Optical characteristics of wood investigated by time-of-flight near infrared spectroscopy

A new optical measurement system, the main components of which are a diode-pumped solid state laser and avalanche photodiodes, was introduced to clarify the optical characteristics of wood from the viewpoint of time-of-flight near infrared spectroscopy. The sample thickness and the wavelength of input pulsed laser clearly influenced the transmitted time-resolved profile. The effective optical path length became 15 times longer than the sample thickness. The optical model based on the diffusion approximation to the radiative transfer equation proved to be useful for thick samples, which can be optically regarded as an ideal diffuser, although wood is a structural material with non-homogeneous cellular structure.