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PhD Defense - Colin McLaughlin

Colin successfully defended his dissertation on April 8, 2010.

Electro-optic polymers for terahertz applications

The rapid development of technologies employing terahertz (THz) radiation has led to numerous industrial and scientific applications. Current THz technologies are limited in their frequency response because of phonon absorbance and poor phase matching in crystalline emitters and detectors, or are limited to high-power bench-top pump laser systems for air-plasma generation and detection. In contrast, amorphous electro-optic (EO) polymer composite materials have the potential for broad bandwidth, spectral gap-free THz emission and detection while requiring a relatively low pump laser power.

In this thesis a theoretical description of THz radiation emission and detection using EO polymers is reviewed, including the effects of laser spectral bandwidth, pulse distortion, and material properties of the EO media. This model is used as a guide to improve the response of a THz system employing electro-optic polymer emitters and detectors. EO polymer composites that have been engineered for terahertz applications are described. These materials show a progression of improvements for use in THz systems, including higher EO coefficients, increased photostability, and reduced aggregation and dimerization.

A study of in-plane (longitudinal) and parallel-plate (transverse) poling of EO polymers for use as THz sensors is presented, including a theoretical description of detection sensitivity for each device. In-plane poling allows access to the full optical nonlinearity of the EO polymer, potentially increasing detection sensitivity by a factor of 2.4 over parallel-plate poled devices. A transmission ellipsometric EO measurement technique is developed for the in-plane poling device and is used in the experimental comparison of the two devices.

EO polymer composites are employed as terahertz emitters and sensors in systems using a communication-wavelength pump laser. A 15 THz wideband response is achieved using the ALTB203/APC composite, and is compared to the organic crystal DAST and to the THz system model. Increasing emitter thickness is studied through stacking multiple EO polymer emitter films. Frequency-dependent terahertz index and absorption of the emitter and sensor films are included into the THz model for a more accurate representation of the terahertz system response.

Given proper phase-matching and low absorption, EO polymer materials can potentially be used in a waveguide geometry to generate broadband THz radiation. Coupling these devices with currently-available ultra-fast fiber lasers could lead to the development of field-deployable, compact, inexpensive THz systems.