Pulse shapes of angle- and time-resolved scattering and interference signals in a flow cytometer

Particles passing through a focused laser beam in a flow cytometer cause time-dependent angular intensity distributions of the scattered light, which can be detected as signal pulses of a few microseconds in length. Extinction effects are observed due to interference between the incident beam and scattered light near the forward direction. We present angle-resolved measurements of such pulses for polymer microparticles using an optical fiber array. Even for homogeneous spherical particles, this can result in pulses with non-trivial shapes that carry information about the particles. We compare with results from mathematical modeling based on generalized Lorenz-Mie theory for the scattering of elliptical Gaussian beams by spherical particles at arbitrary locations.