研究目的
To study electrodynamically interacting pairs of identical nanoparticles (homodimers) in transverse phase gradients, exploring how phase gradients affect the net driving force and optical binding, with implications for understanding multiparticle dynamics in optical matter self-assembly.
研究成果
For small phase gradients, the net force on homodimers shows separation-dependent modulation due to interference effects, with enhanced forces at integer multiples of wavelength and diminished forces at half-integer multiples. Large phase gradients break symmetry, altering optical binding locations and energy landscapes. This enhances the versatility of optical binding for self-assembly, with good agreement between theory and experiment.
研究不足
The experiment is conducted at room temperature, and thermal motion is not fully accounted for in theoretical calculations. The system is nonequilibrium, limiting direct comparison between potential of mean force and PDFs. Hydrodynamic interactions and coverglass proximity effects introduce small corrections not fully modeled.
1：Experimental Design and Method Selection:
The study uses optical trapping with a cw Ti-sapphire laser and a spatial light modulator (SLM) to create ring traps with azimuthal phase gradients. Theoretical models include point-dipole approximation and generalized Mie theory (GMT) for force calculations.
2：Sample Selection and Data Sources:
PVP-coated 150 nm spherical Ag nanoparticles in water are used. Data is collected from dark field microscopy videos of particle dynamics.
3：List of Experimental Equipment and Materials:
Equipment includes a cw Ti-sapphire laser (λ=800 nm in vacuum, 600 nm in water), SLM, 60x microscope objective, and optical filters. Materials are Ag nanoparticles and water.
4：Experimental Procedures and Operational Workflow:
Particles are trapped in a ring trap with controlled phase gradients. Interparticle separations and velocities are measured from video data. Conditional probability distribution functions (PDFs) of center-of-mass velocity are analyzed for different separations.
5：Data Analysis Methods:
Gaussian fits to PDFs, calculation of net forces using eq 2 and GMT, and comparison with theoretical predictions. Stokes' law is used to relate forces to velocities.
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