Xu Zuyan

Multiple Nodeless Superconducting Gaps in (Ba0.6K0.4)Fe2As2 Superconductor from Angle-Resolved Photoemission Spectroscopy

Lin Zhao, Haiyun Liu, Wentao Zhang, Jianqiao Meng, Xiaowen Jia, Guodong Liu, Xiaoli Dong, G. F. Chen, J. L. Luo, N. L. Wang, W. Lu, Guiling Wang, Yong Zhou, Yong Zhu, Xiaoyang Wang, Zuyan Xu, Chuangtian Chen, and X. J. Zhou National Laboratory for Superconductivity, Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China Key Laboratory for Optics, Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing 100190, China (Dated: July 13, 2008)

Pseudogap and Superconducting Gap in Sm FeAs(O1-xFx) Superconductor from Photoemission Spectroscopy

High resolution photoemission measurements are carried out on non-superconducting SmOFeAs parent compound and superconducting SmFeAs(O1-xFx) (x = 0.12, and 0.15) compounds. The momentum-integrated spectra exhibit a clear Fermi cutoff that shows little leading-edge shift in the superconducting state. A robust feature at 13meV is identified in all these samples. Spectral weight suppression near Ef with decreasing temperature is observed in both undoped and doped samples that points to a possible existence of a pseudogap in these Fe-based compounds.

Deep ultraviolet harmonic generation with KBe2BO3F2 crystal

A special prism coupling technique with the KBe2BO3F2 crystal is adopted to produce deep ultraviolet light including the fourth harmonic from an Nd:YAG laser, for which a conversion efficiency as high as 10% has been obtained.

Efficient 266 nm Ultraviolet Beam Generation in K2Al2B2O7 Crystal

The ultraviolet beam at 266 nm was obtained by fourth harmonic generation of 1064 nm Nd:YAG laser radiation through a nonlinear crystal K2Al2B2O7 (KABO). The fundamental frequency of a flash-lamp pumped Nd:YAG laser was doubled in a β-Ba2B2O4 crystal to generate a second harmonic output at the wavelength of 532 nm, and then doubled again in the KABO crystal to generate the fourth harmonic output at 266 nm. The optical conversion efficiency from 532 to 266 nm was investigated for the first time, and 13% was achieved.

106.5 W high beam quality diode-side-pumped Nd:YAG laser at 1123 nm

We demonstrate a diode-side-pumped continuous wave (CW) Nd:YAG laser at 1123 nm with over 100 Ws output power and good beam quality. The resonator adopts convex-convex structure working in a thermally near unstable cavity. By precise coating design a single 1123 nm wavelength is delivered. Under the pumped power of 870 W, an output power of 106.5 W is obtained, corresponding to an optical-optical conversion efficiency of 12.2%. The beam quality of M(2) factor is measured to be 5.6. To the best of our knowledge, this is the highest output power with good beam quality for 1123 nm CW Nd:YAG laser.

Identification of Topological Surface State in PdTe2 Superconductor by Angle-Resolved Photoemission Spectroscopy*

High resolution angle-resolved photoemission measurements have been carried out on transition metal dichalcogenide PdTe2 that is a superconductor with a Tc at 1.7 K. Combined with theoretical calculations, we have discovered for the first time the existence of topologically nontrivial surface state with Dirac cone in PbTe2 superconductor. It is located at the Brillouin zone center and possesses helical spin texture. Distinct from the usual three-dimensional topological insulators where the Dirac cone of the surface state lies at the Fermi level, the Dirac point of the surface state in PdTe2 lies deep below the Fermi level at ~1.75 eV binding energy and is well separated from the bulk states. The identification of topological surface state in PdTe2 superconductor deep below the Fermi level provides a unique system to explore for new phenomena and properties and opens a door for finding new topological materials in transition metal chalcogenides.

33 W quasi-continuous-wave narrow-band sodium D-2a laser by sum-frequency generation in LBO

We demonstrate an all-solid quasi-continuous-wave (QCW) narrow-band source tunable to sodium D-2a line at 589.159 nm. The source is based on sum-frequency mixing between lasers at 1064 nm and 1319 nm in a LBO crystal. The 1064 nm and 1319 nm lasers are produced from two diode side-pumped Nd:YAG master oscillator power amplifier (MOPA) laser systems, respectively. A 33 W output of 589 nm laser is obtained with beam quality factor M-2 = 1.25, frequency stability better than +/- 0.2 GHz and linewidth less than 0.44 GHz. A prototype 589 nm laser system is assembled, and a sodium laser guided star has been successfully observed in the field test.

High-average-power third harmonic generation at 355 nm with CsB3O5 crystal

A 17.7 W average power output at 355 nm by the third harmonic generation (THG) of 1064 nm light has been obtained with the nonlinear optical crystal CsB3O5 (CBO). The fundamental light source is a diode-pumped Nd:YAG laser with a pulse duration of 70 ns and a repetition rate of 7 kHz. A CBO crystal cut for type-II PM angles is used in the experiment. The THG energy conversion efficiency with CBO is twice as large as that with LBO. As a THG crystal, CBO has better performance than that of LiB3O5 crystal (LBO).

Determination of Nonlinear Optical Coefficients of KBe2BO3F2 Crystals

Considering that KBe2BO3F2 (KBBF) is an outstanding deep ultraviolet crystal which can generate the shortest wavelengths in second harmonic generation and sum-frequency generation, we report the determination of the nonlinear optical coefficients of the KBBF crystal. The d11 coefficient was determined to be 0.49 pm/V by the Maker fringes method at the wavelength 1064 nm, which is in agreement well with the theoretical value.

Fermi Surface and Band Structure of (Ca,La)FeAs2 Superconductor from Angle-Resolved Photoemission Spectroscopy

The (Ca,R)FeAs2 (R=La, Pr, etc.) superconductors with a signature of superconductivity transition above 40 K possess a new kind of block layers that consist of zig-zag As chains. We report the electronic structure of the new (Ca,La)FeAs2 superconductor investigated by both band structure calculations and high resolution angle-resolved photoemission spectroscopy measurements. Band structure calculations indicate that there are four hole-like bands around the zone center Γ(0,0) and two electron-like bands near the zone corner M(π, π) in CaFeAs2. In our angle-resolved photoemission measurements on (Ca0.9La0.1)FeAs2, we have observed three hole-like bands around the Γ point and one electron-like Fermi surface near the M(π, π) point. These results provide important information to compare and contrast with the electronic structure of other iron-based compounds in understanding the superconductivity mechanism in the iron-based superconductors.