Optical-vortex diagnostics via Fraunhofer slit diffraction with controllable wavefront curvature.

Area of Science:

• Optics and Photonics
• Quantum Information Science

Background:

• Far-field slit diffraction of optical vortices (OV) is a common method for measuring topological charge (TC) magnitude.
• However, conventional methods fail to determine the sign of the topological charge.
• This limitation arises because the diffraction plane typically aligns with the incident OV beam's waist plane.

Purpose of the Study:

• To develop a method for simultaneously measuring both the magnitude and sign of the topological charge of optical vortices.
• To investigate the influence of wavefront curvature on the far-field diffraction pattern of OV beams.

Main Methods:

• Utilizing Laguerre-Gaussian beams with an introduced spherical wavefront component as incident OV beams.
• Analyzing the far-field diffracted beam profile for asymmetries.
• Correlating observed asymmetries with the incident wavefront curvature and the sign of the topological charge.

Main Results:

• The far-field diffracted beam profile exhibits a distinct asymmetry that is dependent on the incident wavefront curvature.
• This asymmetry directly correlates with the sign of the topological charge.
• The method allows for simultaneous determination of both TC magnitude and sign.

Conclusions:

• The introduction of wavefront curvature into OV beams enables the determination of topological charge sign through far-field diffraction analysis.
• This finding provides a simple and efficient technique for complete TC diagnostics.
• The developed method has potential applications in optical metrology and information processing utilizing OV beams.