Generation of Propagation-Dependent OAM Self-Torque with Chirped Spiral Gratings

Ruediger Grunwald; Mathias Jurke; Max Liebmann; Alexander Treffer; Martin Bock

doi:10.20944/preprints202405.0206.v1

Preprint Article Version 1 Preserved in Portico This version is not peer-reviewed

Version 1 : Received: 2 May 2024 / Approved: 6 May 2024 / Online: 6 May 2024 (07:35:56 CEST)

The application of non-uniform spiral gratings to control structure, topological parameters and propagation of orbital angular momentum (OAM) beams was studied experimentally with coherent near-infrared light. Adapted digital spiral grating structures were programmed into the phase map of a high-resolution liquid-crystal-on-silicon spatial light modulator (LCoS-SLM). It is shown that characteristic spatio-spectral anomalies related to Gouy phase shift can be used as pointers to quantify rotational beam properties. Depending on sign and gradient of spatially variable periods of chirped spiral gratings (CSG), variations of rotation angle and angular velocity as a function of propagation distance were measured. Propagation-dependent self-torque is introduced in analogy to known local self-torque phenomena of OAM beams as obtained by the superposition of temporally chirped or phase modulated wavepackets.

orbital angular momentum; vortex beams; singular optics; spectral anomalies; Gouy effect; spiral gratings; chirped gratings; spatial light modulator; angular velocity; self-torque

Physical Sciences, Optics and Photonics

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Generation of Propagation-Dependent OAM Self-Torque with Chirped Spiral Gratings

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