Ultraviolet laser radiation (Ti: sapphire 4th harmonic) tuneable in the exciton absorption region of KI was used to produce near-surface excitation of potassium iodide samples on the stage of an atomic force microscope. Surface images with lateral resolution of ∼50 nm and vertical resolution of ∼3 nm have been recordedversusexposure to 5.9-eV light. Ultraviolet exposures in air were made both during AFM scanning and with the tip disengaged. Circular pits of a size dependent on uv intensity are formed quickly, followed by appearance of islands ascribed to potassium (oxidized), and finally formation of a rough eroded surface, which continues to develop after termination of the uv irradiation. Thallium doping slows the rate of erosion.