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.

Abstract: An interferometer which comprises: (1) a single, coherent light source; (2) a first converging lens positioned on the optical axis of said coherent light source; (3) a beam-splitting arrangement positioned on said optical axis and spaced from said first converging lens by a distance greater than the focal length of said lens; (4) a second converging lens positioned on said lens; (4) a second converging lens positioned on said optical axis to receive and to focus the two beams emanating in use from the beam-splitting arrangement; and (5) a mirror arrangement positioned so that the beams focussed by said second converging lens impinge on the mirror system and so that the reflected beams are brought to intersect at a focal point and with a large angle between the principal rays of the two beams.

Abstract: Method and apparatus for examining a gemstone to determine a parameter thereof. A thin beam of light is projected onto the stone, the beam is moved relative to the stone, the position where the beam strikes the stone is sensed in a direction different from that in which the beam is projected, and a parameter is determined making use of information derived from such sensing.