title: Potential energy profile of colloidal nanoparticles in optical confinement.
abstract: An optical bottle method is developed to determine the potential-energy profile of colloidal Rayleigh nanoparticles in an optical trap. The three-dimensional distribution of fluorescent particles in the trap is measured by laser scanning confocal fluorescence microscopy. At sufficiently low concentrations at which interactions between the particles are negligible, the single-particle trapping potential-energy profile is determined from the equilibrium number-density profile by use of the Boltzmann distribution. Fluorescence imaging as well as calculations based on a discrete dipole approximation show that effects due to scattering forces are negligible for polystyrene particles of size less than 10% of the wavelength of the trapping laser, thus justifying the assumption of conservative forces in the equilibrium potential-energy determinations. The new optical bottle method measures the entire two-dimensional trapping-potential profile for an individual nanoparticle without the restriction that only one particle be contained in the trap, thus obviating the need for high laser power.
authors: Jinxin
authors: J
authors: Fu
authors: Qiwen
authors: Q
authors: Zhan
authors: Min Yao
authors: MY
authors: Lim
authors: Zhiyuan
authors: Z
authors: Li
authors: H Daniel
authors: HD
authors: Ou-Yang
mesh_terms: D003102:Colloids; D053758:Nanoparticles / Q000737:chemistry*; D052898:Optical Tweezers; D010316:Particle Size; D011137:Polystyrenes / Q000737:chemistry
chemical_list: D003102:Colloids; D011137:Polystyrenes