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Optical pulse compression using similariton propagation in an optical fibre with decreasing dispersion has been demonstrated for the first time. This compression scheme is a practical application of the sech-similariton solution to the generalized nonlinear Schrodinger equation (NLSE) with distributed coefficients recently found using the self-similarity technique. The sech-similariton solution exhibits a characteristic positive linear frequency chirp, which increases in slope as the pulse compresses. The solution does not develop any side pedestals or deformation in pulse shape as it propagates, making it a promising candidate for a new compression technique. Unlike the adiabatic compression technique, rapid compression can be achieved in a fibre with a specifically designed decreasing group velocity dispersion profile since the sech-similariton is an exact solution to the NLSE. A cost-effective and efficient method of realising decreasing dispersion in a fibre has been developed using a comb-like dispersion profiling technique and its feasibility has been experimentally demonstrated. An optimised experimental similariton compressor system has been built using two industry standard fibres which compressed an 11 ps linearly chirped sech input pulse to 400 fs, yielding a compression factor of greater than 25.

Ce travail de thèse porte sur l'étude des propriétés extrinsèques et intrinsèques d'échantillons de GaN massif autosupporté ou épitaxié sur saphir, avec des techniques classiques de spectroscopie (réflectivité et photoluminescence) ainsi qu'avec une technique de réflectivité résolue en temps à l'échelle de la femtoseconde. L'élargissement d'un exciton et sa force d'oscillateur sont difficiles à déterminer de façon indépendante et la simulation des spectres de réflectivité continue ne permet pas de les déterminer avec précision. Les spectres d'autocorrélation enregistrés avec la réflectivité résolue en temps présentent des battements dus à l'excitation simultanée des excitons Xa et Xb ayant des énergies voisines. L'amplitude de ces battements dépend des forces d'oscillateur et leur décroissance en fonction du temps dépend des élargissements des excitons. L'analyse combinée des deux types de réflectivité a permis la détermination précise de ces paramètres en utilisant un modèle distinguant l'élargissement homogène dépendant de la température et inhomogène lié à la qualité cristalline de l'échantillon.

Optical pulse compression using similariton propagation in an optical fibre with decreasing dispersion has been demonstrated for the first time. This compression scheme is a practical application of the sech-similariton solution to the generalized nonlinear Schrodinger equation (NLSE) with distributed coefficients recently found using the self-similarity technique. The sech-similariton solution exhibits a characteristic positive linear frequency chirp, which increases in slope as the pulse compresses. The solution does not develop any side pedestals or deformation in pulse shape as it propagates, making it a promising candidate for a new compression technique. Unlike the adiabatic compression technique, rapid compression can be achieved in a fibre with a specifically designed decreasing group velocity dispersion profile since the sech-similariton is an exact solution to the NLSE. A cost-effective and efficient method of realising decreasing dispersion in a fibre has been developed using a comb-like dispersion profiling technique and its feasibility has been experimentally demonstrated. An optimised experimental similariton compressor system has been built using two industry standard fibres which compressed an 11 ps linearly chirped sech input pulse to 400 fs, yielding a compression factor of greater than 25.

A field system capable of making high-resolution measurements of rainfall is described. The system incorporates a disdrometer, an array of high-resolution raingauges, a general-purpose data acquisition system and ancillary equipment. In an evaluation of the disdrometer, a theory allowing calculation of the effects of windspeed on detection efficiency is presented which has wide applicability. The raingauges are an improved design allowing 10-s temporal resolution of rainfall intensity and 100 m spatial resolution of rain-patch size when used in the array. An extensive data base of measurements made using the field system is described. Duration of rainfall is shown to be approximately log-normal and is consistent with a log-normal distribution of precipitation region size. The fractional duration of rainfall above a threshold intensity varies considerably between rain periods, a result which may be important for electromagnetic attenuation models. Estimation of the shapes of rain patches using the raingauge array is demonstrated and shows considerable promise. Raindrop fallspeeds, measured using the disdrometer, generally show much less deviation from stagnant air terminal velocities than indicated by previously reported results. Much of the spread in the results is shown to be consistent with instrumentation errors although significant residual deviations are still apparent; the fallspeeds are generally slower than stagnant air values would suggest. Measurements of the arrival rate of raindrops at the disdrometer indicate clustering of drops rather than the often assumed Poisson distribution. The clustering is associated with small drops and has reasonable correlation with rainfall intensity. Examination of the cross-correlation of arrival rates of different sized drops show results in contradiction to previous results; small drops are found to lead other sized drops. Using a normalisation method, the shapes of raindrop size distributions measured are shown to be depressed in the mid-radius region.

Introduction: In this chapter the present status of our understanding of the interaction of five and fewer nucleons will be briefly summarized. Some of the gaps in our knowledge will be pointed out, making clear the motivation for the experimental work described in the remainder of the thesis. Since most of the experimental effort by the author has been directed towards scattering of neutrons by protons, the nucleon - nucleon problem will be considered in greater detail. In speaking of this, the simplest problem in nuclear physics, M.L. Goldberger made the following remarks at the 1960 Midwest Conference on Theoretical Physics: "There are few problems in modern theoretical physics which have attracted more attention than that of trying to determine the fundamental interaction between two nucleons. It is also true that scarcely ever has the world of physics owed so little to so many .. . . . . . In general, in surveying the field, one is oppressed by the unbelievable confusion and conflict that exists. It is hard to believe that many of the authors are talking about the same problem, or in fact that they know what the problem is."

Optical pulse compression using similariton propagation in an optical fibre with decreasing dispersion has been demonstrated for the first time. This compression scheme is a practical application of the sech-similariton solution to the generalized nonlinear Schrodinger equation (NLSE) with distributed coefficients recently found using the self-similarity technique. The sech-similariton solution exhibits a characteristic positive linear frequency chirp, which increases in slope as the pulse compresses. The solution does not develop any side pedestals or deformation in pulse shape as it propagates, making it a promising candidate for a new compression technique. Unlike the adiabatic compression technique, rapid compression can be achieved in a fibre with a specifically designed decreasing group velocity dispersion profile since the sech-similariton is an exact solution to the NLSE. A cost-effective and efficient method of realising decreasing dispersion in a fibre has been developed using a comb-like dispersion profiling technique and its feasibility has been experimentally demonstrated. An optimised experimental similariton compressor system has been built using two industry standard fibres which compressed an 11 ps linearly chirped sech input pulse to 400 fs, yielding a compression factor of greater than 25.

A field system capable of making high-resolution measurements of rainfall is described. The system incorporates a disdrometer, an array of high-resolution raingauges, a general-purpose data acquisition system and ancillary equipment. In an evaluation of the disdrometer, a theory allowing calculation of the effects of windspeed on detection efficiency is presented which has wide applicability. The raingauges are an improved design allowing 10-s temporal resolution of rainfall intensity and 100 m spatial resolution of rain-patch size when used in the array. An extensive data base of measurements made using the field system is described. Duration of rainfall is shown to be approximately log-normal and is consistent with a log-normal distribution of precipitation region size. The fractional duration of rainfall above a threshold intensity varies considerably between rain periods, a result which may be important for electromagnetic attenuation models. Estimation of the shapes of rain patches using the raingauge array is demonstrated and shows considerable promise. Raindrop fallspeeds, measured using the disdrometer, generally show much less deviation from stagnant air terminal velocities than indicated by previously reported results. Much of the spread in the results is shown to be consistent with instrumentation errors although significant residual deviations are still apparent; the fallspeeds are generally slower than stagnant air values would suggest. Measurements of the arrival rate of raindrops at the disdrometer indicate clustering of drops rather than the often assumed Poisson distribution. The clustering is associated with small drops and has reasonable correlation with rainfall intensity. Examination of the cross-correlation of arrival rates of different sized drops show results in contradiction to previous results; small drops are found to lead other sized drops. Using a normalisation method, the shapes of raindrop size distributions measured are shown to be depressed in the mid-radius region.

Introduction: In this chapter the present status of our understanding of the interaction of five and fewer nucleons will be briefly summarized. Some of the gaps in our knowledge will be pointed out, making clear the motivation for the experimental work described in the remainder of the thesis. Since most of the experimental effort by the author has been directed towards scattering of neutrons by protons, the nucleon - nucleon problem will be considered in greater detail. In speaking of this, the simplest problem in nuclear physics, M.L. Goldberger made the following remarks at the 1960 Midwest Conference on Theoretical Physics: "There are few problems in modern theoretical physics which have attracted more attention than that of trying to determine the fundamental interaction between two nucleons. It is also true that scarcely ever has the world of physics owed so little to so many .. . . . . . In general, in surveying the field, one is oppressed by the unbelievable confusion and conflict that exists. It is hard to believe that many of the authors are talking about the same problem, or in fact that they know what the problem is."

Optical pulse compression using similariton propagation in an optical fibre with decreasing dispersion has been demonstrated for the first time. This compression scheme is a practical application of the sech-similariton solution to the generalized nonlinear Schrodinger equation (NLSE) with distributed coefficients recently found using the self-similarity technique. The sech-similariton solution exhibits a characteristic positive linear frequency chirp, which increases in slope as the pulse compresses. The solution does not develop any side pedestals or deformation in pulse shape as it propagates, making it a promising candidate for a new compression technique. Unlike the adiabatic compression technique, rapid compression can be achieved in a fibre with a specifically designed decreasing group velocity dispersion profile since the sech-similariton is an exact solution to the NLSE. A cost-effective and efficient method of realising decreasing dispersion in a fibre has been developed using a comb-like dispersion profiling technique and its feasibility has been experimentally demonstrated. An optimised experimental similariton compressor system has been built using two industry standard fibres which compressed an 11 ps linearly chirped sech input pulse to 400 fs, yielding a compression factor of greater than 25.