Single-material waveplates for pupil polarization filtering

An optical inspection system, comprising:

• a light source to emit ultraviolet light to illuminate a target;
• an objective lens to collect ultraviolet light scattered from the target;
• a plurality of single-material gratings to convert a polarization of the ultraviolet light scattered from the target from an elliptical polarization that varies spatially across a collection pupil to a linear polarization that is uniformly oriented across the collection pupil, wherein;
• the plurality of single-material gratings has phase retardation that varies spatially across the collection pupil in accordance with the elliptical polarization,
• the plurality of single-material gratings comprises a first one-dimensional grating and a second one-dimensional grating,
• the first one-dimensional grating has a duty cycle that varies spatially across the collection pupil and an orientation that varies spatially across the collection pupil, and
• the second one-dimensional grating has a duty cycle that varies spatially across the collection pupil and an orientation that varies spatially across the collection pupil;
• and
• a linear polarizer to filter out the ultraviolet light having the linear polarization,
• wherein the first one-dimensional grating and the second one-dimensional grating are disposed between the objective lens and the linear polarizer.