Dehoux Thomas, Ishikawa Kenichi, Otsuka Paul H, Tomoda Motonobu, Matsuda Osamu, Fujiwara Masazumi, Takeuchi Shigeki, Veres Istvan A, Gusev Vitalyi E, Wright Oliver B
Institut Lumière Matière, UMR5306, Université Lyon 1-CNRS, Université de Lyon, 69622 Villeurbanne, France.
Division of Applied Physics, Faculty of Engineering, Hokkaido University, Sapporo 060-8628, Japan.
Light Sci Appl. 2016 May 20;5(5):e16082. doi: 10.1038/lsa.2016.82. eCollection 2016 May.
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.
通过一种超快光学技术，我们追踪尺寸小至亚微米的物体中的聚焦千兆赫兹相干声子脉冲。照射单根金属包覆石英光纤表面的红外光脉冲会产生纵向声子波包。来自光纤表面的可见探测光脉冲的反射使得光纤的振动模式得以检测，而部分透射光脉冲的布里渊光散射则能持续监测透明光纤内部的声波前。由此，我们在时域中探测由弯曲光纤表面产生所导致的声聚焦。一个由三维模拟支持的解析模型表明，我们已追踪到声束聚焦至光纤内部直径约为150纳米的腰部。这项工作显著缩小了皮秒声脉冲聚焦的横向分辨率，该分辨率通常受聚焦光脉冲的衍射极限限制，约为1微米，从而开辟了一系列新的可能性，包括纳米级声学显微镜和纳米级计算机断层扫描。
