Abstract

Laser apparatus for eroding a surface comprises means to select and control the shape and size of the area irradiated by each pulse of laser energy without varying the energy density of the beam. By varying the size of the irradiated area between pulses, some regions of the surface may be eroded more than others and so the surface may be reprofiled. The method and apparatus are suitable, inter alia, for removing corneal ulcers and reprofiling the cornea to remove refractive errors and also for reprofiling optical elements. In one embodiment the beam from the laser enters an optical system housed in an articulated arm and terminating in an eyepiece having a suction cup for attachment to an eye. The optical system includes a beam forming arrangement to correct an asymmetric beam cross-section, a first relay telescope, a beam dimensional control system and a second relay telescope. The beam dimension control system has a stop with a shaped window or a shaped stop portion and movable axially along a converging or diverging beam portion. An alternative beam dimension control system has a stop with a shaped window and positioned between coupled zoom systems. Mirrors, adjustable slits and refractive systems may also be used. The laser is preferably an ArF Excimer laser. The apparatus may include a measurement device to measure the surface profile, and a feedback control system to control the laser operation in accordance with the measured and desired profiles.