Examination of laser damage sites of transparent surfaces and films using total internal reflection microscopy

This paper describes total internal reflection microscopy (TIRM), a microscopic inspection technique useful in examining the laser-damaged surfaces of transparent samples. In this technique, the surface is illuminated from within the sample with a well-collimated polarized laser beam at an angle of incidence just greater than the critical angle. Since total reflection occurs, the illuminated region appears to be dark when viewed from outside the sample except for scatter caused by surface defects such as laser damage sites. We will describe two instruments used for TIRM inspection of samples. Finally, various damaged regions will be shown as they appear under TIRM inspection and under Nomarski microscopy. It will be seen that the two techniques are complementary, and that, on highly polished surfaces, TIRM shows somewhat more detail than does Nomarski microscopy. All of the damage sites shown will be the result of 1.06-pm, 1-nsec irradiation of fused silica or BK-7 surfaces.