Wavelength dependence of machining performance in UV-, VIS- and NIR-laser cutting of wood

Cutting of wood using short-wavelength (266-, 355-, 532-, and 1064-nm) lasers was carried out and wavelength dependence in relation to machining performance and post-processing appearance was investigated. We found that a 355-nm-wavelength laser achieves the greatest machining performance. The variation in machining performance between different wavelengths was due to the different light absorptances of the woods: when we measured the spectral reflectance of the woods, we found that the greater the machining performance for a wavelength, the lower its reflection of light (and thus the greater its absorption). Assuming that the absorption of ultraviolet wavelength of 355 nm by wood is due to lignin, a lignin-free cellulose board was prepared for further investigation, and the same machining and measurements were conducted. The results showed that machining progresses well via the absorption of laser light by lignin at the ultraviolet wavelength of 355 nm. On the other hand, when this cellulose board was impregnated with phenolic resin, there was high absorption of light between the ultraviolet range and wavelengths near 600 nm, machining progressed well at wavelengths of 355 and 532 nm.