The interaction of laser light with a parcel of air with a known density structure can result in one of three reactions. The simplest of these reactions is reflection. Depending on the nature of the density profile, that part of the light that is not reflected can be refracted or scattered. The extent of the refraction and scattering is determined by the density of the particles found in the air. This thesis investigates two concepts that use the above mentioned interactions. The first, the colliding shock lens (CSL) was proposed by Buccellato, Lisi and Michaelis (1993). This device uses the graded index (GRIN) lens formed by the collision of symmetrically arranged shock waves to focus a laser beam. Unfortunately, the first reported colliding shock lenses had optical apertures of the order of millimeters. This is hardly useful in realistic laser systems whose beams typically have a diameter of 10mm. The major part of this thesis involves the scaling up of the optical aperture of the CSL while simultaneously maintaining a fairly short focal length. We show how the behaviour of the CSL varies with factors such as input energy, electrical diameter, geometry and various other factors. By optimising the physical parameters a 1.5cm diameter lens is obtained having a focal length of 1.5m. We develop a simple scaling theory and run a simulation based on the fluid in cell (FLIC) method, and find good correlation in both cases between the experimentally obtained results and the theoretically predicted ones. As a further development of the work on colliding shock lenses we introduce a cylindrical colliding shock lens. This device is shown to be able to line focus a laser beam of 1cm in diameter. At this stage the focus quality is still poor and suggestions are made for further improvements. Lidar is an acronym for light detection and ranging. Such systems are based on the scattering of laser light incident on a parcel of air. We discuss the results of a campaign conducted during the period of June to November 1994 to study aerosol concentrations over Durban. Particular attention is paid to low level aerosols due to sugar cane burning over the Natal coast. These aerosols are known to influence local climate and since vertical profile studies have never been carried out, this investigation gives some useful insight into the atmospheric dynamics. We find that in June (the begining of the burning campaign) the aerosol loading in the lower atmosphere is low. However, there are very stable aerosol layers at 3km and 5km. The density of the aerosols in these layers are decoupled. In September, the turbulent atmosphere over Durban is found to destroy structure in the aerosol layers. Nevertheless, the aerosol loading is high. Scattering ratios and extinction coefficients are calculated to show the long and short term evolution of the aerosols. A new coefficient (the low altitude aerosol coefficent - LAAC) is defined as an indicator for aerosol loading in the lower atmosphere. This coefficient is compared with total column ozone values over Durban. An anti-correlatory behaviour is noticed. We also report the detection of an extremely high aerosol layer (60km) over Durban. This layer is believed to be sodium. The profiles are compared to satellite data to verify the first ever detection of a constituent at these altitudes in Southern Africa. / Thesis (Ph.D.)-University of Natal, 1996.

This work provides a study of the natural frequencies of a cantilevered beam with tip mass and axial load. Displacement feedback control is applied using piezo actuators attached to the top and bottom of the beam. The center of gravity of the mass and its rotary inertia are accounted for in the solution. The analysis of flexible components is essential to provide for the successful design of various engineering structures. This study provides an analytical solution to the dynamic behavior of a cantilevered beam carrying a mass at the free end, while being subjected to constant axial load. The structure is modeled using the Euler-Bernoulli theory and the contributions of the mass, thickness and stiffness of the piezoelectric actuators to the structure are taken into account. The effects of the piezo input voltage polarity is also taken into account. The natural frequencies of the beam can be altered by applying a voltage in the desired polarity and thereby causing an extension or contraction in the piezo actuator. This mechanical response alters the frequencies of the piezoelectric beam. The piezoelectric effect causes a compression or extension strain when a voltage is applied along the direction of polarization. The strain in the piezoelectric beam causes a moment at the free end, which directly affects the natural frequencies. By applying a voltage in the same or opposite direction of the poling of the piezo, the result is a compression or extension perpendicular to the poling. An applied voltage in the same direction can be considered positive and reduces the frequencies, whilst in the opposite direction negative and increases the natural frequencies. In this investigation the piezo layer thickness is varied, which in turn allows for a variable voltage input. For a thicker layer, the voltage can be increased and the actuation strain increased. The frequency content of the dynamically varying forces applied to a structure has the potential to excite the structure at one or more of its natural frequencies. Using piezo actuators, the natural frequencies and the natural frequency gaps can be maximized. Maximizing the natural frequencies is useful to avoid resonance when the external excitation frequency is less than the natural frequency. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2014.

One of the negative effects that a laser beam experiences as it propagates through the atmosphere is intensity fluctuations or scintillation. Because scintillation-- as it pertains to laser radar and laser satellite communication systems-- is the main subject of this research, the assumption of an optical element ( such as a Gaussian lens) along the propagation path in front of the detector is valid. The mathematical addition of optical elements to the propagation path is treated using the ABCD ray matrix method. The expression for scintillation is derived, analyzed, and numerically calculated for positions to the left and right of the image plane, which is behind the collecting lens of a receiver system. Simultaneously, the behavior of the scintillation is investigated when the aperture size of the lens is increased. The results are compared to the aperture averaging effect experienced when the beam is in the image plane. This is a per-unit scintillation decrease because the aperture averages it over the surface of the lens.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1982. / Microfiche copy available in Archives and Barker. / Includes bibliographical references. / by Peter David McQuade. / M.S.

A probability density function is developed for the phase of light that is the result of adding a signal to noise with K-distributed amplitude and uniform phase. The probability density function of the phase associated with the I-K distribution is also developed. In the process of deriving the probability density function of the phase much I as learned about the relationships between different probability density functions. Three different methods of deriving homodyned K statistics are shown to be equivalent. Two different methods of deriving I-K statistics are shown to be equivalent. Theoretical moments of the homodyned K distribution are compared with experimentally measured moments in order to determine the parameters of the model for different conditions of turbulence. An experiment is proposed for measuring the spatial structure function of the phase in a manner that will allow verifying the accuracy of the new probability density functions of the phase.