Terahertz birefringence and attenuation properties of wood and paper

The far-infrared properties of spruce wood are examined with a terabertz time-domain spectrometer. The solid wood is shown to exhibit both birefringence and diattenuation. The birefringence proper-ties are sufficient for construction of a quarter-wave plate operating at 0.36 THz, and a half-wave plate operating at 0.71 THz. The origin of the birefringence is attributed to preferential fiber orientation within the wood. Similar birefringence is observed in lens paper in which the fibers are preferentially oriented in one direction. (c) 2006 Optical Society of America.