Patent ID: 8338744

Claim:
A condensing optical system that condenses a laser beam generated by a laser source at a predetermined focal length, wherein the condensing optical system produces spherical aberration to increase a focal depth, and wherein Expressions (a) and (b) are satisfied as follows: | Z 8 |≧0.1λ or | Z 15 |≧0.05λ, (a) Z 8 /Z 15 ≧3 or Z 8 /Z 15 <1, (b) where λ 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, and Z 15 is a 15th coefficient of the coefficients of the Zernike fringe polynomial of wavefront aberration corresponding to a 5th spherical aberration.