Machining of hard metal alloys such as Ti6Al4V alloys with cutting tools incurs high cost particularly in the replacement of worn out tools. In light of this, lasers offer a non-contact processing method which could potentially reduce costs. Lasers can introduce undesirable processing effects, but with the emergence of high powered ultrashort lasers, these processing defects can be greatly reduced. To date, there have been limited studies conducted within the area of picosecond laser machining process. This research has two primary objectives. Firstly, using lasers as an alternative to mechanical processes. Secondly, using a picosecond laser in machining of Ti6Al4V alloy to maximise material removal rate and minimise defects. In this study, an Nd:YVO4 Edge wave picosecond pulsed laser was used for machining Ti6Al4V alloy in air and at room temperature and pressure to understand laser interaction with the Ti6Al4V alloy. The laser was rated at 300W with up to 20 MHz repetition rate and up to 10 m/s scanning rate. Design of experiments was used to understand the effects of varying laser parameters and establishing the ablation threshold. Once the process parameters were established, the next stage was aimed at improving the material removal rates through various strategies. To understand the material removal process, a state of the art holography method was utilised to visualise the laser material interaction. This research has produced three significant results. It was established that the ablation threshold was 45 mJ/cm2 for picosecond laser machining of Ti6Al4V alloy. For the first time in this field of research, the optimal material removal was achieved when the laser was focused at 15 mm above the sample surface resulting in an improvement from 0.1 to 0.6 mm3/min. The holography visualisation revealed that the material removal rate was significantly reduced as the number of pulses increased due to the presence of plasma. Findings of this research support the future of picosecond laser machining of hard metals for micro as well as macro scale applications. Some of the relevant industries for this area of research include aerospace manufacture, automotive parts manufacturing and even manufacture of personal items such as watches, eye wear and jewellery.

Thesis (Ph.D.)--Bowling Green State University, 2006. / Document formatted into pages; contains xxi, 215 p. : ill. Includes bibliographical references.

Thesis (Ph. D.)--Physics, Georgia Institute of Technology, 2005. / Rick Trebino, Committee Member ; Philip First, Committee Member ; Chandra Raman, Committee Member ; Ali Adibi, Committee Member ; John Buck, Committee Member. Vita. Includes bibliographical referenced.

by Lee Yip-Chi. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1995. / Includes bibliographical references (leaves [129]-[134]). / Acknowledgments / Abstract / Chapter Chapter 1. --- Introduction --- p.1-1 / Chapter 1.1) --- Recent approaches for wavelength-tunable optical pulse generation --- p.1 -2 / Chapter 1.2) --- Self-seeding a gain-switched Fabry-Perot laser diode --- p.1 -5 / Chapter 1.3) --- About this project --- p.1-8 / Chapter Chapter 2. --- Basic theory --- p.2-1 / Chapter 2.1) --- Basic mechanism of gain-switching --- p.2-1 / Chapter 2.2) --- Mechanism of self-seeding --- p.2-5 / Chapter 2.2.1) --- General principle --- p.2-5 / Chapter 2.2.2) --- Dynamics of singlemode formation --- p.2-7 / Chapter 2.2.3) --- Different cases of modal selection --- p.2-8 / Chapter 2.2.4) --- Reduction of turn-on delay time jitter of optical output --- p.2-10 / Chapter Chapter 3. --- Instrumentation --- p.3-1 / Chapter 3.1) --- Second harmonic autocorrelator --- p.3-1 / Chapter 3.1.1) --- Principle --- p.3-1 / Chapter 3.1.2) --- Description of the 2nd harmonic autocorrelator system --- p.3-3 / Chapter 3.1.3) --- Data acquisition --- p.3-4 / Chapter 3.1.4) --- Alignment and Measurement procedures --- p.3-5 / Chapter 3.1.5) --- Pulsewidth determination by curve fitting --- p.3-7 / Chapter 3.2) --- Optical pulse detection by high speed photodetector --- p.3-9 / Chapter 3.2.1) --- High speed photodetectors --- p.3-9 / Chapter 3.2.2) --- Data acquisition --- p.3-10 / Chapter 3.2.3) --- Deconvolution of the measured optical pulsewidth --- p.3-11 / Chapter Chapter 4 --- Self-seeding 830 nm laser diode using conventional grating method --- p.4-1 / Chapter 4.1) --- Introduction --- p.4-1 / Chapter 4.2) --- Design parameters --- p.4-2 / Chapter 4.2.1) --- External cavity length --- p.4-2 / Chapter 4.2.2) --- Grating orientation --- p.4-3 / Chapter 4.3) --- Experiment --- p.4-4 / Chapter 4.3.1) --- Experimental setup --- p.4-4 / Chapter 4.3.2) --- Equipment Description --- p.4-5 / Chapter 4.4) --- Results and discussion --- p.4-6 / Chapter Chapter 5. --- Self-seeding 1.3 μm LD using fiber-optic configuration --- p.5-1 / Chapter 5.1) --- Optimized operation of self-seeded laser diode --- p.5-1 / Chapter 5.1.1) --- General Description --- p.5-1 / Chapter 5.1.2) --- Components --- p.5-1 / Chapter 5.1.3) --- Experimental setup --- p.5-6 / Chapter 5.1.4) --- Feedback rate measurement --- p.5-8 / Chapter 5.1.5) --- Results and discussion --- p.5-9 / Chapter 5.2) --- Electrical bias dependence on the self-seeded LD --- p.5-15 / Chapter 5.3) --- An efficient scheme to improve tuning range and provide continuous tuning --- p.5-20 / Chapter 5.3.1) --- General Description --- p.5-20 / Chapter 5.3.2) --- Principle of thermal control scheme --- p.5-20 / Chapter 5.3.3) --- Experimental setup --- p.5-22 / Chapter 5.3.4) --- Results and Discussions --- p.5-23 / Chapter Chapter 6. --- A novel self-seeding configuration --- p.6-1 / Chapter 6.1) --- Principle --- p.6-1 / Chapter 6.2) --- Highly dispersion-shifted fiber --- p.6-2 / Chapter 6.3) --- Optical fiber-mirror --- p.6-3 / Chapter 6.3.1 --- Fabrication --- p.6-4 / Chapter 6.3.2) --- Characterization: --- p.6-6 / Chapter 6.4) --- Experiment --- p.6-10 / Chapter 6.5) --- Results --- p.6-12 / Chapter 6.6) --- Discussions --- p.6-27 / Chapter 6.6.1) --- Electrical tuning characteristic --- p.6-27 / Chapter 6.6.2) --- Sidemode supression ratio characteristics --- p.6-30 / Chapter 6.6.3) --- Thermal tuning characteristics --- p.6-33 / Chapter 6.7) --- Summary --- p.6-36 / Chapter Chapter 7. --- Half-period delayed dual-wavelength picosecond optical pulse generation using a self-seeded laser diode --- p.7-1 / Chapter 7.1) --- Introduction --- p.7-1 / Chapter 7.2) --- Principle --- p.7-2 / Chapter 7.3) --- Experiment --- p.7-4 / Chapter 7.4) --- Results and discussions --- p.7-5 / Chapter Chapter 8. --- A proposed self-seeding configuration for the programmable multi- wavelength optical pulse generation --- p.8-1 / Chapter Chapter 9. --- Conclusion --- p.9-1 / References / Appendix / List of accepted and submitted publications

Pulse Compression and Dispersion Control in Ultrafast Optics Vikrant K. Chauhan 116 Pages Directed by Dr. Rick P. Trebino In this thesis, we introduced novel pulse compressors that are easy to align and which also compensate for higher order dispersion terms. They use a single dispersive element or a combination of dispersive elements in single-element-geometry. They solve the problem of extra-cavity pulse compression by providing control of the pulse width in almost all of the experiments performed using ultrashort pulses, and they even compensate for higher order dispersion. We performed full spatiotemporal characterization of these compressors and demonstrated their performance. We also developed a theoretical simulation of pulse compressors which is based on a matrix based formalism. It models the full spatiotemporal characteristics of any dispersion control system. We also introduced a simple equation, in its most general form, to relate the total dispersion and magnification introduced by an arbitrary sequence of dispersive devices. Pulse compressor characterization was done using interferometric measurements in the experiments presented in this work, but we also developed a method to measure pulses that uses polarization gating FROG for measuring two unknown pulses. In the last part, we briefly discuss the designing of a high energy chirped pulse amplification system.

In this thesis, Molecular Dynamics simulations of shocked single crystals of Copper and Iron are studied using simulated X-ray diffraction. Strains and volumetric compression in modeled Copper crystals shock-compressed on picosecond time-scales are found. By comparing the shifts in the second and fourth diffraction orders, the density of dislocations is calculated. In Iron, simulated X-ray diffraction is used to verify the modelling of the α-ε phase transition induced by shock-compression on picosecond time-scales. No plastic deformation of Iron is found in the studied pressure range of ~ 15-53 GPa. The results are then compared with data from in situ X-ray diffraction experiments of laser-shocked single crystals. Near-hydrostatic compression of shock-compressed Copper on nanosecond time-scales is confirmed using a new wide-angle film diagnostic capturing diffraction from multiple crystal planes. Also, the first in situ X-ray diffraction evidence of the onset of the α-ε phase transition in laser-shocked single crystal Iron is shown. No plastic yield of the crystal lattice is found, which is in agreement with the simulation results. Results from both the Molecular Dynamics simulations and experiments are used to suggest enhancements in computer modelling of shocked crystals, as well as future experimental studies. In particular, the need for a measurement of dislocation densities during the shock wave passage through a crystal is highlighted, and a method enabling such a measurement is proposed.

Thesis (M. S.)--Physics, Georgia Institute of Technology, 2009. / Committee Chair: Rick Trebino; Committee Member: Jennifer Curtis; Committee Member: John Buck; Committee Member: Mike Chapman; Committee Member: Stephen Ralph.

Thesis (Ph.D.)--Bowling Green State University, 2005. / Document formatted into pages; contains xvii, 133 p. : ill. Includes bibliographical references.

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The increasing use of visible and near infrared light in therapeutic and diagnostic techniques has created a need to model its propagation in tissue. One of the fundamental objectives of such a model is the noninvasive evaluation of the optical properties of tissue. The focus of this thesis was the development of the diffusion approximation in the semi-infinite, slab, cylindrical and spherical geometries. This development required the derivation of approximate boundary conditions which included the zero, extrapolated and partial current boundary conditions. Calculations of the fluence and its related quantities arising from the extrapolated boundary condition were found to be in excellent agreement with the results of the more rigorous partial current boundary condition. A preliminary evaluation of the validity of diffusion theory was performed by comparing its predictions to exact analytical calculations of the fluence in an infinite medium as well as Monte Carlo simulations of the reflectance and transmittance in 1-dimensional planar geometries. In all cases the agreement at late times was excellent. A practical test of the diffusion model was accomplished with the analysis of the reflectance data from a phantom of known optical properties in both the semi-infinite and slab geometries. The model performed well at low concentrations of added absorber, but a considerable discrepancy was found at the highest concentration. A systematic examination of the accuracy of the diffusion model as a function of the fundamental parameters is required to resolve this inconsistency. Approximate expressions describing the equivalent information in the frequency domain were also developed for a semi-infinite medium. These expressions were then used to analyze the phase and modulation obtained from phantoms of known optical properties. Once again reasonable results were obtained at low concentrations of added absorber while a significant discrepancy arose at the highest concentration. The resolution of these discrepancies requires further investigation. / Thesis / Master of Engineering (ME)