Using optical vortex laser induced forward transfer to fabricate a twisted ferrite microcrystal array

We demonstrate direct printing from donor ink containing ferrite nanoparticles by employing laser induced forward transfer with an optical vortex possessing orbital angular momentum (OAM). We show, for the first time, that the as-printed dots are twisted and exhibit spinel Fe3O4 monocrystalline properties without the need for a sintering process. The helicity of the as-printed dots is shown to be selectively controlled merely by reversing the handedness of optical vortices. The diameter of the printed dots was typically measured to be less than 1/10th of the irradiated laser spot (diffraction limit). These results imply that the optical vortex twists and confines the sintered nanoparticles within its dark core to form chiral spinel monocrystalline dots. The observation of mono-crystallization with optical vortex induced forward transfer will offer new fundamental physics such as OAM light–matter interactions and could pave the way toward advanced printable magnetic devices, such as high-density magnetic data storage.