Patent ID: 6118471
Filing Date: 2000-09-12
Classification: G02B,H01S,H04N

Abstract:
A beam diameter control method for changing a diameter of a focused laser beam, comprising:applying an optical path difference to only a portion of light flux of the laser beam and not to the remainder of the light flux of the laser beam, the optical path difference being equal to or more than a coherence length of the laser beam; andfocusing all of the laser beam, including the portion of the light flux to which the optical path difference has been applied and the remainder;whereby the diameter of the focused laser beam is expanded, andwherein the optical path difference is defined by one of:a difference in the optical path length traveled by the portion and the remainder of the light flux, and(n-n.sub.0)t, where n is a refractive index of a transparent member through which the portion of light flux passes, t is a thickness of the member, and n.sub.0 is a refractive index applicable to the remainder of the light flux.