title: Non-collinear interaction of photons with orbital angular momentum.
abstract: We study the nonlinear interaction between two non-collinear light beams that carry orbital angular momentum (OAM). More specifically, two incident beams interact at an angle in a medium with a second order nonlinearity and thus generate a third, non-collinear beam at the second harmonic frequency that experiences a reduced conversion efficiency in comparison to that expected based on conventional phase-matching theory. This reduction scales with the input beam OAM and, differently from previous spiral bandwidth calculations, is due to a geometric effect whereby the input OAM is projected along the non-collinear interaction direction. The effect is relevant even at small interaction angles and is further complicated at large angles by a non-conservation of the total OAM in the nonlinear interaction. Experiments are performed under different conditions and are in excellent agreement with the theory. Our results have implications beyond the specific case studied here of second-harmonic generation, in particular for parametric down-conversion of photons or in general for phase-matched non-collinear interactions between beams with different OAM.
authors: School of Engineering and Physical Sciences, Heriot-Watt University, EH14 4AS Edinburgh, UK.
authors: Thomas
authors: T
authors: Roger
authors: School of Engineering and Physical Sciences, Heriot-Watt University, EH14 4AS Edinburgh, UK.
authors: Julius J F
authors: JJ
authors: Heitz
authors: College of Optical Sciences, The University of Arizona, Tucson, Arizona 85721, USA.
authors: Ewan M
authors: EM
authors: Wright
authors: School of Engineering and Physical Sciences, Heriot-Watt University, EH14 4AS Edinburgh, UK.
authors: Daniele
authors: D
authors: Faccio