Browsing by Subject "Laser ablation"

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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.
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.
Enhancement of high power pulsed laser ablation and biological hard tissue applications
(2006) Kang, Hyun Wook; Welch, Ashley J., 1933-
Pulsed lasers are used therapeutically to selectively remove tissue with minimal thermal and mechanical damage to peripheral tissue. The aims of this research are to understand the governing mechanisms of pulsed infrared laser tissue ablation, to obtain optimal laser parameters for precise laser treatment without collateral damage, and to develop methods for efficient tissue removal with the aid of liquid confinement. The effect of a liquid layer on laser metal ablation was examined. Acoustic pressure and optical reflectance provided information for determining the dominant mechanisms during metal ablation. The liquid-assisted ablation improved ablation efficiency and reduced the ablation threshold by as much as 40 % with respect to ablation in air. The degree of ablation was contingent on thermal and mechanical properties of the type of metal. The dynamics of laser osteotomy in a liquid environment was explored. The underlying mechanisms during liquid-assisted ablation included rapid vaporization, plasma confinement, and cavitation with jet formation. Compared to direct ablation, the liquid-confined ablation with higher ablation volume and augmented acoustic excitation demonstrated the feasibility of liquid-enhanced laser osteotomy. Acoustic transient measurement with a piezoelectric microphone, Schlieren flash photography, and temperature measurement with an IR camera were employed to study ablation mechanisms and the effect of water spray during long-pulsed laser ablation of dental tissues. Spray-assisted ablation created larger pressure transients and enhanced ablation efficiency. Water cooling by the spray provided a safe and efficient modality for dental treatment. Finally, optimal laser parameters for laser lithotripsy such as wavelength and pulse duration were studied. Higher light absorption of the Er:YAG (λ = 2.94 µm) laser produced more material removal than the Ho:YAG laser. In addition, during Ho:YAG laser lithotripsy, a smaller fiber diameter with a shorter pulse duration reduced the operative time and cumbersome process due to retropulsive kidney stone movement, providing efficient laser lithotripsy.
Improved aerosol density sensor for use in laser ablation of microparticle aerosol
(2017-05) Wimmer, Daniel Edward; Becker, Michael F.
The Laser Ablation of Microparticle Aerosol (LAMA) system in the Nanoparticle Research group at the University of Texas at Austin contains an aerosol density sensor (ADS) component that is critical to achieving accurate results when studying nanoparticle properties. The current ADS at work in the system has been found to possess some data accuracy concerns and a certain lack of usability. To improve on the design, a project was initiated to study the existing sensor to determine the weaknesses of the current design, derive a specific set of requirements for a new sensor, and complete the design and testing of a new ADS for use in the LAMA system. Overall, several major design areas were altered. A completely new LabVIEW data acquisition and processing application was created to monitor, log, and display the density data to the operator, several mechanical components were given additional features to preserve the density signal of the sensor, and the low-voltage DC power supply and signal processing circuitry were significantly redesigned. Advanced testing was performed on the final product to verify that it meets all requirements of the research group and is both reliable and accurate.
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, Philippe
This 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.
Laser beam shaping for surgery and microbiopsy
(2022-05-06) King, Jason Brett; Tunnell, James W.; Milner, Thomas E.; Parekh, Sapun; Teichman, Joel MH
Lasers are increasingly being used in surgery in a wide range of medical specialties due to their advantages over alternative surgical tools including precise material removal, limited bleeding due to coagulation around the incision site, and delivery through optical fibers enabling use in body cavities and for minimally invasive surgeries. Advancements in laser technology including new laser wavelengths and higher power continue to improve the performance and implementation of surgical lasers. Temporal beam shaping, or pulse modulation, has been implemented into clinical laser systems to increase efficiency of urological surgeries, leading to faster, safer procedures. However, the precise mechanisms of temporally shaped laser pulses on ablation are not fully understood. The effects of spatial beam shaping on laser tissue ablation have not previously been explored. Understanding the impact of temporal and spatial laser beam on laser ablation will improve the performance and increase the applications of laser surgery. In this dissertation a Ho:YAG laser was temporally and spatially altered and the effects on tissue ablation were explored. The first portion of this dissertation focuses implications of beam shaping on laser ablation efficiency. First, mechanisms of laser ablation with temporal pulse modulation are explored. We explore the mechanisms of pulse modulated ablation including experiments on phantoms and native kidney stones. We discovered that increased ablation efficiency by pulse modulation is composition dependent. Next, increased ablation efficiency by altering laser spatial shape is explored. We discovered that shaping the laser beam into an annular shape led to an increase ablation efficiency is both hard and soft tissues. The second portion of this dissertation focuses on application of spatially shaped laser ablation for laser microbiopsy. A novel method for harvesting sub-microliter (<1 mm³) tissue samples using an annular beam is described. Laser beam shaping, pulse energy, and application of cryogen spray cooling were optimized to successfully harvest tissue sections with observable histological features. Harvested tissues were imaged with confocal microscopy and “virtual H&E” methods were used to digitally color the images to mimic H&E stained tissue sections. Laser microbiopsy with virtual H&E is minimally invasive, precise, and provides images in a fraction of the time of the traditional pathology workflow.
Laser processing of Tb0.3Dy0.7Fe1.92 films
(2007-12) Ma, Dat Truong; Kovar, Desiderio
In 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.
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.
Nanostructured Ag produced by LAMA
(2007-05) Albert, André David; Kovar, Desiderio
The Laser Ablation of Microparticle Aerosol (LAMA) process is a technique for generating aerosolized nanoparticles (NPs) from a variety of starting materials. The NP aerosol produced from the LAMA process can be accelerated through a nozzle and impacted onto a substrate, with a deposition rate up to 60 mg/hour. This direct-write process can be used to create nanostructured lines or films up to hundreds of microns thick. NPs generated from the LAMA process are bare – they are not capped by an organic like NPs generated from chemical processes. This attribute may result in significantly lower processing temperatures for the written lines, even compared to other methods involving NPs produced by chemical processes (e.g., ink-jet printing). In this dissertation, we investigated the use of LAMA-produced Ag lines for bonding surfaces at low process temperatures (100 to 175°C). We studied the effects of process temperature and compression load on the strength of the Ag bonds, as well as the resistivity and the grain size of Ag deposits produced by LAMA. With these measurements and the use of known relationships between grain size and conductivity, we determined the effects of processing parameters on the final density of the Ag deposits. The strength and resistivity measurements compare favorably with similar work but at processing temperatures 50 to 100°C lower than previously achieved. The densification results agree qualitatively with established theory for pressure-assisted sintering.
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.
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.
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.
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, Greg
In 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.
Supersonic jet deposition of laser ablated silver nanoparticles for mesoscale structures
(2006) Huang, Chong; Becker, Michael F.
The Laser Ablation of Microparticle Aerosols (LAMA) technique was used to generate silver nanoparticles and they were supersonically impacted on different substrates to form mesoscale functional structures in this study. The electrical signal of the plume generated by the laser ablation of microparticle aerosol in 1 atm was diagnosed with a series of Faraday cups and the related recombination process was studied to understand the properties of the charged silver nanoparticles in this high pressure dusty plasma. The experimental results shows that the silver NPs carries positive charge and the charge decays approximately exponentially with respect to the traveling time and the 1/e decay time increases about 60% when an anode layer is added near the ablation zone. Supersonically deposited silver nanostructured films were deposited using He and Ar gas through a flat plate and conical nozzles. The films were characterized to vii determine their morphologies, strains, and their conductivity changes with respect to the different annealing processes. It was found that the as deposited films tended to retain the internal feature dimension and crystallite grain size of the deposited nanoparticles. Increased impaction energy increased the film density and promoted sintering and neck formation without significant grain growth for deposition at room temperature. The silver films deposited in helium showed a higher density than in Ar. The annealing of the silver films produced in helium and Ar by using a flat plate nozzle showed a trend of conductivity increase as the annealing temperature increased. And the conductivity of the silver films deposited in helium was relatively higher than that of the film deposited in Ar. After heat treatment at 400ºC for 90 minutes, the silver film deposited in helium has a conductivity of 47% of the bulk silver conductivity. Modeling results shows density of the film deposited through flat plate nozzle in He has relatively higher density than the film deposited in Ar through flat plate nozzle. Annealing did not change the density of the films deposited in the same condition.
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.