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The main topic of this dissertation is about the generation of intense terahertz (THz) pulses with field strengths up to tens of MV/cm and their characterization with energy, pulse duration, and spot size measurements. As a strong THz source, we used two-color laser mixing in air, which can produce coherent, high energy (> µJ), broadband (0.01~100 THz) THz radiation. In this scheme, 800-nm, 1-kHz, 30-fs laser pulses are weakly focused onto a BBO (Beta Barium Borate) crystal to generate the 2nd harmonic (400 nm) pulses. The original (800 nm) and second harmonic (400 nm) pulses are focused together to generate plasma filaments in air, and this works as a broadband source of THz radiation. In particular, we have studied THz energy scaling with various focal length conditions and input laser energies up to 10 mJ. With high laser input energy, the THz output energy does not simply increase but rather saturates or even decreases. We find that this occurs due to plasma-induced laser defocusing, which prohibits efficient laser energy coupling into the plasma. We have overcome this saturation effect by increasing the plasma volume in the longitudinal or transverse direction. At a high repetition rate (1 kHz), we have achieved 2.6 µJ of THz energy with 10 mJ laser energy by elongating the plasma length (~7 cm). This provides a conversion efficiency of 2.6  10-4 from optical to THz energy. Also, at a low repetition rate (10 Hz) with high laser input energy (~50 mJ), we increased the plasma volume in the transverse direction by generating a 2-dimensional plasma sheet and obtained 31 µJ of THz energy. We have also investigated THz generation from two-color laser filamentation in different types of gases (room air, nitrogen, oxygen, carbon dioxide, helium, argon, krypton, and xenon) at various gas pressures. By elongating the plasma length in a long gas cell, we have achieved laser-to-THz conversion efficiency of ~0.1%, one order of magnitude higher than a typical value (0.01%)

A feasibility study of an experimental setup for the irradiation of biological samples at the cyclotron facility installed at the National Centre of Accelerators (Seville, Spain) is presented. This cyclotron, which counts on an external beam line for interdisciplinary research purposes, produces an 18 MeV proton beam, which is suitable for the irradiation of mono-layer cultures for the measurement of proton cell damages and Relative Biological Effectiveness (RBE) at energies below the beam nominal value. Measurements of this kind are of interest for proton therapy, since the variation of proton RBE at the distal edge of the Bragg curve may have implications in clinical proton therapy treatments. In the following, the characteristics of the beam line and the solutions implemented for the irradiation of biological samples are described. When dealing with the irradiation of cell cultures, low beam intensities and broad homogeneous irradiation fields are required, in order to assure that all the cells receive the same dose with a suitable dose rate. At the cyclotron, these constraints have been achieved by completely defocusing the beam, intercepting the beam path with tungsten scattering foils and varying the exit-window-to-sample distance. The properties of the proton beam thus obtained have been analysed and compared with Monte Carlo simulations. The results of this comparison, as well as the experimental measurement of the lateral dose profiles expected at the position of samples are presented. Meaningful dose rates of about 2–3 Gy/min have been obtained. Homogeneous lateral dose profiles, with maximum deviations of 5%, have been measured at a distance of approximately 50 cm in air from the exit window, placing a tungsten scattering foil of 200 µm in the beam path.

When using Shack-Hartmann wavefront sensors (SH) and Zernike coefficients (Zs) in applications where the position of the measurement and the point of interest are far apart, as it is common practice in ophthalmic optics, problems in the interpretation of the values of the Zs arise, related to how the shape of the wavefront propagates along the beam. One typical example is pupil conjugation where an auxiliary lens is added to match the size of the area of the interest of the beam with the size of the entrance pupil of the SH used for measurements. In the present work, we address this problem in the framework of a numerical scheme for modeling the beam propagation. We calculate the wavefronts with exact ray tracing plus the fitting of the impacts so as to match a rectangular grid. This procedure allows the subsequent calculation of the Zs or, similarly, the pupil function at an arbitrary plane perpendicular to the optical axis, The authors acknowledge the 'Agencia Estatal de Investigación' (AEI) and the 'Fondo Europeo de Desarrollo Regional' (FEDER), under project FIS2016-77319-C2-2-R of the Spanish 'Ministerio de Economia, Industria y Competitividad'., Postprint (published version)

Hard x-ray scanning microscopy relies on small and intensive nanobeams. Refractive x-ray lenses are well suited to generate hard x-ray beams with lateral dimensions of 100 nm and below. The diffraction limited beam size of refractive x-ray lenses mainly depends on the focal length and the attenuation inside the lens material. The numerical aperture of refractive lenses scales with the inverse square root of the focal length until it reaches the critical angle of total reflection. We have used nanofocusing refractive x-ray lenses made of silicon to focus hard x-rays at 8 and 20 keV to (sub-)100 nm dimensions. Using ptychographic scanning coherent diffraction imaging we have characterized these nanobeams with high accuracy and sensitivity, measuring the full complex wave field in the focus. This gives access to the full caustic and aberrations of the x-ray optics., QC 20140613

Concentrating solar thermal power tower plants with capacities of 100 MWe or greater require large heliostat fields with heliostats over 1,500 m (nearly a mile) away from the tower. The accuracy and performance of these heliostats must be evaluated and understood as new heliostat designs emerge to reduce costs. Conventional beam characterization systems that use photographs of the reflected beam on a tower-mounted target are typically not large enough to capture the beam at large distances, and the magnitude of the irradiance for long-distance heliostats is quite low (only a fraction of a sun), which can make the beam image difficult to discern from the ambient lighting on the target. The Long-Range Heliostat Target (LRHT) is a vertical array of collimated pyranometers deployed to a test site via flat-bed trailer and quickly erected on an aluminum truss tower. Once the sensors have been aimed at the heliostat, the heliostat beam is swept azimuthally across the array whereupon the data is stitched into a flux map indicating horizontal and vertical beam dimensions and flux intensities. The LRHT was used to evaluate beam shape, peak flux, canting adjustment, and total power of heliostats and single facet reflectors at distances from 300-1700 meters. Results were compared to theoretically rendered flux maps created by computational ray tracing algorithms, and to IR-filtered, visual-band-filtered and non-filtered photographs taken on the beam characterization system (BCS) at the National Solar Thermal Test Facility at Sandia National Laboratories.

The characterization of the transverse phase space of beams is a fundamental requirement for particle accelerators. As accelerators shift toward higher intensity beam regimes, the transverse dynamics of beams becomes more influenced by interparticle forces known as the space charge forces. Therefore, it is increasingly important to take space charge into account in studying the beam dynamics. In this thesis, two novel approaches are presented for measurement of transverse emittance for beams with space charge, an important quality indicator of transverse phase space. It is also discussed the experimental work on orbit characterization and control done for space charge dominated beams of the University of Maryland Electron Ring (UMER). The first method developed for measuring the emittance, utilizes a lens-drift-screen setup similar to that of a conventional quadrupole scan emittance measurement. Measurements of radius and divergence that can be obtained from beam produced radiation, e.g. optical transition, are used to calculate the beam cross correlation term and therefore the rms emittance. A linear space charge model is used in the envelope equations; hence the errors in the measurement relate to the non-uniformity of the beam distribution. The emittance obtained with our method shows small deviation from those obtained by WARP simulations for beams with high space charge, in contrast to other techniques. In addition, a second method is presented for determining emittance that works for beams with intense space charge and, theoretically, does not require an a priori assumption about the beam distribution. In this method, the same lens-drift-screen setup as the previous method is used, except that the beam size and divergence are scanned to find the minimum of product of the measured quantities. Such minimum is shown to be equal to the rms emittance under specific conditions that usually can be satisfied by adjusting the experiment parameters such as the drift len