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Interaction of short-wavelength laser pulses with matter on various time scales
Vozda, Vojtěch ; Kunc, Jan (advisor) ; Caha, Ondřej (referee) ; Timneanu, Nicusor (referee)
An advent of powerful sources producing intense and ultrashort laser pulses containing high-energy photons opened up a wide range of possibilities to conduct experiments formerly achievable only through theoretical calculations and models. This thesis provides a complex overview of processes which occur right after arrival of the first photons, through lattice heating, up to resolidification and formation of irreversible changes. Irradiated spots and craters formed in various materials are examined employing a wide range of microscopic and spectroscopic methods which provide a deep insight into laser-induced modifications such as detachment of a graphene layer from SiC substrate or thermally-induced diffusion of tellurium inclusions through CdTe lattice. An increased emphasis is placed on beam characterization utilizing ablation and desorption imprints in suitable solids. A proper knowledge of the beam fluence profile may serve for evaluation of diverse damage thresholds as well as for modelling of the pulse propagation or consequent retrieval of otherwise unmeasurable opacity of warm dense aluminium plasma heated to temperatures exceeding tens of thousands of Kelvins. Moreover, the method of desorption imprints is extended to accurate characterization of pulses delivered at MHz repetition rate....
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FDTD simulace funčkních fotonických struktur
Novák, Ondřej ; Veis, Martin (advisor) ; Vozda, Vojtěch (referee)
This thesis aims to (i) design and optimize the geometry of magneto-photonic crystal based on ferromagnetic garnet in order to resonantly enhance the magneto-optical re- sponse, (ii) to explore the possibility of using magnetic shape memory alloy to build an optically active photonic element, using advanced FDTD modeling. A Faraday rotation of 180◦ was reached but with low values of transmissivity. An investigation of the origin of such high values of Faraday rotation led to a conclusion that such structure has to be highly sensitive towards a change of a refractive index of its surroundings. This was confirmed, and so further development of this structure can lead to an efficient concentra- tion detector. Three designs of optically active element utilizing deformation of magnetic shape memory material in the external magnetic field were numerically simulated. Two designs (photonic crystal with cylindric holes in a hexagonal lattice and self-standing foil with cylindric holes in a square lattice) proved to be efficient and worth of further development. 1
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Advanced simulations of photonic structures by FDTD method
Vozda, Vojtěch ; Veis, Martin (advisor)
Finite-Difference Time-Domain method (FDTD) is based on numerical solution of Maxwell's equations, nowadays widely used for simulating optical response of photonic structures. This paper provides brief introduction to the FDTD method and several important extensions which make the basic code much more versatile. In order to broaden analysis of photonic structures, transfer matrix method (TMM) is also involved. The code is firstly tested using simple model structures which optical response might be compared with different numerical or even analytical approaches. Debugged code is used to improve photonic crystals for enhanced sensitivity of biosensing devices based on refractive index changes of sensed medium. Last but not the least, properties (sensitivity and Q-factor of resonant peak) of holey waveguide are investigated in one-, two- and three-dimensional simulation. It is shown here, that even this simple structure may compete with complex photonic crystals in the field of biosensors. Powered by TCPDF (www.tcpdf.org)
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Interaction of short-wavelength laser pulses with matter on various time scales
Vozda, Vojtěch ; Kunc, Jan (advisor) ; Caha, Ondřej (referee) ; Timneanu, Nicusor (referee)
An advent of powerful sources producing intense and ultrashort laser pulses containing high-energy photons opened up a wide range of possibilities to conduct experiments formerly achievable only through theoretical calculations and models. This thesis provides a complex overview of processes which occur right after arrival of the first photons, through lattice heating, up to resolidification and formation of irreversible changes. Irradiated spots and craters formed in various materials are examined employing a wide range of microscopic and spectroscopic methods which provide a deep insight into laser-induced modifications such as detachment of a graphene layer from SiC substrate or thermally-induced diffusion of tellurium inclusions through CdTe lattice. An increased emphasis is placed on beam characterization utilizing ablation and desorption imprints in suitable solids. A proper knowledge of the beam fluence profile may serve for evaluation of diverse damage thresholds as well as for modelling of the pulse propagation or consequent retrieval of otherwise unmeasurable opacity of warm dense aluminium plasma heated to temperatures exceeding tens of thousands of Kelvins. Moreover, the method of desorption imprints is extended to accurate characterization of pulses delivered at MHz repetition rate....
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Numerical simulations of optical response of nanostructures using FDTD method
Novák, Ondřej ; Veis, Martin (advisor) ; Vozda, Vojtěch (referee)
Title: Numerical simulations of optical response of nanostructures using FDTD method Author: Ondřej Novák Institute: Institute of Physics of Charles University Supervisor: RNDr. Martin Veis, Ph.D., Institute of Physics of Charles University Abstract: Abstract: The aim of this thesis is to develope an efficient algorythm to compute optical response of nanostructures and to equip it with usefull tools for further data processing. Considered problem is reduced to two dimensions and the method used is the Finite Difference Time Domain (FDTD). This method operates on finite grid called Yee grid and is often called Yee algorithm. En extra emphasis is given on optimalization of the algorithm and writing the computer code efficiently. Evolution equations are written in tensor form and the core algorithm is moved to graphic card using CUDA. Various boundary conditions are introduced to reduce reflections on the edge of the grid. Representation of a real object on the Yee-grid is discussed with introduction of several smoothing methods to improve the shape convergence of simulated object. Useful post- processing methods are introduced - discrete Fourier transform, from which the frequency response of simulated object can be computed and a way to compute the far field from the near field. Finaly, there is an attempt...
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Pokročilé simulace fotonických struktur metodou FDTD
Vozda, Vojtěch ; Veis, Martin (advisor) ; Richter, Ivan (referee)
Finite-Difference Time-Domain method (FDTD) is based on numerical solution of Maxwell's equations, nowadays widely used for simulating optical response of photonic structures. This paper provides brief introduction to the FDTD method and several important extensions which make the basic code much more versatile. In order to broaden analysis of photonic structures, transfer matrix method (TMM) is also involved. The code is firstly tested using simple model structures which optical response might be compared with different numerical or even analytical approaches. Debugged code is used to improve photonic crystals for enhanced sensitivity of biosensing devices based on refractive index changes of sensed medium. Last but not the least, properties (sensitivity and Q-factor of resonant peak) of holey waveguide are investigated in one-, two- and three-dimensional simulation. It is shown here, that even this simple structure may compete with complex photonic crystals in the field of biosensors. Powered by TCPDF (www.tcpdf.org)
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Calculation of optical response of photonic structures by FDTD method
Vozda, Vojtěch ; Veis, Martin (advisor) ; Richter, Ivan (referee)
FDTD method is based on Maxwell's equations and this thesis describe how to make these differential equations computer readable for numerical solution known as the Yee algorithm. Time step dependence on spatial step is examined here in order to obtain stable solution. Discrete Fourier trasform is defined to obtain frequency dependent transmission and reflection coefficients. Programmed simulation is tested on analytically solvable structures even on slightly more complex systems whose optical response was computed by other type of simulation. Finally photonic crystals and their application as biosensors are discussed. Particular shape of photonic crystal is examined in details (frequency spectrum dependence upon spatial resolution, inaccuracy in geometry, different compounds in holes, geometry modification).
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Advanced simulations of photonic structures by FDTD method
Vozda, Vojtěch ; Veis, Martin (advisor)
Finite-Difference Time-Domain method (FDTD) is based on numerical solution of Maxwell's equations, nowadays widely used for simulating optical response of photonic structures. This paper provides brief introduction to the FDTD method and several important extensions which make the basic code much more versatile. In order to broaden analysis of photonic structures, transfer matrix method (TMM) is also involved. The code is firstly tested using simple model structures which optical response might be compared with different numerical or even analytical approaches. Debugged code is used to improve photonic crystals for enhanced sensitivity of biosensing devices based on refractive index changes of sensed medium. Last but not the least, properties (sensitivity and Q-factor of resonant peak) of holey waveguide are investigated in one-, two- and three-dimensional simulation. It is shown here, that even this simple structure may compete with complex photonic crystals in the field of biosensors. Powered by TCPDF (www.tcpdf.org)
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