Abstract
This thesis studies a laser-excited wire antenna (LEWA) that generates radiation covering radio to THz frequencies. The radio wave was produced from a LEWA with its laser-excited tip biased at an anode voltage of +500 V. When irradiated using a laser pulse with 42 mJ energy in a 7 ns pulse width, the LEWA generated radiation power three to four orders of magnitude higher than that generated by a direct laser-excited antenna without a biased voltage. The radiation power scaled with the square of the laser-induced photocurrent between the antenna tip and anode (800 A in our case). With a higher biased anode field and shorter-wavelength excitation laser, this antenna had a potential to reach MW-GW radiation power in a microwave or even in a millimeter-wave spectrum. The microwave LEWA was driven by a Nd:YAG laser amplifier, producing 40 mJ pulse energy in a 460 ps pulse width. We installed the LEWA in front of an S-band metal waveguide, which functions as a spectral filter to pass and reject the radiation above and below the cutoff frequency of the dominant TE10 waveguide mode with a cutoff frequency of 2.08 GHz. Using a ring antenna, we measured 1.7 and 2.6 GHz microwave signals before and after the waveguide, respectively. When the wire was irradiated by a mode-locked Ti:sapphire laser with a 160 fs pulse width focused to 280 GW/cm2 intensity on the wire, we detected THz radiation with a 3 THz bandwidth, reaching the detection limit of our electro-optic sampling system. The amplitude of the detected THz signal was comparable to that generated by a ZnTe emitter under the same experimental condition. Based on the successful demonstration of the LEWA, we further propose the use of the compact and highly efficient LEWA to replace the bulky and high-cost RF system for a particle accelerator. With a conventional S-band photoinjector having a quality factor of ~10000, an S-band MW-class LEWA resonantly coupled to the S-band photoinjector can generate ~ 100 MV/m field for particle acceleration in about 35 ns time. We further design an ultra-compact superradiant free-electron laser (FEL) driven by such a LEWA photoinjector. Our simulation study shows that it is possible to generate MW-level radiation power at THz frequencies from the FEL with a ~1% prebunched beam from the proposed LEWA photoinjector.