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Ultrafast, sub-nanometre-precision and multifunctional time-of-flight detection


Displacement measurement is a fundamental functionality in modern science and technology. Although there has been remarkable progress in the precision of such measurements with various laser ranging methods1,2,3,4,5,6,7,8, they are incapable of capturing fast and complex mechanical displacements. Here, we have established a displacement measurement method using time-of-flight detection9 with femtosecond optical pulses and frequency-locked electrical waveforms. This method uniquely combines ultrafast measurement speed, sub-nanometre precision and non-ambiguity range of more than several millimetres. The achieved performance features unprecedented detection speed and precision. Starting from 24 nm precision for 4 ns acquisition time, the precision can reach 180 pm for 5 ms acquisition time. Using this method, we show real-time detection of single-event, fast and high-dynamic-range mechanical displacements. This capability can lead to the realization of new measurement and analysis platforms for studying broadband, transient and nonlinear mechanical dynamics in real time, which will be useful for directly probing optomechanics10, the onset of cracks11, dynamic deformations12, nonlinear vibrations13, ultrasonic phenomena14 and cell-generated forces15.

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Fig. 1: EOS-TD-based TOF detection method.
Fig. 2: Measurement precision analysis of the EOS-TD-based TOF detection method.
Fig. 3: EOS-TD-based TOF sensor demonstration results.
Fig. 4: EOS-TD-based real-time, nanometre-precision, dynamic displacement measurement results.

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Data availability

The data that support the plots within this paper and other findings of this study are available from the corresponding author upon reasonable request.


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This research was supported by the National Research Foundation of Korea (grant no. 2018R1A2B3001793). We thank Y. Song, J. Suh and Y.-J. Kim for discussions. We thank C.-S. Kang for providing gauge-block assemblies and discussions on the uncertainty analysis. We also thank K. Yu for providing the MEMS sample used for surface profile imaging.

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Authors and Affiliations



J.K. initiated and managed the project. J.K. and Y.N. conceived the main ideas and designed the experiments. Y.N. led the overall experiments. Y.N., C.-G.J., C.A., M.H. and D.K. performed the experiments and obtained data. Y.N., C.-G.J., J.S. and J.K. analysed the data. Y.N. and J.K. wrote the manuscript with input from all authors.

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Correspondence to Jungwon Kim.

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Two patents have been filed based on this work, with Korean patent application numbers 10-2019-0018203 and 10-2019-0018205.

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Supplementary Figs. 1–17 and Table 1.

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Na, Y., Jeon, CG., Ahn, C. et al. Ultrafast, sub-nanometre-precision and multifunctional time-of-flight detection. Nat. Photonics 14, 355–360 (2020).

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