Fig. 1.

Schematic drawing of the experimental set-up. (A) The laser beam is focused through a microscopic objective (dark blue) within the tangential S2 layer of a single latewood fibre, in which cellulose fibril orientation is known to be parallel without an angle with respect to the fibre axis. Spectra are acquired from one position while changing the laser polarization direction in 3° steps (green lines) to investigate the dependency between cellulose fibril orientation and laser polarization direction. (B) The laser beam (microscopic objective, dark blue) is focused on a cross-sectional area (light blue) of embedded wood samples and an area of 40×40 μm scanned with the laser polarization direction (green line) always parallel to the tangential cell wall. By extracting spectra from cell wall areas parallel to the laser polarization direction (black rectangles) the angle between cellulose orientation and the laser polarization direction (α) can be predicted from the spectral characteristics of the cell wall layers in order to calculate the microfibril angle (MFA, θ=90–α).