Dexterous holographic trapping of dark-seeking particles with Zernike holograms

TL;DR

This paper introduces a novel holographic trapping method using difference-of-Gaussians traps created from Zernike phase-contrast holograms, enabling effective manipulation of dark-seeking particles in heterogeneous systems.

Contribution

It presents a new class of dark traps based on superimposed Gaussian modes and a phase-only hologram projection method using Zernike principles, advancing optical manipulation techniques.

Findings

Successfully trapped dark-seeking particles with DoG traps

Demonstrated compatibility with conventional optical tweezers

Validated the approach on various colloidal particles

Abstract

The intensity distribution of a holographically-projected optical trap can be tailored to the physical properties of the particles it is intended to trap. Dynamic optimization is especially desirable for manipulating dark-seeking particles that are repelled by conventional optical tweezers, and even more so when dark-seeking particles coexist in the same system as light-seeking particles. We address the need for dexterous manipulation of dark-seeking particles by introducing a class of "dark" traps created from the superposition of two out-of-phase Gaussian modes with different waist diameters. Interference in the difference-of-Gaussians (DoG) trap creates a dark central core that is completely surrounded by light and therefore can trap dark-seeking particles rigidly in three dimensions. DoG traps can be combined with conventional optical tweezers and other types of traps for use in heterogeneous samples. The ideal hologram for a DoG trap being purely real-valued, we introduce a general method based on the Zernike phase-contrast principle to project real-valued holograms with the phase-only diffractive optical elements used in standard holographic optical trapping systems. We demonstrate the capabilities of DoG traps (and Zernike holograms) through experimental studies on high-index, low-index and absorbing colloidal particles dispersed in fluid media.