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This thesis is the result of the investigation and solution of a mechanicalproblem regarding flywheel malfunctions. A flywheel is, in short, a devicethat relies on a rotating object’s moment of inertia to store energy overshort time spans. This project is part of the development of a fourthflywheel prototype at the division for electricity at Uppsala university,which uses magnetic levitation to keep a hollow cylinder rotating at veryhigh speeds inside a vacuum chamber. Should the magnets fail however, orsome other error occur that leads to an uncontrolled state of rotation, thecylinder needs to be stabilized mechanically by a device usually referredto as ‘back-up bearing’. This contraption might, like an airbag of a car,never be used but needs to be included if an emergency occurs to protectother parts of the flywheel which would otherwise be destroyed by theunrestrained rotor. A theoretical pre-study was conducted to determine what challenges andrespective solutions the design of such a device would encounter, forexample the amount of energy in the rotor and possible ways to dissipate itin the event of a malfunction. The benefits and downsides of materials andmachine elements such as bearings were investigated in order to design aset of backup bearings. The modelling was done using SolidWorks, which wasalso used to conduct thermal and mechanical simulations on differentconcepts. MatLab was used for calculations, using formulae from themanufacturers and from different websites. The project concluded that the sheer energy of the flywheel at top speedpresents considerable thermodynamic difficulties. A solution capable ofhandling this was however achieved, albeit barely. Unfortunately onlysimulations and calculations confirm this result as no practicalexperiments could be conducted, therefore caution is advised in futureexperiments where the flywheel speed approaches maximum levels.

In this thesis, an experimental and theoretical study of two and three vector correlations in the inelastic scattering of NO(X) with various rare gas atoms is presented. Vector correlations for a selection of rare gas systems were determined experimentally, and the observations were interpreted using a variety of classical and quantum mechanical models. The experiment is able to provide state-to-state resolution of the dynamics by means of an electrostatic hexapole and 1+1' resonantly enhanced multi-photon ionisation (REMPI). The simplest vector correlation of interest is the differential cross section (DCS), given by the <b>k</b>-<b>k</b>' correlation. The DCSs were determined experimentally for the NO(X)--Kr and NO(X)--Xe collision systems, both characterised by the relatively deep (&asymp;140cm^-1) attractive well and large extent of the attractive potential. The agreement between the experimental angular distributions and quantum mechanical DCS is very good for both systems. Classical calculations fail to correctly reproduce the form and magnitude of the DCS for either system, reflecting the inherently quantum mechanical nature of the collision. The classical calculations do however provide mechanistic insight into regions where the attractive part of the potential plays an important role in determining the dynamics. In order to investigate narrow angular features in the forward scattered direction, several experimental improvements to molecular beams and the detection ion-optic stack were made. Investigation into these structures revealed a strong contribution from molecular diffraction into the classical shadow of the NO(X), and the simple Fraunhofer model revealed a preference for scattering from an individual m&rarr;m' sub-state. Such measurements are in a region of the DCS where scattering is forbidden classically, and reveal the purely quantum nature of the collision interaction in the forward scattered direction. The low order <b>k</b>-<b>k</b>' correlation was then extended by using linearly or circularly polarised laser excitation. The interaction of the light with the molecular dipole allows the measurement of the <b>k</b>-<b>k</b>'-<b>j</b>' correlation. When linearly polarised light was used for the excitation laser, two of the rank two p^{2}_q(&theta;) renormalised polarisation dependent differential cross sections (PDDCSs), which describe rotational alignment, were obtained. With circularly polarised light, the rank one p^{1}_1-(&theta;) renormalised PDDCSs describing rotational orientation were determined. The collision induced alignment in NO(X)--Xe scattering was found to be well reproduced by classical and impulsive theories, highlighting the fact that the alignment is dominated by the propensity for the projection of <b>j</b> onto the kinematic apse to be conserved. The attractive part of the potential does augment the alignment renormalised PDDCSs, and this is most evident in states with strong features of the attractive part of the potential such as ℓ-type rainbows. The orientation is more strongly influenced by the attractive part of the potential and is also influenced by parity. In addition to the parity effect, there exist two limiting classical mechanisms which govern the orientation, one caused by attraction and the other repulsion. Finally, the bond axis of the NO(X) can be oriented by means of hexapole state selection combined with adiabatic orientation using a set of guiding rods. The integral steric effect, an <b>r</b>-<b>k</b> correlation, was measured for the NO(X)--Kr and NO(X)--Ar spin-orbit changing systems. There are large oscillations in the sign of the steric asymmetry which occur for scattering with the various rare gases. There are also large differences between the rare gases as the potentials become more attractive, and more isotropic. The steric asymmetry is well reproduced by quantum mechanics, however, a classical mechanism becomes dominant at high &Delta;j.

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In this thesis, a joint experimental and theoretical investigation of the vector properties that describe the inelastic scattering of a diatomic radical with an atomic collision partner is presented. A particular emphasis is placed on those correlations that include the final rotational angular momentum, j', of the radical. The depolarisation of both NO(A) and OH(A) brought about through collisions with krypton has been studied, providing a measure of the j-j' correlation, where j is the initial rotational angular momentum associated with the diatom. The total depolarisation cross- sections for both collisional disorientation and disalignment have been measured using quantum beat spectroscopy, and modelled theoretically using quasi-classical trajectory (QCT) calculations. The agreement between experiment and theory for NO(A)-Kr is excellent, but is not observed for OH(A)-Kr under thermal conditions. This has been attributed to the importance of electronic quenching in OH(A)-Kr. The depolarisation cross-sections have also been determined at a higher collision energy for OH(A)-Kr where electronic quenching is less significant, and the experimental results are in better agreement with those obtained theoretically. The NO(A)-Kr depolarisation cross-sections fall with increasing rotational quantum number, N, whereas for OH(A)-Kr, they exhibit less of an N dependence. This trend is mirrored in the elastic depolarisation cross-sections, which have also been determined experimentally for OH(A)-Kr. The significantly attractive and anisotropic nature of the OH(A)-Kr potential energy surface (PES) accounts for these observations. The j-j' correlation is extended to include the initial (relative) velocity (k) in a new theoretical treatment of the k-j-j' correlation. The formalism developed is used with the results from the QCT calculations for NO(A)-Kr and OH(A)-Kr to provide further insight into the mechanism of depolarisation in the two systems. Collisions of NO(A) with krypton do not cause significant depolarisation due to their impulsive nature, and the projection of j onto the kinematic apse is conserved. In contrast, collisions of OH(A) with krypton effectively randomise the direction of j, again showing the influence of the anisotropic and attractive nature of the PES. However, the projection of j onto the kinematic apse is still conserved. The inelastic scattering of NO(X) with argon and krypton has also been investigated, using a crossed molecular beam apparatus. The initial Λ-doublet state of the NO(X) was selected using hexapole focussing, and the products of the collision detected using velocity mapped ion imaging. The state to state differential cross-sections (equivalent to the k-k' correlation, where k' is the final relative velocity) have been measured for collisions which conserve the initial spin-orbit level of the NO(X) with krypton. The same parity dependent effects were seen as have been observed previously for NO(X)-Ar. The collision induced alignment (equivalent to the k-k'-j' correlation) of NO(X) as a result of scattering with argon has also been determined experimentally. The results can be explained classically by considering the conservation of the projection of j onto the kinematic apse.

<p dir="ltr">The objective of this research is to advance the development and application of laser diagnostics in gas phase medium, which ranges from atmospheric non-reacting flows to turbulent reacting flows in high-pressure, high-temperature environments. Laser diagnostic techniques are powerful tools for non-intrusive and in-situ measurements of important chemical parameters, such as temperature, pressure, and species mole fractions, in harsh environments. These measurements significantly advance the knowledge across various research disciplines, such as combustion dynamics, chemical kinetics, and molecular spectroscopy. In this thesis, detailed theoretical models and experimental analysis are presented for three different techniques: 1. Chirped-probe-pulse femtosecond coherent anti-Stokes Raman scattering (CPP fs CARS); 2. Two-color polarization spectroscopy (TCPS); 3. Ultrafast-laser-absorption-spectroscopy (ULAS). The first chapter provides a brief survey of laser diagnostics, including both linear and nonlinear methods. The motivations behind the three studies covered in this dissertation are also discussed. </p><p dir="ltr">In the second chapter, single-shot CPP fs CARS thermometry is developed for the hydrogen molecule at 5 kHz. The results are divided into two parts. The first part concentrates on the development of H₂ CPP fs CARS thermometry for high-pressure and high-temperature conditions. The second part demonstrates the application of H₂ CPP fs CARS in a model rocket combustor at pressures up to 70 bar. In the first part, H₂ fs CARS thermometry was performed in Hencken burner flames up to 2300 K, as well as in a heated gas-cell at temperatures up to 1000 K. It was observed that the H₂ fs CARS spectra are highly sensitive to the pump and Stokes chirp. Chirp typically originates from optical components such as windows and polarizers. As a result, the pump delay is modeled to provide a shift to the Raman excitation efficiency curve. With the updated theoretical model, excellent agreement was found between the simulated and experimental spectra. The averaged error and precision are 2.8% and 2.3%, respectively. In addition, the spectral phase and pump delay determined from the experimental spectra closely align with the theoretical predictions. It is also found that pressure does not have significant effects on the H₂ fs CARS spectra up to 50 bar at 1000 K. The collision model provides excellent agreement with the experiment. This allows the use of low-pressure laser parameters for high-pressure thermometry measurements. In the second part, spatially resolved H₂ temperature was measured in a rocket chamber at pressures up to 70 bar. This is the first demonstration of fs CARS thermometry inside a high-pressure rocket combustor. These results highlight the potential of using H₂ CPP fs CARS thermometry to provide quantitative data in high-pressure experiments for the study of combustion dynamics and model validation efforts at application relevant operating conditions.</p><p dir="ltr">The third chapter presents the development of a TCPS system for the study of the NO (<i>A</i>²Σ⁺-<i>X</i>²Π) state-to-state collision dynamics with He, Ar, and N₂. Two sets of TCPS spectra for 1% NO, diluted in different buffer gases at 295 K and 1 atm, were obtained with the pump beam tuned to the R₁₁(11.5) and ^OP₁₂(1.5) transitions. The probe was scanned while the pump beam was tuned to the line center. Collision induced transitions were observed in the spectra as the probe scanned over transitions that were not coupled with the pump frequency. The strength and structure of the collision induced transitions in the TCPS spectra were compared between the three colliding partners. Theoretical TCPS spectra, calculated by solving the density matrix formulation of the time-dependent Schrödinger wave equation, were compared with the experimental spectra. A collision model based on the modified exponential-gap law was used to model the rotational level-to-rotational level collision dynamics. An unique aspect of this work is that the collisional transfer from an initial to a final Zeeman state was modeled based on the difference in the cosine of the rotational quantum number <i>J</i> projection angle with the z-axis for the two Zeeman states. Rotational energy transfer rates and Zeeman state collisional dynamics were varied to obtain good agreement between theory and experiment for the two different TCPS pump transitions and for the three different buffer gases. One key finding, in agreement with quasi-classical trajectory calculations, is that the spin-rotation changing transition rate in the <i>A</i>²Σ⁺ level of NO is almost zero for rotational quantum numbers ≥ 8. It was necessary to set this rate to near zero to obtain agreement with the TCPS spectra. </p><p dir="ltr">The fourth chapter presents the development and application of a broadband ULAS technique operating in the mid-infrared for simultaneous measurements of temperature, methane (CH₄), and propane (C₃H₈) mole fractions. Single-shot measurements targeting the C-H stretch fundamental vibration bands of CH₄ and C₃H₈ near 3.3 μm were acquired in both a heated gas cell up to ~650 K and laminar diffusion flames at 5 kHz. The average temperature error is 0.6%. The average species mole fraction error are 5.4% for CH₄, and 9.9% for C₃H₈. This demonstrates that ULAS is capable of providing high-fidelity hydrocarbon-based thermometry and simultaneous measurements of both large and small hydrocarbons in combustion gases. </p>