Nanoscale imaging with picosecond ultrasonic computed tomography

GHz CT测试所选的样品是一根玻璃纤维，沿其圆柱体的主轴沿着有两个孔。我们的方法是从样品的一侧激发声波，并在另一侧旋转探测光束，以评估各种角度的传播声场（具有固定的泵浦激发点）。然后将光纤沿其轴向沿着旋转，重复上述操作。模拟石英光纤直径为5 μm。两个直径约为1 μm的轴向空气孔被认为是真空的，因此没有声波可以传播。这使我们能够证明两个孔的检测与其正确的位置，也得到了孔的大小和形状的估计。实验装置的开发，以满足控制探头和样品方向的特定需求。该装置已在平板玻璃上进行了验证，实验仍在进行中，以检测声学信号，并通过实验证明声学计算机断层扫描到亚微米尺度。

The chosen sample for GHz CT testing is a glass fibre containing two holes along the main axis of its cylinder. Our approach is to excite acoustic waves from one side of the sample and to rotate the probe beam on the opposite side to evaluate the propagated acoustic field for various angles (with a fixed pump excitation spot). Then the fibre is rotated along its axis and the operation is repeated.We realised 3D time-domain acoustic simulations using PZFLex software in a similar geometry. The simulated silica fibre is 5 μm diameter. The two axial air holes of diameter around 1 μm are considered to be vacuum so that no acoustic wave can propagate. This allowed us to demonstrate the detection of both holes with their correct position and also get an estimate of the hole size and shape.The experimental setup was developed to match the particular needs of controlling probe and sample orientations. The setup has been validated on flat glass, and experiments are still ongoing in order to detect the acoustic signal and experimentally demonstrate acoustic computed tomography down to sub-micrometre scale.