Total internal reflection microscopy: a surface inspection technique.

Structure at and near the surface of a transparent sample or in a film on a transparent substrate can be observed by illuminating the sample from within using a well-collimated polarized laser beam incident at an angle equal to or greater than the critical angle of the sample material and examining the air side of the surface using an optical microscope. Although the technique is similar to dark-field microscopy, additional information can be obtained here concerning the size and depth of scattering sites on or near the surface. This technique, total internal reflection microscopy (TIRM), is complementary to phase contrast (Nomarski) microscopy. Two TIRM microscopes are shown, one of which is used as an attachment to a commercial Nomarski microscope and the second of which is used in laser damage measurements. This surface inspection technique had been used to study surface polishing and cleaning methods, laser damage nucleation sites, ion milling of optical surfaces, and thin film inclusions. A biological application for liquid medium studies is suggested. A description of the electric fields present at and near the air sample interface is given.