Polystyrene and silica nanoparticles are gathered and form a single disk-like assembly at glass/solution interface upon optical trapping with a focused laser and its size evolves much larger than the focal volume. In addition, linearly aligned aggregates of nanoparticles are prepared at specific edge sites of the assembly, which looks like horns. Transmission spectral and diffraction pattern measurements were carried out, confirming a correlation between the central arrangement of the nanoparticles and the horn formation. This dynamics and mechanism characteristic of optical trapping at interface is discussed from the viewpoint of optical propagation of the trapping laser. The assembly formation started at the focus where trapping laser light is scattered, and the trapping laser propagated trough the prepared assembly expanding its size.
We investigate the optical manipulation of nanoparticles with the resonant nonlinear optical response. Efficient
trapping of nanoparticles observed in experiments under the resonance condition is elucidated by considering optical
nonlinearity. Also, we propose the flexible optical manipulations of nanoparticles that have gain by optical pumping. The
pulling force and the rotational switching are demonstrated, where the stimulated emission from nanoparticles with
inverted population is considered. These results show that utilizing nonlinear optical effect will greatly enhance the
degrees of freedom to manipulate nanoparticles.
We conduct the optical trapping and assembling of polystyrene particles at the glass/solution interface by utilizing tightly focused 1064 nm laser of high power. Previously we reported that this leads to form the assembly sticking out horns consisting of single row of aligned particles through light propagation. Here, we demonstrate the laser power dependence of this phenomenon. With increasing the laser power, the particles are started to distribute around the focal spot and form the assembly larger than focal spot. The shape of the assembly becomes ellipse-like and the color at the central part of the assembly in transmission images is changed. This indicates that the assembly structure is changed, and trapping laser is started to propagate through the adjoining particles leading to horn formation. Strong laser power is necessary to elongate the horns and to align them straightly. We expect that this study will offer a novel experimental approach for assembling and crystallization of nanoparticles and molecules exclusively by optical trapping.
We theoretically propose laser manipulation utilizing the resonant nonlinear optical response.
We calculated the radiation force exerted on a single molecule in a focused laser beam by solving density matrix equations using the non-perturbative method, because the high laser power is necessary for single molecular trapping.
As the result, we coherently elucidate certain recently reported puzzling phenomena that contradict the conventional understanding of laser manipulation.
Further, we demonstrate unconventional forms of laser manipulation which drastically enhances the number of degrees of freedom to manipulate nano-sized objects. For example, we can pull objects by using traveling wave that usually pushes them along the direction of traveling wave.
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