Investigation of near-field optical tweezers based on the edge effect of extraordinary optical transmission in thin microcavity

School of Mechanical Engineering, Xi'an Jiaotong University - Xi'an 710049, China and State Key Laboratory for Strength and Vibration of Mechanical Structures, Xi'an Jiaotong University Xi'an 710049, China

^(a) E-mail: zhlforever@stu.xjtu.edu.cn
^(b) E-mail: ejhwu@mail.xjtu.edu.cn (corresponding author)

Received: 6 May 2023
Accepted: 22 June 2023

Abstract

Optical tweezers are powerful tools capable to trap and manipulate particles directly. However, using conventional optical tweezers for nanosized objects remains a formidable challenge due to the optical diffraction limits and high-power levels required for nanoscale trapping, which usually causes irreversible damage to the captured particles. In this paper, we investigate the near-field edge effect of thin microcavity due to macroscopic quantum effect, and the highly enhanced electric field can reach 2.4 times. Thus, a dual near-field optical trap potential well is generated at the edge of the thin microcavity. We theoretically show that this near-field potential well can stably capture nanoparticles smaller than 10 nm while keeping the incident optical power level below 100 mW. Besides, the relationship between size of the microcavity and optical gradient force has also been carefully studied. Finally, the theoretical model of near-field optical tweezers with double thin microcavity is established, and the electric field magnitude of the double microcavity model is enhanced by 4.5 times compared with single microcavity model, in which the coupling effect of double hole makes smaller particles be stably trapped. Our research presents a huge potential for optical trapping and separation of nanoparticles and biomolecules.