In this thesis, we characterize and test a new MiM cavity for use in the Bouwmeester Optomechanics group. The cavity seems stable over time, though alignment offers some issues. The tip/tilt...Show moreIn this thesis, we characterize and test a new MiM cavity for use in the Bouwmeester Optomechanics group. The cavity seems stable over time, though alignment offers some issues. The tip/tilt alignment of the membrane was achieved to within 700 arcs eventually however. We also explore the use of finesse measurements to determine the absorbance of our membranes. We conclude that optical ring down measurements are preferable in our system and suspect that the PSG4 membranes have higher absorbance as compared to later generations. We present a scheme to determine the thermal gradient of our membrane in-situ, without any modifications required to the principle of the system. We do find, however, that the measurement is very sensitive to drift of the laser detuning. Finally, we explore the observed short term drift in our mechanical mode frequencies. We suspect the thermal expansion of some part of the system of adding additional strain to the membranes, and in doing so raising their mode frequencies, though the exact pathway remains unclear.Show less
Visual and spectroscopic observations were done on laser induced toroidal helium plasmas to determine its geometric properties as well as get an estimate of the temperature. These measurements were...Show moreVisual and spectroscopic observations were done on laser induced toroidal helium plasmas to determine its geometric properties as well as get an estimate of the temperature. These measurements were combined in an effort to gain insight into its underlying thermodynamic processes. At 10μs after creation, the torus was found to have a temperature in the order of 2500K, decreasing to 1000K at 50μs. During this period the volume of the torus increased by a factor in the order of 2.5. It was investigated whether this drop in temperature and increase in volume would follow a model of adiabatic expansion. A least squares fit gave a value of the adiabatic constant of γ = 1.21. More observations must be done to increase the accuracy of these values in order to make substantive conclusions.Show less
We simulated the time evolution of plasma torus knots in resistive, viscous MHD. These torus knots are stationary solutions to the ideal MHD equations, as proposed by Kedia et al. These magnetic...Show moreWe simulated the time evolution of plasma torus knots in resistive, viscous MHD. These torus knots are stationary solutions to the ideal MHD equations, as proposed by Kedia et al. These magnetic fields are parameterised by the winding numbers np and nt and exist of several families of nested magnetic fields around a core field line. In ideal MHD, the topological structure of these solitons is conserved and these fields form stationary solutions, but these properties are not carried over to resistive MHD. We will look at the structure of the magnetic field of such a plasma. We find that a new magnetic surface family arises whose topology depends on the poloidal winding number $n_p$ of the initial magnetic field. The time evolution of the corresponding magnetic energy and helicity is strongly influenced by these np. When np > 1, the new magnetic surfaces have a non-zero Euler characteristic and depend on a zero magnetic field line along the z-axis. The toroidal winding number nt is of lesser influence, and the corresponding zero line contracts and disappears. Both the old and the new structures are preserved over time and we observe the formation of magnetic islands between magnetic surfaces.Show less
By temporally and spatially overlapping a fundamental femtosecond pulse (800 nm wavelength) and its second harmonic (400 nm wavelength) at a focal point in air, plasma is generated which is a good...Show moreBy temporally and spatially overlapping a fundamental femtosecond pulse (800 nm wavelength) and its second harmonic (400 nm wavelength) at a focal point in air, plasma is generated which is a good source of intense and ultrabroadband terahertz waves. We study the correlation between the spectral properties of the two-color laser-induced air plasma and the amplitude of the emitted terahertz electric field while varying the relative phase between the 800 nm and 400 nm beams. We find that the amplitude of the terahertz electric fi eld shows an oscillating behavior when changing the relative phase. In particular, for 0.67 fs time delay between the two beams, which corresponds to a phase shift of pi, terahertz waves with opposite polarities are obtained. However, the spectrum of the ultraviolet light emitted from the laser-induced air plasma does not show any noteworthy changes when varying the relative phase. Therefore, we conclude that there is no correlation between the amplitude of the emitted terahertz electric field and the spectrum of the two-color laser-induced air plasma.Show less
A cavity quantum electrodynamics system consisting of quantum dots in a micropillar cavity may form an essential building block for the creation of a quantum network. Current systems do not allow...Show moreA cavity quantum electrodynamics system consisting of quantum dots in a micropillar cavity may form an essential building block for the creation of a quantum network. Current systems do not allow for the scaling, in a simple manner, to a large network. Therefore, we introduce a scalable approach by coupling a micropillar cavity to single-mode fibers. The steps taken to achieve the fiber coupling are explained and the first tests for researching a fiber coupled cavity quantum electrodynamics system are shown. The first tests show that full input-output fiber based polarization control of a micropillar cavity at 3.5 K is possible which is important for a photon polarization based quantum network. Several experimental challenges are shown and discussed. Despite the experimental challenges, the first tests may pave the way for a more scalable approach for building a large-scale quantum network.Show less
Plasma rings are formed after creating a plasma by ionising helium with a focused laser beam. In order to reionise this ring for further experiments, a second laser beam was focused in the plasma...Show morePlasma rings are formed after creating a plasma by ionising helium with a focused laser beam. In order to reionise this ring for further experiments, a second laser beam was focused in the plasma ring. Beyond expectation no plasma was created. This suppression of the second plasma is caused by a shock wave created by the first plasma. Behind this shock wave the density is much lower than outside the shock wave. Since plasma creation depends on the local density, we find the shock wave suppresses the creation of the second plasma.Show less
The thermodynamic principles of complementary binding of DNA or RNA strands are well known, thus the binding efficiency can be calculated for a given sequence. However, when a two-stranded molecule...Show moreThe thermodynamic principles of complementary binding of DNA or RNA strands are well known, thus the binding efficiency can be calculated for a given sequence. However, when a two-stranded molecule contains mismatches in the base pairs, e.g. a guanine opposite to thymine base, traditional models like the nearest-neighbour model do not suffice. The influence of the location of these mismatches on the binding efficiency, in particular, is not well understood. Understanding the binding behaviour of nucleotide strands is essential to the development of applications that require efficient and highly exclusive binding to specific sequences in RNA or DNA. Such an application is exon skipping, a gene correction therapy to treat Duchenne muscular dystrophy. An alternative model has recently been developed at Leiden University to explain this mismatch location dependency. This study is aimed at comparing its calculations with experimental results obtained by DNA encapsulated silver nanocluster fluorimetry. This type of fluorimetry uses a special labelling technique to relate the emitted intensity of various bulk samples to the binding efficiency. Mismatches are introduced in various locations, and the binding efficiency is measured to determine the dependency on the mismatch location. The binding efficiency as a function of the mismatch location shows a relation that resembles the calculations by the model. Improvements of the method are suggested based on the results, allowing for a valid evaluation of the model.Show less
Using an optical cavity, coupled to a micromechanical oscillator - a relatively heavy mass, double trampoline resonator - we will test whether we can, using the method proposed by Clerk et al. ...Show moreUsing an optical cavity, coupled to a micromechanical oscillator - a relatively heavy mass, double trampoline resonator - we will test whether we can, using the method proposed by Clerk et al. (2008), perform back-action evading measurements (BAE) in the optical domain on a single quadrature of the oscillator’s motion. We will do so by probing the oscillators motion with two optical drives spaced one mechanical resonance frequency above and below the cavity resonance frequency. We will then inject noise in the cavity and analyze the light leaving the cavity. This is intended to show that we can perform classical back-action evading measurements. The long term goal of this project is to find out if this system is capable of reaching or exceeding the standard quantum limit (SQL).Show less
In this thesis, we introduce the language of smooth manifolds, which is the natural setting for general relativity, and show how the restricted Lorentz group is related to the complex special...Show moreIn this thesis, we introduce the language of smooth manifolds, which is the natural setting for general relativity, and show how the restricted Lorentz group is related to the complex special linear group in two dimensions, and argue how this relation shows that spinors come up naturally in general relativity. We then consider fibre bundles and how they come up in general relativity, and how they are necessary to define what a spin structure is, and examine under which assumptions it exists. We conclude with a proper definition of Einstein’s field equation.Show less
In this thesis toroidal plasmas are described by a Hamiltonian system parameterising the magnetic field lines. Application of KAM and Melnikov theory explains the occurance of chaotic island chains...Show moreIn this thesis toroidal plasmas are described by a Hamiltonian system parameterising the magnetic field lines. Application of KAM and Melnikov theory explains the occurance of chaotic island chains bounded by invariant manifolds. In plasma simulations and experiments island chains have shown to be rather stable. This thesis provides a theoretical but nonrigorous argument for this stability and proposes the description of magnetohydrodynamics as a Hamiltonian field theory as a method to rigorously study the stability. Hypotheses are given for a generalisation to nontoroidal structures.Show less
Recently it was observed that laser-induced breakdown creates macroscopic rings of plasma. These rings are of interest because they can be used to construct inherently stable magnetized plasma...Show moreRecently it was observed that laser-induced breakdown creates macroscopic rings of plasma. These rings are of interest because they can be used to construct inherently stable magnetized plasma structures. The goal is to form a better understanding of the processes within and properties of these plasma rings. We study the different stages in the time-evolution of the plasma using an intensified CCD with nanosecond resolution exposure time. Furthermore, the spectrum of the emitted light is studied and through Boltzmann analysis the temperature is derived.Show less
We measured the homogeneous linewidth $\Gamma_h$ of ytterbium atoms inside a whispering gallery mode ring resonator. Using two-pulse photon echoes, we looked at the temperature dependence of $...Show moreWe measured the homogeneous linewidth $\Gamma_h$ of ytterbium atoms inside a whispering gallery mode ring resonator. Using two-pulse photon echoes, we looked at the temperature dependence of $\Gamma_h$ for an applied external magnetic field of $B=0$ and $B=0.3$ T. We found a clear narrowing of the linewidth at each temperature. Furthermore, we found saturation of $\Gamma_h$ for $T<30$ mK for both $B=0$ and $B=0.3$ T. At $T=10$ mK and $B=0.3$ T, we have observed a linewidth of 22 kHz, which is very near the lifetime limit of 1 kHz. Our results for the homogeneous linewidth of ions in glasses show that current theories have to be reconsidered. In addition, our results for $T_2$ ensure that rare earth element-doped cavities are a candidate for AFC quantum memory.Show less
Motional control of mechanical resonators is crucial for their applications. In particular, cooling the mechanical mode to overcome the thermal noise has been greatly explored, and has recently...Show moreMotional control of mechanical resonators is crucial for their applications. In particular, cooling the mechanical mode to overcome the thermal noise has been greatly explored, and has recently been pushed into the quantum regime. In this thesis, we study an almost-forgotten cooling technique: resistive cooling with an artificial cold resistor (ACR) which is physically at room temperature. We perform a proof-of-principle demonstration to cool a mechanical mode of a quartz crystal with a “cold” resistor. The “cold” resistor is realised either by a normal resistor cooled by liquid nitrogen or by an ACR made of a special circuitry. We show that the ACR can cool the mode in the same way as a real cold resistor, and the cooling mechanism can be qualitatively understood in the basic thermodynamic picture. We also discuss the feasibility of applying such resistive cooling to an optomechanical system, with a nested trampoline resonator.Show less
We investigate how electric pre-ionization (PI) of helium affects laser-induced breakdown. Plasma created with and without PI is compared while the effect of PI and the laser pulse energy are...Show moreWe investigate how electric pre-ionization (PI) of helium affects laser-induced breakdown. Plasma created with and without PI is compared while the effect of PI and the laser pulse energy are varied. An attempt is made to explain the differences using the theoretical model of laser-induced breakdown. We see PI lowers the energy needed for laser-induced breakdown and also results in better reproducibility. For some plasmas, the breakdown initially takes place in two isolated regions. The plasma expands and contracts over its 15 ms lifetime. The decay of plasma light intensity is first super-exponential but then becomes approximately exponential. Under our experimental conditions, plasma evolves into a stable torus shape. This structure may prove useful for creating plasma with a non-zero helicity.Show less
