THz spectroscopy of crystals
Description
Terahertz radiation band is crowded with spectral features of many fundamen- tal physical processes, such as molecular rotations, lattice vibrations, intraband transitions, superconducting gaps, etc. This property makes THz spectroscopy a powerful tool for the investigation of novel properties in new materials. In this thesis, I will start from the introduction of basic knowledge of mathematics and physics related to spectroscopy, including group and representation theo- ries, the character tables, classification of crystal lattices, 32 point groups, non- linear optics, infrared and Raman mode, optical activity, symmetry breaking, SOS, magnetic materials and various magnetic interactions. Then I will intro- duce different THz spectroscopy that are commonly used in our lab, focusing on different THz generation and detection methods, followed by the data anal- ysis processes for the extraction of various optical parameters of crystals. At last, I will discuss the three different kinds of materials that I studied during my Ph.D career: quantum paraelectric perovskite crystal KTaO3, chiral stuffed tridymite crystal BaCoSiO4 and ferrimagnetic spinel crystal FeMnO4. In the three materials, I will discuss THz field-induced SHG, THz Kerr effect, opti- cal non-reciprocity, symmetry operational similarity, optical activity and field induced birefringence respectively...