Laser Machining by short and ultrashort pulses, state of the art and new opportunities in the age of the photons

An overview is given of the applications of short and ultrashort lasers in material processing. Shorter pulses reduce heat-affected damage of the material and opens new ways for nanometer accuracy. Even forty years after the development of the laser there is a lot of effort in developing new and better performing lasers. The driving force is higher accuracy at reasonable cost, which is realised by compact systems delivering short laser pulses of high beam quality. Another trend is the shift towards shorter wavelengths, which are better absorbed by the material and which allows smaller feature sizes to be produced. Examples of new products, which became possible by this technique, are given. The trends in miniaturization as predicted by Moore and Taniguchi are expected to continue over the next decade too thanks to short and ultrashort laser machining techniques. After the age of steam and the age of electricity we have entered the age of photons now

Ultrafast Pulsed-Laser Applications for Semiconductor Thin Film Deposition and Graphite Photoexfoliation.

This thesis focuses on the application of ultrafast lasers in nanomaterial synthesis. Two techniques are investigated: Ultrafast Pulsed Laser Deposition (UFPLD) of semiconductor nanoparticle thin films and ultrafast laser scanning for the photoexfoliation of graphite to synthesize graphene. The importance of the work is its demonstration that the process of making nanoparticles with ultrafast lasers is extremely versatile and can be applied to practically any material and substrate. Moreover, the process is scalable to large areas: by scanning the laser with appropriate optics it is possible to coat square meters of materials (e.g., battery electrodes) quickly and inexpensively with nanoparticles. With UFPLD we have shown there is a nanoparticle size dependence on the laser fluence and the optical emission spectrum of the plume can be used to determine a fluence that favors smaller nanoparticles, in the range of 10-20 nm diameter and 3-5 nm in height. We have also demonstrated there are two structural types of particles: amorphous and crystalline, as verified with XRD and Raman spectroscopy. When deposited as a coating, the nanoparticles can behave as a quasi-continuous thin film with very promising carrier mobilities, 5-52 cm2/Vs, substantially higher than for other spray-coated thin film technologies and orders of magnitude larger than those of colloidal quantum dot (QD) films. Scanning an ultrafast laser over the surface of graphite was shown to produce both filamentary structures and sheets which are semi-transparent to the secondary-electron beam in SEM. These sheets resemble layers of graphene produced by exfoliation. An ultrafast laser “printing” configuration was also identified by coating a thin, transparent substrate with graphite particles and irradiating the back of the film for a forward transfer of material onto a receiving substrate. A promising application of laser-irradiated graphene coatings was investigated, namely to improve the charge acceptance of lead-acid battery electrodes. We demonstrated improvements of 63 % in the cycle lifetime and 23 % in the electrode charging conductance.PHDApplied PhysicsUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/120790/1/ioraiqat_1.pd

Femtosecond Laser Interaction with Ultrathin Metal Films: Modifying Structure, Composition, and Morphology

Femtosecond laser pulses allow for the study of materials in unique, and often extreme, conditions. As research regarding femtosecond laser interaction with materials progresses, the mechanisms for damage and modification are better understood. As a result, more complicated configurations of the target material can be explored often revealing new routes to modify materials. This work explores femtosecond laser irradiation of thin metal films and characterizes the resulting morphology, microstructure, and composition using optical microscopy, scanning electron microscopy, atomic force microscopy, transmission electron microscopy, and time-resolved pump-probe microscopy. Three areas are addressed; the removal of ultrathin metal films from non-absorbing substrates, mixing of multilayer Ni-W and Ni-Ag films to form thermally stable nanocrystalline alloys, and in-situ irradiation of Fe catalyst thin films to stimulate chemical vapor deposition of carbon nanotubes. A mechanistic understanding of the materials response was pursued for each case studied including the role of interfaces, and the interaction of solid, liquid, and gaseous phases formed by irradiation. The dynamics of femtosecond laser removal of ultrathin Ni films from glass substrates were measured using time-resolved pump-probe microscopy. Within 50 ps of irradiation the film-substrate interface separated and the removed layer accelerated to a constant velocity, faster than predicted by previous models. The Ni film was driven into extreme thermodynamic states after irradiation that caused the Ni film to rapidly decompose into a liquid-vapor mixture, similar to spinodal decomposition. Spinodal-like decomposition of a bulk metal after irradiation causes homogeneous nucleation of vapor; in this study spinodal-like decomposition caused heterogeneous nucleation at the Ni-substrate interface at relatively low fluences, broadening the range of temperatures to observe this process compared to previous studies. Studying the removal of ultrathin films provides a route to explore the extreme states of matter that occur after femtosecond laser irradiation. It has been predicted in previous studies that rapid cooling after femtosecond laser irradiation can drive homogeneous solidification in pure metals to form nanocrystalline material at the surface, however this is not generally observed. Ultrathin, multilayer films of Ni-W and Ni-Ag were irradiated with a single pulse and the resulting morphology and microstructure of the films were studied at a range of laser fluences. For Ni-W, a thermally stable nanocrystalline film was formed possibly due to solute stabilization of grain boundaries. The method for femtosecond laser mixing of multilayer metal thin films can be applied to create nanocrystalline surface layers for a wide range of alloy compositions that possess robust mechanical properties, increased corrosion resistance, unique magnetic properties, and are used as catalyst. Irradiation of carbon nanotube catalyst during Chemical Vapor Deposition stimulates the growth of aligned forests and in some cases increasing the terminal length of the aligned forest by up to 150X. It is shown that the femtosecond laser stimulates growth by combining Pulsed Laser Vaporization synthesis and Chemical Vapor Deposition, vaporizing the initial population of carbon nanotubes to jump start forest growth. This method provides a novel and simple route to efficient growth in systems where the static growth parameters are not optimized. Laser irradiation may also be used to pattern growth of aligned CNT forests without pre-pattering catalyst via photolithography, or post processing.PHDMaterials Science and EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/138559/1/keegschr_1.pd

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Department of Mechanical EngineeringRecently, a variety of laser-based surface modification methods have been applied to the industry. Laser has many good characteristics of surface modification. A laser is an electromagnetic wave and has a constant beam size. Laser beam is changed to the shape of beam suitable for processing through the optics and is used in the process. The laser beam is eventually irradiated only to the desired area on the surface of the specimen, and the surface is changed by the laser beam. Using lasers, it is very useful to process only the required area and to allow fine controls. Various methods, such as hardening, cladding, mirco-machining, annealing, etc,. are included in laser surface modification. Recently, laser annealing process was applied to the semiconductor industry at Samsung. The application of laser surface modification technology is considered a natural stream, because it has advantages over other technologies. It is a chemically clean process, easy to control process variables and can be operated by remote control, so we can benefit a lot from using lasers. The laser surface modification is very straightforward and easy to apply in various ways. This research suggests different ways of using lasers to change the surface of material, and direction for applying changed properties. In this dissertation, laser surface modification technology is used for optical and joining applications. The first chapter is about the motivation of this research and will describe the processes associated with laser surface modification used and the materials used and include the background of next chapters. Chapter 2 describes the graphenization of Diamond-like carbon using laser annealing and pulsed laser deposition. Diamond-like carbon film is deposited on glass using pulsed laser deposition and coated films is thermally changed through laser annealing. By measuring the transmittance and electrical conductivity of annealed films, we will identify the possibility of being used as transparent conductive films. Chapter 3 will describe how to improve the results obtained in chapter 2. The laser surface treatment used in this chapter is micromachining. The thin film on the surface is fabricated by picosecond laser and removed. Through the etching and patterning process of annealed films, we will describe how to improve electrical conductivity and transmittance. Based on the measurement results, the electrical conductivity and transmittance after patterning and etching process are predicted through a simple calculation. Chapter 4 describes laser induced periodic surface structures (LIPSS) using stainless steel as a material with femtosecond laser. This structure is feature that appears on a surface found only under certain process conditions and is associated with the electric field of the laser. This structure consists of a very small gaping pattern similar to the wavelength of a laser is used for various applications. In this chapter, the reflectance change is obtained depending on the surface geometry, including the surrounding process conditions in which LIPSS occurs. With reflectance from various process conditions, we can change the stainless-steel surface by adjusting the reflectance of the surface as desired. Chapter 5 deals with the coupling of copper materials using laser surface modification. ii Copper has very high reflectance for lasers of commonly used near-infrared. Thus, the pattern is fabricated on the copper surface to reduce the reflectance so that absorption rate for laser beam can be increased. Coupling on patterned surface occur in lower energy than on the normal copper surface. This research presents new attempts to change the optical and electrical properties of material surface and various perspectives using laser applying the optical changes of the surface to the joining applicatons.clos

Research in Basic Sciences: Results of some math and physics projects

Desde nuestra Facultad se presentan trabajos resultados de investigación que le aportan ignificativamente a las aplicaciones de las ciencias básicas y que son el resultado del compromiso y la dedicación de nuestros docentes investigadores, quienes trabajan para abordar problemas complejos y generar soluciones innovadoras y sostenibles. En el primer capítulo se presenta un estudio de las propiedades en nuevos materiales, en este caso del crecimiento de películas delgadas de grafeno en sustrato de silicio utilizando el método de deposición por láser pulsado (DLP) donde se utilizaron 6 técnicas de caracterización (Espectroscopía Raman, IRTF, MEB, SED, MFA, MACA) y como conclusión se tiene que las muestras similares al grafeno presentan propiedades de hidrofobicidad y las muestras de carbono amorfo tienen propiedades hidrofílicas. En el segundo capítulo se presenta un modelamiento matemático y una discusión sobre la existencia de soluciones de segunda clase en una ecuación de Tricomi, se plantea la existencia de soluciones periódicas de una generalización de la ecuación de Tricomi, el estudio se realiza mediante métodos perturbativos; de igual forma, se usa la función de Melnikov para encontrar las condiciones bajo las cuales se conservan las curvas homoclínicas. En el tercer capítulo se plantea una metodología de enseñanza-aprendizaje para enseñar la geometría descriptiva básica y la resolución de problemas a través del software Autocad.Publicación financiada con recursos de la Vicerrectoría de Investigaciones , Innovación y Extensión de la Universidad Tecnológica de PereiraVicerrectoría de Investigaciones , Innovación y Extensión de la Universidad Tecnológica de PereiraCONTENIDO Introducción ..................................................................................................................5 CAPÍTULO UNO Study of graphene growth onto silicon substrates by pulsed laser deposition method/ Estudio del crecimiento de grafeno en sustratos de silicio usando el método de deposición por láser pulsado ......................................................................................9 Henry Riascos Landázani - Juan David Lopez Vargas CAPÍTULO DOS A note about the existence of second-kind periodic solutions in tricomi’s equations/ Una nota sobre la existencia de soluciones de segunda clase en una ecuación de tricomi ......................................................................................................................35 Daniel Cortés Zapata - Alexander Gutiérrez Gutiérrez CAPÍTULO TRES Basic descriptive geometry with AUTOCAD/ Geometría descriptiva básica con AUTOCAD.............................................................49 Alberto García Lópe

Probing multipulse laser ablation by means of self-mixing interferometry

In this work, self-mixing interferometry (SMI) is implemented inline to a laser microdrilling system to monitor the machining process by probing the ablation-induced plume. An analytical model based on the Sedov-Taylor blast wave equation is developed for the expansion of the process plume under multiple-pulse laser percussion drilling conditions. Signals were acquired during laser microdrilling of blind holes on stainless steel, copper alloy, pure titanium, and titanium nitride ceramic coating. The maximum optical path difference was measured from the signals to estimate the refractive index changes. An amplitude coefficient was derived by fitting the analytical model to the measured optical path differences. The morphology of the drilled holes was investigated in terms of maximum hole depth and dross height. The results indicate that the SMI signal rises when the ablation process is dominated by vaporization, changing the refractive index of the processing zone significantly. Such ablation conditions correspond to limited formation of dross. The results imply that SMI can be used as a nonintrusive tool in laser micromachining applications for monitoring the process quality in an indirect way