Methods and apparatus may operate to position a sample, including an imager lens surface, within a processing chamber. Further activities may include creating a layer of reactive material in proximity with the imager lens surface, and exciting a portion of the layer of reactive material in proximity with the imager lens surface to form chemical radicals. Additional activities may include removing a portion of the material in proximity to the excited portion of the imager lens surface to a predetermined level, and continuing the creating, exciting and removing actions until at least one of a plurality of stop criteria occurs.