title: Observation of a Single-Beam Gradient Force Acoustical Trap for Elastic Particles: Acoustical Tweezers.
abstract: We demonstrate the trapping of elastic particles by the large gradient force of a single acoustical beam in three dimensions. Acoustical tweezers can push, pull and accurately control both the position and the forces exerted on a unique particle. Forces in excess of 1 micronewton were exerted on polystyrene beads in the submillimeter range. A beam intensity less than 50  W/cm^{2} was required, ensuring damage-free trapping conditions. The large spectrum of frequencies covered by coherent ultrasonic sources provides a wide variety of manipulation possibilities from macroscopic to microscopic length scales. Our observations could open the way to important applications, in particular, in biology and biophysics at the cellular scale and for the design of acoustical machines in microfluidic environments.
authors.affiliation: Sorbonne Universités, UPMC Univ Paris 06, CNRS, UMR 7588, Institut des NanoSciences de Paris, F-75005 Paris, France.
authors.forename: Diego
authors.initials: D
authors.lastname: Baresch
authors.affiliation: CNRS, UMR 7588, Institut des NanoSciences de Paris, F-75005 Paris, France.
authors.forename: Jean-Louis
authors.initials: JL
authors.lastname: Thomas
authors.affiliation: Sorbonne Universités, UPMC Univ Paris 06, CNRS, UMR 7190, Institut Jean le Rond d'Alembert, F-75005 Paris, France.
authors.forename: Régis
authors.initials: R
authors.lastname: Marchiano