Mie scattering of partially coherent light: controlling absorption with spatial coherence

We study theoretically the absorbed power by a dielectric sphere when it is illuminated with partially coherent light coming from two pinholes. We present a general theory of Mie scattering of partially coherent light (based on the angular spectrum method); this theory is applied to the aforementioned particular scattering problem which is solved analytically. We found that, if the diameter of the sphere is smaller than the skin depth, the absorbed power by the sphere depends complicatedly on the degree of coherence of light between the pinholes. The absorbed power for coherent illumination can be smaller or greater than that for incoherent light between pinholes, depending on the geometrical configuration. Furthermore, there are particular setups in which the absorbed power is independent of the degree of coherence, despite that the intensity distribution of the electric field inside the sphere depends significantly on the spatial coherence. Hence, by tuning the coherence length between the pinholes, the absorbed power by the sphere can be controlled; if a whispering gallery mode is excited, the absorbed power can be varied over a wide range. Our study might have implications in the understanding of light absorption in photovoltaic nano-devices. (C) 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreement