Patent ID: 7706078

Claim:
A laser light irradiation apparatus comprising: a laser oscillator; a beam expander optical system having a zoom function, wherein the beam expander optical system includes a first lens, a second lens, and a third lens in order in a traveling direction of laser light emitted from the laser oscillator; a lens disposed between the laser oscillator and the beam expander optical system; and a mechanism to change a distance between the first lens and the second lens in order to expand or reduce a beam diameter of the laser light, wherein the third lens is cooperated with the second lens to make the laser light parallel, and wherein, when an emission point of the laser oscillator is a first conjugate point, a point at which an image at the first conjugate point is formed through the lens disposed between the laser oscillator and the beam expander optical system is a second conjugate point, a distance between the lens, disposed between the laser oscillator and the beam expander optical system, and the second conjugate point is B, a focal length of the first lens is f, and a distance between the lens, disposed between the laser oscillator and the beam expander optical system, and the first lens is X, X satisfies X=B−|f|.