Modification of microparticles due to intense laser manipulation

Frank Wieben, Jan Schablinski, and Dietmar Block

Single micron-sized melamine-formaldehyde particles are levitated in the sheath of an rf-plasma and exposed to an intense laser beam, while being trapped in optical tweezers. A reversible change in the particles' properties is observed and quantitatively analyzed using reference particles. The investigations indicate a gain in particle charge where the initial charge restores within minutes. Possible reasons for these findings are discussed.

DOI

Theoretical study of artificial Kerr effect on the self-focusing of laser in a dissipative suspension of silver nanoparticles

N. Sepehri Javan, R. Naderali, M. Hosseinpour Azad, and M. N. Najafi

Self-focusing of laser beam propagating through a dissipative suspension of metallic nanoparticles is studied. The impact of the imaginary part of nanoparticle polarizability on the optical force and consequently on the particles' rearrangement in the presence of laser fields with an initial Gaussian profile is considered. It is shown that the absorption of laser leads to the creation of optical force along the wave propagation direction which can cause longitudinal distribution of nanoparticles. Considering fifth order nonlinearity of wave amplitude that comes from the simultaneous considering of normal Kerr effect produced by the inhomogeneity of the refractive index resulted from the ponderomotive force acting on conducting electrons and artificial Kerr nonlinearity caused by the polarization optical force acting on electrically polarized particles, set of differential equations describing nonlinear steady-state evolution of laser beam is derived by using a non-paraxial method. Dynamics of laser for different frequencies is investigated and optimum frequency range for improving focusing property is determined. It is shown that the artificial Kerr effect causes localization of particles near the propagation axis that can substantially reduce the threshold power for occurring self-focusing in comparison with plasma and other rigid plasmonic systems.

DOI

Vertical oscillations of dust particles in a strongly magnetized plasma sheath induced by horizontal laser manipulation

M. Puttscher, A. Melzer, U. Konopka, S. LeBlanc, B. Lynch, and E. Thomas Jr.

Experimental studies are presented where dust particles are suspended in the lower sheath region of an argon rf discharge at a strong vertical magnetic field from B=1.5B=1.5 T up to 2.272.27 T. There the particles arranged in an ordered pattern imposed by the upper mesh electrode. It is observed that the particles jump to a new equilibrium position, where they exhibit self-excited vertical oscillations when illuminated by a horizontal laser beam. The dust motion is weakly damped during an upward jump and strongly damped during the return to the equilibrium after the laser is switched off. A model based on delayed charging is presented that can describe the observed behavior.

DOI

Trapping of intense light in hollow shell

Shixia Luan, Wei Yu, M. Y. Yu, Suming Weng, Jingwei Wang, Han Xu, Hongbin Zhuo and A. Y. Wong

A small hollow shell for trapping laser light is proposed. Two-dimensional particle-in-cell simulation shows that under appropriate laser and plasma conditions a part of the radiation fields of an intense short laser pulse can enter the cavity of a small shell through an over-critical density plasma in an adjacent guide channel and become trapped. The trapped light evolves into a circulating radial wave pattern until its energy is dissipated.

DOI

An optical tweezer for complex plasmas

Jan Schablinski, Frank Wieben and Dietmar Block

This paper describes the experimental realization of an optical trap for microparticles levitating in the plasma sheath. Single particles can be trapped in a laser beam comparable to optical tweezers known from colloidal suspensions. The trapping mechanism is discussed and two applications of the system are shown.

DOI