USE OF A PHASE CONJUGATE MIRROR TO INCREASE SIGNAL FOR RAYLEIGH SCATTERING MEASUREMENTS WITHOUT DEGRADATION OF SPATIAL RESOLUTION
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Publisher:The Ohio State University
Series/Report no.:The Ohio State University. Department of Mechanical and Aerospace Engineering Honors Theses; 2013
Rayleigh and Raman scattering describe the elastic and inelastic scattering of light, respectively, from molecules. Rayleigh scattering is proportional to the number density of the flow and can be used to measure concentrations or temperatures of mixing fluids. Raman scattering is species specific and can be used to measure major species concentration and mixture fraction in combustion systems. However, the signal collected from both Rayleigh and Raman scattering is weak. A retro-reflector is an optic that reflects an incident light beam back along its incoming direction. Thus, in principal, a retro-reflector can increase the collected Rayleigh and Raman signals by "N" times, where "N" is the number of retro-reflections. Typical retro-reflectors used to make high power multipass laser systems degrade the spatial resolution of Rayleigh and Raman measurements because it is not possible to reflect the laser beam back upon itself in environments with strong index of refraction gradients such as those found in combustion systems. A phase conjugate mirror (PCM) can reverse both the propagation direction and phase of an incoming light wave, thus providing the opportunity for "perfect" retro-reflection. This research will be used as a proof of concept showing that the unique characteristics of a PCM can be used to increase the signal for one dimensional Rayleigh scattering imaging without degrading the spatial resolution. Single pass Rayleigh scattering measurements will be compared to double pass Rayleigh scattering measurements using a conventional mirror and double pass Rayleigh scattering measurements using a PCM. Turbulent combustion flow fields will be used to study the effects of flows with index of refraction gradients. Initial Rayleigh scattering measurements using the PCM will serve as a proof of concept for Raman scattering experiments which are signal limited.
Academic Major: Engineering Physics
National Science Foundation
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