Simulation and Modelling

2017

• Active rotational and translational microrheology beyond the linear spring regime

  Gibson, L. J., Zhang, S., Stilgoe, A. B., Nieminen, T. A., & Rubinsztein-Dunlop, H. (2017). Physical Review E, 95(4). https://doi.org/10.1103/PhysRevE.95.042608'

  Abstract BibTex Source

  Active particle tracking microrheometers have the potential to perform accurate broadband measurements of viscoelasticity within microscopic systems. Generally, their largest possible precision is limited by Brownian motion and low frequency changes to the system. The signal to noise ratio is usually improved by increasing the size of the driven motion compared to the Brownian as well as averaging over repeated measurements. New theory is presented here whereby error in measurements of the complex shear modulus can be significantly reduced by analyzing the motion of a spherical particle driven by nonlinear forces. In some scenarios error can be further reduced by applying a variable transformation which linearizes the equation of motion. This enables normalization that eliminates error introduced by low frequency drift in the particle’s equilibrium position. Our measurements indicate that this can further resolve an additional decade of viscoelasticity at high frequencies. Using this method will easily increase the signal strength enough to significantly reduce the measurement time for the same error. Thus the method is more conducive to measuring viscoelasticity in slowly changing microscopic systems, such as a living cell.

  @article{Gibson2017,
    archiveprefix = {arXiv},
    arxivid = {1612.07853},
    author = {Gibson, Lachlan J. and Zhang, Shu and Stilgoe, Alexander B. and Nieminen, Timo A. and Rubinsztein-Dunlop, Halina},
    doi = {10.1103/PhysRevE.95.042608},
    eprint = {1612.07853},
    issn = {24700053},
    journal = {Physical Review E},
    mendeley-groups = {Optical Tweezers/UQOMG},
    month = apr,
    number = {4},
    publisher = {American Physical Society},
    title = {{Active rotational and translational microrheology beyond the linear spring regime}},
    volume = {95},
    year = {2017}
  }
  

• Visual guide to optical tweezers

  Lenton, I. C. D., Stilgoe, A. B., Rubinsztein-Dunlop, H., & Nieminen, T. A. (2017). European Journal of Physics, 38(3). https://doi.org/10.1088/1361-6404/aa6271'

  Abstract BibTex Source

  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 have 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.

  @article{Lenton2017,
    archiveprefix = {arXiv},
    arxivid = {1708.04394},
    author = {Lenton, Isaac C.D. and Stilgoe, Alexander B. and Rubinsztein-Dunlop, Halina and Nieminen, Timo A.},
    doi = {10.1088/1361-6404/aa6271},
    eprint = {1708.04394},
    issn = {13616404},
    journal = {European Journal of Physics},
    keywords = {FDTD,evanescent fields,optical tweezers,scattering,simulation},
    mendeley-groups = {Optical Tweezers/UQOMG},
    month = mar,
    number = {3},
    publisher = {Institute of Physics Publishing},
    title = {{Visual guide to optical tweezers}},
    volume = {38},
    year = {2017}
  }
  

2014

• Optical tweezers: Theory and modelling

  Nieminen, T. A., Du Preez-Wilkinson, N., Stilgoe, A. B., Loke, V. L. Y., Bui, A. A. M., & Rubinsztein-Dunlop, H. (2014). Journal of Quantitative Spectroscopy and Radiative Transfer, 146, 59–80. https://doi.org/10.1016/j.jqsrt.2014.04.003'

  Abstract BibTex Source

  Since their development in the 1980s, optical tweezers have become a widely used and versatile tool in many fields. Outstanding applications include the quantitative measurement of forces in cell biology and biophysics. Computational modelling of optical tweezers is a valuable tool in support of experimental work, especially quantitative applications. We discuss the theory, and the theoretical and computational modelling of optical tweezers. Highlights: •We discuss the theory of optical tweezers. \textcopyright 2014 Elsevier Ltd.

  @article{Nieminen2014,
    author = {Nieminen, Timo A. and {Du Preez-Wilkinson}, Nathaniel and Stilgoe, Alexander B. and Loke, Vincent L.Y. and Bui, Ann A.M. and Rubinsztein-Dunlop, Halina},
    doi = {10.1016/j.jqsrt.2014.04.003},
    issn = {00224073},
    journal = {Journal of Quantitative Spectroscopy and Radiative Transfer},
    keywords = {Laser trapping,Light scattering,Optical force,Optical torque,Optical tweezers},
    mendeley-groups = {Optical Tweezers/UQOMG},
    pages = {59--80},
    publisher = {Elsevier Ltd},
    title = {{Optical tweezers: Theory and modelling}},
    volume = {146},
    year = {2014}
  }
  

2012

• Equilibrium orientations and positions of non-spherical particles in optical traps

  Cao, Y., Stilgoe, A. B., Chen, L., Nieminen, T. A., & Rubinsztein-Dunlop, H. (2012). Optics Express, 20(12), 12987. https://doi.org/10.1364/oe.20.012987'

  Abstract BibTex Source

  Dynamic simulation is a powerful tool to observe the behavior of arbitrary shaped particles trapped in a focused laser beam. Here we develop a method to find equilibrium positions and orientations using dynamic simulation. This general method is applied to micro- and nano-cylinders as a demonstration of its predictive power. Orientation landscapes for particles trapped with beams of differing polarisation are presented. The torque efficiency of micro-cylinders at equilibrium in a plane is also calculated as a function of tilt angle. This systematic investigation elucidates in both the function and properties of micro- and nano-cylinders trapped in optical tweezers. \textcopyright 2012 Optical Society of America.

  @article{Cao2012,
    author = {Cao, Yongyin and Stilgoe, Alexander B and Chen, Lixue and Nieminen, Timo A and Rubinsztein-Dunlop, Halina},
    doi = {10.1364/oe.20.012987},
    issn = {1094-4087},
    journal = {Optics Express},
    mendeley-groups = {Optical Tweezers/UQOMG},
    month = jun,
    number = {12},
    pages = {12987},
    publisher = {The Optical Society},
    title = {{Equilibrium orientations and positions of non-spherical particles in optical traps}},
    volume = {20},
    year = {2012}
  }
  

2011

• T-matrix method for modelling optical tweezers

  Nieminen, T. A., Loke, V. L. Y., Stilgoe, A. B., Heckenberg, N. R., & Rubinsztein-Dunlop, H. (2011). Journal of Modern Optics, 58(5-6), 528–544. https://doi.org/10.1080/09500340.2010.528565'

  Abstract BibTex Source

  We review the use of the T-matrix description of scattering, or the T-matrix method, for the calculation of optical forces and torques, especially for the computational modelling of optical tweezers. We consider both simple particles such as homogeneous isotropic spheres, spherical shells, spheroids, and so on, and complex particles, including anisotropic particles, inhomogenous particles, and geometrically complex particles. \textcopyright 2011 Taylor & Francis.

  @article{Nieminen2011,
    author = {Nieminen, Timo A. and Loke, Vincent L.Y. and Stilgoe, Alexander B. and Heckenberg, Norman R. and Rubinsztein-Dunlop, Halina},
    doi = {10.1080/09500340.2010.528565},
    issn = {09500340},
    journal = {Journal of Modern Optics},
    keywords = {T-matrix method,light scattering,optical tweezers,optically-driven micromachines},
    mendeley-groups = {Optical Tweezers/UQOMG},
    month = mar,
    number = {5-6},
    pages = {528--544},
    title = {{T-matrix method for modelling optical tweezers}},
    volume = {58},
    year = {2011}
  }