Abstract: The known technique of marking (including machining) a workpiece by light energy, e.g. a pulsed laser beam, in order to create a pattern of marks on the workpiece is improved by converting a primary beam into a plurality of individual beamlets that are arranged in an array corresponding to the desired pattern and are each focused independently of the other beamlets. This independent focusing enables the size and energy density (and hence the marking effect) of each beamlet when it strikes the workpiece to be dependent on the relative location of the workpiece and the respective beamlet, while being independent of the size of the overall pattern. This feature enables variation of the ratio between the pitch between individual marks (which determines the size of the overall pattern) and the size of each mark, and hence selection of the optimum value of this ratio for a given situation.

Abstract: A method and apparatus is described for reducing the gas consumption rate by controlling the gas composition in a repetitively pulsed high pressure and/or high energy density TE CO.sub.2 laser. Detrimental gas species formed in the discharge are removed by chemical reaction in the gas phase and the reaction products are removed by a trap in a recirculator loop. In particular, the primary detrimental species is oxygen, the reducing gas added to remove this is hydrogen or deuterium and the resulting oxides of hydrogen or deuterium are removed by a molecular sieve.

Abstract: A method and apparatus for switching an infrared radiation signal laser beam in which a semiconductor, capable of transmitting the signal beam without damage, is provided and upon which the signal beam is incident at an angle which may preferably be Brewster's angle. The surface of the semiconductor is irradiated by a second laser beam which has a sufficiently high frequency to produce free carriers in the semiconductor and which has a sufficient radiation intensity and time duration to produce a free carrier density greater than the critical density for the signal beam resulting in substantially total reflection of the signal beam from the semiconductor surface. In particular, a pulsed CO.sub.2 laser beam which is incident on a polycrystalline n-type germanium semiconductor is reflected by irradiating the semiconductor with a pulsed ruby or Nd:glass laser beam.