2016 Fiscal Year Annual Research Report
Nanoscale imaging with picosecond ultrasonic computed tomography
| Project/Area Number |
16F16063
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| Research Institution | Hokkaido University |
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Principal Investigator |
O・B Wright 北海道大学, 工学研究院, 教授 (90281790)
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| Co-Investigator(Kenkyū-buntansha) |
MEZIL SYLVAIN 北海道大学, 工学研究院, 外国人特別研究員
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| Project Period (FY) |
2016-04-22 – 2018-03-31
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| Keywords | Computed tomography / Picosecond ultrasonics / Nanoscale / Imaging |
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| Outline of Annual Research Achievements |
Our experimental design for picosecond ultrasonics CT was realised. We have found a suitable sample in the form of an aluminium-coated silica cylinder containing axial holes that should serve as a useful test sample. The apparatus, containing x,y,z and goniometer mounts is fully operational and we are at present obtaining preliminary results for this sample using pump pulses at 1000 nm and probe pulses at 500 nm.In addition, we have constructed CT inversion algorithms based on the Radon Transform that can be used to reconstruct the internal structure of the sample. These are ready to use on the preliminary results. In addition to the cylindrical sample, we have made a parallel-side sample that will be used for non-circular-geometry CT measurements. It consists of an array of microscopic polystyrene beads sandwiched inside a thin film. This work is progressing in parallel to the work on the cylindrical sample.
We are also attempting to develop more sophisticated inversion algorithms based on acoustic diffraction theory that can be used to analyse our numerical simulations of the acoustic field inside the sample. These simulations have been carried out for the cylindrical geometry using the commercial software PZFlex at a range of pump spot positions, and are currently being used to test inverse CT algorithms.
We will proceed with low temperature operation after room temperature because of the simplified experimental apparatus.
We have submitted a conference paper on this subject to the 19th International Conference on Photoacoustic and Photothermal Phenomena (ICPPP).
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| Current Status of Research Progress |
Current Status of Research Progress
2: Research has progressed on the whole more than it was originally planned.
Reason
This work is progressing well on the simulation and experimental sides, as described above.
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| Strategy for Future Research Activity |
Room temperature operation up to 10 GHz will be done, implying a lateral spatial resolution down to ~200 nm. In addition new samples will be investigated. The smaller hemisphere diameters ~10-20 micron require an even more stringent optical alignment. However, sample preparation by use of the sample cavity is greatly simplified with water as the ultrasonic couplant. Inorganic and living (immobile) biological samples will be tested and it should be possible to build up a 3D image of the sample. We will also attempt to image the interior of a single biological cell at low temperatures.
We will proceed with application to various nanoscale structures and the demonstration of a lateral spatial resolution down to 20 nm with frequencies up to 200 GHz in low-temperature conditions. Samples such as nanoporous ceramics, nanocrystalline metals or representative biological samples such as chicken tissue will be studied. CT based on contrast in the sound velocity will be attempted: a CT algorithm based on wave diffraction to properly account for the wave-like nature of the ultrasound. Numerical modeling of the acoustic propagation will be carried out to optimize the CT algorithm, the number of source and detection points used, and the vertical and transverse optical spot sizes.
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