Original Article

Citation: Light: Science & Applications (2016) 5, e16082; doi:10.1038/lsa.2016.82
Published online 20 May 2016

Optical tracking of picosecond coherent phonon pulse focusing inside a sub-micron object
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Thomas Dehoux1, Kenichi Ishikawa2, Paul H Otsuka2, Motonobu Tomoda2, Osamu Matsuda2, Masazumi Fujiwara3,4, Shigeki Takeuchi3,5, Istvan A Veres6, Vitalyi E Gusev7 and Oliver B Wright2

  1. 1Institut Lumière Matière, UMR5306, Université Lyon 1-CNRS, Université de Lyon, 69622 Villeurbanne, France
  2. 2Division of Applied Physics, Faculty of Engineering, Hokkaido University, Sapporo 060-8628, Japan
  3. 3Research Institute for Electronic Science, Hokkaido University, Sapporo 001-0020, Japan
  4. 4School of Science and Technology, Kwansei Gakuin University, Sanda, Hyogo 669-1337, Japan
  5. 5Department of Electronic Science and Engineering, Kyoto University, Kyoto 615-8510, Japan
  6. 6Research Centre for Non-Destructive Testing GmbH, Altenberger Strasse 69, A-4040 Linz, Austria
  7. 7Laboratoire d'Acoustique de l'Université, du Maine, Le Mans 72085, France

Correspondence: OB Wright, Email: olly@eng.hokudai.ac.jp

Received 29 September 2015; Revised 18 January 2016; Accepted 22 January 2016
Accepted article preview online 22 February 2016

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Abstract

By means of an ultrafast optical technique, we track focused gigahertz coherent phonon pulses in objects down to sub-micron in size. Infrared light pulses illuminating the surface of a single metal-coated silica fibre generate longitudinal-phonon wave packets. Reflection of visible probe light pulses from the fibre surface allows the vibrational modes of the fibre to be detected, and Brillouin optical scattering of partially transmitted light pulses allows the acoustic wavefronts inside the transparent fibre to be continuously monitored. We thereby probe acoustic focusing in the time domain resulting from generation at the curved fibre surface. An analytical model, supported by three-dimensional simulations, suggests that we have followed the focusing of the acoustic beam down to a ~150-nm diameter waist inside the fibre. This work significantly narrows the lateral resolution for focusing of picosecond acoustic pulses, normally limited by the diffraction limit of focused optical pulses to ~1μm, and thereby opens up a new range of possibilities including nanoscale acoustic microscopy and nanoscale computed tomography.

Keywords:

acoustic–optic; fibre; optical scattering; picosecond; ultrasonics