Development Of Terahertz Radiation Sources for the Manipulation of Charged Particle Beams

Abstract

In this thesis the development of a source of terahertz radiation to be used for the manipulation of charged particle beams is presented and discussed. The source was designed to be a ‘travelling source’ of terahertz radiation. The terahertz radiation was emitted from the generation medium at a different time delay dependent on transverse position. This resulted in an effective surface phase velocity of the terahertz radiation at the crystal-air boundary which has been tuned to match particle beams with a wide range of velocities. The concept was initially tested using ZnTe as the generation medium and afterwards was adapted for use with LiNbO3 which is capable of producing larger terahertz electric fields. Effective surface velocities as low as 0.53 c have been measured which would be suitable for use with particle beams with energies of approximately 90 keV. Effective velocities of approximately equal to c for use with relativistic electrons with MeV or greater energies were also measured. The resulting surface wave effectively acted as a dispersion free travelling wave terahertz pulse over a distance which was dependent on the size of the pump pulse. A peak terahertz electric field of 27.1 kVm−1 was measured for an effective velocity of 0.53 c at a distance of 500 µm from the generation crystal. This field increased with reduced distance from the generation crystal, and it is possible for an order of magnitude improvement in the field values through the optimization of various parameters such as pump pulse duration and crystal temperature. Initial experiments using this terahertz source have been performed. One experiment utilized relativistic electron bunches from the VELA accelerator and another experiment involved non-relativistic, 100 keV, electrons from a photoexcited electron gun. The terahertz source was constructed in a vacuum chamber holding the 100 keV electron gun and photo-excited electrons have been measured passing through the interaction region. A number of effects were seen which are discussed and potential solutions proposed.

Date of Award	1 Aug 2019
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Wendy Flavell (Supervisor) & Darren Graham (Supervisor)