1. Fiber
and Particle Engineering Laboratory, University of Oulu, P.O. Box 4300, FI-90014, Oulu, Finland
2. Fiber
and Polymer Technology, Royal Institute of Technology, SE-10044 Stockholm, Sweden
3. Optoelectronics
and Measurement Techniques Laboratory, Department of Electrical Engineering, University of Oulu, FI-90014, Oulu, Finland
4. Department
of Chemistry, University of Oulu, P.O. Box 3000, FI-90014, Oulu, Finland
5. Department
of Fiber and Polymer Technology, Wallenberg
Wood Science Center, Royal Institute of Technology, SE-10044 Stockholm, Sweden