Photonics Research, 2021, 9 (1): 01000001, Published Online: Dec. 4, 2020
All-optical motion control of metal nanoparticles powered by propulsion forces tailored in 3D trajectories 
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Fig. 1. (a) Ring ξ R = 3 μm ξ u = − 0.28 a = 50 nm v φ ( t ) φ ( t ) ξ ( φ ) ξ ( φ ) ∝ φ Visualization 1 . (c) Cross sections of the considered gold NP; the inset dark-field image shows multiple gold NPs transported in the studied ring traps (Visualization 2 ); (d) predicted and estimated optical propulsion forces for each trap. The propulsion force has been estimated by using the measured intensity profile I ( φ ) Visualization 1 ) coincide with the trapping beam’s shape (measured intensity) and confirm stable confinement and transport of the gold NP in the ring ξ ξ ( φ )
Fig. 2. (a) Calculated cross sections for a single silver NP (a = 30 nm d = 0 nm d = 10 nm R = 3 μm Visualization 3 ; (c) spectral response of the RGB camera along with the scattering cross sections for d = 0 nm d = 10 nm d = 10 nm
Fig. 3. (a) Phase-gradient strength obtained when a ring ξ R = 3 μm β = 10 ° a = 30 nm Visualization 4 ). The corresponding predicted and estimated optical propulsion forces are shown in (c). The maximum value of the phase-gradient force is obtained at φ = 180 ° ξ Visualization 5 . The second row displays the measured beam’s intensity of several optical traps comprising the vibrating string.
Fig. 4. Sketch of the experimental setup used for 3D all-optical transport of NPs. The inverted dark-field microscope (comprising the condenser and objective lenses) has incorporated into two systems: the measurement setup required for visualization and position tracking of the NPs as well as the setup for shaping the laser traps (SLM and the laser device). The laser beam modulated by the SLM is relayed onto the back aperture of the objective lens by using a set of two identical convergent lenses (focal length of 200 mm) working as a 1 × f TL = 200 mm f RL = 200 mm d = 150 mm
Fig. 5. Result of pmrf calculated from measured NP positions. This corresponds to an effective radial trapping potential experienced by a single gold NP in the ring uniform (a) ξ ξ ( φ ) φ ∼ 60 ° φ ∼ 240 ° ξ ( φ )
Fig. 6. (a) Optical transport of silver NPs in a square ξ Visualization 6 ; (b) time-lapse images of the NPs motion during 10 and 6 s, respectively. The pink color observed in the first time-lapse image indicates the presence of a trimer [red color spot in image (a), at time 0.76 s] confined for a time of 4 s; then it escapes from the trap due to strong absorption of light (of the laser trapping beam). The shape of the time-lapse images coincides with the trapping beam’s intensity distribution shown in (b), as expected.
José A. Rodrigo, Mercedes Angulo, Tatiana Alieva. All-optical motion control of metal nanoparticles powered by propulsion forces tailored in 3D trajectories[J]. Photonics Research, 2021, 9(1): 01000001.
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