Determination of refractive index of softwood using immersion liquid method

Immersion liquid method is used to determine refractive indices of wood material. An integrating sphere setup is used to measure optical transmission of liquid containing small wood particles. Sweeping the refractive index of the liquid affects its transmission properties through light scattering caused by refractive index mismatch between solid wood particles and the liquid. The refractive index of the solid material is obtained by finding the refractive index value of the liquid which provides the lowest scattering value (maximum transmission). The refractive indices of softwood samples were determined within a wavelength range from 500 nm to 800 nm. The refractive index of sapwood and heartwood were found to be 1.56 and 1.57 at sodium D-line (589.3 nm), respectively. Measured refractive index values will be used when building models of wood for optical simulations.