Ce travail de thèse porte sur l’estimation de la possibilité d’atteindre le seuil laser dans un matériau organique par pompage électrique. Dans le but ultime de réaliser le laser organique à pompage électrique, un prérequis est d’injecter une haute densité de courant dans un dispositif électroluminescent fonctionnel. Dans un premier temps, le comportement de l’OLED soumise à haute densité de courant est simulé et un modèle d’estimation de seuil laser basé sur la matrice de transfert est proposé. Ces études théoriques indiquent l’existence d’une densité de population maximale d’excitons radiatives au début d’injection de courant et estime la nécessité de 8.7×1016 cm-3 au seuil laser. Ensuite, la caractéristique résolue en temps des μ-OLED à base d’Alq3 : DCM excitées par des impulsions électriques de courtes durées (< 100 ns) et à faible taux de répétition (10 Hz) sont étudiées à l’aide d’un système de microscope confocal calibré. Les caractéristiques de l’OLED sont en bon accord avec les simulations théoriques. Une densité de courant de 3.6 kA/cm² et un pic de luminance de 8.4×106 cd/m² ont été obtenus en injectant des impulsions de 30 ns. Le pic de luminance correspond à une densité de population de 3.6×1017 cm-3, soit supérieure au plus petit seuil laser en littérature. Il est donc possible de réaliser le laser dans cette fenêtre de temps de quelques nanosecondes. / This thesis focus on the estimation of the possibility to achieve the laser threshold in an organic material with electrical pumping. As the ultimate goal is to demonstrate an electrically pumped organic laser, attaining high current density in a working electroluminescent device is pre-required. At first, the response of OLED at high current injection condition is simulated with a theoretical model. And the laser threshold estimation is performed by transfer matrix method. These theoretical studies show that a peak of emissive exciton (singlet) population density should exist at pulse onset, while a population density of 8.7×1016 cm-3 is necessary for lasing. Next, the time-resolved characteristics of μ-OLED based on Alq3 : DCM excited by short (< 100 ns) electrical pulses with low repetition rate (10 Hz) have been studied on the calibrated confocal microscope. The response of μ-OLED is in good agreement with the theoretical simulations. A current density of 3.6 kA/cm² and a luminance peak of 8.4×106 cd/m² have been achieved with 30-ns pulses. This luminance peak corresponds to singlet population density of 3.6×1017 cm-3, which is higher than the smallest laser threshold in literature. We suggest that it is possible to achieve laser effect in the time window of several nanoseconds at pulse onset.

This thesis presents the results of a series of experiments in which electrons are superelastically scattered from various laser excited states of sodium. The atoms, once in the optically prepared state, are forced to relax via the superelastic collision with an electron. The rate of detection of superelastically scattered electrons was measured as a function of the laser polarisation which enabled pseudo Stokes parameters to be determined. These pseudo Stokes parameters are functions of both optical pumping parameters and atomic collision parameters. The optical pumping parameters describe the laser-atom interaction and the atomic collision parameters describe the electron-atom collision process. Three different laser excitation mechanisms were used to optically pump the atoms into various excited states. The first of these used a single laser tuned to the 32S 112(F'=2 hyperfine state)-~32P312 transition. The excited atoms underwent a superelastic collision with an electron leaving the atom in the ground state and pseudo Stokes parameters were measured as a function of both scattering angle and incident electron energy. The second superelastic experiment, utilised a folded step excitation mechanism which employed two lasers tuned from the two hypethne states of the 32S112 ground state respectively to the 32P312 excited state. Power broadening effects in the single laser experiment cause the atoms to be optically pumped into the F= 1 hyperfine ground state. The laser powers used were not great enough to power broaden the hyperfine ground states and as such the F'= 1 sublevel effectively acted as a sink. The folded step excitation method enabled the excited state population to be increased so that data at larger scattering angles could be obtained. Stokes parameters from both of these experiments which had an incident energy range of 10eV to 30eV and an angular range of 5°-25° were compared to three current electron-atom scattering theories and previous experimental data. Overall, fair to good agreement was found between theory and experiments for the individual Stokes parameters. Losses of coherence was observed at small scattering angles (50.200) at 20eV and 25eV incident electron energies which were poorly modelled by the three different theories. The third superelastic experiment involved the use of two lasers of specified polarisation to stepwise excite the atoms to the 32D512 excited state. Superelastic collisions with incident electron energies of 20eV from the 32D512-*32P312~312 collision were studied at three different scattering angles and pseudo Stokes parameters for the case where the polarisations of the radiation from the lasers were parallel were measured. The single step and folded step laser-atom interactions for it excitation were modelled using a full quantum electrodynamical treatment so that the optical pumping parameters from the single and folded step experiments could be investigated. Equations of motion were derived in the Heisenberg picture and it is shown that for the single laser case 59 equations of motion are required to fully model the interaction and for the folded step ease 78 equations of motion are required. The results of calculations demonstrated that the optical pumping parameters were sensitive to laser intensity, laser detuning and the Doppler width of the atomic beam. The theoretical quantum electrodynamical calculation results were in good agreement with the experimental results.

In this thesis, my main focus was to establish a novel composite-cavity fibre laser (CCFL) and to apply it in sensing, particularly in the hydrophone application. The CCFL that I have proposed is formed by writing three wavelength matched fibre Bragg gratings directly into a continuous length of doped fibre. I have also examined the relative advantages and disadvantages of interferometric and intensity-based hydrophone systems, and have established a hydrophone system that can be switched between the two modes of operation, by making use of digital signal processing. I have established a theoretical model to study the lasing and spectral characteristics of the CCFL. My analysis showed that whilst the CCFL have significantly different phase and threshold conditions from the common semiconductor diode lasers with external cavity, the CCFL also have mode-limiting properties that are often sought after. Through simulations, I was able to identify that a non-uniform straining scheme, that is, when one of the sub-cavities of the CCFL is restrained from strain, can improve the sensitivity with respect to existing single cavity fibre lasers, in both the frequency and intensity domains. My simulations also showed that the sensitivity of such a straining scheme can be optimised by tuning the reflectivity of the gratings, sub-cavity lengths, doping concentration and pump power. I have fabricated multiple CCFLs using the in-house grating writing facilities, and have experimentally assessed their power and spectral related lasing characteristics. Whilst having a significantly longer total cavity length compared to typical fibre lasers, the CCFLs demonstrated stable single longitudinal mode operation and narrow linewidth in the order for a few tens of kHz. Asymmetric output power and frequency as a result of unequal sub-cavity lengths were also examined. Finally, I conducted sensing experiments by applying the CCFLs in strain monitoring and intensity-based hydrophone. My results showed that the non-uniform straining scheme had significantly improved the intensity response of the CCFL, and that the acoustic pressure and frequency can be determined by directly sampling and applying Fourier transform to the output intensity of the fibre laser.

<p>This degree project has been carried out in cooperation with Enertech AB in Ljungby and is pilot study to automating all current manual soldering. The soldering process accounts for a large part of the processing cost in the production of a heat pump. The process is also a quality risk and has a major impact on the lifetime of the final product.</p><p>The Main task of this project has been to evaluate automation of the soldering process, to develop automation solutions and a principle layout, to draw the design changes required for the automation and to calculate the supposed solution.</p><p>This pilot study has resulted in a suggested automation solution using laser as a heat source for soldering. Calculations of the solution show that a automating a laser soldering cell is very profitable.</p>

In this thesis electron generation is studied via laser plasma interaction known as laser wakefield acceleration in two regimes of weakly relativistic and highly relativistic laser intensity regimes. The plasma targets consisted of gas jets photonionized by rising edge of the laser pulse to densities as high as 10^20cm3. In the weakly relativistic regime, 210 mJ at 33 fs were focused to intensities of up to 310^18 Wcm2 on the gas targets of 2.4 mm length. In the highly relativistic regime, 3 J of energy compressed in 30 fs were delivered at intensity as high as 6.5 10^18 Wcm2 on targets of 2.4, 5, and 10 mm. Monoenergetic electrons in tens of MeV were observed in weakly relativistic regime, while electron energies as high as 300 MeV were observed in highly relativistic regime. Higher input laser intensity and prepulse levels were found to enhance electron production. Scaling of energy and stability of electron generation were also studied. / Photonics and Plasmas

The purpose of this project was to develop a delivery system optimized for laser interstitial thermotherapy of small tumors of the breast. The proposed approach is to combine laser interstitial thermotherapy with stereotactic imaging for fiber guidance and treatment monitoring. The goals of the dissertation were to design a fiber insertion system for cylindrical diffusing tip optical fibers and to derive optimal laser parameters for coagulation of 1 cm tumor plus a surrounding 1 cm thick rim of healthy tissue. A fiber insertion system compatible with a high resolution stereotactic digital X-ray biopsy system was designed to guide the fiber into the tumor site in similar fashion to the insertion of the biopsy needle. An optical-thermal model consisting of a radiation model, a thermal model, and a coagulation model was developed and validated using ex-vivo porcine tissue. A single integrating sphere optical property measurement system and an inverse Monte Carlo algorithm were developed to measure the optical properties of ex-vivo porcine tissue at 830, 940, and 980 nm. An experimental method was developed to determine the parameters of the Arrhenius model (frequency factor (A) and activation energy (Ea)). The optical-thermal model was validated by comparing the predicted temperature and coagulation to results of laser irradiation experiments at 830, 940, and 980 nm. Using published values of the optical properties of the breast, the model predicts that a 3 cm coagulation size can be produced without vaporization in 10 min with 10.4 W at 980 and 940 nm and 13.2 W at 830 nm. The same outcome can be achieved in 20 min with 4.5 W at 980 and 940 nm and 6.1 W at 830 nm.

INTRODUCCIÓ: La teràpia amb làser a baixa potència (LLLT) a una longitud d'ona i fluència específica manté l'activitat electrofisiològica de nervis perifèrics lesionats en animals d'experimentació, preveu els canvis degeneratius i la formació de cicatrius en neurones motores lesionades de la medul·la espinal, així com accelera la regeneració dels nervis lesionats. El tractament de pacients amb diode làser d'infraroig proper redueix l'espasme muscular i al mateix temps s'ha descrit un augment de la mobilitat muscular.OBJECTIU: Estudiar l'efecte de la LLLT, 655 nm (vermell) i 830 nm (infraroig proper) en l'alliberació de neurotransmissor en la unió neuromuscular del diafragma de rata.MATERIAL i MÈTODE: Es van realitzar dos tipus d'estudi:1) In vitro en 60 músculs diafragmàtics amb els seus respectius nervis frènics2) In vivo en 20 músculs elevator longus de l'orella de ratolí. Els làsers eren diodes de Gallium-Aluminium-Arsenide (GaAlAs):a) 655 nm (vermell) a una densitat d'energia d'1 a 12 Jouls per centímetre quadrat b) 830 nm (infraroig proper) a una densitat d'energia de 4 a 12 J/cm2. 1) Control de la temperatura en el medi de manteniment de la mostra a les dosis màximes utilitzades, comprovant que no es produís cap tipus de modificació que pogués interferir en el registre dels potencials. 2) L'alliberació de neurotransmissor es va estudiar seguint la tècnica convencional de registre intracel·lular de potencial de membrana, en un medi amb concentracions altes de magnesi (bloqueig presinàptic) o curaritzat (bloqueig postsinàptic). Es va mesurar el contingut quàntic, l'amplitud, la latència i el temps mitjà dels potencials de placa terminal (EPPs). També es va analitzar la freqüència i l'amplitud dels potencials espontanis en miniatura, al voltant de la placa terminal (MEPPs). La facilitació de l'alliberació de neurotransmissor es va avaluar després de l'estímul d'un parell de polsos.3) Es va mesurar indirectament la transmissió de la pell de ratolí i la humana, així com la de la musculatura del ratolí per poder fer l'aproximació de quanta energia es necessita a la superfície per poder arribar fins a les sinapsi neuromuscular dels paquets musculars subcutanis.4) Amb la tècnica de neurografia es van avaluar els potencials d'acció compostos (PAMCs) amb dosis superficials d'entre 92,9 - 416,5 J/cm2. RESULTATS: La irradiació de la placa motora amb làser de 655 nm en les condicions dosimètriques testades en aquest estudi no va produir cap efecte estadísticament significatiu en cap dels paràmetres estudiats. El làser de 830 nm a 12 J/cm2 produeix un canvi estadísticament significatiu en la reducció del contingut quàntic (P=0.01) i en l'amplitud (P=0.04) dels EPPs. No s'observaren altres canvis significatius en la resta de paràmetres estudiats. Així com tampoc s'han observat canvis in vivo en els PAMCs ni amb 655 nm ni amb 830 nm als paràmetres estudiats.CONCLUSIÓ: El làser de 655 nm a les dosis testades no afecta, en condicions properes a la normalitat, el funcionament fisiològic de la sinapsi neuromuscular. Per això podem afirmar que la irradiació clínica de la pell o d'altres teixits, a aquesta longitud d'ona, no interfereix col·lateralment en la fisiologia de la sinapsi neuromuscular. El làser de 830 nm a les dosis testades afecta, en condicions properes a la normalitat, el funcionament fisiològic de la sinapsi neuromuscular en un mecanisme independent del calci. Per tant, podem afirmar que, sigui o no l'objectiu de tractament, la irradiació clínica, a aquesta longitud d'ona pot provocar un efecte de relaxació del múscul irradiat. / BACKGROUND: Several recent papers report the efficacy of low energy laser radiation in the red and near-infra-red part of the spectrum in the stimulation and regeneration of tissue under normal and stressful conditions. Gallium-aluminum-arsenic (GaAlAs) lasers, which emit radiation in this region of the spectrum, can reduce spasms and increase neuromuscular activity. The molecular mechanisms of this process, however, are not well understood.OBJETIVE: The objective of this study was to determine the effect of red (655 nm) and near infrared (830 nm) laser radiation on neurotransmission in the neuromuscular junctions of mice.METHODS: Experiments were undertaken on sixty diaphragm muscles and twenty elevating muscles of mouse ears. GaAlAs laser radiation (655 nm and 830 nm) with an energy density between 4 and 12 J/cm2 was employed. The liberation of neurotransmitters was studied through the conventional technique of intracellular measurement in muscles treated with curare or in a medium with a high magnesium concentration. Neurotransmission was evaluated as: 1) The quantum content, amplitude, latency of evoked end-plate potentials (EPPs).2) The frequency and amplitude of the spontaneous end-plate potentials (MEPPs).3) Short-term plasticity of the neurotransmitter release (fast facilitation). The objective of this study was to determine the effect of red (655 nm) and near infrared (830 nm) laser radiation on neurotransmission in the neuromuscular junctions of mice. Was also evaluated by paired pulse stimulation. 4) The compound muscular action potential (CMPA) was evaluated using the neurographic technique. RESULTS: The liberation of neurotransmitter from the motor end-plate in mice, did not present detectable modifications after GaAlAs laser irradiation at 655 nm. The 830 nm laser radiation at 12 J/cm2 promoted a significant reduction in the quantum content (P=0.01) and amplitude of the EPPs (P=0.04), but the latency, the spontaneous liberation of neurotransmitter (MEPPs) and the facilitation for paired pulse was unaltered. No alteration was observed in neuromuscular junctions irradiated with 4 and 12 J/cm2 and alterations were also not detected in CMPA (92.9-416.5 J/cm2).CONCLUSIONS: In conclusion, irradiation with a diode laser emitting at 830 nm and an energy density of 12 J/cm2, can affect the liberation of neurotransmitter evoked in the motive terminal plate of mice in some situations. KEY- WORDS: Laser, GaAlAs, Neurophysiology, Neurography, MEPP, EPP

This degree project has been carried out in cooperation with Enertech AB in Ljungby and is pilot study to automating all current manual soldering. The soldering process accounts for a large part of the processing cost in the production of a heat pump. The process is also a quality risk and has a major impact on the lifetime of the final product. The Main task of this project has been to evaluate automation of the soldering process, to develop automation solutions and a principle layout, to draw the design changes required for the automation and to calculate the supposed solution. This pilot study has resulted in a suggested automation solution using laser as a heat source for soldering. Calculations of the solution show that a automating a laser soldering cell is very profitable.

The objective of the proposed research is to develop multiwavelength lasers as cost-efficient sources for broadband optical access networks. Todays telecommunications networks have widely adopted optical fiber as the backbone transmission medium. Optical fiber systems are promising candidates for the broadband access networks to offer high-speed and future-proof services. To harness the available bandwidth in fiber and to meet the ever-growing bandwidth demand, wavelength division multiplexing (WDM) techniques have been investigated. There have been intense research activities for the creation of new low-cost laser sources for such emerging applications. In this context, multiwavelength fiber ring lasers have been significantly investigated as they present many advantages, including simple structure, low-cost, and selectable multiwavelength operation. We propose a new laser system architecture that emits alternate multiwavelength picosecond pulses operating at room temperature. Optical signal generation is based on a single active component, an unbalanced Mach-Zehnder interferometer, inserted in an actively mode-locked erbium-doped fiber ring laser to provide both intensity modulation and wavelength-selective filtering. Time and frequency controls of the light emission are reached by inserting an additional modulator and a periodic filter in the cavity. This approach focuses on the application of multiwavelength lasers as sources for WDM passive optical networks.

In this thesis, with external cavity semiconductor laser, a high lateral resolution thickness measurement is proposed and demonstrated. The approach is typical an intra-cavity measurement of focused cell thickness by wavelength tuning of an external cavity laser diode. In addition, using blue light of 406nm as laser diode, higher lateral resolution is also observed. Using the proposed thickness method, the lateral resolution and longitudinal resolution have been demonstrated with 20£gm and 0.15£gm, respectively. We also discuss the feasibility of £gm scaled lateral resolution through improvement of laser diode, such as M^2~1.