559 research outputs found

    Dynamical control of one- and two-dimensional optical fibre scanning

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    This thesis investigates the dynamical control of one- and two-dimensional optical fibre scanning. One dimensional scanning is performed with a mechanically biaxial polarisation-preserving fibre mounted on a piezoelectric transducer with one of its principal mechanical axes aligned parallel to the excitation direction. The addition of an apertured reflector in front of the imaging lens allows a position sensing mechanism based on intermittent optical feedback to be integrated into the scanner. Over-scanning the lens generates timing pulses interlaced with back-scattered signals from the target. The timing information can be used for closed loop control of the phase and amplitude of vibration. Suitable control algorithms are developed and their convergence and stability is studied. This thesis also investigates the construction of fibres with enhanced mechanically asymmetry and their dynamical properties during two-dimensional imaging based on Lissajous scan patterns. Dip-coating is proposed as a method of forming two-cored waveguide cantilevers from two separate, parallel fibres that are encapsulated in a plastic coating. The frequency ratio between the two orthogonal bending mode resonances can be controlled with number of coatings. An exact image reconstruction algorithm based on Lissajous scanning is proposed. Latency, transient response and steady-state phase errors are all shown to cause dramatic deterioration of the reconstructed image. Solutions are provided by ensuring the correct starting time for data acquisition and introducing a drive phase correction to one of the axes. Two methods of resolution enhancement are demonstrated. The first is based on combining data sets obtained during separate scans carried out with deliberately applied phase offsets. The second operates by combining data sets from separate imaging operations carried out using the two different fibre cores. Finally, this thesis demonstrates potential applications in optogenetics by combining the two operations of imaging and writing, using different light sources that may also have different wavelengths.Open Acces

    Index to 1981 NASA Tech Briefs, volume 6, numbers 1-4

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    Short announcements of new technology derived from the R&D activities of NASA are presented. These briefs emphasize information considered likely to be transferrable across industrial, regional, or disciplinary lines and are issued to encourage commercial application. This index for 1981 Tech Briefs contains abstracts and four indexes: subject, personal author, originating center, and Tech Brief Number. The following areas are covered: electronic components and circuits, electronic systems, physical sciences, materials, life sciences, mechanics, machinery, fabrication technology, and mathematics and information sciences

    Minimisation of the wire position uncertainties of the new CERN vacuum wire scanner

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    The particle production of an accelerator is characterised by the accelerated species of particles, by their number and energy. The particle rate is determined by the production cross section, a natural constant and the accelerator dependent parameter luminosity. The luminosity is proportional to the number of particles in each beam and inversely proportional to the particle beam transverse dimensions. The luminosity increases with the particle beam density and therefore the probability of interactions too. To optimize the transverse beam sizes, profile monitors are used to measure parameter depending changes. Different monitors can provide beam transversal profile measurements (Wire Scanners, Synchrotron Light Monitors, Rest Gas Profile Monitors), however the wire scanner monitor is considered to be the most accurate of all monitors. Wire scanner instruments measure the transverse beam density profile in a particle accelerator by means of moving a thin wire in an intermittent manner. In the next years the luminosity of the Large Hadron Collider (LHC) will be significantly increased and more accurate beam profile measurement will necessary. The new performance demands a wire travelling speed up to 20 m.s-1 and a position measurement accuracy of the order of few micros. The existing wire scanners does not reach the new requirements as their accuracy achieved is limited by the motorization, the angular position measurement system located outside of the vacuum vessels and the vibration of the thin carbon wire which has been identified as one of the major error sources reducing the knowledge of the wire position. Therefore the development of a new device whose accuracy meets the new requirements was mandatory. This thesis work aims to provide suitable inputs for the design and operation of this new fast wire scanner in order to minimize the uncertainties in the wire position. To accomplish the aims the understanding of the wire vibrations in such a system is one of the main goals of this work. More specifically, the development of a suitable vibration measurement system and the construction of dynamic models of the system are the two goals aimed. For the new scanner design this work intend to propose, the conceptual design, the optimization of the most critical parts and the operation procedure that will allow the new device to reach the required performances imposed by the forthcoming LHC conditions.La producción de partículas de un acelerador se caracteriza por las especies de partículas aceleradas, por su número y energía. La tasa de partículas se determina a partir de la sección transversal de producción, una constante natural, y de un parámetro que depende del acelerador, la luminosidad. La luminosidad es proporcional al número de partículas por haz e inversamente proporcional a la dimensión transversal de los haces. La luminosidad aumenta con la densidad de partículas y por lo tanto también aumenta la probabilidad de interacciones entre los haces. Para optimizar la sección trasversal del haz, se utilizan monitores de perfil de haz. Diversos tipos de monitores pueden proporcionar mediciones del perfil transversal del haz (Escáneres de hilo, Monitores de luz de sincrotrón, Monitores de análisis de gas residual), sin embargo el escáner de hilo está considerado como el más preciso de todos ellos. Los escáneres de hilo miden el perfil del haz atravesándolo con un hilo muy delgado de manera intermitente. En los próximos años la luminosidad del Gran Colisionador de Hadrones (LHC) se incrementará de manera significativa, por lo que serán necesarios sistemas de medida de perfil de haz más precisos que lo actuales. Las nuevas características, requerirán velocidad de desplazamiento del hilo de hasta 20 ms-1 y una precisión en la medida de posición del hilo de tan solo unas micras. Los escáneres actuales no pueden alcanzar estos requerimientos ya que su precisión está limitada por el sistema de motorización, por el medidor angular de posición que está situado fuera del tanque de vacío y por las vibraciones del hilo, la cuales han sido identificadas como una de las mayores fuentes de error a la hora de conocer la posición real del hilo. Por todo esto, el desarrollo de un nuevo dispositivo cuyas características cumplan los nuevos requerimientos era necesario. Este trabajo de tesis tiene como objetivo proporcionar criterios adecuados para el diseño y operación de un nuevo escáner, con el fin de minimizar las incertidumbres en la posición del hilo. Para lograr estos objetivos, el entender las vibraciones del hilo en un sistema de este tipo es un objetivo primordial. De manera más específica el desarrollo de sistemas de medida de vibración adecuados y la construcción de modelos dinámicos del sistema son los dos objetivos concretos perseguidos por este trabajo. De cara al nuevo diseño, este trabajo pretende proponer un diseño conceptual así como definir los criterios para la optimización de las partes más críticas y establecer un procedimiento de operación que permita al nuevo dispositivo alcanzar los requerimientos impuestos por las futuras condiciones del LHC.Postprint (published version
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