ROLE OF HELICAL WIGGER ON THZ RADIATION GENERATION FROM FREE ELECTRON LASER

Abstract

Terahertz (THz, or be called T-ray) wave refers to the electromagnetic wave with the frequency between 0.1 THz (1THz=1000GHz) and 10 THz or wavelength from 30 μm to 3000 μm. In the frequency domain, this region of electromagnetic wave is located between microwave and infrared wave. Different from the great successes in the microwave and infrared light wave, the applications of THz wave are much less investigated in the past few decades. Recently, it has recently been demonstrated that THz wave exhibits several unique features in terms of applications. For example, THz wave can easily penetrate fabrics and plastics, but it will be reflected by metallic materials. Thus, THz wave has a promising application in security screening. In order to realize the applications of THz wave, the compact, efficient, and high power THz sources have become a critical element of researches in THz wave. In this dissertation I have developed the formalism for tunable coherent terahertz radiation generation from a relativistic electron beam, modulated by two laser beams, as it passes through a helical wiggler. The lasers exert a ponderomotive force on beam electrons, and modulate their velocity. In the drift space, velocity modulation translates into density modulation. As the beam bunches pass through the wiggler, they acquire a transverse velocity, constituting a transverse current that acts as an antenna to produce coherent THz radiation. .