Scratch enhancement and measurement in periodic and non-periodic optical elements using digital holography

Scratch or flaw detection plays an important role in imaging optics and optical instrumentation. Even a minute scratch or crack can spoil coating and/or scatter incident light which causes irregularities/noise in the signal. Present paper describes use of digital holography for inspection of periodic and non-periodic optical elements for presence of any type of flaws like scratch, dust particles, irregularity etc. Digital image processing on numerically reconstructed wavefronts of the test samples provides enhanced image of the flaw. Various parameters of the flaws are measured. Experimental results of scratch on a glass plate and a lens and a thin hair on a grating and a mirror are presented.