Dynamic axial stabilization of counter-propagating beam-traps with feedback control

Sandeep Tauro,Jesper Glückstad,Darwin Palima,Andrew Bañas

doi:10.1364/oe.18.018217

Abstract

Optical trapping in a counter-propagating (CP) beam-geometry provides unique advantages in terms of working distance, aberration requirements and intensity hotspots. However, its axial performance is governed by the wave propagation of the opposing beams, which can limit the practical geometries. Here we propose a dynamic method for controlling axial forces to overcome this constraint. The technique uses computer-vision object tracking of the axial position, in conjunction with software-based feedback, for dynamically stabilizing the axial forces. We present proof-of-concept experiments showing real-time rapid repositioning coupled with a strongly enhanced axial trapping for a plurality of particles of varying sizes. We also demonstrate the technique's adaptability for real-time reconfigurable feedback-trapping of a dynamically growing structure that mimics a continuously dividing cell colony. Advanced implementation of this feedback-driven approach can help make CP-trapping resistant to a host of perturbations such as laser fluctuations, mechanical vibrations and other distortions emphasizing its experimental versatility.

Highlights

Optical trapping [1] systems find themselves in a myriad of experimental settings that range from fundamental research such as atom trapping to applied sciences such as biophotonics, biophysics and nano-sciences to mention a few
Its axial performance is governed by the wave propagation of the opposing beams, which can limit the practical geometries
We propose a dynamic method for controlling axial forces to overcome this constraint

Summary

Introduction

Optical trapping [1] systems find themselves in a myriad of experimental settings that range from fundamental research such as atom trapping to applied sciences such as biophotonics, biophysics and nano-sciences to mention a few. This improves transverse stiffness and creates a very strong trap, even for highly scattering objects, using high-NA [13], but can become unstable when minimizing intensity hotspots using lower NA. It needs axial focal shifting for axial manipulation. We summarize our findings and present an outlook in the last section

Experimental setup and side-view vision-feedback implementation

Experimental demonstrations and results

Conclusions