The effect of atmospheric turbulence on an optical wave can seriously degrade the reliability of an optical communication link. One atmospheric effect is scintillation, which is caused by index of refraction fluctuations. Several observations of atmospheric turbulence statistics suggest a modest change in the power law behavior of Kolmogorov' s power spectral density model. The corresponding index of refraction fluctuations are assumed to have spatial power spectra that obey power laws that deviate somewhat from the classical - 11/3 power law. The purpose of this study is to develop analytical models for scintillation and other wave propagation statistics based on non-classical power spectra. This involves random processes, asymptotic theory, and evaluating integrals involving special functions (Bessel functions and hypergeometric functions). Mean irradiance and scintillation index models are derived for a Gaussian-beam wave propagating through an atmosphere experiencing weak irradiance fluctuations. Also, the wave structure function for an unbounded plane wave and spherical wave is derived under weak turbulence theory. Using the derived plane wave structure function, the scintillation index for both a plane and spherical wave experiencing strong irradiance fluctuations is calculated. In addition, a scintillation model that is valid under all irradiance fluctuation conditions is derived for both a plane and spherical wave propagating through non-Kolmogorov atmospheric turbulence.

The average fade time of the fluctuations in the intensity of laser light propagation in the atmosphere is analyzed. Experimental results show that the average fade time for a propagation distance of 208 meters, in the weak turbulence regime, is well described by formulas developed from a Log-Normal distribution. A circuit that calculates real time statistics of fade time is designed, then validated using a sine wave input whose fade time statistics are predetermined. The experimental signal is then tested for stationarity, and the average fade time is measured. A curve fitting is then performed for the experimental data and compared theoretical results.

The main focus of this work is using the infrared-infrared (IR-IR ) double resonance spectroscopic technique to study the 2³Πg, a³Σ⁺u triplet ground states, and the A¹Σ⁺u ~ b³Πu coupled states of the Rubidium dimer molecule. The initial analysis of the 2³Πg state involved separated analysis of the rotational and vibrational Bv and Gv functions to extract the molecular Dunham coefficients from the data. This was to avoid cross correlations between rotational and vibrational parameters because there was limited amount of rotational energy level data which included in addition perturbations between this state and other electronic states in the same region. An initial RKR potential energy curve was constructed based on this analysis. Subsequently this approach was augmented by a joint analysis of the 2³Πg state and the triplet ground state. This analysis was based on bound-free spectra, i.e. fluorescence from bound levels of the upper state to the continuum of the lower state. We present a comparison of these two approaches to the data analysis by testing the resulting potential energy functions through comparison of the calculated ro-vibrational energies against the observed energy level values The fluorescence from a discrete ro-vibrational level of the a bound upper state 2³Πg also includes transitions to discrete bound ro-vibrational levels of the triplet ground state (bound-bound emission). Accurate determination of the transition frequencies of the observed fluorescence spectroscopic lines allowed us to construct a reliable potential energy function that augmented our previous results on this state and corrected misinterpretation of that data in the literature. Similar infrared-infrared (IRIR) double resonance excitation of the 3¹Σ⁺g state was also used to observe resolved fluorescence spectra to the A~b states coupled by strong spin-orbit interaction. From the IRIR resolved fluorescence, we have filled the gap in the data range 12000cm-1 to 14000cm-1 of these coupled states for the Ω=0u⁺ component. / Physics

Interstitial laser photocoagulation (ILP) is a minimally invasive technique for destroying solid, localised tumours thermally by delivering infrared laser energy directly into the targeted volume via percutaneously implanted optical fibres. Using current treatment parameters, each fibre delivers sufficient energy to destroy a volume of one to two cm³; larger lesions may be created by using multiple fibres excited simultaneously. An efficient delivery system has been constructed consisting of several fibres bundled through a single cannula and splayed out through a specially designed tip. This delivery system is simple to use and provides accurate fire placement. By linearly superposing single source solutions to the bioheat transfer equation, a mathematical model for coalescent thermal lesions has been developed. It has been determined that large, clinically useful thermal lesions can be created by implanting four sources at the corners of a square. It has been demonstrated, through 𝘦𝘹 𝘷𝘪𝘷𝘰 experimentation in bovine liver, that the model correctly predicts the dimensions of the thermal lesions. / Thesis / Master of Science (MS)

The mechanical tools currently used in orthopedic and dental surgery are imprecise and may cause heat damage. Ultrashort pulse lasers are a promising replacement, but their ablation efficiency must be improved. The goal of this thesis was to achieve high ablation efficiency, precision, and minimal collateral damage using an ultrafast laser on bovine hard tissue. This work used two types of lasers: a Ti:Sapphire laser (210 fs, 800 nm, 1 kHz) and a fiber laser (1 ps, 1035 nm, 100 kHz - 1 MHz). This thesis begins with a review of the literature on laser-tissue interactions and the effect of certain laser parameters on the ablation process. The next section uses a Ti:Sapphire laser and bovine bone to explore the properties of laser-tissue interactions, including ablation threshold and incubation coefficient. Results showed that as the number of incident pulses goes up, ablation threshold goes down. The threshold range went from 1.08 ± 0.15 J/cm2 at 25 incident pulses to 0.73 ± 0.12 J/cm2 at 1000 pulses. The incubation coefficient, S, was calculated to be 0.90 ± 0.02. The relationship between ablation depth and fluence, scanning speed, and number of successive passes was characterized as a first step towards preparing large-cavity with high removal efficiency using a Ti:Sapphire and fiber lasers. Depth increased with fluence and number of passes, but it decreased with scanning speed. The influence of environmental conditions including air, compressed air flow, still water and flowing water on cavity ablation depth, and rate was investigated using a Ti:Sapphire laser with aim to enhance ablation efficiency. Findings showed that the deepest cavities and fastest ablation rates were achieved with compressed air flow. Air flow also resulted in the most precise cuts, the smoothest surfaces, and the absence of microcracks. This thesis also used a fiber laser to explore the effect of fluence and repetition rate on removal rate and ablation quality. Results indicated that ablation rate increases with fluence and pulse rate. When the repetition rate exceeded 600 kHz, the laser caused thermal and mechanical damage, indicated by the presence of amorphous carbon. The effect of environmental conditions and laser parameters such as repetition rate provide valuable insights into the ultrafast laser ablation mechanisms for medicine and biology field. / Thesis / Doctor of Philosophy (PhD)

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