PhD defence by Mattias Rasmussen

Abstract

THz spectroscopy has proven itself to be an extremely effectively tool for characterizing the electrical and optical properties of novel materials, in a contact-free and nondestructive manner. Of the various THz generation and detections methods, the air-plasma-based methods have shown their prowess in generating and detecting highly intense THz pulses, which possess ultrashort pulse durations and ultrabroad bandwidths. These extreme THz pulses allow us to drive, and probe, nonlinear phenomena in various promising materials, such as graphene.

First, we study the well-known conical emission profile of the air-plasma THz generation method, and afterwards optimize our THz generation yield, by implementing a long-wavelength-driven air-plasma source.

Then, we introduce a solid-state-based alternative to the standard air-based THz detection method, which both provides improved detector performance, in terms of sensitivity and bandwidth, as well as enables us to directly measure the third-order nonlinearity of various materials.

Finally, we use our newly optimized THz generation and detection methods to study the nonlinear conductivity dynamics of graphene.

Supervisors

• Principal supervisor: Associate professor Binbin Zhou, Department of Electrical and Photonics Engineering, DTU
• Co-supervisor: Professor Peter Uhd Jepsen, Department of Electrical and Photonics Engineering, DTU

Evaluation Board

• Examiner: Professor Emmanuel Abraham, LOMA, Bordeaux University, France
• Examiner: Associate prof. David Cooke, McGill University, Canada

Chairman

• Professor Karsten Rottwitt, Department of Electrical and Photonics Engineering, DTU

Master of the Ceremony

• Associate prof. Edmund Kelleher, Department of Electrical and Photonics Engineering, DTU