Lumonics Inc.

Robert K Brimacombe

Edward S Williams

John Reid

The problems of maintaining proper alignment of the mirrors of an excimer laser in the face of thermal and pressure distortions of the ends of the laser vessel and when replacing the mirrors after removal for cleaning are overcome by mounting the mirrors on a separate, fixed supporting frame that is not influenced by movement of the vessel ends. The mounts nevertheless serve to connect the mirrors to the respective vessel ends so as to seal the pressurized gases in the vessel interior from the exterior. This sealing connection is a yielding one that permits relative movement between the vessel ends and the mirrors and hence avoids affecting the alignment of the mirrors. The mounts also include provision for ensuring that, after removal and replacement, wedge shaped mirrors are correctly realigned in respect of rotation about the axis of the laser beam, and that the mirrors can be replaced with their reference surfaces in exactly the original plane.

Excimer laser assembly and an optic mount therefor

Purification of the gas mixture used in an excimer laser is carried out by cooling such mixture in a cryogenic trap to a temperature that is low enough that the lasting gas or gases (e.g. krypton, xenon, fluorine, hydrogen chloride) and the impurities are all substantially fully condensed. This temperature is nevertheless sufficiently high that the buffer gas (neon or helium or a mixture thereof) remains substantially all in gaseous form. The trap is then isolated from the laser vessel and the condensed gases therein are treated to remove at least the condensed impurities from the system. In a xenon chloride laser the condensed impurities can be effectively separated from the condensed laser gases by heating, i.e. differential distillation. After this has been done, the laser gases are returned to the laser vessel. In those instances in which such separation by differential distillation is not practicable, e.g. a krypton fluoride laser, some or all of the condensed lasing gas or gases is removed from the system together with the condensed impurities. Fresh charges of these lasing gases are then supplied to the laser vessel as required. The procedure is characterized by the fact that the buffer gas is retained and reused indefinitely. The method avoids the expense of having to periodically recharge the laser vessel with an entire fill of fresh buffer and lasing gases.

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Kanata, Canada

Robert K Brimacombe