One of the biggest challenges in any airborne radar is to distinguish a target from a strong ground echo. The main problem is that the ground echo, called ground clutter, can be up to a million times stronger than the response from the target in question. Today many different filtering methods are used in airborne radar systems to separate the target signal from the ground clutter. All of them with their own advantages and shortcomings. In an ideal world the optimum filter would completely filter out the unwanted ground echo. But as ideal filters don't exist in reality a filter with low sidelobes and minimum loss in signal-to-interference ratio is sought after. A type of filter which exhibit this behaviour are discrete prolate spheroidal sequences (DPSS). This thesis investigated if DPSS could be used as weight functions in multitaper spectrum estimation to filter out ground clutter in the radar signal. A simple clutter model was developed for generating simulated ground clutter which was then filtered out by multitaper and a traditional method. Results showed that it is possible to use DPSS in multitaper spectrum estimation and that it outperforms a basic traditional method in clutter filtration as long as parameters such as bandwidth and the number of sequences used are chosen properly. The increase in performance against the traditional method comes at a cost of increased computational load with each additional DPSS order used. A full factorial experiment was also performed to investigate which parameters were important for maximising improvement factor and minimum detectable velocity. The results from these showed that a low bandwidth in the generation of the DPSS was preferable and that a high number of time samples and DPSS used improved performance. They also showed that for an increase in number of time samples the bandwidth and number of sequences used need to be adjusted to maintain the same level of the improvement factor. It was concluded that future work should focus on validation with more advanced clutter models and MTI filters in simulations as well as validation against real radar data. If proved successful, optimisation of calculation speeds as well as implementation of adaptive choice of DPSS bandwidth would be beneficial before being implemented in a radar system. / En av de största utmaningarna i ett flygburet radarsystem är att urskilja ett mål från markekot. Problem uppstår eftersom markekot, kallat markklotter, kan vara upp emot en miljon gånger starkare än svaret från målet i fråga. I dagsläget används flera olika filtreringmetoder i flyburna radarsystem för att urskilja målet från markklottret, alla har sina fördelar och nackdelar. I en ideal värld skulle det optimala filtret filtrera ut markklottret fullständigt och endast bevara målsignalen. Eftersom dessa filter inte existerar i verkligheten eftersträvas istället ett filter med låga sidlober och minimal förlust i signal-till-interferens ration. En typ av filter som uppvisar detta beteende är diskreta prolata sfäroid sekvenser (DPSS). Denna uppsats undersöker ifall DPSS kan användas som viktfunktioner i multitaper spektralestimering för att filtrera ut markklotter i en radarsignal. En enkel klottermodell utvecklades för generering av simulerat markklotter som sedan filtrerades ut med multitaper metoden och en traditionell metod. Resultatet visade att det var möjligt att använda DPSS i multitaper spektralestimering och att metodens prestanda överstiger den traditionella meteoden, så länge parametrar som bandbredd och antal använda sekvenser väljs korrekt. Prestandaförbättringen mot den traditionella metoden uppstår mot en kostnad i beräkningstid som ökar med varje DPSS ordning som används. Ett full factorial experiment utfördes också för att undersöka vilka parametrar som hade störst påverkan för att maximera förbättringsfaktorn och minsta detekterbara hastighet. Resultated visade att låg bandbredd vid generering av DPSS var att föredra, samt att ett stort antal använda DPSS och tidssamples ökade prestandan. Resultaten visade också att för ett ökat antal tisdssamples så måste bandbredd och antal sekvenser som används justeras för att bibehålla samma nivå av förbättringsfaktorn. Slutligen rekommenderades det att framtida arbete borde fokusera på validering med mer avancerade klottermodeller och MTI filter i simuleringar, samt validering mot verklig radar data. Om detta visar sig framgångsrikt bör optimering av beräkningstid och implementation av ett adaptivt val av DPSS bandbredd göras före implementering i ett radarsystem.

The demands of multimedia services from mobile user equipment (UE) for achieving high data rate, high capacity and reliable communication in modern mobile wireless systems are continually ever-growing. As a consequence, several technologies, such as the Universal Mobile Telecommunications System (UMTS) and the 3rd Generation Partnership Project (3GPP), have been used to meet these challenges. However, due to the channel fading and the Doppler shifts caused by user mobility, a common problem in wireless systems, additional technologies are needed to combat multipath propagation fading and Doppler shifts. Time-variant channel estimation is one such crucial technique used to improve the performance of the modern wireless systems with Doppler spread and multipath spread. One of vital parts of the mobile wireless channel is channel estimation, which is a method used to significantly improve the performance of the system, especially for 4G and Long Term Evolution (LTE) systems. Channel estimation is done by estimating the time-varying channel frequency response for the OFDM symbols. Time-variant channel estimation using Discrete Prolate Spheroidal Sequences (DPSS) technique is a useful channel estimation technique in mobile wireless communication for accurately estimating transmitted information. The main advantage of DPSS or Slepian basis expansion is allowing more accurate representation of high mobility mobile wireless channels with low complexity. Systems such as the fourth generation cellular wireless standards (4G), which was recently introduced in Sweden and other countries together with the Long Term Evolution, can use channel estimation techniques for providing the high data rate in modern mobile wireless communication systems. The main goal of this thesis is to test the recently proposed method, time-variant channel estimation using Discrete Prolate Spheroidal Sequences (DPSS) to model the WINNER phase II channel model. The time-variant sub-carrier coefficients are expanded in terms of orthogonal DPS sequences, referred to as Slepian basis expansions. Both Slepian basis expansions and DPS sequences span the low-dimensional subspace of time-limited and band-limited sequences as Slepian showed. Testing is done by using just two system parameters, the maximum Doppler frequency Dmax v and K, the number of basis functions of length N = 256. The main focus of this thesis is to investigate the Power spectrum and channel gain caused by Doppler spread of the WINNER II channel model together with linear fitting of curves for both the Slepian and Fourier basis expansion models. In addition, it investigates the Mean Square Error (MSE) using the Least Squares (LS) method. The investigation was carried out by simulation in Matlab, which shows that the spectrum of the maximum velocity of the user in mobile wireless channel is upper bounded by the maximum normalized one-sided Doppler frequency. Matlab simulations support the values of the results. The value of maximum Doppler bandwidth vDmax  of the WINNER model is exactly the same value as DPS sequences. In addition to the Power spectrum of the WINNER model, the fitting of Slepian basis expansion performs better in the WINNER model than that of the Fourier basis expansion.

We demonstrate the improvement of fluorescence immunoassay (FIA) diagnostics in deploying a newly developed compact diode-pumped solid state (DPSS) laser with emission at 315 nm. The laser is based on the quasi-three-level transition in Nd:YAG at 946 nm. The pulsed operation is either realized by an active Q-switch using an electro-optical device or by introduction of a Cr<SUP>4+</SUP>:YAG saturable absorber as passive Q-switch element. By extra-cavity second harmonic generation in different nonlinear crystal media we obtained blue light at 473 nm. Subsequent mixing of the fundamental and the second harmonic in a β-barium-borate crystal provided pulsed emission at 315 nm with up to 20 μJ maximum pulse energy and 17 ns pulse duration. Substitution of a nitrogen laser in a FIA diagnostics system by the DPSS laser succeeded in considerable improvement of the detection limit. Despite significantly lower pulse energies (7 μJ DPSS laser versus 150 μJ nitrogen laser), in preliminary investigations the limit of detection was reduced by a factor of three for a typical FIA.

Le remplacement des lasers à colorant émettant dans la gamme 550-570 nm, à l'aide de lasers solides, représente un véritable enjeu industriel. Les applications sont multiples tant dans le domaine de la recherche biomédicale que dans celui de la métrologie. Quelques solutions ont été développées à 561 nm et à 553 nm. Néanmoins, elles ne permettent pas de fournir des lasers intégrables parfaitement mono-fréquences émettant en continu un faisceau gaussien, d'une puissance supérieure ou égale à 200 mW. Dans ces travaux, nous proposons une étude théorique et expérimentale de cavités lasers solides monolithiques à base de Nd:YAG pompé par diode, doublé en fréquence en intra-cavité, à l'aide d'un cristal non-linéaire de KTP. Ces cavités, constituées de plusieurs cristaux, sont contactées par adhérence moléculaire. Elles ne contiennent aucune optique de mise en forme des faisceaux et présentent la particularité de comporter un double filtre de Lyot. Nous présentons les résultats obtenus avec des cavités émettant à 561 nm pour des puissances supérieures ou égales à 300 mW. Puis, après une étude statistique et une analyse des résultats de test de ces cavités à long terme (> 6000 heures), nous discutons des problèmes éventuels de fiabilité et nous suggérons des axes d'amélioration. Ayant réussi à faire osciller, pour la première fois, la raie à 1106 nm du Nd:YAG, nous montrons ensuite la faisabilité d'un laser compact mono-fréquence continu à 553 nm, émettant une puissance de 200 mW à 500 mW avec un rendement de conversion pompe/laser visible de l'ordre de 19 %. Pour conclure, nous montrons qu'il est possible, dans des cavités de ce type, de faire osciller des raies Raman issues des raies fondamentales et de les doubler en fréquence en intra-cavité. Nous ouvrons ainsi la porte à toute une famille de lasers solides émettant dans la gamme 540-600 nm. / Replacement of dye lasers emitting in the range 550-570 nm, using solid state lasers, is a real industrial issue. There are many applications both in the field of biomedical research than in metrology. Some solutions have been developed for 561 nm and 553 nm. However, they do not provide fully integrated lasers emitting single-frequency continuous Gaussian beam with a power equal or up to 200 mW. In this work, we propose a theoretical and experimental study of solid monolithic cavity lasers based on Nd:YAG diode-pumped, frequency-doubled intra-cavity, using a non-linear crystal of KTP. These cavities, consisting of several crystals, are contacted by molecular adhesion. They contain no optical layout of the beams and they have the particularity of including a double Lyot filter. We present the results obtained with those cavities emitting at 561 nm for powers greater than 300 mW. Then, after a statistical study and analysis of test results of these cavities in the long term (> 6000 hours), we discuss about the potential problems of reliability and we suggest areas for improvement. For the first time, we show that the line at 1106 nm of the Nd: YAG can oscillate in this type of cavity. Then we demonstrate the feasibility of a compact single-frequency laser at 553 nm continuously, emitting a power of 200 mW to 500 mW with a conversion efficiency of pump / visible laser of about 19%. Finally, we show that it is possible, in cavities of this type, to oscillate the Raman lines from the lines of the fundamental and doubled frequency in intra-cavity. We open the door to a whole family of solid state lasers emitting in the range of 540-600 nm.