Sol-Gel Glass Coating Synthesis for Different Applications: Active Gradient-Index Materials, Microlens Arrays and Biocompatible Channels

The intent of this chapter is to review the use of sol-gel processing of silica and silica-titania optical coatings in recent research by the authors in three different areas: the synthesis of active gradient-index (GRIN) materials by multilayer deposition of erbium- and ytterbium-doped silica-titania films, the improvement of the optical and morphological qualities of microlens arrays fabricated by laser ablation and the functionalization of polydimethylsiloxane (PDMS) channel preclinical devices. Through the use of sol-gel, layers with specific properties can be produced. In this regard, undoped and erbium- and ytterbium-doped SiO2-TiO2 films have been produced and characterized using atomic force microscopy (surface topography evaluation) and spectral ellipsometry (determination of optical constants, thickness and porosity of the films). In a second application, a silica sol has been synthesized to coat microlens arrays fabricated by laser ablation. The deposited layer reduces the surface roughness of the microlens array, which yields the improvement of the contrast and the homogeneity of the foci. Finally, PDMS channels fabricated with laser technologies and soft-lithography methods are coated with a sol-gel-derived silica film to avoid the degradation of the material with organic solvents, and their biocompatibility is studied

Laser-induced forward transfer (LIFT) of water soluble polyvinyl alcohol (PVA) polymers for use as support material for 3D-printed structures

The additive microfabrication method of laser-induced forward transfer (LIFT) permits the creation of functional microstructures with feature sizes down to below a micrometre [1]. Compared to other additive manufacturing techniques, LIFT can be used to deposit a broad range of materials in a contactless fashion. LIFT features the possibility of building out of plane features, but is currently limited to 2D or 2½D structures [2–4]. That is because printing of 3D structures requires sophisticated printing strategies, such as mechanical support structures and post-processing, as the material to be printed is in the liquid phase. Therefore, we propose the use of water-soluble materials as a support (and sacrificial) material, which can be easily removed after printing, by submerging the printed structure in water, without exposing the sample to more aggressive solvents or sintering treatments. Here, we present studies on LIFT printing of polyvinyl alcohol (PVA) polymer thin films via a picosecond pulsed laser source. Glass carriers are coated with a solution of PVA (donor) and brought into proximity to a receiver substrate (glass, silicon) once dried. Focussing of a laser pulse with a beam radius of 2 µm at the interface of carrier and donor leads to the ejection of a small volume of PVA that is being deposited on a receiver substrate. The effect of laser pulse fluence , donor film thickness and receiver material on the morphology (shape and size) of the deposits are studied. Adhesion of the deposits on the receiver is verified via deposition on various receiver materials and via a tape test. The solubility of PVA after laser irradiation is confirmed via dissolution in de-ionised water. In our study, the feasibility of the concept of printing PVA with the help of LIFT is demonstrated. The transfer process maintains the ability of water solubility of the deposits allowing the use as support material in LIFT printing of complex 3D structures. Future studies will investigate the compatibility (i.e. adhesion) of PVA with relevant donor materials, such as metals and functional polymers. References: [1] A. Piqué and P. Serra (2018) Laser Printing of Functional Materials. Weinheim, Germany: Wiley-VCH Verlag GmbH & Co. KGaA. [2] R. C. Y. Auyeung, H. Kim, A. J. Birnbaum, M. Zalalutdinov, S. A. Mathews, and A. Piqué (2009) Laser decal transfer of freestanding microcantilevers and microbridges, Appl. Phys. A, vol. 97, no. 3, pp. 513–519. [3] C. W. Visser, R. Pohl, C. Sun, G.-W. Römer, B. Huis in ‘t Veld, and D. Lohse (2015) Toward 3D Printing of Pure Metals by Laser-Induced Forward Transfer, Adv. Mater., vol. 27, no. 27, pp. 4087–4092. [4] J. Luo et al. (2017) Printing Functional 3D Microdevices by Laser-Induced Forward Transfer, Small, vol. 13, no. 9, p. 1602553

From Point Defects to Ripples: Ultrafast Laser Induced High Spatial Frequency Laser Induced Periodic Surface Structures.

The interaction between multiple intense ultrashort laser pulses and solids universally produces a regular surface corrugation. We have identified a coupled mechanism that operates in a specific range of fluences in semiconductors between the band-gap collapse and ultrafast-melt thresholds that produces a unique corrugation known as high spatial frequency laser induced periodic surface structures (HSFL). The structures have period < 0.3 times the laser wavelength and are predominately epitaxial single crystal. HSFL formation is initiated when the intense laser field softens the interatomic binding potential, which leads to an ultrafast generation of point defects. The interplay between surface plasmon polaritons and transient surface morphologies driven by strain relaxation, via diffusing defects, localizes the point defect generation, which results in the evolution and eventual completion of HSFL formation. Changing the material and laser wavelength dependent surface plasmon polariton response allows for either control over the HSFL period or complete inhibition of their formation. Control over the HSFL formation mechanism opens the potential for ultrafast laser directed self-assembly.PhDMaterials Science and EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/116658/1/abere_1.pd

Nonlinear Microscopy for Material Characterization

Making use of femtosecond laser sources, nonlinear microscopy provides access to previously unstudied aspects of materials. By probing third order nonlinear optical signals determined by the nonlinear susceptibility chi(3), which is present in all materials, we gain insight not available by conventional linear or electron microscopy. Third-harmonic (TH) microscopy is applied to supplement laser-induced damage studies of dielectric oxide thin film optical coatings. We present high contrast (S/N\u3e 100 : 1) TH imaging of ~17 nm nanoindentations, individual 10 nm gold nanoparticles, nascent scandia and hafnia films, and laser induced material modification both above and below damage threshold conditions in hafnia thin-films. These results imply that TH imaging is potentially sensitive to laser-induced strain as well as to nanoscale defects or contamination in oxide films. Compared to other sensitive imaging techniques such as Nomarski and dark field, TH imaging exhibits dramatically increased sensitivity to typical material modifications undergone during the formation of optical damage as evidenced by a dynamic range 10^6 : 1. Four-wave mixing (FWM) microscopy is employed to investigate delay dependent FWM signals and their implied characteristic resonant response times in multiple solvents. Mathematical modeling of resonant coherent anti-Stokes Raman scattering (CARS), coherent Stokes Raman scattering (CSRS) and stimulated parametric emission (SPE) processes supplement the FWM studies and suggest a resonant CARS process that accounts for ~95% of the total visible FWM signal which probes a characteristic material response time ~100 fs. This signal enhancement likely indicates the net effects of probing several Raman active C-H stretch bands near 2950 cm^-1. This FWM technique may be applied to characterize the dominant resonant response of the sample under study. Furthermore this technique presents the newfound capability to provide estimates of characteristic material dephasing times in combination with potential spatial resolution ~1 micron. In addition to TH and FWM microscopy, a genetic algorithm is developed and implemented that allows for the synthesis of arbitrary temporal waveforms to maximize the generation of nonlinear optical signals in the focal plane of a microscope without any prior knowledge of the experiment. This algorithm is demonstrated to compensate high order optical dispersion and thereby increase TH microscopy signals ~10x in a fused silica sample

Optically Induced Nanostructures

Nanostructuring of materials is a task at the heart of many modern disciplines in mechanical engineering, as well as optics, electronics, and the life sciences. This book includes an introduction to the relevant nonlinear optical processes associated with very short laser pulses for the generation of structures far below the classical optical diffraction limit of about 200 nanometers as well as coverage of state-of-the-art technical and biomedical applications. These applications include silicon and glass wafer processing, production of nanowires, laser transfection and cell reprogramming, optical cleaning, surface treatments of implants, nanowires, 3D nanoprinting, STED lithography, friction modification, and integrated optics. The book highlights also the use of modern femtosecond laser microscopes and nanoscopes as novel nanoprocessing tools

Focusing and delivery of laser radiation for nano- and microfabrication

The recent advances in nanotechnology and nanofabrication motivate the drive to achieve a tighter focusing of light; this requires a high numerical aperture (NA) optical system. The need for high optical resolution has led scientists to discover the use of optical microlens for improving the performance of high numerical aperture (NA) optical systems. By focusing the laser beam through a microlens, the width of the beam can be reduced according to the needs of the application. In this work, the laser beam was focused by a microspherical lens (NA=0.7) into 150 nm or by tapered fibre into 4 μm diameter spots. The measurements indicate the strong influence of tightly focused beams. This thesis comprises of three parts; the first results chapter investigates the choice of material by considering the material properties and feasibility of fabrication (chapter 2). It has been shown in previous studies that the glass transition temperature of the polymer is an important factor in determining the laser ablation rate. High glass transition temperatures make it a good material candidate for optical waveguides. Polycarbonate (PC), polymethylmethacrylate (PMMA), negative photoresist SU-8, and chitosan have been characterised to choose suitable material as a substrate for soft nanolithography (chapter 3). The choice of material due to the glass transition temperature of the material (from literature), material optical properties are investigated experimentally at the range of wavelength from 190 nm to 1000 nm. Laser ablation experiments on PC, PMMA, SU- 8 and chitosan using a 193 nm ArF laser over a fluence range of 10 mJcm−2 –1000 mJcm−2. The ablation threshold at 193nm was found to be 24, 110, 40, and 95 mJ.cm-2 for PC, PMMA, SU-8, and chitosan respectively. The photoresist SU-8 and chitosan were chosen as both materials are biocompatible, and have a high glass transition temperature. Optical properties measured for these materials found that both materials have much higher absorption coefficients (αSU-8 ~ 4.2×105m-1 and αchitosan ~3.3×105m-1) compared with PC and PMMA (αPC =1×105m-1 and αPMMA=2×105m-1 )at 193 nm.The second part of this thesis reports experimental and computational results of an irradiated laser microsphere supported on biocompatible materials; SU-8 photoresist and chitosan (chapter 3). An ArF excimer laser (193 nm wavelength) was used with 11.5 ns pulse width to modify the underlying substrate, producing a single concave dimple. Atomic force microscopy and scanning electron microscope measurements have been used to quantify the shape and size of laser inscribed dimple. The dimple has a diameter of 150 ± 10 nm FWHM and a depth of 190 ± 10nm on SU-8 compared to 180 ± 10 nm FWHM and a depth of 350 ± 10nm on chitosan due to the optical properties of the materials. Finite-difference time-domain (FDTD) simulations were carried out to simulate the propagation of 193 nm laser radiation, focussed by a 1 µm diameter silica sphere. Finite Element Method (FEM) simulations were carried out to calculate laser- induced temperature rise of the both SU-8 and Chitosan layer beneath the microsphere. The SiO2 microsphere acts as a small ball lens tightly focussing the laser radiation. Delivery of the focussed laser radiation locally heats the substrate beneath the microsphere. As a consequence, mass transport takes place, forming a nano dimple.The third part of this thesis presents the use of a CO2 laser (10.6 μm wavelength) for producing microlenses at the end of silica optical fibre (chapter 4). By focused CO2 laser beam, silica optical fiber is irradiated and heated to the softening points (1800 K) of the silica material. Surface tension and the parameters of the fabrication system shape the melted material into a spherical micro-lens or tapered fiber that remains joined to the optical fiber. Different core diameters (125, 400, 600, 1000, and 1500 μm) of multimode fibres have been used for this fabrication. The roughness of the microlens was reduced to less than 20 ± 1 nm roughness by polishing the surface with a CO2 laser at low power (1- 2 W). Throughout this work, different microlenses (ball/parabolic) and tapered fibres were fabricated at the end of silica optical fibre. The minimum spot diameter at FWHM was close to 160 μm and 110 μm for microball and parabolic lenses, respectively. While the tapers had the minimum waist diameters down to 4 μm and maximum taper length of ~ 3.5 mm using silica multi-mode fibre. Finally, the knife-edge technique and He-Ne laser beam (632.8 nm wavelength) were coupled into a fibre to investigate the properties of the microlenses which produced a minimum spot size of 5 ±1 μm at FWHM in the focal region of the tapered fibre lenses of 125, 400 and 600 μm core diameter of the fibre.As a result, Chitosan and SU-8 have been used as substrate materials for recording tightly focussed focal regions, 193nm ArF laser has been used to realise extremely small, 150nm diameter, Photonic Nano Jets (PNJ’s). FDTD optical simulations accurately predict the spatial properties of microsphere PNJ’s emitting at 193. CO2 laser (10.6 μm) radiation has been used to form tapers and spherical lenses on the distal end of optical fibres. Finally, tight focusing using microspheres and lensed optical fibres could be integrated on lab-on- chip platforms for applications such as optical trapping and cell membrane modifications. An important application related to the results of this study is that focusing laser light produces a force that can be used to remove or trap selected cells or large tissue areas from living cell culture down to a resolution of individual single cells and subcellular components similar to organelles or chromosomes, respectively.The nanostructures fabricated in this chapter can be refined to achieve specific dimensions in; diameter, depth, shape, and periodicity so they can be used as antireflective surfaces for solar-cell applications [1].or could be used in drug delivery [2]. While laser microbeams are frequently used for measurement or imaging of biological parameters as well as using the optical tweezer system for trapping or moving of cells, the future medical applications will be focused on micromanipulation or microdissection methods for delivering molecules or nano drugs into a cell [3]. Delivering such nano- drugs into cancer cells requires overcoming the cell membrane by focusing the laser. This phenomenon is named photoporation which is based on the generation of localized transient pores in the cell membrane using the photonic nano jet [4]

Femtosecond Laser Written Volumetric Diffractive Optical Elements And Their Applications

Since the first demonstration of femtosecond laser written waveguides in 1996, femtosecond laser direct writing (FLDW) has been providing a versatile means to fabricate embedded 3-D microstructures in transparent materials. The key mechanisms are nonlinear absorption processes that occur when a laser beam is tightly focused into a material and the intensity of the focused beam reaches the range creating enough free electrons to induce structural modification. One of the most useful features that can be exploited in fabricating photonic structures is the refractive index change which results from the localized energy deposition. The laser processing system for FLDW can be realized as a compact, desktop station, implemented by a laser source, a 3-D stage and focusing optics. Thus, FLDW can be readily adopted for the fabrication of the photonic devices. For instance, it has been widely employed in various areas of photonic device fabrication such as active and passive waveguides, couplers, gratings, opto-fluidics and similar applications. This dissertation describes the use of FLDW towards the fabrication of custom designed diffractive optical elements (DOE’s). These are important micro-optical elements that are building blocks in integrated optical devices including on-chip sensors and systems. The fabrication and characterization of laser direct written DOEs in different glass materials is investigated. The design and performance of a range of DOE’s is described, especially, laser-written embedded Fresnel zone plates and linear gratings. Their diffractive efficiency as a function of the fabrication parameters is discussed and an optimized fabrication process is realized. The potential of the micro-DOEs and their integration shown in this dissertation will impact on the fabrication of future on-chip devices involving customized iv DOEs that will serve great flexibility and multi-functional capability on sensing, imaging and beam shaping

Caracterización y control de plasmas de ablación láser para la síntesis de nuevos materiales y como medios ópticos no lineales

Tesis inédita de la Universidad Complutense de Madrid, Facultad de Ciencias Químicas, leída el 24-10-2016El trabajo descrito en esta memoria de tesis titulada: “Caracterización y control de plasmas de ablación láser para la síntesis de nuevos materiales y como medios ópticos no lineales”, ha sido realizado en el grupo de Láseres, nanoestructuras y procesado de materiales del Instituto de Química Física “Rocasolano” perteneciente al Consejo Superior de Investigaciones Científicas, CSIC en Madrid. El proceso de ablación láser tiene lugar cuando un haz lo suficientemente intenso interacciona con un material, generalmente designado como blanco de ablación. La radiación del láser es absorbida por el blanco, dando lugar a un aumento de su temperatura. Dependiendo de la intensidad de la radiación, pueden tener lugar procesos como la ruptura de enlaces, fundido y vaporización de las capas más próximas a la superficie y en última instancia la eyección de una pequeña cantidad de material formándose un plasma de ablación. El plasma generado se expande preferentemente en la dirección perpendicular a la superficie del material en forma de lo que se conoce como pluma de ablación. Como consecuencia del proceso, el material sufre una serie de cambios físicos observables en la superficie, siendo el más evidente la formación de un cráter. La ablación láser es por lo tanto un proceso muy complejo que depende de las propiedades de la radiación láser empleada y de las propiedades del material ablacionado. Por este motivo, la investigación encaminada a profundizar en los mecanismos de ablación y a extender y mejorar su aplicación en distintos ámbitos científicos y tecnológicos es de gran interés. Una de las características más destacables de la ablación láser es su universalidad, ya que en principio cualquier material puede ser ablacionado. El proceso de ablación permite retirar una pequeña cantidad de material de forma controlada y transferir a la fase gas especies que de otra forma sería complicado obtener. Todo ello hace de la ablación láser un proceso muy atractivo en campos como el procesado y la síntesis de materiales o el análisis químico, entre otros...The work described in this thesis, entitled: “Characterization and control of laser ablation plasmas for the synthesis of new materials and as optical nonlinear media”, was carried out in the Lasers, nanostructures and materials processing group at the Institute of Physical Chemistry “Rocasolano” of the Spanish National Research Council, CSIC in Madrid. Laser ablation is a physical process taking place as a consequence of the interaction of a sufficiently intense laser beam with a material, usually referred as ablation target. The energy deposited by the laser is absorbed by the target, leading to a temperature increase, which in turn, depending on the laser intensity, can lead to events like bond breaking, melting and vaporization of the surface layers and ultimately to ejection of a small amount of material generating a laser ablation plasma. The induced plasma expands preferentially in the direction normal to the target surface in the form of a plasma plume. As a consequence of the ablation, the material undergoes a series of observable physical changes. Laser ablation is therefore an extremely complex process, depending both on the properties of the laser radiation and on the properties of the target material. For this reason, research aimed at studying the ablation mechanisms and to extend and improve its application in different fields of science and technology is of great interest. One of the main characteristics of laser ablation is its universality, as in principle, all materials can be ablated. This process allows the controlled removal of a small amount of material and to entrain in the gas phase species that otherwise would be difficult to obtain. All these characteristics make laser ablation a highly attractive process in fields such as materials processing and synthesis or chemical analysis among others...Fac. de Ciencias QuímicasTRUEunpu

Fabrication of Lu doped YBCO thin films by pulsed laser deposition technique and their characterization

Thesis (Master)--Izmir Institute of Technology, Physics, Izmir, 2010Includes bibliographical references (leaves: 59-67)Text in English; Abstract: Turkish and Englishxi, 67 leavesNearly twenty years ago YBCO was the first superconductor discovered with a transition temperature above the boiling point of liquid nitrogen, the .fascinating. limit for high temperature superconductivity. From the day forward, the interest in this ceramic compound has not diminished. YBCO is one of the most promising materials for the application of high temperature superconductors (HTS) because it is able to carry a technically useful current density in applied fields at 77 K. A lot of experiments guided to investigate the basic properties of the HTS and to further the theoretica understanding of them also used YBCO, because this progress has been achieved in the preparation of bulk samples, and especially thin films deposited by a various methods. The aim of the experimental investigation presented in this thesis was to produce high quality epitaxial Lutetium doped YBCO thin films on MgO substrates prepared by pulsed laser deposition. For this purpose, bulk Lu2O3 powder was mixed into YBCO by using solid-state reaction method and pressed to make a stoichiometric target for PLD process. KrF excimer laser was worked at 14 Kv with repetition rates ranging from 3 to 5 Hz to deposited Y0.9Lu0.1Ba2Cu3O7-. thin films at a substrate temperature of 800 oC. The surface of the films were characterized by employing XRD, SEM, EDX and AFM techniques