Experimental Study on Micro-faricated Terahertz Devices Using Convection Electrons

Abstract

For the last decade, terahertz waves have been the focus of many researches to lead to a diverse range of potential applications, such as bio-medical imaging systems, security inspection systems, material analysis systems, and high-data-rate communications systems. Though many types of terahertz components have been developed, e.g., terahertz antennas, filters, guides, and detectors, realistic terahertz applications remain rare due to the lack of powerful, efficient, practically sized, inexpensive, and stable terahertz sources which would fill the terahertz gap. While time-domain spectroscopy (TDS) systems are the main streams of terahertz sources due to the instant spectroscopic capabilities throughout the terahertz range, vacuum electronic devices (VEDs) have also garnered interest due to their high-power capabilities resulting from the high kinetic energy of their convection electrons. In this dissertation, 0.1 THz coupled cavities backward wave oscillator (CCBWO) is proposed and studied as preliminary research on terahertz VEDs, applying two-step LIGA as well as ultra nano CNC machining. The circuits are fabricated with less tolerance than a micron and the cold measurements are in excellent agreement with numerical simulation. All other components of the 0.1THz CCBWO system such as 12kV, 50mA electron gun, 2800gauss of PPM, 8% of band center frequency transmitting vacuum window, and -9kV depressed collector are designed, fabricated, and experimented and all the results match strongly to the design. All parts are assembled together and with the bias voltage at beam focusing electrode, desired perveance is observed in the beam test. 0.22THz staggered extended interaction oscillator is also investigated, focusing on the strong interaction even with relatively low voltage. In the half π phase shifted double grating resonator, The large fraction of the fundamental TE mode is longitudinally polarized, and it excites the intense plasma-terahertz wave coupling at the shallow grating, which enables highly efficient RF generation at a relatively low operating voltage. A particle-in-cell (PIC) simulation predicts that the half-period phase-staggered grating resonator generates 0.22 THz wave with output power exceeding 100 W and interaction efficiency of more than 15 % at a low beam acceleration voltage of 5.2 kV.