Dynamic multiple-beam counter-propagating optical traps using optical phase-conjugation

Mike Woerdemann,Konrad Berghoff,Cornelia Denz

doi:10.1364/oe.18.022348

Abstract

Counter-propagating optical traps are widely used where long working distances, axially symmetric trapping potentials, or standing light waves are required. We demonstrate that optical phase-conjugation can automatically provide a counter-propagating replica of a wide range of incident light fields in an optical trapping configuration. The resulting counter-propagating traps are self-adjusting and adapt dynamically to changes of the input light field. It is shown that not only single counter-propagating traps can be implemented by phase-conjugation, but also structured light fields can be used. This step towards more complex traps enables advanced state-of-the-art applications where multiple traps or other elaborated trapping scenarios are required. The resulting traps cannot only be used statically, but they can be rearranged in real-time and allow for interactive dynamic manipulation.

Highlights

Optical trapping has revolutionized many fields of science and engineering since its discovery 40 years ago, including micro- and nano-structuring, biology and biophysics, atom physics and fundamental physics [1]
We demonstrate that optical phase-conjugation can automatically provide a counter-propagating replica of a wide range of incident light fields in an optical trapping configuration
The requirement of a strongly focused laser beam inevitably results in extreme local intensities and the need for microscope objectives with a high numerical aperture

Summary

Introduction

Optical trapping has revolutionized many fields of science and engineering since its discovery 40 years ago, including micro- and nano-structuring, biology and biophysics, atom physics and fundamental physics [1]. One laser beam is tightly focused – usually through a microscope objective that is used for observation anyway – such that it can hold and trap microscopic particles without the aid of any other, counteracting forces. The simplicity and elegance of this approach has led to a vast number of applications of optical tweezers [2], but they suffer from fundamental limitations. The requirement of a strongly focused laser beam inevitably results in extreme local intensities and the need for microscope objectives with a high numerical aperture. These objectives limit the available working distance between objective and specimen to a millimeter or less and make the use of immersion fluid unavoidable. The optical potential well is strongly asymmetric in axial direction with the weakest part being in beam propagation direction

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