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
One of the most notable frequency regions in terms of research currently lies in the ‘frequency gap’ region between microwaves and infrared: terahertz wave. Although new methods for generating and detecting terahertz wave have been developed, few detectors operating at room temperature are able to capture low-energy terahertz beams. Here we introduce the optical heterodyne measurement (nonlinear frequency up-conversion detection) of terahertz wave using parametric wavelength conversion in a nonlinear crystal; this has better sensitivity than many commonly used thermal detectors such as pyroelectric detectors. Additionally, optical heterodyne techniques allow the beams of terahertz wave to be visualized and their frequency and intensity determined directly as visible light. These are very promising for extending applied researches into the terahertz region, and we expect that these will open new research fields such as wireless information communications or non-destructive inspection in the terahertz region.
Part of the book: Terahertz Technology