High-efficiency measurement of all orbital angular momentum modes in a light beam

Abstract

We present an experimental demonstration of a Laguerre–Gauss (LG) spectrum measurement technique using variable focus lenses that is able to measure the strengths of the constituent modes in an unknown incoming light beam with the highest possible efficiency. The experiment modifies the classical projective, phase flattening technique by including a variable-sized pinhole and a two-electronic-lens variable imaging system that is tuned for each mode to give the highest possible detection efficiency irrespective of the beam waist of the LG mode chosen for the projection/decomposition. The modified experiment preserves the orthogonality between the modes with only a 4% cross talk so that superposition states may also be detected efficiently. Our experiment results show efficient detection of orbital angular momentum vortex beams with topological charge l values ranging from 0 to 4, with various beam waists chosen for the decomposition.