Laser beam focusing apparatus and method for focusing a laser beam

摘要

A hollow tube having a pair of openings which have their respective different diameters and are opposed each other is prepared. Then, a pulsed laser beam is introduced into the hollow tube from the larger opening thereof and then, reflected multiply on the inner wall surface of the hollow tube. The introduced pulsed laser beam is focused during the traveling for the smaller opening of the hollow tube to generate a focused laser beam. The thus obtained focused laser beam is output from the smaller opening of the hollow tube.