Optical Angular Momentum

2015

• Energy, momentum and propagation of non-paraxial high-order Gaussian beams in the presence of an aperture

  Stilgoe, A. B., Nieminen, T. A., & Rubinsztein-Dunlop, H. (2015). Journal of Optics (United Kingdom), 17(12). https://doi.org/10.1088/2040-8978/17/12/125601'

  Abstract BibTex Source

  Non-paraxial theories of wave propagation are essential to model the interaction of highly focused light with matter. Here we investigate the energy, momentum and propagation of the Laguerre-, Hermite- and Ince-Gaussian solutions (LG, HG, and IG) of the paraxial wave equation in an apertured non-paraxial regime. We investigate the far-field relationships between the LG, HG, and IG solutions and the vector spherical wave function (VSWF) solutions of the vector Helmholtz wave equation. We investigate the convergence of the VSWF and the various Gaussian solutions in the presence of an aperture. Finally, we investigate the differences in linear and angular momentum evaluated in the paraxial and non-paraxial regimes. The non-paraxial model we develop can be applied to calculations of the focusing of high-order Gaussian modes in high-resolution microscopes. We find that the addition of an aperture in high numerical aperture optical systems does not greatly affect far-field properties except when the beam is significantly clipped by an aperture. Diffraction from apertures causes large distortions in the near-field and will influence light-matter interactions. The method is not limited to a particular solution of the paraxial wave equation. Our model is constructed in a formalism that is commonly used in scattering calculations. It is thus applicable to optical trapping and other optical investigations of matter.

  @article{Stilgoe2015,
    author = {Stilgoe, Alexander B. and Nieminen, Timo A. and Rubinsztein-Dunlop, Halina},
    doi = {10.1088/2040-8978/17/12/125601},
    issn = {20408986},
    journal = {Journal of Optics (United Kingdom)},
    keywords = {Helmholtz wave equation,Ince gauss,optical tweezers,paraxial wave equation,wavfunctions},
    mendeley-groups = {Optical Tweezers/UQOMG},
    month = oct,
    number = {12},
    publisher = {Institute of Physics Publishing},
    title = {{Energy, momentum and propagation of non-paraxial high-order Gaussian beams in the presence of an aperture}},
    volume = {17},
    year = {2015}
  }
  

2014

• Driving corrugated donut rotors with Laguerre-Gauss beams

  Loke, V. L. Y., Asavei, T., Stilgoe, A. B., Nieminen, T. A., & Rubinsztein-Dunlop, H. (2014). Optics Express, 22(16), 19692. https://doi.org/10.1364/oe.22.019692'

  Abstract BibTex Source

  Tightly-focused laser beams that carry angular momentum have been used to trap and rotate microrotors. In particular, a Laguerre-Gauss mode laser beam can be used to transfer its orbital angular momentum to drive microrotors. We increase the torque efficiency by a factor of about 2 by designing the rotor such that its geometry is compatible with the driving beam, when driving the rotation with the optimum beam, rather than beams of higher or lower orbital angular momentum. Based on Floquet’s theorem, the order of discrete rotational symmetry of the rotor can be made to couple with the azimuthal mode of the Laguerre-Gauss beam. We design corrugated donut rotors, that have a flat disc-like profile, with the help of the discrete dipole approximation and the T-matrix methods in parallel with experimental demonstrations of stable trapping and torque measurement. We produce and test such a rotor using two-photon photopolymerization. With a rotor that has 8-fold discrete rotational symmetry, an outer radius of 1.85 \mum and a hollow core radius of 0.5 \mum, we were able to transfer approximately 0.3 h per photon of the orbital angular momentum from an LG04 beam. \textcopyright 2014 Optical Society of America.

  @article{Loke2014,
    author = {Loke, Vincent L. Y. and Asavei, Theodor and Stilgoe, Alexander B. and Nieminen, Timo A. and Rubinsztein-Dunlop, Halina},
    doi = {10.1364/oe.22.019692},
    issn = {1094-4087},
    journal = {Optics Express},
    mendeley-groups = {Optical Tweezers/UQOMG},
    month = aug,
    number = {16},
    pages = {19692},
    publisher = {The Optical Society},
    title = {{Driving corrugated donut rotors with Laguerre-Gauss beams}},
    volume = {22},
    year = {2014}
  }