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Design of Optimum Antennas for Wideband THz Pulses Generation Using Photoconductivity
, M.Sc. Thesis Sharif University of Technology ; Ahmadi-Boroujeni, Mahdi (Supervisor)
Abstract
One of the most common devices for terahertz (THz) wave generation and detection is a Terahertz photoconductive antenna. Impedance matching between the antenna and the photoconductive material is a primary factor to obtain high optical-THz conversion efficiency. Because of the time dependant conductivity of the photoconductive material, impedance mismatching is an obstacle for generating high power THz pulses. Moreover, the range of laser power (when using Ti:Sapphire) from the excitation source varies from a few tens of milliwatts to a few watts while the radiated THz power as compared to this laser pump power is very low (in the order of a few μW); this means a low power conversion...
Conceptual models for Seawater Intrusion Simulation
, M.Sc. Thesis Sharif University of Technology ; Ataie Ashtiani, Behzad (Supervisor)
Abstract
Ground water resources are the main source of water supply in many regions. During last decades ground water quality has been deteriorated due to many sources of contamination. Seawater intrusion in coastal aquifers is one of these sources. With development of different numerical models, simulation of seawater intrusion in coastal and island aquifers has been used greatly in analyzing the condition of these aquifers. The first step in performing a numerical modeling is determination of a suitable conceptual model. Considering the complexity of a real problem, a proper conceptual model should show the true condition of the problem as well as lead to a cost and time effective simulation. In...
Design and Study of Lenses with Resolution Beyond the Diffraction Limit
, M.Sc. Thesis Sharif University of Technology ; Rejaei, Behzad (Supervisor) ; Khavasi, Amin (Supervisor)
Abstract
In this article some systems wich have a resolution beyond the diffraction limit and much more than the conventional lenses (like convex lenses, optical microscopes that have a resolution in order of wavelength) have been reviewed. These structures can be used in many different areas like Electron-Beam lithography (Photoleptography and Nano lithography), printing integrated optical circuits and chips, accurate cell imagings (entering and exiting of proteins in cells) and etc. This kind of imaging is called ”subwavelength imaging”. Generally some remarkable properties of these structures are propagation of all the spatial frequencies or amplifying the evanescent waves. One of the most known...