Lasing from femtosecond laser filaments is a relatively new field of study that has been studied since its first observation in 2003. Such lasing effect is of interest to the scientific community due to its possible application in remote sensing. This thesis studies the lasing dynamics of the excited molecular nitrogen ion N2+ which emits primarily at 391 nm and 428 nm wavelengths. We start by studying the ellipticity dependence of the gain from filaments in ambient air. We then study the ellipticity dependence in a vacuum in a supersonic gas jet to remove the complexity of filamentation. We show that recollision doesn't play a significant role in creating a population inversion by comparing the ellipticity dependence of the gain and high harmonic generation. The rest of this thesis is devoted to shining some light on another possible mechanism. We characterize the gain by its temporal profile, jet position dependence, and density dependence.

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Halide perovskite-based photovoltaics are the fastest-growing solar technology in nowadays. Because of the low production costs, perovskite-based photovoltaics are competitive for commercial applications in the marketplace. Additionally, due to the remarkable optoelectronic properties, perovskites are also promising for other optoelectronics, including photodetector, light emitting diode and laser. However, for commercial applications in optoelectronics, there are still several crucial obstacles: (i) a robustness patterning technique is missing for nanofabrication of perovskite devices, (ii) hysteresis effect exits in perovskite devices, and (iii) the stability issue of perovskite. To address these problems, we have performed the fundamental study on perovskite from four aspects: orthogonal patterning, metal contact, carrier transport, and light emission stability. Due to the ionic nature, halide perovskite can be easily dissolved by most of the commonly used organic solvents, which means conventional lithography patternings are not applicable for perovskite, limiting the extensive applications of perovskite electronics. To adress this, we introduced chlorobenzene and hexane and proposed an orthogonal electron beam lithography method for fabrication of perovskite nanodevices without damaging their electrical and optical properties. By this orthogonal method, we fabricated a two-dimensional single crystalline (C6H5C2H4NH3)2PbI4 photodetector with device channel length of few hundred nanometers and outstanding photosensing capability. The hysteresis effect in perovskite is highly related to the interfacial recombination and ionic transport, which requires abundant fundamental understanding on perovskite contact and transport to help to solve this issue. In this study, we performed the lithography patterning method and the transfer length measurement on cm-sized single crystalline perovskite bulk single crystal for indicating the metal contact interface and charge transport, which are requared for efficienct device design and improving the device performance. For stable light emission, we fabricated perovskite nanowires in the nanopores of anodic aluminum oxide substrate using an inkjet printing technique. Lasing behaviors and color-tunable light emission of perovskite nanowires are demonstrated in this study, and the photostability is much better than reported all-inorganic perovskite quantum dots. We believe these fundamental studies provide solutions to some critical issues in current perovskite technology, thus paving the way for future optoelectronic applications.

Quantum coherence and interference (QCI) is a phenomenon that takes place in all multi-level atomic systems interacting with multiple lasers. In this work QCI is used to create several interesting effects like lasing without inversion (LWI), controlling group velocity of light to extreme values, controlling the direction of propagation through non-linear phase matching condition and for controlling the correlations in field fluctuations. Controlling group velocity of light is very interesting because of many novel applications it can offer. One of the unsolved problems in this area is to achieve a slow and fast light which can be tuned continuously as a function of frequency. We describe a method for creation of tunable slow and fast light by controlling intensity of incident laser fields using QCI effects. Lasers are not new to the modern world but an extreme ultra-violet laser or a x-ray laser is definitely one of the most desirable technologies today. Using QCI, we describe a method to realize lasing at high frequencies by creating lasing without inversion. Role of QCI in creating correlations and anti-correlations, which are generated by vacuum fluctuations, in a three level lambda system coupled to two strong fields is discussed.

Depuis 2012, les pérovskites hybrides halogénées de type CH3NH3PbX3 (X = I, Br ou Cl) sont apparues comme très prometteuses non seulement dans le domaine du photovoltaïque mais aussi pour les dispositifs émetteurs de lumière comme les diodes électroluminescentes et les lasers. L'un des avantages cruciaux de ces matériaux semiconducteurs est leur méthode de déposition à basse température et en solution. Le réglage de la longueur d'onde d'émission des pérovskites dans tout le spectre visible par de simples substitutions chimiques dans la partie halogénée est un autre atout. En particulier, les pérovskites halogénées montrent une grande efficacité de luminescence dans le vert et pourraient répondre au problème du "green gap" dans les sources laser (le "green gap" fait référence à la baisse d'efficacité des diodes électroluminescente et diodes laser à semi-conducteurs émettant dans le vert).Le travail de doctorat mené ici a porté sur la réalisation d’un laser pompé optiquement à base de la pérovskite hybride CH3NH3PbBr3 émettant dans le vert. La structure réalisée consiste en une microcavité verticale à base d’une couche mince de 100 nanomètres de CH3NH3PbBr3 déposé par "spin-coating" (dépôt par enduction centrifuge), insérée entre un miroir diélectrique et un miroir métallique. Nous avons démontré, à température ambiante, le régime de couplage fort entre le mode photonique de la microcavité et l'exciton de la pérovskite. Ce régime de couplage fort conduit à la création de quasi-particules appelées les exciton-polaritons, qui sont une superposition cohérente d’états photonique et excitonique. En augmentant la puissance injectée optiquement, nous avons obtenu un effet laser dans cette microcavité. L’étude des propriétés d’émission de ce laser met en évidence que nous avons réalisé un laser aléatoire, émettant dans le vert, filtré directionnellement par la courbe de dispersion du polariton de basse énergie. Ce filtrage par la courbe de dispersion du polariton permet le contrôle de la directionnalité de l’émission laser sur une grande gamme d’angles : des angles aussi grands que 22° ont été obtenus expérimentalement. / Since 2012, the hybrid halide perovskites of CH3NH3PbX3 (X = I, Br or Cl) type have emerged as very promising not only in the field of photovoltaics but also for light-emitting devices such as light-emitting diodes and lasers. One of the crucial advantages of these semiconductor materials is their low temperature and solution deposition method. The tuning of the perovskites emission wavelength throughout the visible spectrum by simple chemistry substitutions in the halogenated part is another asset. In particular, the halide perovskites show a high luminescence efficiency in the green and could address the "green gap" problem in laser sources (the "green gap" refers to the drop in efficiency of light-emitting diodes and laser diodes emitting in the green).The thesis work carried out here is focused on the development of an optically pumped laser based on the hybrid halide perovskite CH3NH3PbBr3 emitting in the green. The structure consists of a vertical microcavity based on a 100-nanometre thin film of CH3NH3PbBr3 deposited by spin-coating, inserted between a dielectric mirror and a metal mirror. We have demonstrated, at room temperature, the strong coupling regime between the microcavity photonic mode and the exciton of the perovskite. This strong coupling regime leads to the creation of quasi-particles called exciton-polaritons, which are a coherent superposition of photonic and excitonic states. By increasing the optically injected power, we obtained a laser effect in this microcavity. The study of the emission properties of this laser shows that we have produced a random laser, emitting in the green, filtered directionally by the dispersion curve of the lower polariton. This filtering by the polariton dispersion curve allows the directionality of the laser emission to be controlled over a wide range of angles: angles as large as 22° were obtained experimentally.

Here we present direct investigation of the lasing behaviour by performing gain spectroscopy of solution-based CQDs enabled via in-situ tuning of the feedback wavelength of an open-access hemispherical microcavity. The investigation is performed on two different types of CQDs, namely spherical CdSe/CdS core-shell CQDs and nanopletelets (NPs). The lasing threshold and the differential gain/slope efficiency of the fundamental cavity mode are measured as a function of their spectral position over a spectral range of ∼ 32 nm and of ∼ 42 nm for the spherical CQDs and NPs, respectively. The results of the gain spectroscopy are described using theoretical models, providing insights into the mechanism governing the observed lasing behaviour. Furthermore, the open-access cavity architecture provides a very convenient way of producing in-situ tunable lasing, and single-mode lasing of the fundamental cavity mode over a spectral range of ∼ 25 nm and ∼ 37 nm is demonstrated using spherical CQDs and NPs, respectively. In addition, the stability of laser emission is investigated, with the lasing intensity of the fundamental cavity mode remaining constant over a time period of almost 6 mins. It is hoped that the results will provide a detailed understanding of the lasing behaviour of CQDs. This information can be fed back into the design of CQDs in which the lasing threshold can be reduced to the point where useful devices can be constructed, and in the design of resonant optical feedback structures for which the appropriate wavelength must be carefully selected.

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In this report a model of a tunable narrow linewidth laser used for telecommunications is presented. The model uses both theoretical analysis and experimental data to create the mathematical models governing its behaviour and is aimed to be useful in a development environment with requirements on accuracy, efficient implementation and adaptability to future design. Results show that the model presented achieves high accuracy in both optical and electrical measurements. In summary the model could be useful in a development environment with further improvements in adaptability possible in the future.

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