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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.
![](../images/trap.jpg)
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.
![](../images/depolar.jpg)
Fig. 2: The intensities of light scattered by a single trapped sodium particle.
Publications
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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
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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
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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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