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On the 60th anniversary of the Budker Institute of Nuclear Physics of the Siberian Branch of the Russian Academy of Sciences. On the 100th anniversary of the birth G.I. Budker

Beams of photons with nonzero orbital angular momentum projection: new results
B.A. Knyazev,
V.G. Serbo
Budker Institute of Nuclear Physics, Siberian Branch of the Russian Academy of Sciences, prosp. akad. Lavrenteva 11, Novosibirsk, 630090, Russian Federation
Solving Maxwell's equations in cylindrical coordinates yields states in quantum theory with definite values of energy ħ ω, longitudinal momentum ħ k_{z} and total angular momentum projection ħ m on the axis z (where ħ is the Planck constant). Experimentally, for the last quantity values of up to m ∼ 10^{4} have been obtained. The wave front of such a state is like a meat grinder screw, with the lines of force of the Poynting vector representing a screw line. From plane waves, such states differ by the nonzero orbital momentum projection on the direction of motion, and from spherical waves, by the definite direction of motion. For brevity, these states are referred to as 'twisted photons'. In this paper, recent experimental and theoretical results on twisted photons are reviewed, to which the present authors actively contributed. Detailed discussion is given to recent experiments on the production of high intensity beams of terahertz (140 μ m) twisted photons performed on the Novosibirsk freeelectron laser at the Budker Institute of Nuclear Physics. Recent theoretical work on the interaction of twisted photons with atoms is summarized. Due to their extra degree of freedom—the projection of the total angular momentum on the direction of motion—twisted photons represent a novel research tool of potentially wide application in physics.
