Browsing by Subject "Laser ablation"
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Item Development of femtosecond laser endoscopic microsurgery(2011-05) Hoy, Christopher Luk, 1982-; Ben-Yakar, Adela; Hall, Matthew J.; Ho, Paul S.; Sokolov, Konstantin V.; Tunnell, James W.Femtosecond laser microsurgery has emerged as a remarkable technique for precise ablation of biological systems with minimal damage to their surrounding tissues. The combination of this technique with nonlinear optical imaging provides a means of microscopic visualization to guide such surgery in situ. A clinical endoscope capable of image-guided femtosecond laser microsurgery will provide physicians a means for cellular-level microsurgery with the highest precision. This dissertation focuses the development of a miniaturized fiber-coupled probe for image-guided microsurgery, towards future realization as a clinical endoscope. The first part of the dissertation describes the development of an 18-mm diameter probe. This development includes delivery of femtosecond laser pulses with pulse energy in excess of 1 µJ through air-core photonic bandgap fiber, laser beam scanning by a microelectromechanical system scanning mirror, and development of a new image reconstruction methodology for extracting increased temporal information during Lissajous beam scanning. During testing, the 18-mm probe compares favorably with the state-of-the-art as a microscopic imaging tool and we present the first known demonstration of cellular femtosecond laser microsurgery through an optical fiber. The second part of the dissertation explores further refinement of the design into a streamlined package with 9.6 mm diameter and improved imaging resolution. Study of the optical performance through analytical and computer-aided optical design indicates that simple custom lenses can be designed that require only commercial-grade manufacturing tolerances while still producing a fully aberration-corrected microsurgical endoscope. With the 9.6-mm probe, we demonstrate nonlinear optical imaging, including tissue imaging of intrinsic signals from collagen, using average laser powers 2-3× lower than the current state-of-the-art. We also demonstrate the use of the 9.6-mm probe in conjunction with gold nanoparticles for enhanced imaging and microsurgery through plasmonics. Finally, in the third part of this dissertation, we detail bench-top development of a new clinical application for combined femtosecond laser microsurgery and nonlinear optical imaging: the treatment of scarred vocal folds. We show the utility of femtosecond laser microsurgery for creating sub-epithelial voids in vocal fold tissue that can be useful for enhancing localization of injectable biomaterial treatments. We demonstrate that a single compact fiber laser system can be utilized for both microsurgery and imaging. Furthermore, the proposed clinical technique is shown to be achievable with parameters (e.g., pulse energy, focused spot size) that were found to be attainable with fiber-coupled probes while still achieving ablation speeds practical for clinical use.Item Engineering nanocomposite polymer membranes for olefin/paraffin separation(2011-12) Gleason, Kristofer L.; Becker, Michael F.; Kovar, Desiderio; Hallock, Gary A.; Keto, John W.; Goodenough, John B.In this dissertation, I have investigated applying the laser ablation of microparticle aerosol (LAMA) process to the production of nanocomposite polymer membranes for olefin/paraffin separation. Experimental results for three major thrusts are presented: 1) an investigation into the scalability of the LAMA process, 2) a new laser ablation technique for nanoparticle production from aqueous feedstocks, and 3) characterization of olefin-selective polymer nanocomposite membranes produced using LAMA. The propensity for Ag nanoparticles to form agglomerates in LAMA is investigated. Nanoparticle samples were collected on TEM grids at several feedstock aerosol densities. As the density increased, the particle morphology shifted from single nanoparticles 5 nm in diameter to chained agglomerates of 20 nm diameter primary particles. The results are in agreement with a numerical model of Brownian agglomeration and diffusion. Factors influencing nanoparticle morphology, such as temperature, initial nanoparticle charge, and feedstock aerosol density are discussed. It is shown that agglomeration occurs on a much longer timescale than the other processes, and can be treated independently. A new nanoparticle synthesis technique is presented: laser ablation of aqueous aerosols. A Collison nebulizer is used to generate a mist of ~10 [mu]m diameter water droplets containing dissolved transition metal salts. Water from the droplets quickly evaporates, leaving solid particles which are ablated by an excimer laser. Ablation results in plasma breakdown and photothermal decomposition of the feedstock material. For AgNO₃ ablated in He gas, metallic Ag nanoparticles were produced. For Cu(NO₃)₂ ablated in He gas, crystalline Cu₂O nanoparticles were produced. For Ni(NO₃)₂ ablated in He gas, crystalline NiO nanoparticles were produced. A combination of AgNO₃ and Cu(NO₃)₂ ablated in a reducing atmosphere of 10%H₂/He yielded nonequilibrium Ag-Cu alloy nanoparticles. Membranes composed of poly(ethylene glycol diacrylate) (PEGDA) and Ag nanoparticles were produced by the LAMA process. Permeation and sorption measurements for the light olefins and paraffins were conducted for these membranes. The membranes showed very little improvement in olefin/paraffin selectivity compared with neat PEGDA membranes. Using the LAMA implementation described here, it was impossible to produce membranes with high Ag loading. Whether membranes containing more Ag would exhibit improved selectivity remains an open question.Item Enhancement of high power pulsed laser ablation and biological hard tissue applications(2006) Kang, Hyun Wook; Welch, Ashley J., 1933-Item Generation of Core/shell Nanoparticles with Laser Ablation(2012-10-19) Jo, Young KyongTwo types of core/shell nanoparticles (CS-NPs) generation based on laser ablation are developed in this study, namely, double pulse laser ablation and laser ablation in colloidal solutions. In addition to the study of the generation mechanism of CS-NPs in each scheme, the optical properties of designed CS-NPs are determined with UV-VIS-NIR spectroscopy and EM field simulation. In the first scheme, which is double pulse laser ablation, two laser beams are fired in a sequence on two adjacent targets with different material. We have successfully demonstrated the generation of Sn/Glass, Zn/Glass, Zn/Si, Ge/Si, and Cu/Zn CS-NPs. Key factors affecting the generation of CS-NPs are (1) surface tensions of the constructing materials affecting the associated Gibbs free energy of CS-NPs, (2) physical properties of selected background gases (i.e., He and Ar), (3) delay time between two laser pulses, and (4) the amount of laser energy. The second scheme examined for the generation of CS-NPs is through laser ablation of solid targets in colloidal solutions. Compared to the double pulse laser ablation, this second approach provides better control of the size and shape of the resulting CS-NPs. Two colloidal solutions, namely, Au and SiO2 colloidal solution are applied in the second scheme. Key factors affecting the formation of CS-NPs with the second scheme and are (a) the adhesion energy between the shell and the core material, (b) the diameter of the core and (c) the laser ablation time and the laser energy. Red shift of absorption peaks are measured in both SiO2/Au and SiO2/Ag colloids compared with pure nanoparticles (NPs). The amount of red-shift is very sensitive to the shell thickness of the CS-NPs. The same red shift is reproduced with the corresponding full wave analysis. The observed red shift can be attributed to the additional surface plasmon resonance at the interface of metal/dielectric of the CS-NPs compared with pure nanoparticles. Through adjusting the material and size combination, the absorption peak of the CS-NPs can be tuned in a limit range around the intrinsic absorption peak of the metal of the CS-NPs. The freedom of adjusting the absorption peak makes CS-NPs is favorable in bio and optical applications.Item Laser ablation of a terfenol-D (Tb₀.₃Dy₀.₇Fe₁.₉₂) microparticle aerosol and subsequent supersonic nanoparticle impaction for magnetostrictive thick films(2006) O'Brien, Daniel Thomas; Becker, Michael f.; Pernod, PhilippeThis dissertation describes using microparticles of the (giant) magnetostrictive material Terfenol-D (Tb0.3Dy0.7Fe1.92) in the Laser Ablation of Microparticle (LAM) aerosols process for the generation of nanoparticles and their subsequent supersonic impaction to form nanostructured magnetostrictive thick films. Solid Terfenol-D was ground to a powder having diameters from 0.3 to 3 µm. This microparticle powder was then aerosolized and ablated by a KrF ultraviolet, pulsed laser in a continuously flowing aerosol process. The nanoparticles formed from the ablation were then accelerated through a supersonic nozzle into vacuum where they impacted onto a substrate at room temperature forming a film. The nanoparticles were amorphous, as shown by x-ray diffraction analysis of the deposited films and by Transmission Electron Microscopy of individual particles, and had a size distribution typical of the LAM process: 3 to 20 nm in diameter with a mean size less than 10 nm. The deposited films were characterized using the cantilever method to determine magnetostriction and elastic modulus. Values of magnetostriction were on the order of 15 ppm for LAM deposited films. The films were porous, due to their granular nature, reducing the elastic modulus to about 15 GPa. The reduced magnetostriction (1/30 that of comparable thin films) was due to oxidation. Spectroscopic analysis of the ablation plasma provided data in determining the source of the oxidation. Calculations showed that the extent of oxidation in the films was dependent on the microparticle feedstock size. For typical aerosol densities used in the LAM process, calculations showed that material made from microparticles having a diameter larger than 3 µm was not significantly affected by background gas impurities or by an oxide shell on the microparticles, whereas 0.3 µm diameter microparticles resulted in completely oxidized nanoparticles and hence films that were completely oxidized. From the behavior of the deposited films, the aerosolized microparticles had a mixture of diameters in between these two cases.Item Laser processing of Tb0.3Dy0.7Fe1.92 films(2007-12) Ma, Dat Truong; Kovar, DesiderioIn the past decade, there has been an increased interest in magnetostrictive materials for micro actuators and sensors. Of particular importance are the Fe₂R intermetallics, where R = Tb, Dy. In this study, films of Tb[subscript 0.3]Dy[subscript 0.7]Fe[subscript 1.92] were prepared by three laser processing techniques (pulsed laser deposition, flat plate ablation and laser ablation of microparticles) to explore the effect of processing parameters on particle size, crystallinity and magnetic properties. The laser used in the experiments was a KrF laser with a 12 ns pulse width. Pulsed laser deposition of an alloyed target in vacuum produces dense amorphous films with the similar composition to the target, low coercivity (46 Oe) and good magnetostriction ([lambda][subcript two horizontal lines] = 305 ppm at 2300 Oe). Flat plate ablation and laser ablation of microparticles produced amorphous nanoparticles at 1 atm. The particles were subsequently jet deposited onto substrates to form thick films. Nanoparticle films produced by flat plate ablation resulted in oxidized and segregated particles due to extended, non-uniform plume expansion, laser target modification, and open porosity. Laser ablation of microparticles produced thick films with M[subscript s] = 13.8 emu/g. Two types of annealing treatments were performed to close porosity and increase Youngs modulus. Annealing of LAM films at temperatures up to 700°C in-situ and 950°C in a reducing atmosphere did not result in coarsening of the particles or crystallization of the Laves phase due to the core-shell structure of nanoparticles (rare earth oxide shell, Fe rich core) brought about by oxidation-induced segregation.Item Nanoparticles produced via laser ablation of microparticles(2001-12) Henneke, Dale Edwin; Mullins, C. B.; Brock, J. R. (James Rush), 1930-Several different nanoparticle synthesis techniques exist. One synthesis method uses the laser ablation of microparticles (LAM) entrained in an aerosol technique to produce charged nanoparticles. Here, we discuss nanoparticles made using the LAM process. Since nanoparticles made in this fashion are charged in the ablation process, they are not overly susceptible to agglomeration. The synthesized particles appear to have diameters that are dependant on background pressure, but are relatively insensitive to gas type. Once the particles have been made, they must be collected in a capping solution to prevent agglomeration from occurring. Two distinct methods of collection have been devised. The first collection scheme uses an impactor to remove any large (>300 [nm]) unablated material. The charged nanoparticle aerosol is then supersonically impacted directly into a surfactant capping solution. The suspension is then gathered for subsequent processing. In the second collection method, the charged nature of the nanoparticles is utilized to deflect the aerosol in an electric field. The electric field drives the particles onto a surfactant laden electrode. Size distributions for silver were determined using a transmission electron microscope; the mean particle diameter was found to be 5 [nm]. The collected nanoparticles were found to be flocculated; this can be explained by inadequate coverage of the capping molecule. For this reason, an annealing step to provide better surface coverage of the cap is performed. As the suspensions are heated, the size of the flocculents decreases. The decrease in flocculent size indicates that nanoparticles are leaving the main group and going into suspension.Item Nanostructured Ag produced by LAMA(2007) Albert, André David; Kovar, DesiderioItem Nanostructured Ag produced by LAMA(2007-05) Albert, André David; Kovar, DesiderioItem The osteology of Sarahsaurus aurifontanalis and geochemical observations of the dinosaurs from the type quarry of Sarahsaurus (Kayenta Formation), Coconino County, Arizona(2013-05) Marsh, Adam Douglas; Rowe, Timothy, 1953-Sarahsaurus aurifontanalis is the most recent sauropodomorph dinosaur to be discovered and named from the Early Jurassic of North America. The dinosaur is represented by a mostly complete and articulated holotype specimen that preserves a unique manual phalangeal count of 2-3-4-2-2 and accessory pubic foramen adjacent to the obturator foramen. The holotype of Sarahsaurus comprises a braincase and isolated cranial elements, but the skull previously referred to this taxon, MCZ 8893, can only be provisionally referred to Sarahsaurus until additional crania are found associated with postcranial material. Sarahsaurus comes from the middle third of the Kayenta Formation, which is considered to be Early Jurassic in age despite the absence of a radiometric date from that unit. A new technique used to obtain a U-Pb radiometric date from the type quarry of Sarahsaurus in the Kayenta Formation was influenced by secondary uranium enrichment in the open system of the fossil bone. That suggests that uranium within the Kayenta Formation may be the result of the movement of groundwater during the Laramide orogeny in the Late Cretaceous and Early Eocene, and lends support to the hypothesis that the uplift of the Colorado Plateau began relatively early in Late Cretaceous to the Eocene.Item Oxide-metal nanoparticles using laser ablation of microparticle aerosols(2009-08) Nahar, Manuj; Kovar, Desiderio; Becker, Miachel F.We have studied a continuous aerosol process for producing oxide nanoparticles with sizes of 10-60 nm that are decorated with smaller 1-3 nm metallic nanoparticles. Such particles may be useful in a number of areas including catalysis and as contrast enhancement agents in biomarkers. To produce the oxide nanoparticle carriers, an aerosol of 1-10 [micrometer] oxide particles are ablated using an excimer laser. The resulting oxide nanoparticle aerosol is then mixed with 1-2 [micrometer] metallic particles and this mixed aerosol is ablated a second time. The oxide nanoparticles are too small to ablate but act as seeds for the nucleation of metallic nanoparticles on the surface of the oxide. The nanoparticle sizes can be varied by changing the gas type or gas pressure in the aerosol. We demonstrate the feasibility of such an approach using two oxides, SiO₂ and TiO₂, and two metals, Au and Ag.Item Pulsed laser-induced material ablation and its clinical applications(2003) Lee, Ho; Diller, K. R. (Kenneth R.); Welch, Ashley J., 1933-Removing portions of a material, using a laser is referred to as laserinduced material ablation. The general goal of laser ablation is the efficient removal of material with minimum damage to the surrounding region. The appropriate selection of laser parameters, which determine the ablation mechanism, is essential to achieving a successful outcome. The research described in this dissertation was designed to evaluate the ablation mechanisms associated with pulsed lasers operating with different pulse durations and their medical applications. The role of a transparent liquid layer during a laser ablation process was studied. In comparison with a dry ablation process, the liquid-assisted ablation process resulted in augmented ablation efficiency and reduced ablation threshold. The results indicate that increased photon energy conversion to mechanical energy is responsible for the enhanced material ablation. Transparent targets were exposed to the one picosecond mid-IR pulse in order to investigate the origin of laser-induced surface damage. The results indicate that the surface damage was initiated by the laser-induced plasma created through the optical breakdown process. The retropulsive momentum of calculus during the Ho:YAG laser lithotripsy was measured using a high speed camera. The correlation between laser-induced crater shape, the trajectory of debris, and the retropulsive momentum is discussed. Due to the strong interaction between the laser pulse and calculus, the endoscopic delivery fiber may be subjected to damage resulting in diminished fragmentation efficiency. Deterioration of the delivery fiber during lithotripsy was quantified in terms of transmission loss and change in exit beam profile. To test the feasibility of Er:YAG laser lithotripsy, the fragmentation efficiency of Ho:YAG and Er:YAG lasers was compared. The results suggest that although the Er:YAG laser produced more precise drilling it did not create more fragmentation of calculus than the Ho:YAG laser for multiple pulse processes.Item Size distributions and nonlinear optical enhancement of silver nanoparticles produced by LAM(2011-05) Erickson, Nathan William; Keto, John W.; Becker, Michael; Downer, Michael; Fink, Manfred; Sitz, GregIn this dissertation, I will look into the size distribution of silver nanoparticles produced by laser ablation of microparticles (LAM). I will investigate the role of both pulsed and continuously operating nozzles on the size distribution. In addition, I will examine any deviations from the previously observed log-normal size distribution for silver nanoparticles comparing previous collection techniques involving supersonic jet impaction with a current time of flight mass spectrometer (TOF-MS). These new observations will be made in situ using a Wiley-McLaren TOF-MS with a reflector and multiphoton ionization and will mainly focus on the smaller sized nanoparticles. An introduction to enhancing a second harmonic optically generated signal will also be investigated involving silver nanocomposites while utilizing a polarized crossed-beam femtosecond laser technique.Item Supersonic jet deposition of laser ablated silver nanoparticles for mesoscale structures(2006) Huang, Chong; Becker, Michael F.Item Synthesis of amorphous metallic nanoparticles using a laser ablation process(2013-08) Gutierrez, Jean-Gil Rémy; Becker, Michael F.Amorphous metals have been discovered in 1960 and, because of their structures, exhibit very unique mechanical, magnetic and chemical properties that can have various applications. These properties qualify them as the potential material of the future. This work focuses on a new laser ablation technique to synthesize nanoparticles of amorphous metals from aqueous feedstock. One of the critical factors in the production of amorphous metal is the cooling rate used to synthesize them. The laser ablation of microparticle aerosol (LAMA) process used in this work, with a cooling rate estimated of 10¹² K/s, has all the characteristics required for the production of such metallic glasses. A Collison nebulizer is used to generate microdroplets of a nitrate solution containing the corresponding ratio of metals for the production of a Zr-Al-Ni based alloy. Once dried and conditioned, these microdroplets leave solid microparticles which are ablated by an excimer laser producing nanoparticles that are then filtered by virtual impaction. In order to characterize the nanoparticles obtained with this process nanoparticulate films produced by LAMA have been analyzed by optical profilometry, scanning electron microscopy (SEM) equipped with energy-dispersive x-ray spectroscopy (EDS) and transmission electron microscopy (TEM) equipped with EDS. The results agree with a hypothesis that the films contain oxidized, amorphous metal on the surface of the films. When the films are thin, they are fully oxidized, and simultaneous segregation of Zr occurs to the surface. The hypothesis and the results are discussed.Item Thermal-mechanical modeling of laser ablation hybrid machining(Texas Tech University, 2001-05) Matin, KaiserHard, brittle and wear-resistant materials like (ceramics pose a problem when being machined using conventional machining processes. Machining ceramics even with a diamond cutting tool is very difficult and costly. Near net-shape processes, like laser evaporation, produce micro-cracks that require extra finishing. Thus it is anticipated that ceramic machining will have to continue to be explored with new-sprung techniques before ceramic materials become commonplace. This numerical investigation results from the numerical simulations of the thermal and mechanical modeling of simultaneous material removal from hard-to-machine materials using both laser ablation and conventional tool cutting utilizing the finite element method. The model is formulated using a two dimensional, planar, computational domain. The process acronymed, LAHM (Laser Ablation Hybrid Machining), uses laser energy for two purposes. The first purpose is to remove the material by ablation. The second purpose is to heat the unremoved material that lies below the ablated material in order to "soften" it. The softened material is then simultaneously removed by conventional machining processes. The complete solution determines the temperature distribution and stress contours within the material and tracks the moving boundary that occurs due to material ablation. The temperature distribution is used to determine the distance below the phase change surface where sufficient "softening" has occurred, so that a cutting tool may be used to remove additional material. The model used for tracking the ablative surface does not assume an isothermal melt phase (e.g., Stefan problem) tor laser ablation. Both surface absorption and volume absorption of laser energy as a function of depth have been considered in the models. LAHM, from the thermal and mechanical point of view, is a (complex machining process involving large deformations at high strain rates, thermal effects of the laser, removal of materials and contact between workplace and tool. The theoretical formulation associated with LAHM for solving the thermal-mechanical problem using the finite element method is presented. The thermal formulation is incorporated in the user defined subroutines called by ABAQUS/Standard. The mechanical portion is modeled using ABAQUS/Explicit’s general capabilities of modeling interactions involving contact and separation. The results obtained from the FEA simulations showed that the cutting force decreases considerably in both the LAHM Surface Absorption (LAHM-SA) and LAHM volume absorption (LAHM-VA) models relative to the LAM model. It is observed that the HAZ can be expanded or narrowed depending on the laser speed and power. The cutting force is minimal at the last extent of the HAZ (heat affected zone). In both the models the laser ablates material thus reducing material stiffness as well as relaxing the thermal stress. The stress values obtained showed compressive yield stresses just below the ablated surface and chip. The failure occurs by conventional cutting where tensile stress exceeds the tensile strength of the material at that temperature. In this hybrid machining process, the advantages of both the conventional and laser machining processes were realized.