PhotoniX, Volume. 4, Issue 1, 27(2023)

Confocal nonlinear optical imaging on hexagonal boron nitride nanosheets

Gwanjin Lee1, Konkada_Manattayil Jyothsna2, Jonghoo Park3, JaeDong Lee1, Varun Raghunathan2, and Hyunmin Kim4,5、*
Author Affiliations
  • 1Department of Physics and Chemistry, DGIST, DGIST, Daegu 42988, Republic of Korea
  • 2Department of Electrical Communication Engineering, Indian Institute of Science, Indian Institute of Science Bangalore, India
  • 3School of Electronics Engineering, Kyungpook National University, Kyungpook National University, Daegu 41566, Republic of Korea
  • 4Division of Biotechnology, DGIST, DGIST, Daegu 42988, Republic of Korea
  • 5Department of Interdisciplinary Engineering, DGIST, DGIST, Daegu 42988, Republic of Korea
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    Optical microscopy with optimal axial resolution is critical for precise visualization of two-dimensional flat-top structures. Here, we present sub-diffraction-limited ultrafast imaging of hexagonal boron nitride (hBN) nanosheets using a confocal focus-engineered coherent anti-Stokes Raman scattering (cFE-CARS) microscopic system. By incorporating a pinhole with a diameter of approximately 30 μm, we effectively minimized the intensity of side lobes induced by circular partial pi-phase shift in the wavefront (diameter, d0) of the probe beam, as well as nonresonant background CARS intensities. Using axial-resolution-improved cFE-CARS (acFE-CARS), the achieved axial resolution is 350 nm, exhibiting a 4.3-folded increase in the signal-to-noise ratio compared to the previous case with 0.58 d0 phase mask. This improvement can be accomplished by using a phase mask of 0.24 d0. Additionally, we employed nondegenerate phase matching with three temporally separable incident beams, which facilitated cross-sectional visualization of highly-sample-specific and vibration-sensitive signals in a pump-probe fashion with subpicosecond time resolution. Our observations reveal time-dependent CARS dephasing in hBN nanosheets, induced by Raman-free induction decay (0.66 ps) in the 1373 cm-1 mode.

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    Gwanjin Lee, Konkada_Manattayil Jyothsna, Jonghoo Park, JaeDong Lee, Varun Raghunathan, Hyunmin Kim. Confocal nonlinear optical imaging on hexagonal boron nitride nanosheets[J]. PhotoniX, 2023, 4(1): 27

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    Paper Information

    Category: Research Articles

    Received: Jan. 8, 2023

    Accepted: Aug. 2, 2023

    Published Online: Sep. 18, 2023

    The Author Email: Kim Hyunmin (hyunmin.kim@dgist.ac.kr)

    DOI:10.1186/s43074-023-00103-6

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