tailieunhanh - Recent Optical and Photonic Technologies_2

Tham khảo sách 'recent optical and photonic technologies_2', kỹ thuật - công nghệ, năng lượng phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 10 Terahertz Time-Domain Spectroscopy of Metallic Particle Ensembles Kenneth J. Chau University of British Columbia Canada 1. Introduction The terahertz THz frequency range is the region of the electromagnetic spectrum between the microwave and optical bands spanning from THz to 10 THz. Historically electromagnetic radiation in this frequency range has been inaccessible due to the lack of widespread electronic or laser-based radiation sources. Electronic radiation sources such as crystal oscillators are generally confined to operate at frequencies below 100 GHz while laser radiation sources are generally confined to operate at frequencies above 30 THz. In recent years the development of femtosecond lasers and quantum electronics have enabled a wide range of implementations to both generate and detect THz radiation 14 . One of the earliest and most widespread techniques is THz time-domain spectroscopy. THz timedomain spectroscopy is based upon the generation of a broad-band free-space THz transient which is detected using a femtosecond pulse to sample the THz electric field in the time-domain. THz spectroscopic measurements are performed by illuminating materials with a THz pulse and measuring the pulse after reflection from or transmission through the material. The electromagnetic properties of the material are inferred from changes in the amplitude and phase of the measured electric field pulse relative that of the incident electric field pulse. THz time-domain spectroscopy has been applied in transmission mode to characterize the THz-frequency optical constants of dielectrics and superconductors 5 8 15 16 and in reflection mode to characterize the reflection amplitude and associated phase change due to semiconductors such as InSb 6 and highly doped silicon 17 18 . The implementation of THz time-domain spectroscopy requires that the reflected transmitted THz pulse undergo measurable transformation upon interacting with the material spectroscopic measurements .