Abstract

The inadequacy of the optical trapping model based on ray optics in the case of describing the optical trapping performance of annular and doughnut laser beams is discussed. The inadequacy originates from neglecting the complex focused field distributions of such beams, such as polarization and phase, and thus leads to erroneous predictions of trapping force. Instead, the optical trapping model based on the vectorial diffraction theory, which considers the exact field distributions of a beam in the focal region, needs to be employed for the determination of the trapping force exerted on small particles. The theoretical predictions of such a trapping model agree with the experimentally measured results.

© 2005 Optical Society of America

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References

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App. Phys. Lett. (1)

M. Gu, J. B. Haumonte, Y. Micheau, and J. W. M. Chon, "Laser trapping and manipulation under focused evanescent wave illumination," App. Phys. Lett. 84, 4236-4238 (2004).
[CrossRef]

Appl. Phys. Lett. (4)

J. W. M. Chon, X. Gan, and M. Gu, "Splitting of the focal spot of a high-numerical aperture objective in free space," Appl. Phys. Lett. 81, 1576-1578 (2002).
[CrossRef]

M. Gu, D. Morrish, and P. C. Ke, "Enhancement of transverse trapping efficiency for a metallic particle using an obstructed laser beam," Appl. Phys. Lett. 77, 34-36 (2000).
[CrossRef]

W. M. Lee and X. C. Yuan, "Observation of three-dimensional optical stacking of microparticles using a single Laguerre-Gaussian beam," Appl. Phys. Lett. 83, 5124-5126 (2003).
[CrossRef]

V. R. Daria, P. J. Rodrigo, and J. Glückstad, "Dynamic array of dark optical traps," Appl. Phys. Lett. 84, 323-325 (2004).
[CrossRef]

Biophys. J. (1)

A. Ashkin, "Forces of a single-beam gradient laser trap on a dielectric sphere in the ray optics regime," Biophys. J. 61, 569-581 (1992).
[CrossRef] [PubMed]

J. Mod. Opt. (1)

N. B. Simpson, D. McGloin, K. Dholakia, L. Allen, and M. Padgett, "Optical tweezers with increased axial trapping efficiency," J. Mod. Opt. 45, 1943-1949 (1998).
[CrossRef]

Nature (1)

A. Ashkin, J. M. Dziedzic, and T. Yamane, "Optical trapping and manipulation of single cells using infrared laser beams," Nature 330, 769-771 (1987).
[CrossRef] [PubMed]

Opt. Commun. (1)

A. T. O'Neil and M. J. Padgett, "Axial and latteral trapping efficiency of Laguerre-Gaussian modes in inverted optical tweezers," Opt. Commun. 193, 45-50 (2001).
[CrossRef]

Opt. Express (3)

Opt. Lett. (1)

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Figures (4)

Fig. 1.
Fig. 1.

The maximal TTE as a function of the normalized obstruction size ε (the inner radius of the obstruction normalized by its outer radius) for a polystyrene particle of radius 1 µm immersed in water and illuminated by a focused laser beam at λ=532 nm. (a) Theoretical comparison between the RO and vectorial diffraction models with NA=1.25. The maximal TTE for the two models are normalized to start from the same point at ε=0. (b) Experimental measurements with NA=1.2. The theoretical values are normalized by the experimental p value at ε=0.

Fig. 2.
Fig. 2.

ATE of polystyrene particles suspended in water and illuminated by a highly focused laser beam. NA=1.2 and λ=1.064 µm. (a) The maximal backward ATE as a function of the particle radius. (b) ATE of a 2 µm radius particle as a function of the focusing position.

Fig. 3.
Fig. 3.

TTE of a 2 µm radius polystyrene particle suspended in water and illuminated by a highly focused laser beam as a function of the focusing position. NA=1.2 and λ=1.064 µm. (a) In the polarization direction. (b) In the direction perpendicular to the polarization direction.

Fig. 4.
Fig. 4.

Generation of a doughnut beam of charge 1 using a computer controlled SPM. (a) Applied phase-ramp with 256 phase levels. (b) Intensity profile. (c) Interference pattern.

Tables (1)

Tables Icon

Table 1. The maximal TTE for an annular beam and a doughnut beam of charge 1.

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