| 摘要 |
PURPOSE:To prevent an acoustooptical medium from the generation of dew condensation independently of atmospheric temperature, humidity, etc. by setting up the temperature of an acoustooptic modulator to a temperature higher than a dew point when the temperature of the dew point exceeds a prescriber temperature. CONSTITUTION:A Peltier element 18 is fitted to a piezo-electric converter 21 and controlled by a control device 17 to keep the temperatures of the converter 21 and the acoustooptical medium 20 at prescribed values. The temperature of the dew point is calculated on the basis of the output signals of a temperature sensor 15 and a humidity sensor 16. Since the Peltier element 18 is driven and temperature of the modulator 4 is controlled so that the temperature difference between the temperature of the converter 4 and the dew point temperature is not reduced less than a previously set up prescribed temperature, the surface of the modulator 4, especially the medium 20, can be prevented precisely from dew condensation.
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