| 摘要 |
Ultrashort pulse laser processing bores, welds or cuts objects (work pieces) by converging ultrashort laser pulses by a lens on the objects (work pieces) positioned at the focus and heating small spots or narrow lines on the objects (work pieces). Shortage of a focal depth of the lens prevents the ultrashort pulse laser processing from positioning the object (a work piece) and forming a deep, constant-diameter cylindrical hole. Z-parameter is defined to be Z = 2fc Š t/ Š i<2>, where Š t is a FWHM pulse width of the ultrashort pulse laser, Š i is a FWHM beam diameter of the ultrashort pulse, f is a focal length of the lens and c is the light velocity in vacuum. Selection of an optical system including a diffraction-type lens which gives the Z-parameter less than 1 (Z < 1) prolongs the focal depth. Expansion of the focal depth facilitates the positioning of objects (work pieces) and enables the ultrashort pulse laser apparatus to bore a deep, constant-diameter cylindrical hole. |
