Characterization of Micron-Sized, Optical Coating Defects by Photothermal Deflection Microscopy

Information about the localized absorbing defects in optical thin films is required for a better understanding of laser-induced damage. Photothermal deflection microscopy offers a nondestructive optical diagnostic which can yield spatially resolved absorption data on simple and multiple-layer AR and HR dielectric coatings. This paper describes the computer-controlled apparatus used to generate absorption maps of dielectric thin films and an experiment in which a partial correlation between localized absorption sites and damage caused by nanosecond laser irradiation at 351 nm is established.

An absolute calibration of absorption for our measurement technique is presented here. Micron-sized absorbtive defects of Cu were introduced into our coatings to provide a means of calibration. Also presented here are some preliminary data on the modification of the absorption signatures measured by photo-thermal deflection as a function of the location of the defect within the coating layers.