Pitchfork beam shaping for laser micorvia drilling

Abstract

Laser beam shaping allows redistribution of laser power and phase across the cross-section of the beam for drilling perfectly cylindrical holes. The main purpose of this paper is to show that pitchfork beams improve the microvia quality significantly. An optical system, which comprises three lenses, is designed using conventional diffraction analysis and ray tracing technique to transform a Gaussian beam into a pitchfork beam. The first two lenses are the phase elements through which a Gaussian laser beam is transformed into a super Gaussian beam. The ray tracing technique of geometrical optics is used to design these phase elements. The third lens is the transform element which produces a pitchfork profile at the focal plane due to the diffraction effect. Another aspect of this paper is to demonstrate a pinhole scanning power meter to measure the laser beam profile at the focal plane where the irradiance is very high. This measurement technique is used to verify the existence of the pitchfork beam at the high irradiance plane.