LIGHT CONDENSING OPTICAL SYSTEM, LASER PROCESSING METHOD AND APPARATUS, AND METHOD OF MANUFACTURING FRAGILE MATERIAL

摘要

A condensing optical system having a condensed light spot with a small size and a large focal depth without causing a problem of a decrease in intensity of the condensed light spot or discontinuity of an intensity distribution in front and rear areas of a focal position is provided. The condensing optical system that condenses a laser beam generated by a laser source at a predetermined focal length is designed to satisfy Expressions (a) to (d), thereby producing 3rd and 5th spherical aberrations:
(a) |Z 8 | ‰¥ 0.1» or |Z 15 | ‰¥ 0.05», (b) Z 8 /Z 15 ‰¥ 3 or Z 8 /Z 15 < 1, (c) |Z 8 | < 1.4», and (d) |Z 15 | < 0.5»,
where » is a wavelength, Z 8 is an 8th coefficient of coefficients of the Zernike fringe polynomial of wavefront aberration corresponding to a 3rd order spherical aberration, and Z 15 is a 15th coefficient of the coefficients of the Zernike fringe polynomial of wavefront aberration corresponding to a 5th spherical aberration.