Asymmetric optical vortex in plasma density gradient

Abstract

A vortex laser pulse is incident on a plasma with a density gradient along one transverse direction and a homogeneous density along the other one. As the laser pulse propagates in the plasma, the transverse energy distribution becomes asymmetric along the direction with the homogeneous density, which is shown from particle-in-cell simulations. We demonstrate theoretically that the asymmetric energy distribution results from the rate of plasma density change along the transverse energy flow of the vortex beam. Meanwhile, the degree of asymmetry is found to be positively related to the topological charge of the vortex beam as well as the density gradient of the plasma. Our finding provides a new approach for measuring the topological charge of a vortex beam, and also implies an available probe of the inhomogeneity of an optical medium.

Phase transformation of a vortex beam in a liquid-based inferior mirage

“…This is the case for y in = 8.3 mm, where the beam follows a U-shaped trajectory, exits the solution non-inverted and vertically stretched (figure 4(f)), conserving the topological charge. Similar astigmatic changes, unrelated to handedness reversal have recently been reported in a plasma density gradient [17].…”

“…We observe a small difference of vertical symmetry between an astigmatic non-inverted beam (figure 4(f)), where the main axis is tilted to the left, and an astigmatic fully inverted beam (figure 4(j)), where the main axis is tilted to the right, which is more perceptible in our numerical results. This indicates that the non-inverted and the inverted beam are of opposite topological charge [17]. This can be verified by determining the average orbital angular momentum of the beams using a tilted convex lens.…”