Visual guide to optical tweezers

Abstract

It is common to introduce optical tweezers using either geometric optics for large particles or the Rayleigh approximation for very small particles. These approaches are successful at conveying the key ideas behind optical tweezers in their respective regimes. However, they are insufficient for modelling particles of intermediate size and large particles with small features. For this, a full field approach provides greater insight into the mechanisms involved in trapping. The advances in computational capability over the last decade has led to better modelling and understanding of optical tweezers.Problems that were previously difficult to model computationally can now be solved using a variety of methods on modern systems. These advances in computational power allow for full field solutions to be visualised, leading to increased understanding of the fields and behaviour in various scenarios. In this paper we describe the operation of optical tweezers using full field simulations calculated using the finite difference time domain method. We use these simulations to visually illustrate various situations relevant to optical tweezers, from the basic operation of optical tweezers, to engineered particles and evanescent fields.

Focus on advanced optics—optical enlightenment

“…Or that the realm of molecular nonlinear optics would begin to feature more in bio-imaging-where it now offers unprecedented scales of resolution-rather than in telecom, its initially triggering domain of applications? The development of optomechanics, with optical tweezers and other confining techniques [14,15], also appears to be here to stay, with a better understanding and new applications running far beyond the reach of the pioneering but limited laboratory experiments in the 1980s. We hope that these domains, all represented in this issue, will find their way sooner rather than later into the canon of teaching from high schools to universities and engineering colleges, with the assistance of material devoted to pedagogic issues and low cost implementations at the introductory level [16][17][18][19].…”

Measurement of forces in optical tweezers with applications in biological systems

“…Finite-difference time-domain (FDTD) and frequency-domain (FDFD) [18][19][20] are classes of finite-difference methods widely used to solve partial differential equations, including Maxwell's equations. While these methods are similar in the representation of derivatives, they are significantly different in the way of finding solutions.…”

Calibration of optical tweezers for force microscopy

“…A discussion of T-matrix calculation methods can be found in Qi et al [2014]. A discussion of methods to calculate optical tweezers scattering without the T-matrix, and with finite-difference methods can be found in Lenton et al [2017b].…”