Speaker: Professor Lu Deng，National Institute of Standards and Technology, NIST

Time: 14:00 pm,  October 15, 2018 for talk 1 and 14:00 pm,  October 17, 2018 for talk 2

Venue：Yizhi Hall (West Campus)

Biography:

    Dr. Lu Deng received his BS degree in theoretical particle physics from USTC in China in 1982 and Ph.D. in nuclear physics and optical physics in 1989 from Baylor University in 1989 under a full scholarship. He was a Petroleum Research Fund Fellow (University of California, Davis) and US Department of Energy ORAU/ORIES Fellow (US DOE Oak Ridge National Laboratory) in early and mid 1990s'. He worked with two 1997 Nobel Laureates Prof. Steven Chu (in 1990, Stanford University) and Dr. William Phillips (1997-2000, NIST). He joined NIST in 1997 and has co-authored more than 125 research papers in the past 24 years including 3 in Science, 1 in Nature (cover illustration), 2 in SCIENCE ADVANCES (equivalent to the combination of Nature Physics and Nature Communications) and more than 20 in PRL. He was instrumental in developing NIST's first sodium BEC and has contributed significantly to the first rubidium BEC setup in China. He has been actively contributing to the cold atom physics community in China since 1999. He was a recipient of OSA 2002 Archie Machan Prize and NIST 2002 E.U. Condon Award for his contribution to BEC research. Recent most notable ground breaking research include discovery of a new nonlinear optical crystal thought to not exist under ambient conditions (SCIENCE ADVANCES), matter-wave induced optical wave transparency (PRL Editors' suggestion), novel nonlinear optical atomic magnetometry technology (SCIENCE ADVANCES). Since 2009 he pioneered a new research field in cold atom physics, i.e., Nonlinear Optics with Quantum Gases, that opens a new chapter to the matured field of nonlinear and quantum optics.

Abstract:

    1，Symmetry-breaking inelastic wave-mixing atomic magnetometry    

    The nonlinear magneto-optical rotation (NMOR) effect has prolific applications ranging from precision mapping of Earth’s magnetic field to biomagnetic sensing. Studies on collisional spin relaxation effects have led to ultrahigh magnetic field sensitivities using a single-beam Λ scheme with state-of-the-art magnetic shielding/compensation techniques. However, the NMOR effect in this widely used single-beam Λ scheme is peculiarly small, requiring complex radio-frequency phase-locking protocols. We show the presence of a previously unknown energy symmetry–based nonlinear propagation blockade and demonstrate an optical inelastic wave-mixing NMOR technique that breaks this NMOR blockade, resulting in an NMOR optical signal-to-noise ratio (SNR) enhancement of more than two orders of magnitude never before seen with the single-beam Λ scheme. The large SNR enhancement was achieved simultaneously with a nearly two orders of magnitude reduction in laser power while preserving the magnetic resonance linewidth. This new method may open a myriad of applications ranging from biomagnetic imaging to precision measurement of the magnetic properties of subatomic particles.    

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

    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 mm3. A robust polarization-preserving effect is also observed, raising the possibility of advanced optical technological applications.