This thesis is concerned with the use of zone plate interferometers for the precise location of position. The thesis begins by discussing the use of the zone plate as an optical component and examines the wavefront aberrations that can occur in higher orders of diffraction. Interferometers applicable to the measurement of position are then reviewed, including interferometers that incorporate optical zone plates as beam dividers and beam combiners. A zone plate interferometer for defining and locating multiple positions in three-dimensions is reported. Here, a three-dimensional array of positions is defined by a two-dimensional array of reflective zone plates. An optical probe containing two zone plates completes the interferometer, and is used to locate the positions. The displacement sensitivity of the probe can be controlled at the optical design stage. The variation of sensitivity with wavefront geometry is explored and expressions are derived for the transverse and axial sensitivity in terms of the conjugates of the illuminating wavefronts. Various wave front configurations were experimented with and the resulting position location patterns recorded. The measured values of sensitivity to displacement are compared to theory. A version of this interferometer was designed and developed by the author, for checking the performance of three-coordinate measuring machines used in engineering metrology. The results of trials with the interferometer, comparing the performance of measuring machines in several government laboratories, are reported. The averaged repeatability of setting, on one optically defined position, was found to be 1 μm in the transverse directions and 6 μm in the axial direction. Resulting from this work, two simple devices for pointing are described. Each uses a pair of zone plates to define an optical axis. In one case, the axis is precisely located by positioning a coherent light source and observing the interference bands generated by the device. In the other, moire bands are observed in incoherent illumination.

Thesis (Ph.D)--Electrical and Computer Engineering, Georgia Institute of Technology, 2009. / Committee Chair: Glenn S. Smith; Committee Member: Andrew F. Peterson; Committee Member: Gregory D. Durgin; Committee Member: John W. Schultz; Committee Member: Waymond R. Scott, Jr.. Part of the SMARTech Electronic Thesis and Dissertation Collection.

Hard x-ray free-electron lasers are novel sources of coherent x-rays with unprecedented brightness and very short pulses. The radiation from these sources enables a wide range of new experiments that were not possible with previous x-ray sources. Many of these experiments require the possibility to focus the intense x-ray beam onto small samples. This Thesis investigates the possibility to use diffractive zone plate optics to focus the radiation from hard x-ray free-electron lasers. The challenge for any optical element at free-electron laser sources is that the intensity in a single short pulses is high enough to potentially damage the optics. This is especially troublesome for zone plates, which are typically made of high Z elements that absorb a large part of the incident radiation. The first part of the Thesis is dedicated to simulations, where the temperature behavior of zone plates exposed to hard x-ray free-electron laser radiation is investigated. It is found that the temperature increase in a single pulse is several hundred Kelvin but still below the melting point of classical zone plate materials, such as gold, tungsten, and iridium. Even though the temperature increases are not high enough to melt a zone plate it is possible that stresses and strains caused by thermal expansion can damage the zone plate. This is first investigated in an experiment where tungsten gratings on diamond substrates are heated to high temperatures by a pulsed visible laser. It is found that the gratings are not damaged by the expected temperature fluctuations at free-electron lasers. Finally, a set of tungsten zone plates are tested at the Linac Coherent Light Source where they are exposed to a large number of pulses at varying fluence levels in a prefocused beam. Damage is only observed at fluence levels above those typically found in an unfocused x-ray free-electron laser beam. At higher fluences an alternative is to use a diamond zone plate, which has significantly less absorption and should be able to survive much higher fluence. Damage in diamond structures is investigated during the same experiment, but due to a remaining tungsten etch mask on top of the diamond the results are difficult to interpret. Additionally, we also demonstrate how the classical Ronchi test can be used to measure aberrations in focusing optics at an x-ray free-electron laser in a single pulse. The main result of this Thesis is that tungsten zone plates on diamond substrates can be used at hard x-ray free-electron laser sources. / <p>QC 20130514</p>

This Thesis describes the development of hard X-ray zone plates intended for focusing radiation at X-ray free-electron lasers (XFELs). XFELs provide unprecedented brightness and zone plates which are put in the intense X-ray beam are at risk of being damaged. Therefore, it is crucial to perform damage tests in order to design zone plates which can survive the XFEL beam. Zone plates are diffractive nanofocusing optics and are regularly used at high brightness synchrotron beamlines in the soft and hard X-ray regime. The resolution of a zone plate is proportional to its outermost zonewidth and thus depends on the smallest feature that can be fabricated. State-of-the-art nanofabrication processes developed for zone plates are able to produce zonewidths down to 10 nm. However, for hard X-rays, the zone plates need to be of sufficient thickness to efficiently focus the radiation. Thus, the limit in the fabrication of hard X-ray zone plates lies in the high aspect-ratios. This Thesis describes two processes developed for high aspect-ratio nanostructuring. The first process uses tungsten as diffractive material. Aspect-ratios up to 1:15 have been accomplished. Furthermore, a mounting method of a central stop directly on the zone plate is also presented. The other fabrication process uses diamond, in which aspect-ratios of 1:30 have been demonstrated. Both processes rely on thin-film deposition techniques, electron-beam lithography, and reactive ion etching. Thanks to the materials’ excellent thermal properties these types of zone plates should be suitable for XFEL applications. Tungsten and diamond diffractive optics have been tested at an XFEL at Stanford (LCLS), and damage investigations were performed in order to determine the maximum fluence that could be imposed on the optics before degradation occured. The conclusion of these damage tests is that tungsten and diamond diffractive optics can survive the XFEL beam and could potentially be used in beamline experiments relying on nanofocused X-ray beams. Finally in this Thesis, characterization of two zone plates using an interferometer is presented, where it is also shown that the interferometric method can be used to pin-point beamline instabilities. / <p>QC 20150112</p>

Soft x-ray microscopy in the water-window (λ = 2.28 nm – 4.36 nm) is based on zone-plate optics and allows high-resolution imaging of, e.g., cells and soils in their natural or near-natural environment. Three-dimensional imaging is provided via tomographic techniques, soft x-ray cryo tomography. However, soft x-ray microscopes with such capabilities have been based on large-scale synchrotron x‑ray facilities, thereby limiting their accessibility for a wider scientific community. This Thesis describes the development of the Stockholm laboratory soft x-ray microscope to three-dimensional cryo tomography and to new optics-based contrast mechanisms. The microscope relies on a methanol or nitrogen liquid-jet laser-plasma source, normal-incidence multilayer or zone-plate condenser optics, in-house fabricated zone-plate objectives, and allows operation at two wavelengths in the water-window, λ = 2.48 nm and λ = 2.48 nm. With the implementation of a new state-of-the-art normal-incidence multilayer condenser for operation at λ = 2.48 nm and a tiltable cryogenic sample stage the microscope now allows imaging of dry, wet or cryo-fixed samples. This arrangement was used for the first demonstration of laboratory soft x-ray cryo microscopy and tomography. The performance of the microscope has been demonstrated in a number of experiments described in this Thesis, including, tomographic imaging with a resolution of 140 nm, cryo microscopy and tomography of various cells and parasites, and for studies of aqueous soils and clays. The Thesis also describes the development and implementation of single-element differential-interference and Zernike phase-contrast zone-plate objectives. The enhanced contrast provided by these optics reduce exposure times or lowers the dose in samples and are of major importance for harder x-ray microscopy. The implementation of a high-resolution 50 nm compound zone-plate objective for sub-25-nm resolution imaging is also described. All experiments are supported by extensive numerical modelling for improved understanding of partially coherent image formation and stray light in soft x-ray microscopes. The models are useful tools for studying effects of zone plate optics or optical design of the microscope on image formation and quantitative accuracy in soft x-ray tomography. / QC 20110221

Diffractive zone-plate lenses are widely used as optics in high-resolution x-ray microscopes. The achievable resolution in such microscopes is presently not limited by the x-ray wavelength but by limitations in zone-plate nanofabrication. Thus, for the advance of high-resolution x-ray microscopy, progress in zone-plate nanofabrication methods are needed.   This Thesis describes the development of new nanofabrication processes for improved x-ray zone-plate optics. Cold development of the electron-beam resist ZEP7000 is applied to improve the resolution of soft x-ray Ni zone plates. The influence of developer temperature on resist contrast, resolution, and pattern quality is investigated. With an optimized process, Ni zone plates with outermost zone widths down to 13 nm are demonstrated. To enhance the diffraction efficiency of Ni zone plates, the concept of Ni-Ge zone plates is introduced. The applicability of Ni-Ge zone plates is first demonstrated in a proof-of-principle experiment, and then extended to cold-developed Ni zone plates with outermost zone widths down to 13 nm. For 15-nm Ni-Ge zone plates a diffraction efficiency of 4.3% at a wavelength of 2.88 nm is achieved, which is about twice the efficiency of state-of-the-art 15-nm Ni zone plates. To further increase both resolution and diffraction efficiency of soft x-ray zone plates, a novel fabrication process for W zone plates is developed. High resolution is provided by salty development of the inorganic electron-beam resist HSQ, and cryogenic RIE in a SF6 plasma is investigated for high-aspect-ratio W structuring. We demonstrate W zone plates with 12-nm outermost zone width and a W height of 90 nm, resulting in a 30% increase in theoretical diffraction efficiency compared to 13-nm efficiency-enhanced Ni-Ge zone plates. In addition to soft x-ray zone plates, some lenses for hard x-ray free-electron-laser applications were also fabricated during this Thesis work. Fabrication processes for the materials W, diamond, and Pt were developed. We demonstrate Pt and W-diamond zone plates with 100-nm outermost zone width and respective diffraction efficiencies of 8.2% and 14.5% at a photon energy of 8 keV. / QC 20111114

In this research, Fresnel zone plates were studied using an accurate, full-electromagnetic simulator based on the body-of-revolution finite-difference time-domain (BOR-FDTD) method. This tool was used to investigate zone plates for two different applications: zone plates used as antennas in communication systems and zone plates used as focusing elements in free-space, focused-beam measurement systems. Through detailed studies of zone plates for these applications, a number of general characteristics of the zone plate were given a more in-depth look than they have been given in the past. For the first application, parametric studies were performed for Soret, folded, and grooved-dielectric, phase-correcting zone plates for antenna applications. These studies were used to generate new design graphs, from which general observations are made about the effect of varying different parameters on the focusing ability of a zone plate. For the grooved-dielectric, phase-correcting zone plate, these studies show that a number of factors influence the focusing ability in ways that are unexpected, based on many of the simple techniques typically used to analyze zone plates. Each of these factors is evaluated individually. For the second application, a zone plate was designed to be used as a focusing element in a free-space, focused-beam measurement system. To determine the suitability of zone plates for this application, simulations and measurements of the electric field were used to compare this zone plate to a doubly-hyperbolic lens. A complete focused-beam system, using two zone plates as focusing elements, was used to measure the permittivity of different dielectric materials. These measurements are compared to results for a system that uses doubly-hyperbolic lenses and to published values. A technique for increasing the usable bandwidth of a zone plate in a focused-beam system was proposed and tested. Finally, as a topic for future research, the question is posed: Using the BOR-FDTD method, can a similar volume of material be shaped in a way that results in improved focusing performance compared to a traditional zone plate? Some insight into this open-ended question can be gained by examining preliminary results of the optimization of zone plates using of a genetic algorithm.

This thesis discusses optoelectronic devices at mm-wave frequencies, focusing on optoelectronic beamforming and non-mechanical beam steering based on an optically excited Fresnel zone plate plasma. The optically controlled zone plate, termed the photo-injected Fresnel zone plate antenna (piFZPA) within this work, is introduced and a comprehensive theoretical framework developed. The design and optimisation of Fresnel zone plates are detailed, which determine the inherent performance of the piFZPA. A range of zone plates were designed, fabricated, and characterised at 94 GHz with up to 46 dBi gain, -26 dB sidelobe levels, and 67% aperture efficiency being measured for a quarter-wave design. The control of (sub) mm-wave beams by optical modulation of the complex permittivity of a semiconductor substrate is discussed. The significance of the free-carrier plasma dynamics, the effective lifetime, surface recombination, and the limits of the substrate which are imposed by the spatial resolution of the free-carrier plasma are highlighted, with the optimisation of these parameters discussed. The passivation quality of high-resistivity silicon wafers were characterised using a mm-wave photoconductance decay method, which yielded lifetime improvements from τ[subscript(eff)] = 60 us up to τ[subscript(eff)] ≈ 4,000 us, resulting in lowered recombination velocities (S = 15 cm/s). W-band characterisations of the passivated wafers illustrate the significance of surface recombination, with measured attenuations of up to 24 dB. Novel theoretical models are developed throughout this thesis, which yield insight into the requirements of optoelectronic devices, and are shown to agree well with measured data. The theoretical framework developed details the requirements, limitations, suitability, and design of piFZPAs at any frequency. A range of transmission-type piFZPAs are demonstrated and characterised at 94 GHz, both on-axis and off-axis, based on a novel architecture, with up to 8% aperture efficiency. Finally, the hybridisation of the piFZPA technique and well established visible display technologies, which has been developed throughout this thesis, enable low-cost, simple, and highly flexible optoelectronic devices, highlighting this method as an attractive solution to adaptive beamforming and non-mechanical steering at mm-wave and submm-wave frequencies.

Tesis por compendio / [ES] La capacidad de controlar y modificar los haces de energía ha sido motivo de investigación por parte de la comunidad científica desde largo tiempo atrás. En el campo de la acústica, este control energético de las ondas mecánicas tiene numerosas aplicaciones. Desde las aplicaciones industriales, alimentarias, farmacéuticas, etcétera hasta la biomedicina. Esta tesis se basa en la aplicación del control y modulación focal de los ultrasonidos para el uso en este último campo. Se puede modular y controlar los focos de ultrasonidos de diferentes formas. En este caso, se han desarrollado lentes planas que utilizan el principio de la difracción para lograr focalizar los haces. Las ventajas del uso de lentes planas de focalización permiten ser implementadas de forma sencilla en procesos de mecanización e incluso mediante impresión 3D. Se propone utilizar transductores planos que al emitir sobre una lente acústica, se produzca una conformación focal de características controladas. La lente conocida como lente de Fresnel (FZP) ha sido escogida como base de diseño en la implementación de las diferentes soluciones que logran cumplir con los objetivos marcados. Mediante la aplicación de modificaciones en una FZP se puede lograr pasar de una lente con capacidades extraordinarias de focalización a una lente capaz de controlar la resolución lateral y la profundidad de foco e incluso mejorar la ganancia. El objetivo final de aplicación es el uso en transductores de ultrasonidos de alta intensidad conocidos como HIFU. Mejorar la capacidad de resolución hace que se puedan desarrollar mejores terapias oncológicas que supongan un índice mayor de éxito en la lucha contra el cáncer. En la presente tesis se ha propuesto, además, una novedosa lente FZP basada en el cambio de fase que puede resultar un antes y un después en aplicaciones biomédicas. Se ha conseguido no solo mejorar la eficiencia de una FZP, sino que se ha conseguido implementar en materiales compatibles con resonancia magnética. Se han desarrollado modelos numéricos basados en el método de los elementos finitos que emulan la física involucrada. Las medidas han sido realizadas en condiciones controladas por un sistema robotizado de alta precisión. Todos los resultados obtenidos y publicados han sido desarrollados de forma numérica y experimental, validándose el método de trabajo y dando consistencia a las soluciones propuestas. / [CA] La capacitat de controlar i modificar els feixos d'energia ha sigut motiu d'investigació per part de la comunitat científica des de llarg temps arrere. En el camp de l'acústica, este control energètic de les ones mecàniques té nombroses aplicacions. Des de les aplicacions industrials, alimentàries, farmacèutiques, etcètera fins la biomedicina. Esta tesi es basa en l'aplicació del control i modulació focal dels ultrasons per a l'ús en este últim camp. Es pot modular i controlar els focus d'ultrasons de diferents formes. En este cas, s'han desenvolupat lents planes que utilitzen el principi de la difracció per a aconseguir focalitzar els feixos. Els avantatges de l'ús de lents planes de focalització permeten ser implementades de forma senzilla en processos de mecanització i inclús per mitjà d'impressió 3D. Es proposa utilitzar transductores plans que a l'emetre sobre una lent acústica, es produïsca una conformació focal de característiques controlades. La lent coneguda com a lent de Fresnel (FZP) ha sigut triada com a base de disseny en la implementació de les diferents solucions que aconseguixen complir amb els objectius marcats. Per mitjà de l'aplicació de modificacions en una FZP es pot aconseguir passar d'una lent amb capacitats extraordinàries de focalització a una lent capaç de controlar la resolució lateral i la profunditat de focus i inclús millorar el guany. L'objectiu final d'aplicació és l'ús en transductores d'ultrasons d'alta intensitat coneguts com HIFU. Millorar la capacitat de resolució fa que es puguen desenvolupar millors teràpies oncològiques que suposen un índex major d'èxit en la lluita contra el càncer. En la present tesi s'ha proposat, a més, una nova lent FZP basada en el canvi de fase que pot resultar un abans i un després en aplicacions biomèdiques. S'ha aconseguit no sols millorar l'eficiència d'una FZP, sinó que s'ha aconseguit implementar en materials compatibles amb ressonància magnètica. S'han desenvolupat models numèrics basats en el mètode dels elements finits que emulen la física involucrada. Les mesures han sigut realitzades en condicions controlades per un sistema robotitzat d'alta precisió. Tots els resultats obtinguts i publicats han sigut desenvolupats de forma numèrica i experimental, validant-se el mètode de treball i donant consistència a les solucions proposades. / [EN] The ability to control and modify energy beams has been the subject of research by the scientific community for a long time. In the acoustic field, this energetic control of mechanical waves has numerous applications. From industrial, food, pharmaceutical applications, et cetera, to biomedicine. This thesis is based on the ultrasound control and focal modulation applications. It is possible to modulate and control the ultrasound focii in different ways. In this case, flat lenses were developed based on the principle of diffraction to focus the beams. The advantages of using flat focusing lenses allow them to be easily implemented in machining and drilling processes and even through 3D printing. It was proposed to use planar transducers that when emitting on an acoustic lens, controlled characteristics of focal conformation were produced. The lens known as Fresnel Zone Plane (FZP) was chosen as the implementation design basis for the different solutions that manage to fulfill the objectives set. By applying modifications to an FZP it was possible to go from a lens with extraordinary focusing capabilities to a lens that was capable to control lateral resolution, depth of focus and even improving the gain. The final objective application was the use in high intensity ultrasound transducers known as HIFU. Improving the ability to resolve makes it possible to develop better cancer therapies that represent a higher rate of success in the fight against cancer. In the present thesis, a novel FZP lens based on phase change has also been proposed that can be a before and after in biomedical applications. It has not only been possible to improve the efficiency of an FZP, but it has also been possible to implement it in materials compatible with magnetic resonance imaging. Numerical models based on the finite element method were developed for emulating the involved physics. Measurements were carried out under controlled conditions by a high precision robotic system. All the results obtained and published were developed numerically and experimentally, validating the working method and giving consistency to the proposed solutions. / I want to acknowledge the following public funding sources that have made possible this research: Grant BES-2016-077133 (Ministerio de Ciencia, Innovación y Universidades de España) Project TEC2015-70939-R (MINECO/FEDER). Tomsk Polytechnic University within the framework of Tomsk Polytechnic University Competitiveness Enhancement Program. / Tarrazó Serrano, D. (2020). Design, modelling, characterization and implementation of acoustic lenses for modulation of ultrasound beams [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/159895 / TESIS / Compendio

Tesis por compendio / [ES] La focalización de ultrasonidos tiene muchas aplicaciones en una gran variedad de áreas tanto científicas como industriales. Los ultrasonidos focalizados son una de las herramientas principales usada por médicos en todo el mundo para obtener imágenes biomédicas de diferentes tipos de tejidos y órganos de manera no invasiva. En las últimas décadas, el uso de ultrasonidos focalizados de alta intensidad (HIFU, por sus siglas en inglés) ha surgido como una de las técnicas principales para el tratamiento de cáncer mediante la ablación térmica de tumores de manera no invasiva. Además, los ultrasonidos focalizados están emergiendo en los últimos años como uno de los métodos más prometedores para el tratamiento de las enfermedades cerebrales, con la aparición de nuevas técnicas disruptivas como la apertura reversible de la barrera hematoencefálica o la neuromodulación. En entornos industriales, los ultrasonidos son ampliamente utilizados como uno de los métodos principales para la evaluación no destructiva de materiales y estructuras, debido a que las ondas acústicas pueden penetrar en los objetos a distancias donde la luz no puede debido a la elevada absorción y dispersión. En este sentido, diseñar estructuras capaces de focalizar ultrasonidos es de una gran relevancia tanto para la comunidad científica como para los sectores médicos e industriales. Esta tesis presenta nuevos diseños de lentes acústicas capaces de controlar los parámetros principales del haz de ultrasonidos focalizados, proporcionando diferentes tipos de perfiles de focalización adecuados para una gran variedad de aplicaciones y escenarios. En particular, se han diseñado y adaptado al campo de los ultrasonidos las lentes de Fresnel (Fresnel Zone Plates, FZPs), ampliamente utilizadas en el campo de la óptica. Se ha presentado una nueva técnica de modulación espacio-temporal capaz de controlar la posición del foco de ultrasonidos tanto en espacio como en tiempo, aumentando así la versatilidad de este tipo de dispositivos. También se ha demostrado el funcionamiento en el campo de la acústica de nuevos diseños basados en aplicar secuencias binarias a una lente de Fresnel convencional, como las secuencias fractales de Cantor o las secuencias de M-bonacci generalizadas, capaces de modificar las propiedades de focalización de las lentes, incluyendo el número, posición y forma de los focos acústicos. Además, se introduce un nuevo diseño de lentes esféricas rellenas de líquido capaces de generar jets ultrasónicos, con mucho potencial en aplicaciones de imagen de alta resolución en campo cercano. Se ha demostrado que, cambiando el líquido interno de la lente o ajustando el ratio de mezcla entre dos líquidos, se pueden controlar los parámetros principales del jet. Los diseños propuestos en la tesis han sido validados tanto empleando simulaciones numéricas como realizando medidas experimentales, allanando el camino para el uso de este tipo de estructuras en aplicaciones de focalización de ultrasonidos. / [CA] La focalització d'ultrasons té moltes aplicacions en moltes àrees científiques i industrials. Els ultrasons focalitzats són una de les eines principals utilitzada per metges a tot el món per obtenir imatges biomèdiques de diferents tipus de teixits i òrgans de manera no invasiva. En les últimes dècades, els ultrasons focalitzats d'alta intensitat (HIFU, per les seues sigles en anglès) han aparegut com una de les tècniques principals per al tractament de càncer mitjançant l'ablació de tumors de manera no invasiva. A més, els ultrasons focalitzats estan emergint en els últims anys com un dels mètodes més prometedors per al tractament de les malalties cerebrals, amb l'aparició de noves tècniques disruptives com l'obertura reversible de la barrera hematoencefàlica o la neuromodulació. En entorns industrials, els ultrasons són àmpliament utilitzats com un dels mètodes principals per a l'avaluació no destructiva de materials i estructures, pel fet que les ones acústiques poden penetrar en els objectes a distàncies on la llum no pot a causa de l'elevada absorció i dispersió. En aquest sentit, dissenyar estructures capaces de focalitzar ultrasons és d'una gran rellevància tant per a la comunitat científica com per als sectors mèdics i industrials. Aquesta tesi presenta nous dissenys de lents acústiques capaços de controlar els paràmetres principals del feix d'ultrasons focalitzats, proporcionant diferents tipus de perfils de focalització adequats per a una gran varietat d'aplicacions i escenaris. En particular, s'han dissenyat i adaptat al camp dels ultrasons les lents de Fresnel (Fresnel Zone Plates, FZPs), àmpliament utilitzades en el camp de l'òptica. S'ha presentat una nova tècnica de modulació espai-temporal capaç de controlar la posició del focus d'ultrasons tant en espai com en temps, augmentant així la versatilitat d'aquest tipus de dispositius. També s'ha demostrat el funcionament en el camp de l'acústica de nous dissenys basats en aplicar seqüències binàries a una lent de Fresnel convencional, com les seqüències fractals de Cantor o les seqüències de M-bonacci generalitzades, capaces de modificar les propietats de focalització de les lents, incloent el nombre, posició i forma dels focus acústics. A més, s'introdueix un nou disseny de lents esfèriques plenes de líquid capaces de generar jets ultrasònics, amb molt potencial en aplicacions d'imatge d'alta resolució en camp proper. S'ha demostrat que, canviant el líquid intern de la lent o ajustant la ràtio de barreja entre dos líquids, es poden controlar els paràmetres principals del jet. Els dissenys proposats en la tesi han estat validats tant emprant simulacions numèriques com realitzant mesures experimentals, aplanant el camí per a l'ús d'aquest tipus d'estructures en aplicacions de focalització d'ultrasons. / [EN] Ultrasound focusing has many applications in a wide range of fields. Focused ultrasound is one of the main tools used by doctors all over the world to obtain biomedical images of different kind of tissues non-invasively. In the past decades, high intensity focused ultrasound (HIFU) appeared as one of the fundamental techniques for cancer treatment through non-invasive thermal tumor ablation. In addition, focused ultrasonic waves are recently emerging as one of the main tools to treat brain diseases, with novel disruptive techniques such as blood-brain barrier opening or neuromodulation. In industrial environments, ultrasonic waves are widely employed as one of the primary methods for the non-destructive evaluation (NDE) of materials and structures, as acoustic waves are able to penetrate deep into objects otherwise opaque using optical techniques. In this sense, designing structures capable of focusing ultrasonic waves is of great interest and relevance for the scientific, the industrial, and the biomedical sectors. This thesis devises new designs of acoustic lenses capable of controlling the main parameters of the focused ultrasound beam, achieving different kinds of focusing profiles suitable for a wide variety of scenarios. In particular, Fresnel Zone Plates (FZPs), commonly used in optics, are designed and adapted to the ultrasound domain. A novel spatio-temporal modulation technique capable of controlling the ultrasound focus location in both time and space is presented, increasing the versatility of this kind of devices. New design techniques based on applying a binary sequence to FZPs are also demonstrated, such as Cantor fractal sequences or generalized M-bonacci sequences, which modify the focusing properties of the lens, including the number, location, and shape of the different acoustic foci. In addition, acoustic jets generated by liquid-filled spherical lenses are devised for near-field high resolution imaging, demonstrating their applicability in the ultrasound domain. It is demonstrated that, by changing the inner liquid of the spherical lens or by tuning the mixing ratio between two liquids, the main focal parameters of the ultrasonic jet can be accurately controlled. The proposed designs are validated using both numerical simulations and experimental measurements, paving the way for the use of these kind of structures in focused ultrasound applications. / This work would not have been possible without the following funding sources: PAID-01-18 personal FPI grant from Universitat Politècnica de València; Spanish government MINECO TEC2015-70939-R project; Spanish government MICINN RTI2018-100792-B-I00 project; Generalitat Valenciana AICO/2020/139 project. / Pérez López, S. (2021). Design of Acoustic Lenses for Ultrasound Focusing Applications [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/179907 / TESIS / Compendio