Tuning and Focusing of Terahertz Radiation by DC Magnetic Field in a Laser Beating Process

The role of an external DC magnetic held in tuning the frequency and power of terahertz (THz) radiation and obtaining focused radiation is clarified in a beating process using two spatial-triangular lasers, where a nonlinear ponderomotive force acting on the electrons provides oscillating current in longitudinal and transverse directions. The transient transverse current oscillating at the beating frequency produces THz radiations in extraordinary mode, when the beating frequency of lasers matches the upper hybrid frequency for the resonant excitation. Based on the maximum momentum transfer with the application of density ripples, this scheme is realized with high efficiency (>;0.01), where the radiation may attain >;10⁷ V/cm held amplitude. This held can be further enhanced using higher amplitudes of density ripples and lasers fields. The consequences of any deviation from the triangular profile of lasers are also discussed by comparing the results with rounded triangular shape lasers.