| abstract |
Apparatus using a high power laser beam for heat treating a surface, such as a metal surface to harden the surface scans the metal surface which has been coated with radiation absorbing material such as carbon, so that the scanned areas of the metal surface are rapidly heated to above the critical temperature of the metal. Since the heating is very shallow, the heated surface cools very rapidly and so the surface is hardened. The intensity profile of a typical high power laser beam is not flat and so as the beam scans the metal surface, heating of the surface across the width of the beam is not uniform. A flat beam intensity profile is obtained in the present invention by dithering (spacially oscillating) the beam continuously as it sweeps the metal surface. The cross-section area of the dithered beam is substantially greater than the cross-section area of the initial beam from the high power laser and the intensity profile across the dithered beam can be tailored and is dependent upon the initial beam intensity profile and the configuration of the dither. The intensity profile across the dithered beam can be further tailored by blocking portions of the dithered beam. |