Chapters authored
Research on Hydrogen-Bonded Materials Using Terahertz Technology
We measured terahertz (THz) characterization of hydrogen-bonded materials using THz time domain spectroscopy (TDS) with a gas-cooling cryostat. The temperature and frequency dependencies of the complex dielectric constants of icy materials were measured over a wide temperature range. We checked the dielectric parameters of ices and gas hydrates using a mathematical model. Ice exhibits increasing absorption with frequency in the THz range because of the low-frequency tail of the infrared-absorption band. This behavior is also observed in gas hydrates. The parameters describing the frequency dependence of ε″ are treated as functions of temperature. From the THz spectroscopy on gas hydrates, we showed that the dielectric constants of the gas hydrates in the THz range can be analyzed using methods for ice. The complex dielectric constants in the THz range contribute to the infrared polarization and phonon absorption of the water molecules on the hydrogen-bonding matrices, so we suggest that THz-TDS is useful for physical and chemical studies of gas hydrates.
Part of the book: Terahertz Spectroscopy
High-Brightness and Continuously Tunable Terahertz-Wave Generation
One of the interesting frequency regions lies in the “frequency gap” region between millimeter wave and infrared, terahertz (THz) wave. Although new methods for generating terahertz radiation have been developed, most sources cannot generate high-brightness (high-peak-power and narrow-linewidth) and continuously tunable terahertz waves. Here, we introduce the generation of high-brightness and continuously tunable terahertz waves using parametric wavelength conversion in a nonlinear crystal; this is brighter than many specialized sources such as far-infrared free-electron lasers. We revealed novel optical parametric wavelength conversion using stimulated Raman scattering in lithium niobate as a nonlinear crystal without stimulated Brillouin scattering using recently developed microchip Nd:YAG laser. Furthermore, we show how to optimize the tuning curve by controlling the pumping and seeding beam. These are very promising for extending applied research into the terahertz region, and we expect that this source will open up new research fields such as nonlinear optics in the terahertz region
Part of the book: High Power Laser Systems