High efficiency phase flattening based Laguerre-Gauss (LG) spectrometer   using variable focus lenses
  We propose a novel high-efficiency no-moving-parts Laguerre-Gauss (LG) spectrometer using two variable focus lenses and a variable sized pinhole that overcomes the limitations of the classical, projective, phase flattening technique for measuring the Laguerre-Gauss (LG) spectrum of light beams. Simulation results show that the coupling losses are virtually zero and the only losses are ring losses which are mode-dependent but beam waist-independent. Hence, the detection efficiency for all modes is simultaneously the maximum possible irrespective of the beam waist of the LG modes chosen for the decomposition. The losses can also be easily pre-calibrated to remove the efficiency bias amongst different modes. 
Mumtaz Sheikh, Haad Yaqub Rathore, Sohaib Abdul Rehman
physics.optics