Method and apparatus for characterization of optical systems

A method, comprising:

• using optics having an optical axis to project an image of a reticle having more than one periodic feature therein;
• detecting an interference pattern in the image of the reticle substantially simultaneously at multiple locations and in a direction coaxial with the optical axis;
• and
• analyzing the interference pattern to obtain characterization of the optics.

A method, comprising:

• illuminating more than one periodic pattern in an object plane of an optical system;
• using the optical system to image the periodic patterns onto an image volume;
• and
• analyzing an interference pattern in an image of the periodic patterns formed within the image volume, whereby optical system characteristics are determined from the interference pattern.

An apparatus, comprising:

• an optical system;
• illumination means for projecting an image of a reticle having more than one periodic feature thereon within a volume of image space;
• means for detecting interference patterns in the image at different locations comprising different depths of focus within the volume of image space;
• and
• means for analyzing the interference patterns and determining optical system imaging characteristics.