title: Ambient-condition growth of high-pressure phase centrosymmetric crystalline KDP microstructures for optical second harmonic generation.
abstract: Noncentrosymmetric potassium dihydrogen phosphate (KH2PO4 or KDP) in the tetragonal crystal phase is arguably the most extensively studied nonlinear optical crystal in history. It has prolific applications ranging from simple laser pointers to laser inertial confinement fusion systems. Recently, type IV high-pressure KDP crystal sheets with a monoclinic crystal phase having centrosymmetric properties have been observed. However, it was found that this new crystal phase is highly unstable under ambient conditions. We report ambient-condition growth of one-dimensional, self-assembled, single-crystalline KDP hexagonal hollow/solid-core microstructures that have a molecular structure and symmetry identical to the type IV KDP monoclinic crystal that was previously found to exist only at extremely high pressures (>1.6 GPa). Furthermore, we report highly efficient bulk optical second harmonic generation (SHG) from these ambient condition-grown single-crystalline microstructures, even though they have a highly centrosymmetric crystal phase. However, fundamental physics dictates that a bulk optical medium with a significant second-order nonlinear susceptibility supporting SHG must have noncentrosymmetric properties. Laue diffraction analysis reveals a weak symmetry-breaking twin-crystal lattice that, in conjunction with tight confinement of the light field by the tubular structure, is attributed to the significant SHG even with sample volumes <0.001 mm(3). A robust polarization-preserving effect is also observed, raising the possibility of advanced optical technological applications.
authors: State Key Laboratory of Crystal Materials, Shandong University, Jinan 250100, P. R. China.
authors: Yan
authors: Y
authors: Ren
authors: State Key Laboratory of Crystal Materials, Shandong University, Jinan 250100, P. R. China.
authors: Xian
authors: 0000-0003-2003-8076
authors: X
authors: Zhao
authors: National Institute of Standards and Technology, Gaithersburg, MD 20899, USA.
authors: Edward W
authors: EW
authors: Hagley
authors: National Institute of Standards and Technology, Gaithersburg, MD 20899, USA.
authors: Lu
authors: L
authors: Deng
mesh_terms: D003460:Crystallization; D007834:Lasers; D015394:Molecular Structure; D017711:Nonlinear Dynamics; D010710:Phosphates / Q000737:chemistry*; D017680:Potassium Compounds / Q000737:chemistry*; D011312:Pressure; D017550:Spectroscopy, Fourier Transform Infrared; D013818:Thermogravimetry; D014961:X-Ray Diffraction
chemical_list: D010710:Phosphates; D017680:Potassium Compounds; C013216:potassium phosphate
keywords: Centrosymmetric; High-pressure; Potassium Di-hydrogen Phosphate; Second harmonic generation; crystal growth; microstructures; one-dimensional; self-assembly