Sub-nanometer metrology of chirped phase masks by optical Moire

Optical Moire fringe formation between a linear and chirped phase mask has been investigated theoretically and experimentally and used to determine the chirp rate. Period difference determination down to similar to 0.4 nm is demonstrated using a 1080 nm period linear grating and a nominally 1 nm/mm chirped grating. Direct optical diffraction is also used to independently assess the chirp rate. (C) 1999 Elsevier Science B.V. All rights reserved.