Optical tracking of picosecond coherent phonon pulse focusing inside a sub-micron object

作者：Thomas Dehoux, Kenichi L. Ishikawa, Paul H. Otsuka, Motonobu Tomoda, Osamu Matsuda, Masazumi Fujiwara, Shigeki Takeuchi, István A. Veres, Vitalyi Gusev, Oliver B. Wright · 发表于：Light Science & Applications · 年份：2016 · DOI：10.1038/lsa.2016.82 · 被引用次数：32 · 研究领域：Mechanical and Optical Resonators、Photoacoustic and Ultrasonic Imaging、Ultrasonics and Acoustic Wave Propagation

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 ~1 μm, and thereby opens up a new range of possibilities including nanoscale acoustic microscopy and nanoscale computed tomography. Using an ultrafast optical technique, researchers in France, Japan and Austria have tracked focused phonon pulses in sub-micrometre objects. Confining light and sound waves in micro- and nanoscale structures promises enhanced interaction between light and sound, and hence superior control over light for various important applications. Until now, no one had succe...