title: Coherent transfer of orbital angular momentum to excitons by optical four-wave mixing.
abstract: We demonstrate the coherent transfer of optical orbital angular momentum (OAM) to the center of mass momentum of excitons in semiconductor GaN using a four-wave mixing (FWM) process. When we apply the optical vortex (OV) as an excitation pulse, the diffracted FWM signal exhibits phase singularities that satisfy the OAM conservation law, which remain clear within the exciton dephasing time (approximately 1ps). We also demonstrate the arbitrary control of the topological charge in the output signal by changing the OAM of the input pulse. The results provide a way of controlling the optical OAM through carriers in solids. Moreover, the time evolution of the FWM with OAM leads to the study of the closed-loop carrier coherence in materials.
authors.affiliation: 1Department of Applied Physics, Hokkaido University, N13W8 Kita-ku, Sapporo, Japan.
authors.forename: Y
authors.initials: Y
authors.lastname: Ueno
authors.forename: Y
authors.initials: Y
authors.lastname: Toda
authors.forename: S
authors.initials: S
authors.lastname: Adachi
authors.forename: R
authors.initials: R
authors.lastname: Morita
authors.forename: T
authors.initials: T
authors.lastname: Tawara
mesh_terms: D003198:Computer Simulation; D005708:Gallium / Q000737:chemistry*; D008027:Light; D008956:Models, Chemical; D012542:Scattering, Radiation
chemical_list: C473348:gallium nitride; D005708:Gallium