Controllable three-dimensional helical energy backflow in an optical focusing field

Area of Science:

• Optics and Photonics
• Nanotechnology

Background:

• Light energy typically propagates forward.
• Special light fields can exhibit counter-intuitive energy backflow.
• Controlling light energy backflow is crucial for applications.

Purpose of the Study:

• To propose a method for generating and controlling a 3D helical energy backflow (HEB) optical field.
• To investigate the manipulation capabilities of the HEB field.

Main Methods:

• Designing an exponential helical conical phase mask.
• Utilizing tightly focused light fields.
• Varying exponential phase index and topological charge.

Main Results:

• Successfully generated a 3D HEB optical field with an ultra-long longitudinal length.
• Extended the HEB region up to 47.6λ by adjusting parameters.
• Demonstrated optical pulling forces on nanoparticles within the HEB field.

Conclusions:

• The proposed method offers a novel approach to generating and controlling 3D HEB optical fields.
• The HEB field can be used for 3D manipulation of nanoparticles, drawing them towards the light source.
• Potential applications include advanced nanoparticle manipulation and detection techniques.