No description available.

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

This report describes a project performed at Linnaeus University with the task of solving the Schrodinger equation for electrons in homonuclear diatomic molecules, using the finite element method in Python. The Schrodinger equation is solved for the hydrogen atom, nitrogen atom, hydrogen molecule and nitrogen molecule using a finite element method. The results of the hydrogen atom showed a high accuracy compared to the analytical solution, given that the domain had high enough resolution. The solutions of the hydrogen molecule, nitrogen atom and nitrogen molecule showed reasonable accuracy although the resolution appeared sufficient. This foundation of Python code can be further built upon to explore more molecules and more properties, such as total energies and vibrational energies.

In this project we simulate explosions of nano water droplets using molecular dynamics. The water droplets are put under the exposure of a high-energy X-ray laser, which induces a quick Coulomb explosion. The explosion patterns, reporting the resulting position of the atoms, are then analyzed in different ways. Methods to deduce the initial shape of an ellipsoidal water droplet based on its explosion pattern are developed.

We constructed a standalone optical trapping system that was steerable in three dimensions and allowed for sufficient imaging of one цm particles with a CCD camera. The motion of the trapped particles was monitored by both a position sensitive detector as well with the CCD camera. The trap stiffness was evaluated by the power spectrum method and the equipartition theorem. For calibration of the stiffness of the trap, we found that the power spectrum method with data assessed by the PSD was most straightforward and accurate. The equipartition method was compromised by noise, low resolution and the bandwidth of the detector. With a HeNe laser run at 10 mW output power the trap strength of our system reached ~2 pN/um. The results also showed a decrease in the trap stiffness and particle's position variance when the size of trapped particles increased.

No description available.

Assessing the mixing of two liquids is a critical task in the biotechnical industry. At Cytiva, affinity chromatography columns depend on a well-mixed aqueous salt solution to release the target from the affinity resin. A mixer is often incorporated into the flow path to ensure effective mixing of the liquids.These mixers generate complex three-dimensional flowfields, and existing measurement techniques frequently average the flow depth, thereby losing essential spatial information. This project introduces and implements a novel method for assessing mixing in four dimensions, requiring simultaneous imaging of the flow from multiple view points. The flowfield is reconstructed from the image data using a least squares tomographic reconstruction technique. Additionally, a methodwas developed to reconstruct the same flowfield numerous times using different underlying section meshes. These results are then interpolated on a common grid and averaged. The findings demonstrate that this method accurately resolves the flowfield qualitatively and quantitatively. The averaging method enables lower downsampling factors and higher overall accuracy. However, challenges such as achieving uniform pipe illumination and enhancing data acquisition rates remain. Addressing these issues is essential for fully resolving three-dimensional flowfields over time. Future work will improve lighting and data acquisition to enhance the method’s applicability for higher Reynolds number applications.

In this thesis we study device-independent quantum key distribution based on energy-time entanglement. This is a method for cryptography that promises not only perfect secrecy, but also to be a practical method for quantum key distribution thanks to the reduced complexity when compared to other quantum key distribution protocols. However, there still exist a number of loopholes that must be understood and eliminated in order to rule out eavesdroppers. We study several relevant loopholes and show how they can be used to break the security of energy-time entangled systems. Attack strategies are reviewed as well as their countermeasures, and we show how full security can be re-established. Quantum key distribution is in part based on the profound no-cloning theorem, which prevents physical states to be copied at a microscopic level. This important property of quantum mechanics can be seen as Nature's own copy-protection, and can also be used to create a currency based on quantummechanics, i.e., quantum money. Here, the traditional copy-protection mechanisms of traditional coins and banknotes can be abandoned in favor of the laws of quantum physics. Previously, quantum money assumes a traditional hierarchy where a central, trusted bank controls the economy. We show how quantum money together with a blockchain allows for Quantum Bitcoin, a novel hybrid currency that promises fast transactions, extensive scalability, and full anonymity. / En viktig konsekvens av kvantmekaniken är att okända kvanttillstånd inte kan klonas. Denna insikt har gett upphov till kvantkryptering, en metod för två parter att med perfekt säkerhet kommunicera hemligheter. Ett komplett bevis för denna säkerhet har dock låtit vänta på sig eftersom en attackerare i hemlighet kan manipulera utrustningen så att den läcker information. Som ett svar på detta utvecklades apparatsoberoende kvantkryptering som i teorin är immun mot sådana attacker. Apparatsoberoende kvantkryptering har en mycket högre grad av säkerhet än vanlig kvantkryptering, men det finns fortfarande ett par luckor som en attackerare kan utnyttja. Dessa kryphål har tidigare inte tagits på allvar, men denna avhandling visar hur även små svagheter i säkerhetsmodellen läcker information till en attackerare. Vi demonstrerar en praktisk attack där attackeraren aldrig upptäcks trots att denne helt kontrollerar systemet. Vi visar också hur kryphålen kan förhindras med starkare säkerhetsbevis. En annan tillämpning av kvantmekanikens förbud mot kloning är pengar som använder detta naturens egna kopieringsskydd. Dessa kvantpengar har helt andra egenskaper än vanliga mynt, sedlar eller digitala banköverföringar. Vi visar hur man kan kombinera kvantpengar med en blockkedja, och man får då man en slags "kvant-Bitcoin". Detta nya betalningsmedel har fördelar över alla andra betalsystem, men nackdelen är att det krävs en kvantdator.