Development of optical diagnostics of plasma-related phenomena and applications

Abstract: Optical diagnostics techniques based on coded imaging were developed and applied for plasma-related phenomena and applications. The signal of interest is first encoded with a sinusoid pattern either by structured laser illumination or implement of a diffractive optical element, such as a grating, along the optical path of the signal. The coded signal will then be extracted from the raw data by a lock-in based algorithm, such as frequency recognition algorithm for multipleexposures (FRAME). Two types of non-thermal plasma sources, i.e., gliding arc discharges and nanosecond pulsed discharges, were investigated. Volumetric information of molecular distributions around a gliding arc was captured using laser-induced fluorescence with structured illumination and FRAME. Laser scattering imaging during the formation of a nanosecond pulsed discharge on a at methane-air flame was extracted from luminous plasma emission using structured laser illumination. Furthermore, a technique named periodic shadowing was applied for streak camera measurements, where both higher temporal contrast and effective dynamic range were achieved. The gliding arc plasma discharge was also applied in an industrial prototype burner as plasma-assisted combustion has been proven to be a promising technique to increase energy efficiency as well as reduce environmentally harmful emission. With the help of 0.1% additional energy, the lean blow-out limit of a hundred kilowatt burner was extended from a global equivalence ratio of 0.47 to 0.45.