Spin Unlocked Vortex Beam Generation on Nonlinear Chiroptical Metasurfaces

Area of Science:

• Optics and Photonics
• Materials Science
• Nonlinear Optics

Background:

• Optical vortices carrying spin angular momentum (SAM) and orbital angular momentum (OAM) are crucial for optical information processing.
• Optical metasurfaces are widely used for generating and steering vortex beams.
• Existing metasurfaces often exhibit spin-locked OAM generation due to strong spin-orbit interaction, limiting full angular momentum control.

Purpose of the Study:

• To propose and demonstrate a novel approach for achieving spin-unlocked OAM generation using geometric phase-controlled nonlinear chiroptical metasurfaces.
• To enable independent control over the spin and orbital angular momentum states of light.

Main Methods:

• Design and fabrication of nonlinear chiroptical metasurfaces composed of plasmonic meta-atoms with opposite handedness.
• Utilizing strong spin-dependent circular dichroism effects inherent in the meta-atoms.
• Encoding specific phase singularities and phase gradients onto different channels of the metasurface.

Main Results:

• Experimental demonstration of spin-unlocked second harmonic beam steering.
• Successful decoupling of spin and orbital angular momentum control.
• Validation of the proposed metasurface design for advanced optical manipulation.

Conclusions:

• The developed nonlinear chiroptical metasurfaces effectively overcome the limitations of spin-locked OAM generation.
• This work paves the way for multifunctional nonlinear optical devices with enhanced control over light's angular momentum.
• Potential applications in advanced optical information processing and manipulation.