Indirect precise angular control using four-wave mixing
  Here we show indirect precise angular control using a four-wave mixing (FWM) process. This was performed with a superposition of light with orbital angular momentum (OAM) in an M-Type configuration of a hot 85Rb atomic ensemble. A gear-shaped interference pattern is observed at FWM light with a donut-shaped input signal. The gear could be rotated and is controlled through the change of the polarization of the pump laser. Our experimental results that are based on nonlinear coherent interactions have applications in image processing and precise angular control. 
Wei Zhang, Dong-Sheng Ding, Yun-Kun Jiang, Bao-Sen Shi and Guang-Can   Guo
quant-ph physics.optics