CO2 laser interactions with wood tissues during single pulse laser-incision

Abstract

Incising is a technique used to improve fluid flow in impermeable woods during wood treatment processes. Previous studies relating to the laser-incision of wood have neglected many aspects such as detailed analysis of the anatomy of the wood, including consideration of tangential/radial faces and earlywood/latewood interactions with the laser beam. By considering wood anatomy, a complete investigation of the CO2 laser-incision processes is presented that yields new knowledge of laser beam interaction with growth rings when incising into tangential/radial faces, and the low-density earlywood and higher density latewood within the growth ring. Southern Yellow Pine, Radiata Pine, European Redwood and Beech, each having different bulk densities, were laser-incised using a 2 kW ROFIN CO2 laser with radiation in the far-infrared regime (10.6 μm). Microstructural characterisations were carried out to better understand the effect of CO2 laser-incision and its parameters on the depth, diameter and quality of the incised holes. The laser-incised hole shapes were found to be uniform in depth, however, the hole circularity was significantly affected by the presence of earlywood and latewood tissues. Maximum and minimum diameters of incised holes were measured in the Radiata Pine (~1.3 mm) and in the Beech (~0.7 mm), respectively. Similarly, for equal laser powers used, the maximum and minimum depths of laser-incised holes were measured in the European Redwood (~33 mm) and in the Beech (~25 mm), respectively, with the laser incident on the radial face of the samples. CO2 laser pulse duration had a greater effect on diameter and depth of incised holes when compared to laser power and showed that the CO2 laser pulse duration is a dominant parameter when designing CO2 laser-incision processes.