Spin angular momentum modulation via spin-orbit interaction in fractional orbital angular momentum beams

Area of Science:

• * Quantum optics and photonics.
• * Structured light field generation and manipulation.

Background:

• * Spin angular momentum (SAM) and orbital angular momentum (OAM) are independent in paraxial fields but coupled in confined fields via spin-orbit interactions (SOI).
• * Conventional OAM beams with integer topological charges (TCs) lead to discrete SAM states, hindering continuous SAM control.
• * SOI enables the creation of structured light with topological characteristics like optical skyrmions.

Purpose of the Study:

• * To explore fractional orbital angular momentum (FOAM) beams for achieving continuous and precise control of SAM.
• * To establish a direct mathematical relationship between FOAM's fractional effective TCs and SAM vector orientation distributions.
• * To experimentally verify theoretical predictions and demonstrate a novel inverse detection method for FOAM TCs.

Main Methods:

• * Theoretical derivation of the relationship between FOAM fractional effective TCs and SAM vector orientation.
• * Experimental verification using a custom-built near-field mapping system to map SAM distributions.
• * Development of an inverse detection method for measuring FOAM fractional effective TCs.

Main Results:

• * Demonstrated a direct mathematical link between FOAM fractional effective TCs and SAM vector orientation.
• * Experimentally mapped distinct SAM distributions regulated by FOAM beams.
• * Achieved high accuracy (10⁻⁵ theoretical, 10⁻² experimental) in measuring FOAM fractional effective TCs using the inverse detection method.

Conclusions:

• * FOAM beams provide a pathway for continuous and precise control of SAM, overcoming limitations of discrete TCs.
• * The study enhances the fundamental understanding of the SOI mechanism in light-matter interactions.
• * Potential applications include advanced light field manipulation, optical communication, and novel photonic devices.