Dear Dr. Ashok Kumar U,

to measure the depth of micro scratch / dent on the polished surface without damaging the sample, you can use either a metallographic optical microscope with the possibility of measuring, by display, the Z axis focusing the bottom of the defect and then the surface of the substrate (precision +/- 1 µm). A more interesting alternative is represented by the use of a 3D no-contact optical profilometer with the possibility of obtaining very detailed maps of the surface morphology.

Best regards, Pierluigi Traverso

1) 3D no-contact optical profilometer, 2) Atomic force microscopy (AFM)