| 摘要 |
PURPOSE: To prevent the thermal expansion of a stand by the thermal influence from optical parts and the change of a laser beam path by controlling the operation of a force cooling means in accordance with the detection signal of a temp. detecting means. CONSTITUTION: A mask 4, mirror 5 and objective lens 6 which are the optical parts are heated by continuous irradiation with the laser beam and the temp. of the stand 2 itself is increased by the thermal influence thereof until a preset rising temp. is attained. A fan motor 14 is then operated in accordance with the detection signal from a temp. detector 11 and blasting toward radiation fins 12 is started. The blasting by a fan 13 is continued until the temp. of the stand 2 falls down to the lower limit temp. The fan motor 14 stops after the lower limit temp. is attained. As a result, the optical parts are maintained at a temp. at which the change does not arise in the laser beam path. |
