Formation of light fields with variable orbital angular momentum using a diffractive spiral-toroidal lens

Abstract

The paper considers the formation of light fields with a variable orbital angular momentum (OAM) using a diffractive spiral-toroidal lens, the radius of which has a given angular dependence. The OAM can be transmitted from radiation to matter, which is used in the rotation of optically trapped microparticles and in the processing and structuring of the surface of photosensitive materials.
We consider the field formation not only in the focal plane, but also at a given distance before and after. We show that depending on the ratio of the radius of the optical element R and the maximum radius of the spiral-toroidal structure ρmax, light fields of various types are formed. If R>ρmax, then the field in the focal plane has the most compact size with the maximum energy concentration. When we leave the focal plane in any direction, the field widens and blurs. If R<ρmax, then the formed field retains its structure for a long time outside the focal region, only changing the scale.
While analyzing the generated fields, not only the distributions of the OAM were calculated, but also the transverse energy flux density (TEFD), which is proportional to the product of the field intensity and the phase gradient. Thus, the displacement from the focal plane for different types of formed beams and the introduction of an additional phase gradient, leads to changes not only in the distribution of the OAM, but also in the TEFD, which expands the possibilities of structured laser radiation in various applications.

Speaker

Valentin I. Logachev
Samara National Research University, Samara, Russia
Russia

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