Active chiral control of GHz acoustic whispering-gallery modes

Abstract

We selectively generate chiral surface-acoustic whispering-gallery modes in the gigahertz range on a microscopic disk by means of an ultrafast time-domain technique incorporating a spatial light modulator. Active chiral control is achieved by making use of an optical pump spatial profile in the form of a semicircular arc, positioned on the sample to break the symmetry of clockwise-and counterclockwise-propagating modes. Spatiotemporal Fourier transforms of the interferometricallymonitored two-dimensional acoustic fields measured to micron resolution allow individual chiral modes and their azimuthal mode order, both positive and negative, to be distinguished. In particular, for modes with 15-fold rotational symmetry we demonstrate ultrafast chiral control of surface acoustic waves in a micro-acoustic system with picosecond temporal resolution. Applications include nondestructive testing and surface acoustic wave devices.

Principles and advances in ultrafast photoacoustics; applications to imaging cell mechanics and to probing cell nanostructure

“…The generation of surface and guided waves is favored when the shape of the pump laser spot on the sample surface is not a disc but made instead of periodically spaced optical lines, thus concentrating most of the input energy into controlled phonon wave vectors along one direction on the surface. Suitable transient gratings can be obtained by shaping the pump pulses with optical masks, creating two-beam interference on the surface, or by using electrically-addressed spatial light modulators [59] , [60] . This technique was used to characterize thin liquid and solid films and it could also be used to generate bulk shear waves [61] .…”