Search for a command to run...
The Terahertz (THz) region in the electromagnetic (EM) spectrum is defined between 0.1 and 10 THz, which lies between the microwave and optical domains. For more than half a century, the THz domain was colloquially known as the THz gap due to a lack of technologies that can help explore this region's potential. The THz technology has matured over the last few decades to the extent that it can be implemented to explore scientific and industrial applications. In general, the THz technology can be classified into four categories: sources, detectors/receivers, post-detection/processing electronics, and applications. This dissertation is dedicated to categories two and four: the development of THz detectors and the exploration of their applications at particle accelerators, such as in longitudinal electron beam diagnostics. During the 20th century, particle accelerator facilities emerged around the world as high-power radiation sources. The high-power radiation generated at these facilities can be utilized for various applications, including fundamental research, medical applications, industrial applications, understanding the universe, preserving the environment and culture, among others. Free Electron Lasers (FELs) are based on electron accelerators, which can generate bright, tunable, powerful, and ultrashort radiation pulses for various applications. However, these machines require several diagnostic tools to precisely and accurately determine machine-operable parameters, which are necessary to generate the desired radiation (beam) parameters. Among various essential diagnostic tools, a THz detector used to perform longitudinal diagnosis of the generated beam must feature a temporal resolution in the range of a few nanoseconds to picoseconds (based on the specific machine), along with the need to be ultra-broadband, compact, and robust. This serves as the primary inspirational pillar for this dissertation, which aims to develop THz detectors compatible with these application requirements. Currently, various types of THz detectors, such as Golay cells, pyroelectric, and bolometers, are used at FEL facilities for diagnostic purposes; however, for this respective application, they have several shortcomings, including too slow speed, limited operational bandwidth, or high operational costs. To address these challenges, a novel THz detector is required that can overcome the challenges of the currently commonly employed diagnostic tools. Concisely, the inspiration and goal of this dissertation is: “development and realization of compact, robust & cost-effective ultra-broad and ultra-fast direct THz detectors for promising THz applications such as longitudinal beam diagnostics at electron-based particle accelerator facilities”. All developed detectors in this dissertation are based on a single-pixel configuration. Three types of THz detectors are developed: GaAs-based TeraFETs, GaAs-based Schottky diodes, and thin-film-based Schottky diodes. This dissertation can be divided into four quadrants. The first quadrant is dedicated to modeling an intermediate frequency (IF) equivalent circuit for TeraFET up to 67 GHz. The devices for the IF circuit are characterized using an on-waver vector network analyzer (VNA). De-embedding is used to extract characteristic values of lumped element parameters and compare them with the Hall measurements. Quadrant two is dedicated to the development of detectors' packaging and integration, enabling an IF bandwidth up to 67 GHz. The IF bandwidth characterization is performed using table-top THz pulsed sources based on photo-conductive antenna and non-linear optical crystal (LiNbO$_{3}$). A UXR series 110 GHz real-time oscilloscope from Keysight Technologies and an MS2760A spectrum analyzer from Anritsu Corporation are used as readout electronics for IF characterization. Successful development of ~70 GHz IF bandwidth is realized. The robustness of the detectors is tested by a radiation hardness test performed at the ELBE facility, HZDR, Dresden. Quadrant three is dedicated to the development of ultra-broadband THz detectors, which encompasses antenna studies and device geometrical designs. The THz operational bandwidth of these detectors is characterized using a table-top CW system as well as the THz facility FELBE at HZDR, Dresden. The developed detectors demonstrate an ultra-broadband THz operational bandwidth from 0.05 to 54.8 THz, which is the new state-of-the-art for this type of detector's technology. The last quadrant encompasses the practical application of the developed detectors for longitudinal electron bunch diagnostics at the superradiant THz source TELBE at HZDR, Dresden. As an application for longitudinal bunch diagnostics, the preliminary test of the developed THz detectors is performed at one of the bunch compression monitoring (BCM) stations along the beamline. Both technologies, GaAs-based TeraFETs and thin-film-based Schottky diodes, combined, can potentially be used in the electron bunch charge range of single-digit pC to 100s of pC (tested from 18 pC to 220 pC). For the first time in literature, GaAs-based TeraFETs are implemented for BCM measurements. The development of THz detectors carried out in this dissertation examined the capabilities of these detectors and set new benchmarks. Empirical observations unveil the science, while mathematics is the language of science, and this dissertation aligns with this concept, as some obtained results challenge current theory and demand new theoretical exploration. At the same time, further technological development of these detectors is required to make THz technology available for non-expert users. The quest for the development of THz technology continues...