second of the optical surfaces.

A system for measuring particle contamination on an optical surface comprising:

• a non-coherent light source to illuminate a detector with non-coherent light traveling through a path that includes the optical surface;
• processing equipment to identify shadows on the detector, the shadows being indicative of particle contamination on the optical surface;
• and
• a particle contamination level analyzer to estimate a particle contamination level for the optical surface based on contrast levels of the shadows identified for the optical surface.

A system for measuring particle contamination on an optical surface comprising:

• a non-coherent light source to illuminate a detector with non-coherent light traveling through a path that includes the optical surface;
• processing equipment to identify shadows on the detector, the shadows being indicative of particle contamination on the optical surface;
• and
• a particle contamination level analyzer to estimate a particle contamination level for the optical surface based on contrast levels of the shadows identified for the optical surface,
• wherein the optical surface is a first of a plurality of optical surfaces, the system further comprising a light source controller to change a position of the non-coherent light source, the processing equipment to distinguish shadows caused by particle contamination on the first of the optical surfaces from shadows caused by particle contamination on other of the optical surfaces of the plurality based on movement of the shadows, and
• wherein the shadows on the detector include a first set of shadows indicative of particle contamination on the first of the optical surfaces, and a second set of shadows on the detector indicative of particle contamination on a second of the optical surfaces, and wherein a changed position of the non-coherent light source changes a position of the first set of shadows to a first changed position on the detector and changes a position of the second set of shadows to a second changed position on the detector,
• wherein the processing equipment identifies the first and second changed positions to distinguish the first set of shadows from the second set of shadows, and
• wherein the particle contamination level analyzer estimates the particle contamination level for the first optical surface based on contrast levels of shadows of the first set and estimates the particle contamination level for the second optical surface based on contrast levels of shadows of the second set.

A system for measuring particle contamination on an optical surface comprising:

• a non-coherent light source to illuminate a detector with non-coherent light traveling through a path that includes the optical surface;
• processing equipment to identify shadows on the detector, the shadows being indicative of particle contamination on the optical surface;
• and
• a particle contamination level analyzer to estimate a particle contamination level for the optical surface based on contrast levels of the shadows identified for the optical surface,
• wherein shadows on the detector having greater contrast levels are indicative of larger size particles than shadows of lesser contrast levels, and wherein the particle contamination level analyzer estimates- an average particle contamination level for the optical surface by comparing the contrast level of the shadows on the detector with contrast levels in a calibration file to determine particle sizes associated with shadows, the average particle contamination level for the optical surface being based on a number of particles within predetermined ranges of sizes.