Anomalous forward scattering of dielectric gain nanoparticles

For usual lossy and lossless dielectric spherical particles, it can never realize zero forward scattering, since their Mie expansion coefficients cannot be totally offset at forward direction. By introducing suitable gain in dielectric spherical particles, we find that the electric and magnetic dipolar responses can achieve complete destructive interference at forward direction under certain incident wavelength. When the radius of particle is much smaller than the incident wavelength, the quadrupole and other higher order Mie coefficients are negligible, thus zero forward scattering can be observed and simultaneously backscattering will get enhanced. However, if the quadrupole Mie coefficients are of the same order of magnitude with dipolar terms, coherent effect between them may result in the scattering minimum and maximum shift away from forward and backward directions, respectively. These results may provide new insight into the manipulation of light scattering direction at nanoscale.