Optical trapping map of dielectric spheres

Area of Science:

• Optical physics
• Nanotechnology
• Biophysics

Background:

• Focused Gaussian laser beams are widely used for manipulating spherical dielectric particles.
• Axial trapping efficiency depends on particle radius, refractive index ratio, and numerical aperture.
• Existing metrics like trapping efficiency and stiffness have limitations in defining particle capture and stability.

Purpose of the Study:

• To conduct a comprehensive simulation of optical trapping parameter space.
• To identify and characterize optical trapping regions and their landscape.
• To propose a new metric, 'trapping quality,' for improved assessment of optical trapping performance.

Main Methods:

• Comprehensive three-dimensional (3D) simulation of optical trapping parameters.
• Analysis of iso-surface landscapes and ridge-like contours in the parameter space.
• Development of a new metric based on maximum forward and restoration values of axial trapping efficiency.

Main Results:

• Discovery of distinct optical trapping regions forming an iso-surface landscape with ridge-like contours.
• Demonstration of limitations in using conventional trapping efficiency and stiffness metrics.
• Proposal and definition of 'trapping quality' as an alternative quantitative measure.

Conclusions:

• The identified ridge regions offer potential for effective particle sorting applications.
• Optical trapping blind spots can be utilized to avoid photothermal damage.
• The study provides insights into maintaining optical trapping under dynamic parameter changes, such as particle swelling.