Laser modulated scattering as a nondestructive evaluation tool for defect inspection in optical materials for high power laser applications

Laser modulated scattering (LMS) is introduced as a tool for defect inspection and characterization of optical materials for high power laser applications. LMS is a scatter sensitive version of the well-known photothermal microscopy techniques. Because only the defects of a super-polished optic generate a scattering signal, the technique is essentially a method for dark-field photothermal microscopy. Experimental results show that the technique (1) measures the local absorption properties of defects, contamination, and laser damage sites; (2) when used in conjunction with DC scattering, can differentiate between absorbing and non-absorbing defects; and (3) detects thermal transport inhomogeneities.