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Optical trapping and axial manipulation with annular laser beams
Sumit Yadav1, Abdul Alim1, Arijit K De2
1Condensed Phase Dynamics Group, Department of Physical Sciences, Indian Institute of Science Education and Research (IISER) Mohali, Knowledge City, Sector 81, SAS Nagar, Punjab 140306, India.
The Review of Scientific Instruments
|October 28, 2025
Summary
Researchers explored laser beam shapes for stable optical traps. Annular beams offer better trapping efficiency than Gaussian beams by balancing forces and aberrations, enabling precise particle manipulation.
Area of Science:
- Optics and Photonics
- Optical Tweezers
- Laser Physics
Background:
- Gaussian beams are conventionally used for optical trapping.
- The optimal laser beam shape for stable optical traps remains an active area of research.
- Understanding the interplay of forces and aberrations is crucial for efficient optical trapping.
Purpose of the Study:
- To investigate and compare the trapping efficiencies of concentric annular beams against the conventionally used Gaussian beam.
- To explore the factors influencing trapping efficiency, including gradient force, scattering force, and aberration effects.
- To develop a novel technique for controlled axial manipulation of trapped particles using annular beams.
Main Methods:
- A theoretical model was developed, decomposing a focused Gaussian beam into concentric light cones.
- Experiments were conducted using laser beam-shaping techniques to implement concentric annular beams.
- A spatial light modulator was employed for real-time switching between different ring beams.
Main Results:
- Contrary to preconceptions, tighter focusing does not necessarily lead to better trapping efficiency.
- Trapping efficiency is determined by a balance between gradient force, scattering force, and optical aberrations.
- Annular beams exhibit intrinsic axial focus shifts that can be exploited for particle manipulation.
Conclusions:
- Concentric annular beams can provide more stable optical traps compared to Gaussian beams.
- A new method for controlled axial manipulation of trapped particles was demonstrated using annular beams.
- This technique enables stable axial positioning for practical 3D particle manipulation applications.
