UV laser machining of wood

Wood was treated with lasers of 349- and 355-nm wavelength and 5- and 12-ns pulse width. First, holes were drilled in the wood, and high aspect ratio holes of 20-µm diameter and 5-mm depth were obtained within several seconds at 80 mW of output. The diameter of the holes was relatively uniform in the depth direction. Incising was then conducted on the wood surface at 667 holes/cm², which resulted in no damage of the surface texture nor visually recognizable machining marks. Holes drilled with the laser were deepest when the focal point of the laser was set at the surface of the wood. Hole diameter on the surface was about 20 µm, and heat affected zone surrounding the holes was not recognized. With the aim of increasing the machining speed, the same process was conducted using a 5 W device as opposed to a 80 mW device, and machining time was reduced to 1/500th of the original time. The energy required to drill a hole of the same depth was also reduced to 1/10th of the original energy. In this test, changing the focusing lens to alter the optical focusing parameters changed the shape of the holes in the depth direction. When cutting of wood was attempted under these conditions at a speed of 50 mm/s, a cutting width of approximately 20 µm at a thickness of several millimeters was achieved.