Lens contamination preventive device of light-beam heater

摘要

A lens contamination preventive device comprises a gas jetting device for jetting out gas and a gas suction device for suctioning gas which are disposed to face each other with respect to an optical axis of light emitted through a lens. The gas jetting device and the gas suction device are disposed so as to form a layer of gas jet stream in the vicinity of a surface of the lens. The gas jetting device has a gas jetting port, a width of which is greater than a diameter of the lens. The gas suction device has a rate of suction greater than a rate of jet from the gas jetting device.