<p>  </p> <p>The investigation of laser-matter interactions has gained interest over the years due to the importance of these interactions in materials synthesis, diagnostics, electronics, and photonics. In-situ transmission electron microscopy (TEM) techniques are invaluable for real-time monitoring of dynamic processes in these systems at the nanoscale. In this work, the effect of pulsed laser heating on the reactions of energetic materials, plasmonic structures, and multilayer thin films has been studied by utilizing ultrafast transmission electron microscopy (UTEM) techniques. Heat transfer and electric field calculations have been carried out to compare and support the experimental findings. </p> <p>The photothermal reaction of an aluminum-fluoropolymer composite is studied to show the effect of pulsed laser heating on reactions of reactive materials. An aluminum nanoparticle - THV (terpolymer of tetrafluoroethylene, hexafluoropropylene, and vinylidene fluoride) sample is subjected to rapid heating and cooling cycles by employing the integrated laser system of an UTEM. TEM images and real-time movies (30 frame/s) are acquired to reveal the changes during the reaction. Heat transfer simulations proved that the temperature of the sample was high enough to trigger the decomposition of THV and start its reaction with Al nanoparticles. Electron diffraction patterns revealed that the reaction product was the rare and metastable η-phase aluminum fluoride (AlF3). The experimental and theoretical results showed that rapid pulsed laser heating and subsequent cooling of a nanoscale sample influences the phases that can form and be utilized to investigate other systems.</p> <p>Pulsed laser-assisted merging and alloying of noble metals are also studied to explore the fabrication of beaded gold-silver nanowires with a variety of morphology and composition. In-situ laser heating of plasmonic silver nanowire (Ag NW) - gold nanoparticle (Au NP) couples are performed inside an UTEM, and direct visualization of the evolution process gives insights into the formation mechanism. Experimental results show that silver melts at the surface to bridge the nanometer-sized gap between the NP and the NW, forming a cup-like morphology underneath the Au NP via capillary action. Progressive laser irradiation leads to wetting of the Au NP and the formation of a valley in the Ag NW around the NP, which flattens gradually by partial embedding of the NP. Inter-diffusion of Au into Ag and vice versa sets in at this stage, leading to depletion of Au from the Au-rich NP region. Prolonged irradiation and heating lead to gradual inter-mixing of Au-Ag, forming a beaded Au-doped Ag nanowire with homogeneous composition. Such a step-by-step understanding of the merging and alloying process has implications in nanowelding, which holds a future in designing efficient, transparent conductors and printed electronics. Numerical simulations are performed to calculate the electromagnetic enhancement at the interface of adjacent NPs and NWs and provide information on heat generation rates in NP-NW couples at the early stages of the nanowelding process. </p> <p>In the third chapter, laser-induced irreversible dynamics in electron beam sensitive organic energetic crystals and ultrathin multilayer films are studied by single-shot UTEM imaging. After various sample preparation methods are developed and compared for the well-controlled synthesis of nanoscale ammonium perchlorate samples on TEM grids, decomposition dynamics of ammonium perchlorate crystals are captured via single-shot imaging. The experimental data showed that the sublimation and decomposition are visible ~30 ns after the sample excitation laser in crystals smaller than 5 µm. Dependency of decomposition to crystal porosity and thickness is also observed with crack formation in some cases. In the following section, pulsed-laser irradiation is utilized to realize deformation in thin multilayer films under high temperatures, and triggered dynamic processes are investigated through single-shot imaging. Laser-assisted periodic wrinkle formation is demonstrated on SiN membranes coated with Ti/Ni bilayers. The resulting structures showed periodic wrinkling of the SiN membrane and corrugated surface formation on both sides of the film. Overall, the dissertation highlights the potential of ultrafast transmission electron microscopy in discovering fundamental processes related to, but not limited to, reactive materials, plasmonic nanomaterials, and ultrathin multilayer films. </p>

In this thesis, an error analysis based method is proposed to calculate single shot hit probability (PSSH) values of a fire control system. The proposed method considers that a weapon and a threat are located in three dimensional space. They may or may not have relative motion in three dimensions with respect to each other. The method accounts for the changes in environmental conditions. It is applicable in modeling and simulation as well as in top down design of a fire control system to reduce the design cost. The proposed method is applied to a specific fire control system and it is observed that PSSH values highly depend on the distance between the weapon and the threat, hence they are time varying. Monte Carlo simulation is used to model various defense scenarios in order to evaluate a heuristic developed by G&uuml / lez (2007) for weapon-threat assignment and scheduling of weapons&rsquo / shots. The heuristic uses the proposed method for PSSH and time of flight computation. It is observed that the difference between the results of simulation and heuristic depends on the scenario used.

In this thesis, mathematical modeling and heuristic approaches are developed for surface-to-air weapon-target allocation problem with time varying single shot hit probabilities (SSHP) against linearly approaching threats. First, a nonlinear mathematical model for the problem is formulated to maximize sum of the weighted survival probabilities of assets to be defended. Next, nonlinear objective function and constraints are linearized. Time varying SSHP values are approximated with appropriate closed forms and adapted to the linear model obtained. This model is tested on different scenarios and results are compared with those of the original nonlinear model. It is observed that the linear model is solved much faster than the nonlinear model and produces reasonably good solutions. It is inferred from the solutions of both models that engagements should be made as late as possible, when the threats are closer to the weapons, to have SSHP values higher. A construction heuristic is developed based on this scheme. An improvement heuristic that uses the solution of the construction heuristic is also proposed. Finally, all methods are tested on forty defense scenarios. Two fastest solution methods, the linear model and the construction heuristic, are compared on a large scenario and proposed as appropriate solution techniques for the weapon-target allocation problems.

Biometriska lösningar för åtkomstkontroll är ett blomstrande koncept. Precise Biometrics är ett företag som fokuserar på just biometriska lösningar relaterade till åtkomstkontroll. YOUNiQ är en produkt som fokuserar på ansiktsigenkänning. Denna produkt använder ansiktsigenkännig för att ge åtkomst till registrerade användare i systemet. Ett problem som uppstår vid att använda ansiktsigenkänning är att alla som befinner sig tillräckligt nära kameran blir skannade, även de som inte är registrerade. Denna avhandlingen har som mål att implementera ett avsiktsmedvetet system som använder en utlösare för att starta ett system. Istället för att använda ansiktsigenkänning på alla individer använder systemet gester som en utlösare för att starta systemet. Denna avhandlingen fokuserar inte på ansiktsigenkännning utan istället på utlösaren för att starta en process. Utvecklingsfasen sker i form utav en iterativ process för att skapa en prototyp. För att utvärdera systemet utfördes testfall för varje gest som är inkluderat i systemet. Efter testfallen var färdigställda sattes dem i ett verkligt scenario för att simulera en komplett interaktion med systemet. Utvärderingen användes sedan för att bestämma och vägleda för implementationen av ett avsiktsmedvetet system. Denna implementation kan ses som en signal till underliggande funktioner för att extrahera biometrisk data för till exempel ansiktsigenkänning. / Biometric solutions for access control is a thriving concept, Precise Biometrics is a company that focuses on just that. YOUNiQ is a product that focuses on facial identification for access control, with it comes an issue in where every person's face is being identified. This means identifying people that do not want to use the facial identification module. This thesis focuses on implementing an intent-aware system, a system which uses a trigger to begin a process. This thesis was done in collaboration with engineers at Precise Biometrics. Instead of identifying faces without permission the intent-aware system uses a trigger based on different hand gestures to begin the process. This thesis does not focus on face identification but instead the trigger before a specific process begins. The development phase consisted of an iterative process in creating the prototype system. In order to evaluate the system, test cases were done to verify accuracy of each hand gesture. Thereafter, a scenario was created to simulate an activation of the prototype system. The evaluation was used to determine the convenience and guidance when implementing intent-aware systems. Furthermore, the system can be seen as a form of trigger to allow for extracting biometric data in for example face identification.

No description available.

A new approach to the absolute measurement of two-dimensional optical path differences is presented in this thesis. The method, which incorporates a white light interferometer and a hyperspectral imaging system, is referred to as Hyperspectral Interferometry. A prototype of the Hyperspectral Interferometry (HSI) system has been designed, constructed and tested for two types of measurement: for surface profilometry and for depth-resolved displacement measurement, both of which have been implemented so as to achieve single shot data acquisition. The prototype has been shown to be capable of performing a single-shot 3-D shape measurement of an optically-flat step-height sample, with less than 5% difference from the result obtained by a standard optical (microscope) based method. The HSI prototype has been demonstrated to be able to perform single-shot measurement with an unambiguous 352 (m depth range and a rms measurement error of around 80 nm. The prototype has also been tested to perform measurements on optically rough surfaces. The rms error of these measurements was found to increase to around 4× that of the smooth surface. For the depth-resolved displacement field measurements, an experimental setup was designed and constructed in which a weakly-scattering sample underwent simple compression with a PZT actuator. Depth-resolved displacement fields were reconstructed from pairs of hyperspectral interferograms. However, the experimental results did not show the expected result of linear phase variation with depth. Analysis of several possible causes has been carried out with the most plausible reasons being excessive scattering particle density inside the sample and the possibility of insignificant deformation of the sample due to insufficient physical contact between the transducer and the sample.

No description available.

The Swedish armed forces use the Single Source Intelligent Cell (SSIC), developed by Saab, for analysis of aerial reconnaissance video and report generation. The analysis can be time-consuming and demanding for a human operator. In the analysis workflow, identifying vehicles is an important part of the work. Artificial Intelligence is widely used for analysis in many industries to aid or replace a human worker. In this paper, the possibility to aid the human operator with air reconnaissance data analysis is investigated, specifically, object detection for finding cars in aerial images. Many state-of-the-art object detection models for vehicle detection in aerial images are based on a Convolutional Neural Network (CNN) architecture. The Faster R-CNN- and SSD-based models are both based on this architecture and are implemented. Comprehensive experiments are conducted using the models on two different datasets, the open Video Verification of Identity (VIVID) dataset and a confidential dataset provided by Saab. The datasets are similar, both consisting of aerial images with vehicles. The initial experiments are conducted to find suitable configurations for the proposed models. Finally, an experiment is conducted to compare the performance of a human operator and a machine. The results from this work prove that object detection can be used to supporting the work of air reconnaissance image analysis regarding inference time. The current performance of the object detectors makes applications, where speed is more important than accuracy, most suitable.

Modern state-of-the-art object detection models are based on convolutional neural networks and can be divided into single-shot detectors and two-stage detectors. Two-stage detectors exhibit impressive detection performance but their complex pipelines make them slow. Single-shot detectors are not as accurate as two-stage detectors, but are faster and can be used for real-time object detection. Despite the fact that single-shot detectors are faster, a large number of calculations are still required to produce a prediction that not many embedded devices are capable of doing in a reasonable time. Therefore, it is natural to ask if single-shot detectors could become faster even. Pruning is a technique to reduce the size of neural networks. The main idea behind network pruning is that some model parameters are redundant and do not contribute to the final output. By removing those redundant parameters, fewer computations are needed to produce predictions, which may lead to a faster inference and since the parameters are redundant, the model accuracy should not be affected. This thesis investigates two approaches for pruning the SSD-MobileNet- V2 single-shot detector. The first approach prunes the single-shot detector by a large portion and retrains the remaining parameters only once. In the other approach, a smaller portion is pruned, but pruning and retraining are done in an iterative fashion, where pruning and retraining constitute one iteration. Beyond comparing two pruning approaches, the thesis also studies the tradeoff between model accuracy and inference speed that pruning induces. The results from the experiments suggest that the iterative pruning approach preserves the accuracy of the original model better than the other approach where pruning and finetuning are performed once. For all four pruning levels that the two approaches are compared iterative pruning yields more accurate results. In addition, an inference evaluation indicates that iterative pruning is a good compression method for SSD-MobileNet-V2, finding models that both are faster and more accurate than the original model. The thesis findings could be used to guide future pruning research on SSD-MobileNet- V2, but also on other single-shot detectors such as RetinaNet and the YOLO models. / Moderna modeller för objektsdetektering bygger på konvolutionella neurala nätverk och kan delas in i ensteg- och tvåstegsdetektorer. Tvåstegsdetektorer uppvisar imponerande detektionsprestanda, men deras komplexa pipelines gör dem långsamma. Enstegsdetektorer uppvisar oftast inte lika bra detektionsprestanda som tvåstegsdetektorer, men de är snabbare och kan användas för objektdetektering i realtid. Trots att enstegsdetektorer är snabbare krävs det fortfarande ett stort antal beräkningar för att få fram en prediktering, vilket inte många inbyggda enheter kan göra på rimlig tid. Därför är det naturligt att fråga sig om enstegsdetektorer kan bli ännu snabbare. Nätverksbeskärning är en teknik för att minska storleken på neurala nätverk. Huvudtanken bakom nätverksbeskärning är att vissa modellparametrar är överflödiga och inte bidrar till det slutliga resultatet. Genom att ta bort dessa överflödiga parametrar krävs färre beräkningar för att producera en prediktering, vilket kan leda till att nätverket blir snabbare och eftersom parametrarna är överflödiga bör modellens detektionsprestanda inte påverkas. I den här masteruppsatsen undersöks två metoder för att beskära enstegsdetektorn SSD-MobileNet-V2. Det första tillvägagångssättet går ut på att en stor del av detektorn vikter beskärs och att de återstående parametrarna endast finjusteras en gång. I det andra tillvägagångssättet beskärs en mindre del, men beskärning och finjustering sker på ett iterativt sätt, där beskärning och finjustering utgör en iteration. Förutom att jämföra två metoder för beskärning studeras i masteruppsatsen också den kompromiss mellan modellens detektionsprestanda och inferenshastighet som beskärningen medför. Resultaten från experimenten tyder på att den iterativa beskärningsmetoden bevarar den ursprungliga modellens detektionsprestanda bättre än den andra metoden där beskärning och finjustering utförs en gång. För alla fyra beskärningsnivåer som de två metoderna jämförs ger iterativ beskärning mer exakta resultat. Dessutom visar en hastighetsutvärdering att iterativ beskärning är en bra komprimeringsmetod för SSD-MobileNet-V2, eftersom modeller som både snabbare och mer exakta än den ursprungliga modellen går att hitta. Masteruppsatsens resultat kan användas för att vägleda framtida forskning om beskärning av SSD-MobileNet-V2, men även av andra enstegsdetektorer, t.ex. RetinaNet och YOLO-modellerna.

Doctor of Philosophy / Department of Physics / Zenghu Chang / The first part of this thesis describes our novel design, test, and application of our X-ray streak camera to the pulse duration measurement of soft X-rays. We demonstrated a significant improvement in the resolution of the x-ray streak camera by reducing the electron beam size in the deflection plates. This was accomplished by adding a slit in front of the focusing lens and the deflection plates. The temporal resolution reached 280 fs when the slit width was 5 μm. The camera was operated in an accumulative mode and tested by using a 25 fs laser with 2 kHz repetition rate and 1-2% RMS pulse energy stability. We conclude that deflection aberrations, which limit the resolution of the camera, can be appreciably reduced by eliminating the wide-angle electrons. We also employed the same streak camera to demonstrate that it is capable of measuring the pulse duration of X-rays. We measured the pulse duration of X-rays emitted from Ni-like Ag and Cd grazing-incidence laser to be ~5ps. The measured value agrees with the prediction made by the model and the measurement made by changing the delay as a function of the pulse duration. The streak camera was also tested with various sources of X-ray such as high harmonics generation of soft x-rays from an argon atom using a high power Ti:sapphire laser source of KLS. The result of the measurement manifests its capability for serving as a detector in the study of ultrafast dynamics in the field of physics, chemistry, biology and medical sciences. The second part of this thesis describes our design of a spectrometer to study the effect of the Carrier envelope (CE) phase on polarization gated extreme-ultraviolet (XUV) super-continuum generation. Because the challenge of making single shot experiment possible is to generate a sufficient number of photons, our setup has been built to allow generation of high order harmonics at the maximum phase matched pressure. This is the first time to our knowledge that phase matching in the polarization gating process has been studied so far. We measured the maximum phase matching pressure to be ~ 55 Torr which is the pressure above which quadratic increase in intensity of the high harmonics spectrum ceases to appear. At this pressure the number of photons per laser shot was 104 which is sufficient for measuring the single shot XUV spectrum in the range 34 to 45 eV. The spectral profile was a super-continuum for some shots and discrete high harmonics for other shots. It is believed that the shot to shot variation of the spectra is due to the changes of the carrier envelope phase of the few-cycle laser pulses used for the polarization gating. An improved CE phase stabilization system in KLS further eliminated the statistical noise in our observation by allowing us to integrate data over several laser cycles for each CE phase value. The effect of CE phase on a polarization gated XUV spectrum was tested by changing the CE phase with two different methods. In the first method, the CE phase was changed by changing the thickness of fused silica plates on the beam path, and the result shows the shift in the spectral peak of the XUV when the gate width approached less than one optical cycle. As gate width was made less than half the optical cycle, the spectrum was observed with continuum harmonics separated by π radians. We believe that the presence of continuum and discrete harmonics spectra in the observation is due to single and double attosecond pulses generated in the polarization gating. In the second method the carrier-envelope phase of pulses from a grating-based chirped pulse amplification laser was varied smoothly to cover a 2π range by controlling the grating separation. The phase is measured simultaneously by an f-to-2f setup and by the variation of XUV spectra from polarization gated high harmonic generation. A very good similarity between the effect of single and double slits in Yong’s experiment and that of CE phase on the XUV spectrum in the polarization gating experiment has been found, giving better agreement with the theory. The effect of optical properties such as the Gouy phase shift on the polarization gated spectrum has also been studied in the course of investigating the best experimental optimizations to generate the most CE phase sensitive XUV spectrum with less statistical noise. This is the first time to our knowledge experimental study of the effect of the Gouy phase shift on a polarization gated XUV spectrum has been made.