Effects of Chirality and Coherence on Light Scattering
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In the first part of this dissertation, we study the light scattering properties of particles with chiral structures. Special attention is paid to the dinoflagellates, known for their circular polarization effects and as a causative agent of the red tide. Based on experimental observations and previous works, we build a helical plywood liquid crystal model for the nucleus of dinoflagellates, and apply the Discrete Dipole Approximation (DDA) method to investigate the light scattering properties of dinoflagellates. The backscattering signals display strong sensitivity to the wavelength of the incident beam, and they are most prominent when the wavelength matches the pitch of the chromatic helix. Our results indicates a promising means to monitor and detect the specific species of dinoflagellates. In the second part of the dissertation, we investigate the the problem of light scattering when the incident light has finite coherence length. The conventional Lorenz-Mie theory and DDA method are generalized to include a partially spatially coherent source. The formalism is applied to atmospheric particles such as water droplets and hexagonal ice crystals. Given that the solar source is partially coherent, our results have practical implications in remote sensing. Using the same technique, we also study the effects of incoherence on particle characterization using digital holographic microscopy. We show that holography is rather robust against incoherence and demonstrate the possibility of retrieving the coherence length of the illumination.