Single sodium nanodroplets in an opto-electric quadrupole trap

Brief description

We investigate the scattering of polarized laser light by single sodium particles trapped in an home-made electro-optical trap. It consists of a quadrupole trap, which is cross-illuminated with a focused Ar+ laser beam realizing the trapping in 3rd dimension Fig.1. For trapping of clusters with a wide spectrum of masses and charges we applied a common dc voltage between the electrodes and the cell wall instead of applying it pairwise between electrodes. The trap is mounted in the heat-pipe type stainless-steel cell filled with helium buffer gas and sodium deposit and heated up to the temperature of few hundred degrees Kelvin.

Fig. 1: Schematic diagram of the electro-optical trap.

Clusters are produced outside the trap, when the sodium vapour is illuminated by Ar+ laser light. Those light induced clusters grow spontaneously from atomic size up to the radius of few hundred nanometers as a result of light induced homogeneous nucleation. We manage to extract and to keep in the trap from one to twenty clusters during about one hour in a single experiment Movie1. When caught in the trap, droplets grow farther, up to the size of several microns.

We measure the intensity of the elastically scattered light by a single trapped particle at right angle to the direction of the incident laser beam by using a CCD camera. Studying the dynamics of the two-nanoparticls system as a probe Movie2 we could determine the effective potential of the trap.

The scattering experiment is performed for four different polarization geometries of the polarizator-analizator (PA) system: ss, sp, pp and ps. The observed unexpectedly large crosspolarization intensities Ips and Isp Fig.2 mean, that the Mie theory (for a spherical objects) in far field approximation can not be used for an adequate interpretation of the experimental observation. Our present main aim is to explain the presence of crosspolarisation intensities.

Fig. 2: The intensities of light scattered by a single trapped sodium particle.


  1. Bazhan W, Kolwas K, Kolwas M
    Depolarization of light scattered by a single sodium nanoparticle trapped in an electro-optical trap.
    OPTICS COMMUNICATIONS 211: 171-181 OCT 28 2002

  2. Markowicz P, Jakubczyk D, Kolwas K, Kolwas M
    Evolution of size and charge of sodium nanoparticles in an electro-optical trap.
    J PHYS B-AT MOL OPT 33: (24) 5513-5524 DEC 28 2000

  3. Markowicz P, Jakubczyk D, Kolwas K, Kolwas M.
    Trapping of light-induced sodium clusters in a modified quadrupole trap.
    J PHYS B-AT MOL OPT 33: (18) 3605-3614 SEP 28 2000

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