Acoustic tractor beam.

Negative radiation forces act opposite to the direction of propagation, or net momentum, of a beam but have previously been challenging to definitively demonstrate. We report an experimental acoustic tractor beam generated by an ultrasonic array operating on macroscopic targets (>1 cm) to demonstrate the negative radiation forces and to map out regimes over which they dominate, which we compare to simulations. The result and the geometrically simple configuration show that the effect is due to nonconservative forces, produced by redirection of a momentum flux from the angled sides of a target and not by conservative forces from a potential energy gradient. Use of a simple acoustic setup provides an easily understood illustration of the negative radiation pressure concept for tractor beams and demonstrates continuous attraction towards the source, against a net momentum flux in the system.

[1]  Sandy Cochran,et al.  Mechanical evidence of the orbital angular momentum to energy ratio of vortex beams. , 2012, Physical review letters.

[2]  E. F. Nichols,et al.  The Pressure Due to Radiation. (Second Paper.) , 1903 .

[3]  W Sibbett,et al.  Controlled Rotation of Optically Trapped Microscopic Particles , 2001, Science.

[4]  Aristide Dogariu,et al.  Optically induced 'negative forces' , 2012, Nature Photonics.

[5]  Andrew G. Glen,et al.  APPL , 2001 .

[6]  He,et al.  Direct observation of transfer of angular momentum to absorptive particles from a laser beam with a phase singularity. , 1995, Physical review letters.

[7]  Philip L Marston,et al.  Axial radiation force of a bessel beam on a sphere and direction reversal of the force. , 2006, The Journal of the Acoustical Society of America.

[8]  Farid G. Mitri,et al.  Negative axial radiation force on a fluid and elastic spheres illuminated by a high-order Bessel beam of progressive waves , 2009 .

[9]  E. F. Nichols,et al.  The Pressure Due to Radiation , 1903 .

[10]  A Dogariu,et al.  On the concept of "tractor beams". , 2010, Optics letters.

[11]  K. Neuman,et al.  Optical trapping. , 2004, The Review of scientific instruments.

[12]  Shy Shoham,et al.  Towards multifocal ultrasonic neural stimulation: pattern generation algorithms , 2010, Journal of neural engineering.

[13]  Philip L Marston,et al.  Axial radiation force exerted by general non-diffracting beams. , 2012, The Journal of the Acoustical Society of America.

[14]  Mikael Evander,et al.  Acoustofluidics 20: applications in acoustic trapping. , 2012, Lab on a chip.

[15]  Kishan Dholakia,et al.  Optical Tweezers With Increased Axial Trapping Efficiency , 1998 .

[16]  G. Settles.  Schlieren and shadowgraph techniques , 2001 .

[17]  S. Chu,et al.  Observation of a single-beam gradient force optical trap for dielectric particles. , 1986, Optics letters.

[18]  G. Navon,et al.  Bypassing absorbing objects in focused ultrasound using computer generated holographic technique. , 2011, Medical physics.

[19]  David G Grier,et al.  Optical conveyors: a class of active tractor beams. , 2012, Physical review letters.

[20]  Helge Kragh,et al.  Adolfo Bartoli and the problem of radiant heat , 1989 .

[21]  A. Ashkin.  Acceleration and trapping of particles by radiation pressure , 1970 .

[22]  Tomáš Čižmár,et al.  Shaping the future of manipulation , 2011 .

[23]  Oto Brzobohatý,et al.  Experimental demonstration of optical transport, sorting and self-arrangement using a /`tractor beam/' , 2013 .

[24]  Tomáš Čižmár,et al.  Optical conveyor belt for delivery of submicron objects , 2005 .

[25]  Mordechai Segev,et al.  Negative radiation pressure and negative effective refractive index via dielectric birefringence. , 2012, Optics express.

[26]  Jun Chen,et al.  Optical pulling force , 2011 .

[27]  M. Mansuripur,et al.  Single-beam trapping of micro-beads in polarized light: Numerical simulations. , 2006, Optics express.

[28]  Karen Volke-Sepúlveda,et al.  Transfer of Angular Momentum to Matter from Acoustical Vortices in Free Space , 2009 .

[29]  W Sibbett,et al.  Optical guiding of microscopic particles in femtosecond and continuous wave Bessel light beams. , 2004, Optics express.

[30]  Philip L Marston,et al.  Radiation force of a helicoidal Bessel beam on a sphere. , 2009, The Journal of the Acoustical Society of America.

[31]  Jonathan Leach,et al.  Direct measurement of the skew angle of the Poynting vector in a helically phased beam. , 2006, Optics express.

[32]  Cheng-Wei Qiu,et al.  Single gradientless light beam drags particles as tractor beams. , 2011, Physical review letters.

[33]  Philip L Marston,et al.  Geometrical interpretation of negative radiation forces of acoustical Bessel beams on spheres. , 2011, Physical review. E, Statistical, nonlinear, and soft matter physics.

[34]  Cheng-Wei Qiu,et al.  Linear momentum increase and negative optical forces at dielectric interface , 2013, Nature Photonics.

[35]  D. Grier.  A revolution in optical manipulation , 2003, Nature.

[36]  Martyn Hill,et al.  Efficient finite element modeling of radiation forces on elastic particles of arbitrary size and geometry. , 2013, The Journal of the Acoustical Society of America.

[37]  Z. Fellah,et al.  Theory of the acoustic radiation force exerted on a sphere by standing and quasistanding zero-order Bessel beam tweezers of variable half-cone angles , 2008, IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control.

[38]  Arthur Ashkin,et al.  Optical Levitation by Radiation Pressure , 1971 .

[39]  A Dogariu,et al.  Negative nonconservative forces: optical "tractor beams" for arbitrary objects. , 2011, Physical review letters.