This master thesis deals with simultaneous measurement and discrimination of temperature and strain using fiber Bragg gratings(FBGs). Saab Avionics is seeking for a further development of the overheat detection system that gives a warning when a heat leakage is detected. A further development is to distinguish between temperature and strain and give a warning when strain occurs that correspond to a temperature increase of 10°C. The present work was performed for Saab Avionics and the experiments were carried out in Kungliga Tekniska Högskola(KTH) at department of Laser Physics.  The aim of this thesis was to study some methods for simultaneous measurement of temperature and strain with FBGs and try to discriminate them. Two methods were investigated, a sensor design containing a boron-codoped germanosilicate fiber and a germanosilicate fiber and fibers with different cladding diameters. The gratings were heated in an oven and stressed with solder between a translation stage and a stationary stage. For the boron-codoped germanosilicate fiber the temperature sensitivity was ~ 2 times lower than the germanosilicate fiber, while they had similar strain responses. For the second sensor design with different cladding diameters, for a 80 μm cladding diameter the strain response was ~ 2.5 times higher that the 125 μm cladding diameter, while for a 100 μm cladding diameter the strain response is ~ 1.6 times higher than the 125 μm cladding diameter. For a 125 μm, a 100 μm and a 80 μm cladding diameter the temperature sensitivities were similar.

In this thesis, collisions involving the H2 reaction complex are studied theoretically and the processes considered are mutual neutralization, double charge transfer, associative ionization, dissociative recombination and resonant ion-pair formation. These processes are examples of reactions that involve several excited states and where the Born-Oppenheimer approximation is not applicable. The H2 system is one of the simplest examples of a diatomic molecule and it thus provides an optimal system on which theory can be tested. The purpose of the present work is to develop a theoretical model in which the cross sections of all of the above processes can be computed, using the same set of potential curves and couplings. This theoretical model is not limited to H2 and may serve as a basis for which more complicated systems can be studied. In this work, calculations that include effects such as rotational couplings and autoionization are carried out on H+ + H- mutual neutralization using this model. These effects have not previously been considered in studies on mutual neutralization for this system. Moreover, the theoretical model is applied in preliminary calculations on double charge transfer, associative ionization and dissociative recombination and future developments are discussed.

Third row (3d) metals, such as iron have become a candidate for a broad class of photocatalysts that have a large abundance on Earth and a low toxicity to humans and the environment. Unlike many commonly used photocatalysts that contain expensive precious metals, iron is cheap. Many important chemical processes such as the Haber-Bosch process or the Fenton’s reagent have employed an iron catalyst, however, in terms of metal complex photochemistry, this has been overshadowed by 4d and 5d metals with large affinities for unsaturated and saturated hydrocarbons.  In an effort to understand the innate differences between a broad range of transition metals, electron configurations of the metal and its’ coordinating ligands are a natural starting point. The d-block orbitals can accommodate at most 10 electrons, while the splittings between the occupied and unoccupied orbitals are determined by the metal and the type of coordinating ligands. This often produces complicated electronic structures, with multiple low-lying spin states that can couple. To describe these electronic structures, robust quantum chemistry methods are required which can describe many geometric configurations of a metal complex in a variety of bonding conifgurations. Often these methods are coupled with dynamical simulation tools that can probe molecular processes in both the ground and excited electronic states in an isolated and bulk liquid environment. The present work aims to address many of these points by considering two different iron complexes: the brown-ring complex ([Fe(H2O)5(NO)]2+) and ironpentacarbonyl (Fe(CO)5). In the brown-ring complex, the ground state molecular dynamics (GSMD) have been simulated using Car-Parrinello molecular dynamics (CPMD) and the electronic properties have been presented. It is shown that a dynamical equilibrium between species have a unique spectroscopic signature, while the multireference character of the complex in the electronic ground state reveals a unique bondingconfiguration. In ironpentacarbonyl the excited state molecular dynamics (ESMD) have been performed to understand the mechanistic details that promote dissociation of one or more carbonyl ligands following excitation. In parallel to this study, the reactivity of the molecular fragments with the surrounding solvent molecules have been characterized.

Optical tweezers can trap micron-sized objects such as cells, bacteria, and microspheres, and has become an important instrument for measuring forces associated with various physical and biological phenomena. In this thesis work, I constructed an optical tweezers instrument to trap 2µm diameter beads using a HeNe-laser operating with a wavelength of 632.8nm. Trapped beads were imaged using a charge-coupled device (CCD) camera. Since quantitative use of optical tweezers relies on the precise calibration of the trapping stiffness, I used a position sensitive detector (PSD) to measure the Brownian motion of trapped beads. The lateral stiffness of the optical tweezers was evaluated by fitting a Lorentzian to the power spectrum of the Brownian motion of the trapped 2µm beads, which were found to be 6.4(2)pN/µm in the x-direction and 6.0(1)pN/µm in the y-direction. Thus, I realized an optical tweezers setup that could trap and measure the position of micron-sided particles and I developed algorithms to calibrate the stiffness of the trap.

No description available.

The physical adsorption of a fluid by a solid is a subject of broad scientific and engineering interest. In this dissertation we explore some of the molecular aspects of this phenomenon through the use of computer simulations. We have developed a Monte Carlo simulation technique in the isobaric-isothermal ensemble for studying adsorption equilibria at a planar fluid-solid interface. This technique has characteristics which make it particularly useful for studies of adsorption involving fluid mixtures and for thermodynamic states near phase boundaries. Simulation at constant pressure has a number of advantages. Principal among these is that it closely parallels the manner in which adsorption is often studied experimentally. We have applied the isobaric Monte Carlo method in three studies of the molecular physics of adsorption. The first investigates the relationship between adsorption of a vapor in the approach to saturation and wetting phenomena. We have found conclusive evidence for a transition between partial and complete wetting of the interface in the fluid argon-solid carbon dioxide model system. This transition is accompanied by first-order surface phase transitions between thin and thick adsorbed films, called prewetting transitions. The observation of these transitions verify important predictions of modern theories of interfacial thermodynamics, especially density functional theory. The second and third studies examine the molecular basis for adsorption separations of vapor and liquid mixtures. Simulation results for loading and selectivity obtained for binary vapor mixtures are compared with predictions of two dimensional adsorbate and ideal adsorbed solution theories for vapor mixture adsorption. Through these comparisons we demonstrate how simulations can be used to assess the consequences of theoretical assumptions and approximations. We also demonstrate the feasibility of using simulations to study the molecular aspects of liquid mixture adsorption. Surface excess isotherms and density profiles for two model systems are obtained via simulation.

To improve our understanding about giant molecular clouds (GMC) associated with R-associations, a $\sp{12}CO\ J=1-0$ map of 167,000 spectra with 45$\sp{\prime\prime}$ resolution and 25$\sp{\prime\prime}$ spacing, a $\sp{13}CO\ J=1-0$ map of $\sim$40,000 spectra with 1.5$\sp\prime$ resolution and 1$\sp\prime$ spacing, IRAS BIGMAP images, and maps of high density molecular tracers for the dense cores are obtained for the GMC Monoceros R2 ($D=830\pm 50\ pc$). These data reveal that the large-scale structure of Mon R2 is dominated by an expanding bubble shell ($\sim$30 pc) with front side moving towards us at a radial velocity of $\sim$4-5 km $s\sp{-1}$. Distortions of this shell are obvious, suggesting of the inhomogeneity of the cloud before the formation of the bubble. There is no evidence for red-shifted shell at the far side of the bubble. There are at least two generations of star formation in Mon R2. The older generation of stars with an age of $6-10\times 10\sp6$ years are represented mostly by reflection nebulae. The younger generation of stars with an age of $\sim$10$\sp5$ years are represented mostly by IRAS point sources. It is proposed that the large-scale expanding bubble shell is the result of combined effects of ionizing flux and stellar winds originating from the older generation of young stellar objects, but perhaps dominated by O type stars which either are obscured or left main sequence. It is suggested that the formation of the younger generation of stars has been triggered by the older generation of stars. The main and the GGD12-15 cores are located on the large-scale expanding shell, and their harboring both generations of stars can be explained were the cores preexisting clumps. Our CO data reveal an eggplant-shaped bipolar outflow shell, whose shape can be satisfactorily modeled with radially directed stellar winds sweeping up ambient material with momentum conservation. An inversion method is implemented for analyzing dust emission spectra at FIR wavelengths in terms of a continuous dust temperature distribution, and has been applied to IRAS BIGMAP images of Mon R2. Computer programs are developed for identifying clumps and determining their properties in molecular emission maps. The results support the reality of size-linewidth and mass-linewidth relations for clumps in individual GMCs.

Stimulated Raman scattering (SRS) is a powerful imaging technique that has become popular during the last decades for its ability to image species specific in a sample with high accuracy. The purpose of this thesis is twofold. Firstly, to demonstrate 3D spatial control of where in the sample SRS is generated. Secondly, the spatial behavior of the SRS generation is investigated by experiments and simulations. SRS is a nonlinear scattering phenomenon that is produced when a sample is illuminated with two laser beams, called Stokes and pump beams, whose frequency difference corresponds to a molecular vibration caused by inelastic scattering of an incoming photon. The Stokes beam will stimulate the scattering of the pump beam photons, which leads to an intensity gain in the Stokes beam and an intensity loss in the pump beam. Imaging of SRS is usually performed by point scanning a sample in a laser scanning microscope by the two laser beams. Thereafter, the image is constructed pixel by pixel by detecting either the gain or the loss. Our aim is to perform direct field of view SRS imaging. Two experimental setups are presented in this thesis, one for the 3D spatial control of SRS and one for the investigation of the spatial generation of SRS.  The working principle of imaging is the same in both setups. A cylindrical sample volume was illuminated with the Stokes beam and the SRS was generated by focusing the pump beam into this volume. The diameter of the illuminated cylinder was around 10 mm. The two beams were combined before the sample using a dichroic mirror and after the sample the pump beam was removed by a second dichroic mirror.  The Stokes light was then image onto a camera providing a field of view of around 9.4 mm by 7.94 mm. A phase spatial light modulator (SLM) was used to control the shape and position of the pump beam in three dimensions (3D) in the illuminated volume. The results show that the SLM allowed for control of the position and shape of the generated SRS signal. In the second experimental setup the pump beam was focused into the sample by a lens and the spatial generation of the SRS was investigated. A second dichroic mirror blocking the pump beam was inserted into the sample at different interaction lengths to study the resulting SRS signal. Further, the pump intensity was varied to study the effect on the physical width of the SRS signal. The experimental results were compared to computer simulations. The simulations were based on diffraction theory for the beam propagation and the interaction between the light beams and the material was modeled with a phase modulation due to the induced Kerr effect caused by high pump intensity. The results shows that most of the SRS generation takes place close to the focus of the pump beam.

Protecting sensitive information is important, especially in defence applications. As cameras become more common, developing countermeasure systems that limit the information gathering capabilities of imaging sensors would be beneficial. Such a countermeasure system can be based on laser dazzling of imaging sensors, which will impair the information gathering capabilities of the sensor if the countermeasur esystem is designed correctly. In order for laser dazzling to be viable as a countermeasure in practical use cases, the dazzling effect needs to be predictable and practically achievable. An existing model predicting the dazzle effect of continuous wave laser irradiance on the front optics of imaging sensors was successfully verified. This was achieved by collecting experimental data using three complementary metal-oxide semiconductor (CMOS) imaging sensors. An amplitude modulated laser was used to dazzle an imaging sensor with the automatic gain control (AGC) and automatic exposure (AE) functions of the sensor enabled. The AGC function dynamically adjusts the image gain and the AE function dynamically adjusts the shutter speed of the sensor to optimise the settings for the given lighting conditions. The impact of the AGC and AE function corrections on the image information content was investigated for a set of lighting conditions, modulation frequencies and modulation duty cycles by collecting data with a CMOS sensor. The dazzling effect was compared to the dazzling effect when using continuous wave lasers. The analysis indicate that the amplitude modulated laser dazzling performance is subpar to the continuous wave laser dazzling performance for the tested configurations. Additionally, the predictability of the modulated laser dazzling effect is complex and depends on more parameters. A model based on this technique would also be sensitive to parameter changes. The weak predictability combined with the subpar performance compared to the continuous wave laser dazzling limits the usefulness of amplitude modulated laser dazzling in practical use cases.

Over the last few years, the available computing power allows us to have a deeper insight into photonics components than we ever had before. In this thesis we use the finite element method (FEM) to explore the behavior of the waves in 2D planar microcavities. We demonstrate the tunability of the cavity over a wide range of frequencies taking into account both the thermo-mechanical and the thermo-optical effect. Geometry and material choices are done so that the latter is predominant. We also demonstrate an odd mode disappearing phenomenon reported here for the first time as far as we know. Using this knowledge, we design two structures with these remarkable properties. One of the devices will be used as micro-sized solid-state dye laser with Rhodamine 6G as the active medium and SU-8 polymer as a cavity material in sizes that have never been reached before. This opens new opportunities not only for future implementation for “labs-on-a-chip” (LOC) but also for a higher integration density of optical communication systems. The second device is a wavefront shaper creating plane waves from a point source performing the functions of beam shaper and beam splitter with plane wave as the output result. After an introduction to FEM and comparison with a rival algorithm, some issues related to FEM in electromagnetic simulation are resolved and explained. Finally, some fabrication techniques with feature sizes <100 nm, such as electron beam lithography (EBL) and nano-imprint lithography (NIL), are described and compared with other lithographic techniques. / QC 20101119