Trapping of rare earth-doped nanorods using quasi Bessel beam optical fiber tweezers

R A Minz,J Fick,S K Mondal,A Kumar,S Nic Chormaic,K Lahlil,T Gacoin,U Tiwari

doi:10.1364/osac.417151

Abstract

We demonstrate optical trapping of rare earth-doped NaYF4:Er/Yb nanorods of high aspect ratio (length 1.47 μm and diameter 140 nm) using a quasi Bessel beam (QBB) generated by positive axicon optical fiber tips. Propulsion or trapping of the nanorods is demonstrated using either single or dual fiber nano-tip geometries. The optical force exerted on the trapped nanorods, their velocities, and their positions have been analyzed. We determine the trap stiffness for a single nanorod to be 0.12 pN/μm (0.003 pN/μm) by power spectrum analysis and 0.13 pN/μm (0.015 pN/μm) by Boltzmann statistics in the direction perpendicular to (along) the fiber axes for an average optical power of 34 mW. The experiments illustrate the advantage of using a QBB for multiple nanorod trapping over a large distance of up to 30 μm.

Highlights

Since their earliest demonstrations [1], optical tweezers have found many applications in physics, biology, chemistry and medical research; a very comprehensive review of the field is contained in [2]
The properties of the optical trap are studied by applying the power spectrum analysis (PSA) [36,37] or the Boltzmann statistics method to the particle position fluctuations [38]
The NaYF4:Er/Yb nanorods were prepared by 45 mM (1.8 g) of NaOH in 6 ml of water mixed with 15 ml of ethanol (EtOH) and 30 ml of oleic acid (OA) under stirring

Summary

Introduction

Since their earliest demonstrations [1], optical tweezers have found many applications in physics, biology, chemistry and medical research; a very comprehensive review of the field is contained in [2]. There have been numerous research efforts to optically manipulate particles of different shapes, sizes, materials, and even using different optical arrangements [3,4,5,6] compared to the original configuration that used a high numerical aperture (NA) lens to create a single beam, gradient trap Due to their small footprint, ease of alignment, and integration with existing optical setups, trapping experiments with optical fibers are one specific platform that has seen strong progress in recent years. Different approaches can be used [30,32,33] and a modified optical fiber tip [30,34] has proven to convert a Gaussian beam into a QBB with very low divergence and a very small spot size, while being very integrated into experimental setups Such fibre-based QBBs have already been used for micro- and nanoparticle trapping [28,35]. The properties of the optical trap are studied by applying the power spectrum analysis (PSA) [36,37] or the Boltzmann statistics method to the particle position fluctuations [38]

Optical fiber tips for quasi Bessel beam generation

Fiber-based optical tweezers setup

Nanorod preparation and characterization

Nanorod trapping using two fiber axicon tips

Results and discussion

Conclusion