Research ArticleAPPLIED PHYSICS

Ambient-condition growth of high-pressure phase centrosymmetric crystalline KDP microstructures for optical second harmonic generation

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Science Advances  26 Aug 2016:
Vol. 2, no. 8, e1600404
DOI: 10.1126/sciadv.1600404

Figures

  • Fig. 1 High-quality self-assembled single-crystalline KDP hexagonal hollow-core microstructures.

    (A) Low-resolution SEM images showing a high-quality scalene hexagonal hollow-core microstructure with a large length-to-diameter ratio. (B) High-resolution SEM images showing the shapes, smooth surfaces, and wall thickness of the microstructures.

  • Fig. 2 XRD spectra and molecular structures of tetragonal and monoclinic crystal phase KDP samples.

    Red trace: XRD spectrum of powder of commonly used tetragonal phase (bulk) KDP crystal (inset: molecular structure and packing arrangement). Blue trace: XRD spectrum of a small sample of single-crystal monoclinic-phase KDP microstructures showing a characteristic XRD pattern substantially different from the usual tetragonal-phase KDP crystal (inset: molecular structure and packing arrangement).

  • Fig. 3 Reciprocal lattice and Laue diffraction pattern of single-crystalline KDP.

    (A) (0kl) plane of tetragonal KDP crystal and the corresponding Laue diffraction pattern (shown for [001]). (B) (0kl) plane of a monoclinic single-crystalline KDP microstructure and the corresponding Laue diffraction pattern (shown for [001]; data taken from single-crystal diffractometer). (C) (hk0) plane showing the presence of TC lattice (see below the image) in monoclinic single-crystalline KDP microstructures, which breaks the inversion symmetry of the system, resulting in the observed strong SHG.

  • Fig. 4 Guided-wave propagation in a single-crystalline KDP hexagonal microstructure.

    (A and B) SHG intensity distribution across the exit facet of (A) a hollow-core microtube (nominal diameter, 15 μm; wall thickness, 3 μm) and (B) a solid-core microrod (nominal diameter, 25 μm). Note that the SHG light fills the entire solid core, indicating a transversely confined bulk SHG effect. Typically, the yield of solid-core structures is a factor of three to five times higher SHG than that of the hollow-core structures. (C) Very weak 532-nm light is transversely focused on the left end of a microstructure. (D) CCD image captured above the sample showing no leakage light for a large segment of the microstructure (the small green spot in the middle is from the microstructure holder). At the right end, a bright light spot represents the light propagated through the microstructure by guided mode, vividly demonstrating efficient guided-wave propagation.

  • Fig. 5 Global quasi–type I phase-matched guided-wave SHG in single-crystalline KDP hexagonal microstructures with a robust polarization-maintaining effect.

    (A and B) SHG power Embedded Image(2ω) as a function of the pump power Embedded Image(ω) from microstructures of (A) d = 15 μm and L = 1 mm, and (B) d = 25 μm and L = 1.1 mm. The blue curve in (A) is the fit using Embedded Image(2ω) = C22Embedded Image2(ω). (C) Linear polarization of the pump laser. (D) Polarization measurement of the residual 1064-nm pump at the exit of the microstructure. (E) Polarization measurement of the SHG at the exit of the microstructure. The orthogonal polarizations between the pump and SHG light at the exit indicate this as a type I phase-matched SHG generation process with guided-mode propagation of the SHG light.

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