Generalized quasi mode theory of macroscopic canonical quantization in cavity quantum electrodynamics and quantum optics I. Theory

The quasi mode theory of macroscopic quantization in quantum optics and cavity QED developed by Dalton, Barnett and Knight is generalized. This generalization allows for cases in which two or more quasi permittivities, along with their associated mode functions, are needed to describe the classical optics device. It brings problems such as reflection and refraction at a dielectric boundary, the linear coupler, and the coupling of two optical cavities within the scope of the theory. For the most part, the results that are obtained here are simple generalizations of those obtained in previous work. However the coupling constants, which are of great importance in applications of the theory, are shown to contain significant additional terms which cannot be 'guessed' from the simpler forms. The expressions for the coupling constants suggest that the critical factor in determining the strength of coupling between a pair of quasi modes is their degree of spatial overlap. In an accompanying paper a fully quantum theoretic derivation of the laws of reflection and refraction at a boundary is given as an illustration of the generalized theory. The quasi mode picture of this process involves the annihilation of a photon travelling in the incident region quasi mode, and the subsequent creation of a photon in either the incident region or transmitted region quasi modes.

Generalized quasi mode theory of macroscopic canonical quantization in cavity quantum electrodynamics and quantum optics II. Application to reflection and refraction at a dielectric interface

The generalization of the quasi mode theory of macroscopic quantization in quantum optics and cavity QED presented in the previous paper, is applied to provide a fully quantum theoretic derivation of the laws of reflection and refraction at a boundary. The quasi mode picture of this process involves the annihilation of a photon travelling in the incident region quasi mode, and the subsequent creation of a photon in either the incident region or transmitted region quasi modes. The derivation of the laws of reflection and refraction is achieved through the dual application of the quasi mode theory and a quantum scattering theory based on the Heisenberg picture. Formal expressions from scattering theory are given for the reflection and transmission coefficients. The behaviour of the intensity for a localized one photon wave packet coming in at time minus infinity from the incident direction is examined and it is shown that at time plus infinity, the light intensity is only significant where the classical laws of reflection and refraction predict. The occurrence of both refraction and reflection is dependent upon the quasi mode theory coupling constants between incident and transmitted region quasi modes being nonzero, and it is seen that the contributions to such coupling constants come from the overlap of the mode functions in the boundary layer region, as might be expected from a microscopic theory.

Multiple bifurcations in atom optics

We report the observation of multiple bifurcations in a nonlinear Hamiltionian system: laser-cooled atoms in a standing wave with single-frequency intensity modulation. We provide clear evidence of the occurrence of bifurcations by analyzing the atomic momentum distributions.

Blended Learning project with Applied Optics. Case study

To show with the case of Applied Optics (AO), the adequacy of blended learning to the teaching/learning process in experimental Science and technology (S&T).

Development of procedures for the design, optimization and manufacturing of customized orthopaedic and trauma implants: Geometrical/anatomical modelling from 3D medical imaging

Tese de Doutoramento (Programa Doutoral em Engenharia Biomédica)

Optical-geometrical effects on the photoluminescence spectra of Si nanocrystals embedded in SiO2

We demonstrate that thickness, optical constants, and details of the multilayer stack, together with the detection setting, strongly influence the photoluminescence spectra of Si nanocrystals embedded in SiO2. Due to multiple reflections of the visible light against the opaque silicon substrate, an interference pattern is built inside the oxide layer, which is responsible for the modifications in the measured spectra. This interference effect is complicated by the depth dependence of (i) the intensity of the excitation laser and (ii) the concentration of the emitting nanocrystals. These variations can give rise to apparent features in the recorded spectra, such as peak shifts, satellite shoulders, and even splittings, which can be mistaken as intrinsic material features. Thus, they can give rise to an erroneous attribution of optical bands or estimate of the average particle size, while they are only optical-geometrical artifacts. We have analyzed these effects as a function of material composition (Si excess fraction) and thickness, and also evaluated how the geometry of the detection setup affects the measurements. To correct the experimental photoluminescence spectra and extract the true spectral shape of the emission from Si nanocrystals, we have developed an algorithm based on a modulation function, which depends on both the multilayer sequence and the experimental configuration. This procedure can be easily extended to other heterogeneous systems.

Spanning avalanches in the three-dimensional Gaussian random-field Ising model with metastable dynamics: Field dependence and geometrical properties

Spanning avalanches in the 3D Gaussian Random Field Ising Model (3D-GRFIM) with metastable dynamics at T=0 have been studied. Statistical analysis of the field values for which avalanches occur has enabled a Finite-Size Scaling (FSS) study of the avalanche density to be performed. Furthermore, a direct measurement of the geometrical properties of the avalanches has confirmed an earlier hypothesis that several types of spanning avalanches with two different fractal dimensions coexist at the critical point. We finally compare the phase diagram of the 3D-GRFIM with metastable dynamics with the same model in equilibrium at T=0.

Multiscaling and information content of natural color images

Naive scale invariance is not a true property of natural images. Natural monochrome images possess a much richer geometrical structure, which is particularly well described in terms of multiscaling relations. This means that the pixels of a given image can be decomposed into sets, the fractal components of the image, with well-defined scaling exponents [Turiel and Parga, Neural Comput. 12, 763 (2000)]. Here it is shown that hyperspectral representations of natural scenes also exhibit multiscaling properties, observing the same kind of behavior. A precise measure of the informational relevance of the fractal components is also given, and it is shown that there are important differences between the intrinsically redundant red-green-blue system and the decorrelated one defined in Ruderman, Cronin, and Chiao [J. Opt. Soc. Am. A 15, 2036 (1998)].

Analytical Study on the Influence of Geometrical Parameters on the Fatigue Strength of Welds with Undercuts

The purpose of this study is to analyze the influence of geometric parameters on the fatigue strength of the welded joint. The thesis includes the analytical study pertaining to variation of undercut and the weld toe radius. The theoretical part includes the concepts of fracture mechanics, different stages of the crack propagation and finally the results. The numerical results are obtained from FRANC2D/L. The results show that the fatigue strength of the welded structure depends on the parameters of the welds such as the weld toe radius, weld angle, height of the undercut and plate thickness. The results show that the fatigue life can be improved by having the undercut as minimum as possible. However there has been significant variation on the fatigue life of the structure when the weld toe radius is increased.

Laser cladding with scanning optics

Scanning optics create different types of phenomena and limitation to cladding process compared to cladding with static optics. This work concentrates on identifying and explaining the special features of laser cladding with scanning optics. Scanner optics changes cladding process energy input mechanics. Laser energy is introduced into the process through a relatively small laser spot which moves rapidly back and forth, distributing the energy to a relatively large area. The moving laser spot was noticed to cause dynamic movement in the melt pool. Due to different energy input mechanism scanner optic can make cladding process unstable if parameter selection is not done carefully. Especially laser beam intensity and scanning frequency have significant role in the process stability. The laser beam scanning frequency determines how long the laser beam affects with specific place local specific energy input. It was determined that if the scanning frequency in too low, under 40 Hz, scanned beam can start to vaporize material. The intensity in turn determines on how large package this energy is brought and if the intensity of the laser beam was too high, over 191 kW/cm2, laser beam started to vaporize material. If there was vapor formation noticed in the melt pool, the process starts to resample more laser alloying due to deep penetration of laser beam in to the substrate. Scanner optics enables more flexibility to the process than static optics. The numerical adjustment of scanning amplitude enables clad bead width adjustment. In turn scanner power modulation (where laser power is adjusted according to where the scanner is pointing) enables modification of clad bead cross-section geometry when laser power can be adjusted locally and thus affect how much laser beam melts material in each sector. Power modulation is also an important factor in terms of process stability. When a linear scanner is used, oscillating the scanning mirror causes a dwell time in scanning amplitude border area, where the scanning mirror changes the direction of movement. This can cause excessive energy input to this area which in turn can cause vaporization and process instability. This process instability can be avoided by decreasing energy in this region by power modulation. Powder feeding parameters have a significant role in terms of process stability. It was determined that with certain powder feeding parameter combinations powder cloud behavior became unstable, due to the vaporizing powder material in powder cloud. Mainly this was noticed, when either or both the scanning frequency or powder feeding gas flow was low or steep powder feeding angle was used. When powder material vaporization occurred, it created vapor flow, which prevented powder material to reach the melt pool and thus dilution increased. Also powder material vaporization was noticed to produce emission of light at wavelength range of visible light. This emission intensity was noticed to be correlated with the amount of vaporization in the powder cloud.

Mechanical design and optics simulation of the illuminated Volvo Iron mark

Utilization of light and illumination systems in automotive industry for different purposes has been increased significantly in recent years. Volvo as one of the leading companies in manufacturing of luxury cars has found the great capacity in this area. The performance of such an illumination systems is one of the challenges that engineers in this industry are facing with. In this study an effort has been made to design a system to make the iron mark of Volvo being illuminated and the system is being evaluated by optics simulation in software using Ray optics method. At the end, results are assessed and some optimizations are carried out. Different kind of light guides, front side of the iron mark and some possible arrangement for LED also evaluated and different materials tested. The best combination from uniformity, color and amount of luminance aspect selected as a possible solution for this special project which can be used as a base for further studies in Volvo.