Theoretical and experimental study of terahertz wave generation in waveguides

Date of Award

2011

Degree Name

M.S. in Electro-Optics

Advisor/Chair

Advisor: Peter E. Powers

Abstract

This thesis examines THz generation using difference frequency generation (DFG) in a nonlinear crystal. Two narrow line-width, detuned, infrared lasers are mixed in the nonlinear crystal to produce a similarly narrow line-width THz wave. Due to its longer wavelength, the THz beam has a much larger diffraction than the input laser beams. As a result, it is difficult to maintain an overlap between the THz beam and the input laser beams in traditional bulk DFG crystals. To overcome this limitation, we propose a THz waveguide design which confines the THz beam to a smaller area. Because of the differences in wavelengths, the THz waveguide needs to be carefully designed to ensure the THz beam overlaps with the input pump beams to achieve phase matched interaction between the waves. The approach used for the waveguide design applies a numerical beam propagation simulation of the nonlinear interaction between the near infrared laser beams and generated THz beam. A design is considered assuming a quasi-phase matched GaP core and a cladding, using a silicon nano-composite material. A numerical model is constructed based on the split-step beam propagation method (BPM) to simulate the DFG THz generation process using experimentally determined THz indices of refraction. The BPM method enables us to study the details of the interactions and to optimize the waveguide geometry and the quasi-phase matching period for efficient THz beam generation. The results of the modeling in different waveguide structures are compared and the model is used to maximize the output THz wave power, by optimizing the core size and pump beam sizes for the waveguide for a given quasi-phasing matching period.

Keywords

Terahertz technology, Wave guides Design and construction, Wave guides Mathematical models

Rights Statement

Copyright © 2011, author

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