Current projects

THz imaging and spectroscopy of wood

The project deals with three key aspects in THz technology, which can have a significant scientific impact on the understanding and characterization of properties of wood and cellulose based materials:


1. Anisotropic optical properties of wood

As the anisotropic optical properties of wood and cellulose correlate strongly with the cellulose microfibril orientation, THz radiation is an excellent medium for probing the spatial structure of wood relevant to mechanical properties. In light of a more efficient and advanced use of wood, a better insight into structure-mechanics relationships and into wood-water interaction are needed.


Zolliker P., Rüggeberg M., Valzania L. & Hack E. "Extracting Wood Properties from Structured THz Spectra: Birefringence and Water Content". IEEE Transactions on Terahertz Science and Technology, 2017, 7(6), 722-731.

Cao J., Rüggeberg M., & Zolliker P. Towards detection of helical orientated cellulose structures in wood using THz time-domain spectroscopy. In Proceedings of the 44th international conference on infrared, millimeter and terahertz waves IRMMW-THz 2019 (p. (2 pp.). Paris, France (2019).


2. THz imaging of wood

THz radiation is very sensitive to humidity and water. Due to the different spectral properties of water compared to those of the cell wall polymers it allows for a spatially and temporally resolved measurement of water content and diffusion in wood. Our goal is to build and use a spectroscopic THz imaging setup in a humidity controlled environment. This will allow performing advanced research by in-situ imaging of wood structure and diffusion processes.


Zolliker, P., Shalaby, M., Söllinger, E., Mavrona, E., & Hack, E. "Real-Time High Resolution THz Imaging with a Fiber-Coupled Photo Conductive Antenna and an Uncooled Microbolometer Camera", Sensors 2021, 21, 3757.


3. Exploring wood and cellulose based materials as THz devices

The strong anisotropic properties of wood mainly caused by the preferred orientation and inhomogeneous distribution of cellulose fibers motivates to synthesize cellulose based materials with tailored optical properties for THz devices (half wave plates, quarter wave plates, polarizers)


Zolliker, P., Mavrona, E., Hack, E., Markus Rüggeberg, M., Zeng, Z., Siqueira, G., &

Nyström, G. "Wood: base material for optical elements for terahertz waves?" In 2020 45th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz), 2020.

Zeng, Z., Mavrona, E., Sacré, D., Kummer, N., Cao, J., Müller L., Hack, E., Zolliker, P. & Nyström, G. "Terahertz Birefringent Biomimetic Aerogels Based on Cellulose Nanofibers and Conductive Nanomaterials", ACS Nano 15 (4), 7451-7462, 2021.

External funding:

SNF project 200021_179061 "Revealing key properties of wood and cellulose with spectroscopic THz imaging"


Contributors and collaborators

Peter Zolliker, Elena Mavrona, Jingming Cao, Daniel Sacré, Laboratory for Transport at Nanoscale Interfaces, Empa

Markus Rüggeberg, Institute for Wood Technology, TU Dresden

Ingo Burgert, Wood Materials Science Laboratory, Institute for Building Materials, ETH Zürich

Gustav Nyström Laboratory for Cellulose & Wood Materials, Empa



Selection of past projects

THz Spectroscopy on phase transition of VO2

The optical properties of the VO2 films were measured using a THz time-domain spectrometer in the transmission configuration to monitor the semiconductor-to-metal phase transition as a function of the sample treatment with extensive γ-irradiations.

in collaboration with Itani Madiba, University of South Africa (UNISA),  Pretoria, South Africa and Artur Braun, High Performance Ceramics Lab, Empa (2016-2019)



Mechanical contact of skin and textiles: THz imaging and modelling of the interface

In diesem Projekt soll mit bildgebenden Verfahren die Kontaktstelle zwischen Haut und Materialoberfläche untersucht werden. Um eine genügende Auflösung zu erreichen werden Experimente aufgebaut, die von der Laserinterferometrie inspiriert sind. Zusätzlich werden Auswerteverfahren entwickelt, um den Feuchtegehalt, die Oberflächenstruktur und die Kontaktfläche sowie deren druckabhängige Veränderung quantitativ zu ermitteln. Möglich wird dies durch die Verwendung von unschädlicher Wärmestrahlung, sogenannten Terahertz-Wellen, die eine Wellenlänge im Bereich von 0.1-0.5 mm haben. Diese Strahlung kann Textilien durchdringen und wird von der Haut je nach Feuchtegehalt reflektiert oder absorbiert.
SNF Project in collaboration with Erwin Hack and Lorenzo Valzania, Laboratory for Transport at Nanoscale Interfaces, Empa, and Prof. Th. Feurer, University Bern (2015-2019)


THz Holography

Exploration of digital holographic for Terahertz imaging transmission and reflection. A Quantum Cascade Laser  as well as  a high-power continuous wave (CW) laser are used as THz sources together with a high resolution (640×480 pixel) uncooled micro-bolometer array as imaging device. Wave propagation to parallel and non-parallel planes is used to reconstruct the objects. Synthetic aperture methods are applied for resolution enhancement. We aim for a lateral resolution of about 100 μm and a relative phase sensitivity of about 0.5 rad corresponding to a depth resolution of 5-10 μm.

 In collaboration with Erwin Hack, Laboratory for Transport at Nanoscale Interfaces, Empa (2013-2015)



Realistic visualization of material surface appearance on a handheld device

(as project leader)

CTI project in collaboration with X-Rite Regensdorf (2012-2013)


Psychometric Scaling

(as principal investigator)

PhD project for Matthias Scheller Lichtenauer under supervision of Prof. J. Giesen

- Measurement and Modeling of Multi-Attribute Psychometric Scales

- Psychometric Scaling of Dynamic Multi-attribute Stimuli

SNF funded project in collaboration with University of Jena (2010-2013)




Bestimmung papierabhängiger Parameter zur Anpassung digitaler Druckdaten

(as collaborator)

CTI project as a collaboration of The Media Technology Lab with Ugra, St. Gallen 2007 - 2009


Gamut Mapping as Optimization Problem

(as principal investigator)


PhD Project for Zofia Baranczuk under supervision of Prof. J. Giesen

funded by Hasler foundation in collaboration with Universität Jena (2007 - 2010)


Einbau einer Kalibrationsmethode zur Linearisierung des Photopapiers

(as project leader)

funded by Swiss Imaging Technologies, Regensdorf (2004) in a collaboration with Media Techonolgy Lab at Empa

Neural networks in photofinishing

(as industry collaborator)

KWF Project (now Innosuisse) with Gretag Imaging and ETH Zürich (Prof. G. Tröster) for PhD work of Michael Kocheisen with (1994-1997)


High Tc Superconductors

(as Postdoc)

Postdoc projects "Analyse structurale sur poudre par la radiation synchrotron aux rayons X et par la diffraction neutronique" and "Détermination des structures en utilisant l'effet de la diffraction anomale"

at Brookhaven National Lab in collaboration with University of Geneva funded by SNF (1987-1989)


Metall hydrides

(as PhD student)

PhD Project "Synthèse, structure et propriétés des hydrures métalliques ternaires Mg2FeH6, Mg2CoH5 et Mg2NiH4"

at University of Geneva under supervision of Prof. K. Yvon, partially financed by SNF/NEFF, (1983 - 1987).