Giant Optical Manipulation Vladlen G. Shvedov, 1,2,3 Andrei V. Rode, 1 Yana V. Izdebskaya, 2,3 Anton S. Desyatnikov, 2 Wieslaw Krolikowski, 1 and Yuri S. Kivshar 2 1 Laser Physics Center, ResearchSchool of Physics and Engineering, Australian National University, Canberra ACT 0200, Australia 2 Nonlinear Physics Center, Research School of Physics and Engineering, Australian National University, Canberra ACT 0200, Australia 3 Department of Physics, Taurida National University, Simferopol 95007, Ukraine (Received 22 July 2010; revised manuscript received 13 August 2010; published 10 September 2010) We demonstrate a new principle of optical trapping and manipulation increasing more than 1000 times the manipulation distance by harnessing strong thermal forces while suppressing their stochastic nature with optical vortex beams. Our approach expands optical manipulation of particles into a gas media and provides a full control over trapped particles, including the optical transport and pinpoint positioning of 100 m objects over a meter-scale distance with 10 m accuracy. DOI: 10.1103/PhysRevLett.105.118103 PACS numbers: 87.80.Cc, 37.10.Mn, 37.10.Pq Introduction.—Since its discovery 40 years ago, the ability to remotely control and move objects in space by the radiation pressure of light provides a useful tool for manipulating microscopic particles [1–3], living cells [4], nanoparticles [5], and atoms [6,7], and is increasingly employed in biology and physics [3,8]. However, the op- eration of weak radiation pressure forces, such as a gra- dient force in optical tweezers [2,4] and a scattering force in optomechanics [9], is restricted to small spatial scale, typically hundreds of microns. In contrast, thermal or radiometric forces can be much stronger [10], and they may extend a spatial scale of all-optical manipulation [11]. However, radiometric forces dominate for light-absorbing particles interacting with surrounding media, and thus far their stochastic nature prevent stable large-scale trapping of particles and aerosols [3,12]. When a surface of an aerosol particle is heated nonun- iformly by light, the surrounding gas molecules rebound off the surface with different velocities creating an inte- grated force on the particle. This effect was discovered by Ehrenhaft [13] and is known as photophoresis [10,14]. A rough comparison [15] of the radiation pressure force exerted by a beam with power P, F a ¼ P=c, and the photophoretic force for particles with zero thermal con- ductivity, F pp ¼ P=3 [16], shows that for air at room temperature the latter dominates by several orders of mag- nitude, F pp =F a ¼ c=3 ffi 6  10 5 , where c is the speed of light, and  is the molecular velocity. A possibility to trap micron-sized particles in a vortex beam by employing thermal photophoretic forces was demonstrated in our recent studies [11,17] of millimeter- long optical guiding of light-absorbing aerosols with a pair of counter-propagating doughnutlike vortex beams. These earlier experiments [11] paved a road to a novel idea of utilizing the photophoretic force [18] for a reliable large- scale transport of trapped particles. In this Letter we dem- onstrate, for the first time to our knowledge, that the optical-to-mechanical energy conversion due to photo- phoretric forces can be specially tailored to trap and trans- port macroparticles in air by using a slowly diverging vortex beam. We achieve a stable transport of 100 m particles over the meter-scale distance, which is more than 1000 times larger than the scale of any previously reported optical manipulation technique. Our approach is based on the use of a doughnutlike vortex beam [see Fig. 1] which allows us to hold light-absorbing particles in the center of the beam while minimizing the effect of stochastic nature of the thermal forces. We derived theoretical dependence of the particles speed on the vortex beam parameters, the particle size and thermal conductivity, and viscosity of the gaseous media. The experimental study of the relation between the particle velocity and its size is also presented. Optical vortex pipeline.—We realize a giant optical manipulation using a new class of extended optical traps FIG. 1 (color online). Experimental setup of an optical trap- ping system for long-range transport of aerosol particles. The vortex beam is formed by the diffraction hologram DH; L1 and L2 are collimators which control the beam parameters, and the propagation direction is controlled by the moving mirror M. Particle transport visualization is performed in the longitudinal (microscope MO1) and transverse (microscope MO2) directions; BS—beam splitter; T—glass target; NF—notch filter to cut off the laser radiation;WL—white light source; and C—cuvette with particles. The inset shows the intensity distribution inside the vortex-induced pipeline. It varies from low [dark grey (blue)] to high [grey (red)] values. The arrow shows the direction z of the particles’ transport, the latter are represented by (yellow) balls. PRL 105, 118103 (2010) PHYSICAL REVIEW LETTERS week ending 10 SEPTEMBER 2010 0031-9007= 10=105(11)=118103(4) 118103-1 Ó 2010 The American Physical Society