Photoinduced Doughnut-Shaped Nanostructures
  We show that an incoherent unpolarized single-beam illumination is able to photoinduce nano-doughnuts on the surface of azopolymer thin films. We demonstrate that individual doughnut-shaped nano-objects as well as clusters of several adjacent nano-doughnuts can be formed and tailored with wide range of typical sizes, thus providing a rich field for applications in nanophotonics and photochemistry. 
A. M. Dubrovkin, R. Barille, E. Ortyl, S. Zielinska
physics.optics cond-mat.mtrl-sci