Date of Award
Doctor of Philosophy in Electrical Engineering - (Ph.D.)
Electrical and Computer Engineering
John Francis Federici
Ken K. Chin
William N. Carr
In recent years, generation of ultra-short electromagnetic pulses with frequency components in the terahertz (THz) range has been achieved by various techniques. Among those different methods, photo-conducting antennas have proven to be the most efficient source of THz radiation. THz spectrometers utilizing such photo-conducting antennas as transmitters and receivers are meanwhile routinely used for spectroscopic studies in the frequency regime between 0.1 to 5THz, which can be covered by neither conventional optical nor microwave spectrometers. However, THz emission power from the existing photo-conducting antenna is not sufficient for many applications (such as electro-optic sampling for real time THz detection and imaging, THz near field spectroscopy, remote chemical sensing, etc.).
This dissertation presents a systematic study of a new family of more efficient THz antennas, ranging from engineering simulation, device fabrication, system characterization and their applications. We, for the first time, have designed the THz dipole antennas with relatively sophisticated shapes to optimize the fringing electric field in the regime where the THz pulse is generated. We demonstrate that this is the most efficient THz emitters, to our knowledge, with a record high THz average power of 2-3µW with mW laser excitation. The previously reported state-of-the-art THz radiation power under similar condition are 38nW and 10nW.
With the singular electric field terahertz emitters, we are enabled to impact the terahertz spectroscopy imaging technology with even higher band width, sensitivity, spatial resolution, and compactness. In this dissertation, we also present our demonstrations on these improvements, including:
(1) The significant improvement on performance of THz spectroscopy systems with a signal to noise ratio as high as ~106;
(2) The feasibility of a THz focal plane imaging system using real time delay scanning in shot noise limited free space electro-optic sampling (FSEOS) that requires only 20mW of laser power;
(3) A record high THz imaging space resolution of ~30µm is achieved with new integrated near field terahertz imaging probes;
(4) A compact all solid-state terahertz system, operating with a diode pumped Cr:LiSaF laser.
We also demonstrate a few applications empowered by this high sensitivity, including chemical sensing, photo induced conductivity measurement of Si nano-structure thin film and semi-insulating GaAs.
Cai, Yi, "Enhanced terahertz pulse generation and detection using electric field singularities in photo-conducting antennas" (1998). Dissertations. 932.