Terahertz wave has been used in many fields due to its unique characteristics. Recently, it is also widely
applied to analyze magnetic materials. However, new approaches have been required due to the need for more
efficient terahertz wave sources and the limitations of the analysis method using terahertz waves. In this thesis,
we propose two approaches to overcome the current issues in the field of nonlinear organic crystal as to develop
THz technology. We also propose a noble perspective in magnetic analysis of rare-earth trans-metal ferrimagnets
to improve our understanding in material with THz technology. The validity and versatility of the suggested
methods are confirmed with electrical and optical measurements, especially THz emission spectroscopy.
The first approach is control of refractive index by manipulating the bandgap to improve the phase-matching
condition in the near-infrared range. The refractive index and absorption, measured in the optical and the
terahertz range, indicated that the phase-matching condition was more improved in the near-infrared range. The
effect of the improved phase-matching condition was confirmed through terahertz generation. Furthermore,
based on the previous results, we developed new nonlinear organic crystal that can exhibit high efficiency in the
near-IR range.
The second approach is utilizing off-diagonal nonlinear components for efficient THz generation, including
suppressing or eliminating the self-absorption of organic crystals in the THz range. From this, the interaction
between phonons and THz waves was minimized and we can confirm the spectrum without absorption by
phonons in the below 4 THz.
The third approach is an analysis of magnetic properties of rare-earth transition-metal ferrimagnetic material
through energy-dependent measurements. We observed clearly different responses to external magnetic fields
according to the energy level and measured spin-glass-like behaviors by THz emission spectroscopy.