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A general acoustic force field can be decomposed into a conservative gradient force (GF) and a non-conservative scattering force (SF), which have very different physical and mathematical properties. However, the profiles of such forces for Mie particles are unknown, let alone their underlying physics. Here, by using a fast Fourier transform approach, we calculated the GF and SF for spherical particle of various sizes and various incident waves. For the same focused incident waves, the normalized GF and SF are similar for different particle sizes, while the total force can be quite different owing to the varying relative strength between the GF and SF. GF and SF possess symmetries that are not found in the incident waves, indicating that these physically and mathematically distinct forces have symmetries that are hidden from the beam profile. For a vortex beam carrying a well-defined topological charge, acoustic forces alone cannot trap particles.

A multi-scale optical model for organic light-emitting devices containing scattering layers is presented. This model describes the radiation of embedded oscillating dipoles and scattering from spherical particles. After successful model validation with experiments on a top-emitting white OLED, we show how this tool can be used for optimization with specific targets.

A multi-scale optical model for organic light-emitting devices containing scattering layers is presented. This model describes the radiation of embedded oscillating dipoles and scattering from spherical particles. After successful model validation with experiments on a top-emitting white OLED, we show how this tool can be used for optimization with specific targets.

The transverse force profile of a particle in an optical trap is important for the designs of optical trapping-based force transducers. We mapped these force profiles for micron-size polystyrene beads using a pair of overlapping optical traps produced by two highly focused Gaussian beams with unequal intensity; the stronger trap serves as a force transducer to measure the force of the weaker trap in both linear and nonlinear regimes. For particles with size smaller or comparable to the laser wavelength, the force profiles follow closely the gradient of the Gaussian profile, but as the particle size increases, the force profiles deviate from the shape of the gradient of Gaussian for the distance beyond the position of the maximum force. The distance from the center of the trap to the position of the maximum trapping force was found to increase linearly with the particle size. The experimental results are in good agreements with our theoretical model, based on a combination of the Mie theory, vector Debye integral, and Maxwell stress tensor; except that the experimental particle-size dependence of the maximum trapping forces was found to be weaker than that predicted by the theory. © 2012 SPIE.

The transverse force profile of a particle in an optical trap is important for the designs of optical trapping-based force transducers. We mapped these force profiles for micron-size polystyrene beads using a pair of overlapping optical traps produced by two highly focused Gaussian beams with unequal intensity; the stronger trap serves as a force transducer to measure the force of the weaker trap in both linear and nonlinear regimes. For particles with size smaller or comparable to the laser wavelength, the force profiles follow closely the gradient of the Gaussian profile, but as the particle size increases, the force profiles deviate from the shape of the gradient of Gaussian for the distance beyond the position of the maximum force. The distance from the center of the trap to the position of the maximum trapping force was found to increase linearly with the particle size. The experimental results are in good agreements with our theoretical model, based on a combination of the Mie theory, vector Debye integral, and Maxwell stress tensor; except that the experimental particle-size dependence of the maximum trapping forces was found to be weaker than that predicted by the theory. © 2012 SPIE.