Patent ID: 7157677

Claim:
A method for measurement of a two-dimensional intensity distribution of un-reflected laser light in a cross section, comprising the steps of: disposing an image pickup device in front of the cross section with respect to a direction of the un-reflected laser light incident on the cross section; disposing an intercepting unit in the cross section in such a manner as to intercept a part of the un-reflected laser light; picking up, by use of the image pickup device, a light and shade image indicating another intensity distribution of the un-reflected laser light which is partially intercepted by the intercepting unit; adjusting a focus of an optical system of the image pickup device in such a manner that a pattern of the resultant light and shade image satisfies predetermined conditions; and retracting the intercepting unit from an optical path of the un-reflected laser light, and measuring the two-dimensional intensity distribution of the un-reflected laser light in the cross section by use of the image pickup device.