IRRADIATING METHOD FOR LASER

PURPOSE:To make the focal plane of irradiated laser coincident always with the surface of an article despite the change in the diameter of the article by converting the laser to laser having an annular focus and irradiating the laser thereof to the article. CONSTITUTION:Laser 1 having a circular section is reflected by a circular conical mirror 11 and is conducted to a curved reflecting mirror 13. The laser 3 reflected by the mirror 13 is shaped to a torus-shaped beam parallel approximately with a cylindrical article 6 or 7 so as to form the focal plane in the position determined by the radius R of curvature of the mirror 13. The laser 3 is relfected by a relfecting mirror 12 of a circular conical bore provided on the optical path thereof and is irradiated to the outside circumferential surface of the article 6 or 7 from the direction normal thereto. During this time, the installation position X of the mirror 12 is moved axially, by which the position of the focal plane can be regulated as desired. As a result, the focal plane of the laser light is matched always to the inside and outside surfaces of the cylindrical article and the laser worked layers of stable film thicknesses are obtained.