Beatwave Photoinjector as THz Source

Attaining high peak fields at terahertz (THz) frequencies is among the highest priorities among the common R&D goals of the DOE-NSF-NIH triad. However, THz science and technology have been underdeveloped because of the unavailability of effective and affordable THz sources. The few THz facilities currently available are based on free electron lasers (FELs), which are too bulky, expensive, and inefficient to serve as commercial sources. This project will design, build, and test a compact, pulsed THz source ¿ a Cherenkov radiator comprising a capillary dielectric tube driven by an over-focused electron beam from a low-energy laser-driven photoinjector ¿ that can deliver at least 100 kW peak power. The photoelectrons are produced from a metal cathode illuminated with a sub-picosecond laser. In Phase I, feasibility was demonstrated for the transport of an over-focused, low-loss, electron beam of 0.15 MA/cm2 of peak current density and a few MeV of energy. Microjoule levels of radiated THz energy were produced using a pulsed DC or RF gun and a capillary tube. In Phase II, the development of the THz source will be completed. An in-vacuum THz radiator will be designed and fabricated as an inset for a conventional photoinjector, complemented by laser multiplexing and a THz radiation detector unit. Then, experiments will be conducted to demonstrate (1) beam alignment and transport of an over-focused, high-density electron beam; and (2) the measurement of THz radiation in single-bunch and multi-picosecond, microbunch modes. Commercial Applications and Other Benefits as described by the awardee: The terahertz radiator unit should find application for various types of photoelectron guns, including DC, RF, and DC-RF photoinjectors. The compact THz source should be a powerful tool for myriad applications in physics, material science, chemistry, imaging, spectroscopy, biology, medicine, environmental monitoring, homeland security, defense, and communications.