[No abstract available] / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Relativistic electron motion in a time varying, uniform, uni-directional electric field is examined. The information obtained is applied to study the dynamics of an electron beam which is injected uniformly at low energy into a high field intensity, long transit angle pre-accelerator cavity. Numerical calculations are made for a particular cavity, and the results are presented in graphical form. The equations of motion of an electron in a travelling wave are derived and used to obtain numerical data on a particular main accelerator. This data is presented in graphical form and is designed to be used in conjunction with the pre-accelerator results to supply information on the joint operation of the pre-accelerator and the main accelerator. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate

Third order nonlinear optical properties of organic compounds with $\pi$ electron delocalization are currently receiving much attention in view of potential applications in switching and optical information processing. Polymers of Benzidine were synthesized by hydrogen peroxide reaction catalyzed by horseradish peroxidase enzyme. The polymerization reaction was carried out at room temperature in a monophasic organic solvent with a small amount of water at pH 7.5. The technique of Degenerate Four Wave Mixing with picosecond and nanosecond pulses was employed to measure the third order susceptibility $\chi\sp{(3)}$ of polybenzidine. The observed values for $\chi\sp{(3)}$ are of order 10$\sp{-9}$ to 10$\sp{-8}$ esu. In order to understand the origin of these high values of $\chi\sp{(3)}$, we measured the real and imaginary components of $\chi\sp{(3)}$. Investigation of total energy transmission as a function of incident intensity and fluence at 532 nm for picosecond and nanosecond laser pulses using a frequency doubled Nd:YAG laser indicates reverse saturable absorption. The experiments are carried out for the sample in solution in Dimethyl Sulfoxide and Methanol (DMSO:MeOH) 4:1 ratio. As we observe the nanosecond and picosecond curves to be superimposed for intensity dependence and not for fluence, we conclude that the third order nonlinearity is predominantly due to two photon absorption. Values for Im $\chi\sp{(3)}$ determined by our experiments are of order 10$\sp{-9}$ to 10$\sp{-8}$ esu. We measure the real part of $\chi\sp{(3)}$ by optical Kerr gate technique. The value is about one order lower compared to the imaginary component. In view of the reverse saturable absorption characteristics observed for the samples, the material is a good candidate for applications in optical power limiting.

Charge transport and spin transport (spintronics) over nanometer spatial scales are topics of fundamental scientific and technological interest. If the potential of nano-devices and spintronics is to be realized, ways must be developed to inject and control ballistic charge and spin currents, as well as to measure their motion. Here, using novel polarization and phase sensitive optical pump probe techniques, we not only inject ballistic charge and spin currents in GaAs, Ge, and Si but also follow the subsequent carrier motion with < 1 nm spatial and 200 fs temporal resolution. Unlike most free space measurements, the spatial resolution of these techniques is not limited by diffraction, and therefore these techniques provide a unique platform for studying ballistic transport in semiconductors and semiconductor structures. The injection process relies on quantum interference between absorption pathways associated with two-photon absorption of a fundamental optical field and one-photon absorption of the corresponding second harmonic. By utilizing the phase, polarization, photon energy, and intensity of the optical fields we can control the type of current injection (spin current or charge current) and the direction and magnitude. In GaAs we present the first time resolved measurements of charge and spin currents injected by this process and also show the ballistic direct and inverse Spin Hall Effect. These techniques are extended to the more technologically relevant group IV semiconductors Si and Ge. The charge currents injected in these materials show similar qualitative behavior. The electrons and holes are injected with oppositely directed average ballistic velocities that move apart and return to a common position on sub-picosecond time scales. The spin currents however, are very different. The spin up and spin down carrier profiles move apart and remain apart until their spin profiles decay. In GaAs the profile decay on picosecond time scales however, in Ge they decay on femtosecond time scales since the electrons quickly scatter to the side valleys. Unlike GaAs and Ge, the spin orbit coupling in Si is much too small to produce measurable spin currents.

Rapid development of genetically encoded fluorescent indicators has provided a diverse chemical toolkit to probe complex biological systems, leading to the expansion of fluorescence microscopy for biological research and applications. However, the inherent constraints on resolution, speed and field of view have hindered the development of high speed, three dimensional fluorescence imaging over large spatial scales for biological microscopy. This thesis describes two strategies based on confocal microscopy to provide single-shot volumetric fluorescence imaging over large scales. In the first part, we describe a multiplane line-scan imaging strategy, which uses a series of axially distributed reflecting slits to probe different depths within a sample volume. Our technique, called line-scan multi-z confocal microscopy, enables the simultaneous imaging of an optically sectioned image stack with a single camera at frame rates of hundreds of hertz, without the need for axial scanning. We demonstrate the applicability of our system to monitor fast dynamics in biological samples by performing calcium imaging of neuronal activity in mouse brains and voltage imaging of cardiomyocytes in cardiac samples. In the second part, we describe a fiber bundle-based endomicroscopy technique, which provides pseudo-volumetric imaging over large field of views, without the need for axial scanning. Our technique uses a gradient refractive index lens to achieve an axially extended illumination and a series of reflecting pinholes of different diameters to simultaneously probe different number of fiber cores. The fluorophores are localized from the series of acquired images using a convolution neural network. We validate our system by localizing fluorescent beads distributed in a volume sample.

No description available.

Light loss in single mode fiber optical switches is investigated. Loss due to reflection, aberration and fiber misalignment are evaluated. A simple model of image to fiber end face overlap for the fiber/lens system is developed. The intensity distribution of light in the fiber and imaging system is assumed to be gaussian. It was found that aberration is a major cause of loss and that fiber misalignment did not cause as much loss as expected. Loss due to reflection is assumed to be minimal due to the presence of anti-reflection coatings on the optical components. / Master of Science

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No description available.

No description available.