Manipulating and detecting ultrahigh frequency sound waves

Science Focus

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Gold plasmonic nanostructures shaped like Swiss-crosses can convert laser light into ultrahigh frequency (10GHz) sound waves. An advance has been achieved towards next generation ultrasonic imaging with potentially 1,000 times higher resolution than today’s medical ultrasounds. Researchers with the U.S. Department of Energy (DOE)’s Lawrence Berkeley National Laboratory (Berkeley Lab) have demonstrated a technique for producing, detecting and controlling ultrahigh frequency sound waves at the nanometer scale. Through a combination of subpicosecond laser pulses and unique nanostructures, a team led by Xiang Zhang, a faculty scientist with Berkeley Lab’s Materials Sciences Division, produced acoustic phonons – quasi-particles of vibrational energy that move through an atomic lattice as sound waves – at a frequency of 10 gigahertz (10 billion cycles per second). By comparison, medical ultrasounds today typically reach a frequency of only about 20 megahertz (20 million cycles per second.) The 10GHz phonons not only promise unprecedented resolution for acoustic imaging, they also can be used to “see” subsurface structures in nanoscale systems that optical and electron microscopes cannot. “We have demonstrated optical coherent manipulation and detection of the acoustic phonons in nanostructures that offer new possibilities in the development of coherent phonon sources and nano-phononic devices for chemical sensing,

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