Tham khảo tài liệu 'recent optical and photonic technologies part 5', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 6 Terahertz-wave Parametric Sources Shin ichiro Hayashi1 and Kodo Kawase1 2 1RIKEN 2Nagoya University Japan 1. Introduction Terahertz waves are the electromagnetic radiation whose frequency ranges from millimeter waves to the far infrared shown in Figure 1. While both sides of this range have had a long history of research and development leading to already commercially available sources detectors meters and many additional devices the terahertz wave range is still in its infancy representing the last unexplored part of the electromagnetic spectrum between radio waves and visible light. This delayed development was mainly caused by the difficulty of producing reliable and strong terahertz wave generators as well as the unavailability of sensors that can detect this unusual radiation. Technology extrapolation from both neighboring sides has been facing difficult problems Up-conversion from the microwaves is inefficient due to the frequency being too high down-conversion from the infrared is limited by the energy gaps. 10 mm 1mm 100 m 10 m 1 m 100 nm 10 nm 1 nm . I__I I_lL_ I_I__I. Micro wave Terahertz wave infrared visible Ultra violet X-ray 1-------1-----T I I-------------------- --------1--------1 10 GHz THz 1 THz 10 THz 100 THz 1 PHz 10 PHz 100 PHz Fig. 1. A schematic showing the terahertz wave within the electromagnetic spectrum. In recent years terahertz wave sources have received considerable attention for use in many applications. Especially recent research using terahertz waves transmission imaging and fingerprint spectra have had an important contribution in the bioengineering and security fields such as in material science solid state physics molecular analysis atmospheric research biology chemistry drug and food inspection and gas tracing Tonouchi 2007 . There are several ways to generate terahertz waves. In the laboratory one of the most widespread processes is the optical rectification or photoconductive .
