Optical Trapping-Formed Colloidal Assembly with Horns Extended to the Outside of a Focus through Light Propagation

Kudo, Tetsuichi; Wang, Shun Fa; Yuyama, Ken‐ichi; Masuhara, Hiroshi

doi:10.1021/acs.nanolett.6b00123

Cited by 63 publications

(92 citation statements)

References 29 publications

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“…f) Optical micrographs and model (inset) of a closely packed assembly of 500 nm polystyrene nanoparticles via metal nanostructures. Figures adapted and reproduced with permission: (b), Copyright 2002, APS Physics; (d), Copyright 2011, APS Physics; (e), Copyright 2016, ACS Publications; (f), Copyright 2011, ACS Publications.…”

Section: Introductionmentioning

confidence: 99%

“…Following these pioneering demonstrations, more complex assembly of nanoparticles in two and three dimensions have been recently realized (Figure d–f), validating the use of definitions such as new ordered states of matter and optical crystals. In recent years, traps based on optical binding have been developed to exploit size, shape and chirality of the nanoobjects, to realize a wide range of nontrivial mesostructures (Figure e), often in combination with other approaches such as plasmonic structures (Figure f) or light‐assisted templated self‐assembly …”

Section: Introductionmentioning

confidence: 99%

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Nanoscale Optical Trapping: A Review

Bradac

2018

Advanced Optical Materials

111

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The First TrapIn 1969, a "back-of-the-envelope" calculation inspired Ashkin to conduct a simple experiment and determine whether it was feasible to use light radiation pressure to accelerate objects to practical speeds. Photons carry momentum hν/c (with h, ν and c being the Planck's constant, the frequency of the photon and the speed of light, respectively). If light from a source with power P shines on a mirror, P/hν photons hit the surface every second and transfer a total momentum of (2P/hν)(hν/c) = 2P/c onto it. A perfectly reflecting mirror should therefore-due to conservation-acquire an equal momentum in the same direction light propagates.Based on this crude calculation, Ashkin predicted that a light source of power P = 1 W, would produce a force (on an ideally reflecting mirror) of ≈10 nN-indeed small in absolute terms. [3] Nevertheless, if a laser beam is used as the light source and is focused on a spot of ≈1 µm 2 to hit a particle ≈1 µm in diame ter, the resulting force does become relevant. Assuming the particle is perfectly reflective and has a density of 1 g cm −3 , the calculated acceleration is ≈10 9 cm s −2 , i.e., roughly 10 6 times the acceleration of gravity. In the experiment, Ashkin conducted to test his hypotheses, [2] a cw argon laser (wavelength λ = 514.5 nm, waist radius w 0 = 6.2 µm at the focal point) was employed to accelerate latex spheres (diameter 0.59, 1.31, and 2.68 µm), which were freely suspended in water, in a glass chamber. With just milliwatts of laser power, Ashkin observed that the particles were pushed in the direction of the mildly focused Gaussian laser beam, with values for the acceleration consistent with his rough predictions. Interestingly, he also observed an unanticipated phenomenon. Particles located in the fringes of the beam were drawn toward the beam axiswhere the light intensity is the highest-before being accelerated and pushed with ≈µm s −1 speeds toward the back of the chamber. They would disperse by Brownian motion away from the beam axis once the laser was switched off, yet they would be drawn again toward the center of the beam upon turning the laser back on-as the radiation pressure had a transverse component to the force, as well as the predicted longitudinal one.The origin of both the transversal and longitudinal force is usually understood by considering two distinct regimes, depending on the relative size of the particles to the wavelength of the laser beam: the geometrical (ray optics) regime and the Rayleigh (dipole approximation) regime.Optical trapping is the craft of manipulating objects with light. Decades after its first inception in 1970, the technique has become a powerful tool for ultracold-atom physics and manipulation of micron-sized particles. Yet, optical trapping of objects at the intermediate-nanoscale-range is still beyond full grasp. This matters because the nanometric realm is where several promising advances, from mastering single-molecule experiments in biology, to fabricating hybrid devices for nanoelectronics and photonics, a...

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Nanoscale Optical Trapping: A Review

Bradac

2018

Advanced Optical Materials

111

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“…The particles form a ring structure in deionized water because they are confined by the gradient forces generated by the diffraction spot. It is the same as the previous studies, and the particles are trapped against the surface and can not escape from the traps [15,21,25]. However, the aggregation is unstable without the laser confinement.…”

Section: Forming Steady Patterns Of Particles In a Salt Solutionmentioning

confidence: 68%

“…It is generally believed that the particles are trapped only in an irradiated diffraction limited spot where optical force is exerted on the particles by a laser beam. However, in recent years, it has been demonstrated that single beam optical tweezers can gather lots of colloidal particles outside the focus of trapping laser at the glass-solution interfaces [16][17][18][19][20][21][22]. The mechanism of the above phenomenon is complicated.…”

Section: Introductionmentioning

confidence: 99%

Optical Assembling of Micro-Particles at a Glass–Water Interface with Diffraction Patterns Caused by the Limited Aperture of Objective

2018

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Optical tweezers can manipulate micro-particles, which have been widely used in various applications. Here, we experimentally demonstrate that optical tweezers can assemble the micro-particles to form stable structures at the glass–solution interface in this paper. Firstly, the particles are driven by the optical forces originated from the diffraction fringes, which of the trapping beam passing through an objective with limited aperture. The particles form stable ring structures when the trapping beam is a linearly polarized beam. The particle distributions in the transverse plane are affected by the particle size and concentration. Secondly, the particles form an incompact structure as two fan-shaped after the azimuthally polarized beam passing through a linear polarizer. Furthermore, the particles form a compact structure when a radially polarized beam is used for trapping. Thirdly, the particle patterns can be printed steady at the glass surface in the salt solution. At last, the disadvantage of diffraction traps is discussed in application of optical tweezers. The aggregation of particles at the interfaces seriously affects the flowing of particles in microfluidic channels, and a total reflector as the bottom surface of sample cell can avoid the optical tweezers induced particle patterns at the interface. The optical trapping study utilizing the diffraction gives an interesting method for binding and assembling microparticles, which is helpful to understand the principle of optical tweezers.

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“…There have been various methods developed to assemble two-dimensional colloidal crystals [11][12][13][14] . Since the discovery of optical tweezers [15] , optical forces have been widely studied [16][17][18][19] and can be used for the assembly and reconfiguration of particles [20][21][22][23][24] . The optical gradient forces drive the particles into the optical trap, and the particles will form a two-dimensional colloidal crystal.…”

mentioning

confidence: 99%

Laser-accelerated self-assembly of colloidal particles at the water–air interface

Zhong

Wang

2017

中国光学快报

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We experimentally demonstrate that optical tweezers can be used to accelerate the self-assembly of colloidal particles at a water-air interface in this Letter. The thermal flow induced by optical tweezers dominates the growth acceleration at the interface. Furthermore, optical tweezers are used to create a local growth peak at the growing front, which is used to study the preferential incorporation positions of incoming particles. The results show that the particles surfed with a strong Marangoni flow tend to fill the gap and smoothen the steep peaks. When the peak is smooth, the incoming particles incorporate the crystal homogeneously at the growing front.

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Optical Trapping-Formed Colloidal Assembly with Horns Extended to the Outside of a Focus through Light Propagation

Cited by 63 publications

References 29 publications

Nanoscale Optical Trapping: A Review

Nanoscale Optical Trapping: A Review

Optical Assembling of Micro-Particles at a Glass–Water Interface with Diffraction Patterns Caused by the Limited Aperture of Objective

Laser-accelerated self-assembly of colloidal particles at the water–air interface

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