The study of pulsed n. m. r. in single crystal metallic samples, initiated by McLachlan, has been extended to liquid helium temperatures with special emphasis on Sn¹¹⁹ . Contrary to McLachlan's belief it was found that cooling to 4. 2°K and lower afforded significant improvements to the signal to noise ratio and in many cases the n. m. r. signals (including spin echoes in Sn¹¹⁹ ) could readily be seen on an oscilloscope without the use of a signal averager. The theory of magnetic resonance in metallic samples was studied in some detail with particular emphasis on the experimental situation where matters are complicated by the high conductivity which modulates both the amplitude and the phase of the exciting r.f. magnetic field as it penetrates into the sample. It is shown theoretically that several assumptions must be made to show that the conventional methods of pulsed n. m. r. used to measure T₂ (by either spin echo or free induction decay) and T₁ yield true meaningful results. In particular it is found that the spin lattice relaxation time T₁ is obtained by the conventional two pulse sequence only when the magnetic field is exactly on resonance; this was observed to be the case experimentally as well. In sharp distinction to McLachlan's findings for Sn¹¹⁹, the spin-spin relaxation time T₂ obtained by FID methods (175 ± 18μsec) was much smaller than that obtained by spin echo techniques (390 ± 48μsec) in the present research on Sn¹¹⁹. The spin-lattice relaxation time was also measured at liquid helium temperatures and yielded a value of 56 ± 4 millisec deg for T₁, in excellent agreement with Dickson although twice as large as McLachlan’s value. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

In the present investigation, zinc was plated onto a cadmium crystal to determine the effect on the scattering parameter.

Photonic crystals are media with periodically varying optical properties. Photonic crystals enable exquisite control of light propagation in integrated optical circuits and also emulate advanced physical concepts. However, common photonic crystals directly pattern the optical medium and thus are unfit for in-operando on/off controls. In this dissertation, we introduced, fabricated, and studied the properties of graphene polaritonic crystals. Our polaritonic crystal system consists of a pristine sheet of graphene in a back-gated platform with nano-structured gate insulators. We employed scattering-type scanning near-field optical microscopy (s-SNOM) to study the novel properties of polaritons propagating in the polaritonic crystal. We demonstrated the formation of a polaritonic bandgap, variations of the polaritonic local density of states, and the emergence of polaritonic domain wall states. We also revealed the programmable control of the polariton propagation direction and reconstructed the polaritonic bandstructure from real-space polariton images. The exploration of topological polaritonic phenomena in the polaritonic crystal relies on the selective excitation of topologically non-trivial modes using a chiral polariton launcher. We searched for the design of an efficient chiral polariton launcher. Throughout the journey, we visualized the polaritonic vortex mode of hBN phonon-polaritons. We discovered that the optical spin angular momentum of hBN phonon-polaritons resembles nano-scale meron spin textures. The meron spin texture possesses a half-integer topological charge determined by the handedness of the incident beam. The polaritonic crystal platform studied in this dissertation sheds light on the exploration of topologically non-trivial polaritonic states, such as valley plasmons and topological edge states. In addition, our electrostatically-tunable polaritonic crystals are derived from standard metal oxide semiconductor field-effect transistor technology and pave a way for practical on-chip light manipulation.

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Liquid crystal (LC) has been widely used for displays, spatial light modulators, variable optical attenuators (VOAs) and other tunable photonic devices. The response time of these devices is mainly determined by the employed liquid crystal material. How to obtain fast response for the LC devices is a fundamentally important and technically challenging task. In this dissertation, we investigate several methods to improve liquid crystal response time, for examples, using dual-frequency liquid crystals, polymer stabilized liquid crystals, and sheared polymer network liquid crystals. We discover a new class of material, denoted as sheared polymer network liquid crystal (SPNLC) which exhibits a submillisecond response time. First, dual-frequency liquid crystals and polymer network methods are demonstrated as examples for the variable optical attenuators. Variable optical attenuator (VOA) is a key component in optical communications. Especially, the sheared PNLC VOA shows the best result; its dynamic range reaches 43 dB while the response time is in the submillisecond range at 1550 nm wavelength, which is 50 times faster than the commercial LC-based VOA. Second, we report a new device called axially-symmetric sheared polymer network liquid crystals (AS-SPNLC) and use it as LC devices. An axially-symmetric sheared polymer network liquid crystal has several attractive features: 1) it is polarization independent, 2) it has gradient phase change, and 3) its response time is fast. It can be used for polarization converter and divergent LC lens. In addition, a new method for simultaneously measuring the phase retardation and optic axis of a compensation film is demonstrated using an axially-symmetric sheared polymer network liquid crystal. This simple technique can be used for simultaneously measuring the optic axis and phase retardations of both A- and C-plates. These compensation films have been used extensively in wide-view LCD industry. Therefore, this method will make an important impact to the LCD industry.

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