Effect of Beam Quality on Single Pulse Laser Drilling

摘要

The Nd:YAG laser drilling process involves many complex interactions that are determined by the properties of the material being drilled and the characteristics of the drilling pulse. The properties of the drilling pulse which are known to be of importance are its wavelength, energy, temporal profile (pulse length and shape) and its spatial profile (focussed spot size and spatial energy distribution). The spatial energy distribution within the focussed spot is partially determined by the beam quality, described by the beam propagation factor, M{sup}2. Although high beam quality (low M{sup}2) is generally accepted to be desirable in most laser drilling applications, its effect on laser drilled holes has not been fully quantified. This paper discusses the importance of beam quality, and quantifies its effect on the depth and entrance diameter of laser drilled holes in aluminium and titanium. Experimental results for single pulse drilling are presented, which determine the hole depth and entrance diameter as functions of beam quality. Physical explanations are proposed to explain the observations. The effect of beam quality on the sensitivity of the drilling process to changes in material thickness and its effect on the size distribution with arrays of holes are described. Holes drilled in aluminium and titanium with varying energies and pulse durations are compared for a number of different beam qualities.