Because of the contamination of the focusing mirror, the new type of welded joint breaks the traditional single focusing protective mirror mode, and applies the double drawer structure to make the inner and outer double protective mirrors. The inner and outer protective mirror drawers are independent of each other. When changing the outer protective mirror drawer, it will not interfere with the inner protective mirror drawer. In this way, the laser intracavity optical components can be better protected and the possibility of contamination of the focusing mirror can be greatly reduced.