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Multiple synthetic beacons are required for atmospheric-turbulence compensation in an extended-field-of-view multi-conjugate adaptive optics (MCAO) telescope. In this paper, we report on the first successful implementation of a microsecond-pulse sodium guidestars constellation laser system, based on a small angle precise polarized combining and splitting technology. At Lijiang Observatory of China, four-ways ∼20 W yellow laser beam with kHz repetition-rate and hundred- μ s pulse width were projected into the sky through one small-aperture launching telescope, and generated a distinctive four-point grouping on a field of view of 40″ with variable configurations of linear, parallelogram, rhomboid and square. The sodium return signal could easily avoid Rayleigh light interference by the pulse synchro controlling technology delivering a higher spatial resolution. Moreover, the increase in return photons for alternated circularly and alternated linearly polarized light has been investigated. We believe that the above results could serve as a future reference for the MCAO system on large-aperture telescopes worldwide. [ABSTRACT FROM AUTHOR]

We demonstrated a high-peak-power acousto-optic Q-switched Nd:YAG laser emitting at 1338 nm. The resonator adopted a symmetrical convex-convex cavity with a two-rod configuration, which is side-pumped by a $\mu $ s long pulse laser diode. At the beginning, the free running mode and Q-switched mode operated with single-wavelength emission at 1319 nm and dual-wavelength emission at 1319 and 1338 nm, respectively. By means of using a 8 mm-thick birefringence filter to increase the intra-cavity loss at 1319 nm, single wavelength operation of 1338 nm was achieved with spectral width of 0.31 nm. Under the pump power of 390 W, the Q-switched laser delivers 28.7 W of average output power with an optical conversion efficiency of 7.4%. The pulse width was measured to be 124 ns with a repetition rate of 400 Hz, and the corresponding peak power is up to 0.58 MW. [ABSTRACT FROM AUTHOR]

High temperature superconductivity in cuprates is realized by doping the Mott insulator with charge carriers. A central issue is how such an insulating state can evolve into a conducting or superconducting state when charge carriers are introduced. Here, by in situ vacuum annealing and Rb deposition on the Bi2Sr2Ca0.6Dy0.4Cu2O8 + δ (Bi2212) sample surface to push its doping level continuously from deeply underdoped (Tc = 25 K, doping level p ∼ 0.066) to the near-zero doping parent Mott insulator, angle-resolved photoemission spectroscopy measurements are carried out to observe the detailed electronic structure evolution in the lightly hole-doped region for the first time. Our results indicate that the chemical potential lies at about l eV above the charge transfer band for the parent state at zero doping, which is quite close to the upper Hubbard band. With increasing hole doping, the chemical potential moves continuously towards the charge transfer band and the band structure evolution exhibits a rigid band shift-like behavior. When the chemical potential approaches the charge transfer band at a doping level of ∼0.05, the nodal spectral weight near the Fermi level increases, followed by the emergence of the coherent quasiparticle peak and the insulator–superconductor transition. Our observations provide key insights in understanding the insulator–superconductor transition in doping the parent cuprate compound and for establishing related theories. [ABSTRACT FROM AUTHOR]

We report a continuous-wave end-pumped Nd:YVO4 zigzag slab laser with multilayer amplified spontaneous emission (ASE) absorbing coatings. The coatings are deposited on the slab faces. A five-layer structure consists of SiO2-Ti-SiO2-Ti-Au, and the thicknesses are 2520 nm, 10 nm, 160 nm, 24 nm and 200 nm, respectively. The designed coatings show good performance for the ASE control in the experimental tests. A stable-unstable hybrid laser oscillator along orthogonal directions in the slab aperture is further configured, achieving the 117W output at a pump of 328 W. The beam quality factors M2 in the unstable direction and stable direction are 1.57 and 1.66, respectively. [ABSTRACT FROM AUTHOR]

Spectral beam combining is an effective way to achieve high-brightness direct diode laser output. We present an experimental study on spectral beam combining with external cavity based on transmission grating. Using a series of cylindrical transform lenses with different focal lengths, spectral beaming combining efficiency is greatly improved, and the results of wavelength intervals are consistent with the theoretical calculations. With the injection current of 90 A, a 75.1 W cw 930 nm output power with wavelength span of 18.6 nm and spectral beam combining efficiency of 92.7% is achieved, the beam parameter product is 5.77 mm⋅mrad. [ABSTRACT FROM AUTHOR]

We demonstrate a high power two-dimensional vertical-cavity surface-emitting laser (VCSEL) array cooled by liquid metal. An output power of 1.1 kW at 808 nm with 39% power conversion efficiency (PCE) is obtained under continuous-wave (CW) operation. To the best of our knowledge, this is the highest output power reported for a laser diode array with liquid metal cooling. Moreover, the wavelength drift is only 1.2 nm from lasing threshold to 1.1 kW output power. Using this laser diode array as pumping module, a solid-state Nd:YAG slab laser at 1064 nm reaches 312 W output power. This verifies that the laser diode array cooled by liquid metal can be used as a pumping source for high power lasers. The higher power scaling can be achieved by two-dimensional geometric extension to the macro-channel heat sink and increasing the flux of the liquid metal. [ABSTRACT FROM AUTHOR]

We briefly review recent results on photoemission spectroscopy based on the deep and vacuum ultraviolet diode pumped solid-state lasers which we have developed. Cascaded second harmonic generation with the nonlinear crystal KBe2BO3F2 (KBBF) is used to generate deep ultraviolet and vacuum ultraviolet laser radiation, which complements traditional incoherent light sources such as gas discharge lamps and synchrotron radiation, and has greatly improved resolution with respect to energy, momentum, and spin of photoemission spectroscopy. Many new functions have been developed with the advantages of high photon energy, narrow linewidth, high photon flux density, and so on. These have led to the observation of various new phenomena and the amassment of new data in the fields of high temperature superconductivity, topological electronics, Fermi semi-metals, and so forth. These laser systems have revived the field of photoemission spectroscopy and provided a new platform in this frontier research field. [ABSTRACT FROM AUTHOR]

We report a new approach to effectively improve the optical-to-optical efficiency for quasi-continuous-wave (QCW) lasers by adjusting the pump pulse duration. During our single-slab laser test, an optical-to-optical conversion efficiency of 57% and a slope conversion of 67.8% are obtained with a maximum average output power of 7.3 kW, operating at a pulse repetition rate of 160 Hz with 470- $\mu \text{s}$ pulse duration. To the best of our knowledge, this represents the highest optical-to-optical efficiency for a QCW face-pumped Nd:YAG slab laser with such high power output ever reported. [ABSTRACT FROM AUTHOR]

The multiwavelength characteristics of stimulated Raman scattering (SRS) in YVO4crystal excited by a picosecond laser at 1064nm are investigated theoretically and experimentally. Laser output with seven wavelengths is achieved coaxially and synchronously at 894, 972, 1175, 1312, 1486, 1713 and 2022nm in a YVO4crystal. The maximum total Raman output energy is as high as 2.77 mJ under the pump energy of 7.75 mJ. A maximum total Raman conversion efficiency of 47.8% is obtained when the pump energy is 6.54 mJ. This is the highest order of Stokes components and the highest output energy generated by YVO4reported up to date. This work expands the Raman spectrum of YVO4crystal to the near-IR regime, with seven wavelengths covered at the same time, paving the way for new wavelength generation in the near-IR regime and its multiwavelength application. [ABSTRACT FROM AUTHOR]

We briefly review the main methods for generating deep ultraviolet (DUV) or vacuum ultraviolet (VUV) light sources, and describe in detail our progress in the design and development of precise and practical DUV all-solid-state lasers based on second harmonic generation. Their incorporation into various kinds of advanced analytic instruments is also discussed. Already, many significant results have been obtained and new phenomena discovered with these state-of-the-art tools. In the last part, we look at possible future developments in the field of DUV/VUV all-solid-state lasers and their potential applications in an even broader range of research fields. [ABSTRACT FROM AUTHOR]

In this letter, a high pulse energy and high beam quality 819.7 nm Ti:sapphire laser pumped by a frequency-doubled Nd:YAG laser is demonstrated. At incident pump energy of 774 mJ, the maximum output energy of 89 mJ at 819.7 nm with a pulse width of 100 μs is achieved at a repetition rate of 5 Hz. To the best of our knowledge, this is the highest pulse energy at 819.7 nm with pulse width of hundred microseconds for a Ti:sapphire laser. The beam quality factor M is measured to be 1.18. This specific wavelength with the high pulse energy and high beam quality at 819.7 nm is a promising light source to create a polychromatic laser guide star together with a home-made 589 nm laser via exciting the sodium atoms in the mesospheric atmosphere. [ABSTRACT FROM AUTHOR]

A high-efficiency picosecond (ps) 532-nm green laser with high pulse energy and high peak power at 5-kHz repetition rate was demonstrated by second-harmonic generation (SHG) from a 1064-nm master oscillator power amplifier (MOPA). The MOPA was based on the Innoslab structure under diode directly pumping, producing 4.8-mJ, 25-ps fundamental laser at the repetition rate of 5 kHz after a three-stage Innoslab amplification system. With a pulse energy of 2.93 mJ in the fundamental and using a type I noncritically phase matched lithium triborate crystal, the pulse energy of SHG was up to 1.96 mJ per pulse with a pulse width of 18.9 ps, which corresponds to a peak power of 104 MW in the green and SH conversion efficiency as high as 67%. The SHG green beam quality factor was measured to be M^2 = 1.75 . [ABSTRACT FROM PUBLISHER]

A widely tunable picosecond midinfrared (MIR) optical parametric amplifier (OPA) with wavelength ranging from 6.4 to 11 \mu \textm based on the BaGa4Se7 crystal was demonstrated. The MIR OPA was pumped by a 30 ps 1064-nm Nd:YAG laser and injected by a KTiOPO4 (KTP)-based narrow-bandwidth widely tunable near-infrared seed. The wide spectral generation using type-I ( \texto\,\,\to \,\, \texte\,\,+\,\,\texte ) critically phase-matched parametric amplification in BaGa4 Se7 was investigated. The output energies were measured to be \sim 38~\mu \textJ at 11 \mu \textm and up to \sim 100~\mu \textJ at 6.4 \mu \textm under pumping energy of $\sim 4.1$ mJ. Further, the type-I phase-matching angles of BaGa4Se7 crystal for idler light generation in the range of 6.4–11 \mu \textm were experimentally measured and the discrepancy between the experiment and theoretical calculation was discussed. [ABSTRACT FROM PUBLISHER]

We report a high power high beam quality quasi-continuous-wave (QCW) diode-end-pumped Nd:YAG slab am-plifier at 1319nm. The strongest 1064 nm parasitic oscillation has been successfully suppressed by reasonable coating design. In a five-pass configuration, the amplifier yields a 42.3 W linearly polarized 1319nm output at repetition rate of 1 kHz with pulse duration of 75and beam quality factors of Mx² = 1.13 and My² = 2.16 in the orthogonal directions. The fluctuation of the amplifier output power is measured to be ±0.6 %. Furthermore, a computational model of QCW pulse amplification is employed to examine the amplification process. [ABSTRACT FROM AUTHOR]

High resolution laser-based angle-resolved photoemission measurements are carried out on Bi2Sr2CuO6+7δ super-conductor covering a wide doping range from heavily underdoped to heavily overdoped samples. Two obvious energy scales are identified in the nodal dispersions: one is the well-known 50-80 meV high energy kink and the other is <10meV low energy kink. The high energy kink increases monotonously in its energy scale with increasing doping and shows weak temperature dependence, while the low energy kink exhibits a non-monotonic doping dependence with its coupling strength enhanced sharply below TC. These systematic investigations on the doping and temperature dependence of these two energy scales favor electron-phonon interactions as their origin. They point to the importance in involving the electron-phonon coupling in understanding the physical properties and the superconductivity mechanism of high temperature cuprate superconductors. [ABSTRACT FROM AUTHOR]

A 785 nm diode-side-pumped high-power high-pulse-repetition-frequency Q-switched 2m Tm:YAG laser system is reported. Under a pump power of 1300 W, a 171.4 W average output power is achieved at a pulse repetition frequency of 10 kHz. To our knowledge, this is the highest average output power for a diode-pumped all solid-state Q-switched 2m Tm:YAG laser. The laser output corresponds to an optical-to-optical conversion efficiency of 13.3% and a slope efficiency of 18.9%. [ABSTRACT FROM AUTHOR]

This paper demonstrated a high power and high beam quality diode-pumped 1319-nm Nd:YAG master oscillator- power amplifier laser system. A thermally near-unstable resonator with four-rod birefringence compensation flat-flat cavity was adopted as the master oscillator. A solid etalon was inserted in the unidirectional ring resonator to compress the laser linewidth. Under a repetition rate of 500 Hz and pulse width of 160 μs, the master oscillator delivers an average output power of 16.8 W at 1319 nm with linear polarisation, beam quality factor M2 = 1.16 and linewidth of 3.2 GHz. A double-pass power amplifier with two amplifier stages was employed for higher power scaling and the output power was amplified to be 25.9 W with M2 = 1.43. [ABSTRACT FROM AUTHOR]

This paper investigates the scattering effect of domestic 0.5 at% ceramic Nd:YAG. An effective method has been utilized to measure the scattering and absorption coefficients. An end-pumped continuous wave (CW) Nd:YAG ceramic laser was also demonstrated. A maximum output power of 6.7 W at 1064 nm was obtained at an 808-nm pump power of 32.9 W. Conversion efficiency and slope efficiency have been achieved. This indicates that scattering has an important effect on the optical performance of ceramic Nd:YAG. [ABSTRACT FROM AUTHOR]

Presents information pertaining to the electronic properties of the compound cavity optical parametric oscillator (OPO). What the computational results showed; Comparison of the theoretical results with those of the experimental data from a compound-cavity OPO.

We develop a picosecond widely tunable laser in a deep-ultraviolet region from 175 nm to 210 nm, generated by two stages of frequency doubling of a 80-MHz mode-locked picosecond Ti:sapphire laser. A β-BaB2O4 walk-off compensation configuration and a KBe2BO3F2 prism-coupled device are adopted for the generation of second harmonic and fourth harmonics, respectively. The highest power is 3.72 mW at 193 nm, and the fluctuation at 2.85 mW in 130 min is less than -2%. [ABSTRACT FROM AUTHOR]

Tomographic imaging and three-dimensional reconstruction based on a high-gain picosecond optical parametric amplifier (OPA) is demonstrated. More than 40 dB intensity amplification of the image is achieved from the high-gain OPA. The images of various longitudinal positions of the target are extracted by the gated nature of the OPA, then a three-dimensional (3-D) surface topography of the target is reconstructed. The gated and high-gain property of the OPA allows tomographic optical imaging together with 3-D profile reconstruction of the target in turbid media. [ABSTRACT FROM AUTHOR]

High-resolution angle-resolved photoemission measurements are carried out on transition metal dichalcogenide PdTe2 that is a superconductor with a Tc at 1.7 K. Combined with theoretical calculations, we discover 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 deeply 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 deeply below the Fermi level provides a unique system to explore new phenomena and properties and opens a door for finding new topological materials in transition metal chalcogenides. [ABSTRACT FROM AUTHOR]

CuxBi2Se3 is a superconductor that is a potential candidate for topological superconductors. We report our laser-based angle-resolved photoemission measurement on the electronic structure of the CuxBi2Se3 superconductor, and a detailed magneto-resistance measurement in both normal and superconducting states. We find that the topological surface state of the pristine Bi2Se3 topological insulator remains robust after the Cu-intercalation, while the Dirac cone location moves downward due to electron doping. Detailed measurements on the magnetic field-dependence of the resistance in the superconducting state establishes an irreversibility line and gives a value of the upper critical field at zero temperature of ∼4000 Oe for the Cu0.3Bi2Se3 superconductor with a middle point Tc of 1.9K. The relation between the upper critical field Hc2 and temperature T is different from the usual scaling relation found in cuprates and in other kinds of superconductors. Small positive magneto-resistance is observed in Cu0.3Bi2Se3 superconductors up to room temperature. These observations provide useful information for further study of this possible candidate for topological superconductors. [ABSTRACT FROM AUTHOR]

The layered transition metal chalcogenides have been a fertile land in solid state physics for many decades. Various MX2-type transition metal dichalcogenides, such as WTe2, IrTe2, and MoS2, have triggered great attention recently, either for the discovery of novel phenomena or some extreme or exotic physical properties, or for their potential applications. PdTe2 is a superconductor in the class of transition metal dichalcogenides, and superconductivity is enhanced in its Cu-intercalated form, Cu0.05PdTe2. It is important to study the electronic structures of PdTe2 and its intercalated form in order to explore for new phenomena and physical properties and understand the related superconductivity enhancement mechanism. Here we report systematic high resolution angle-resolved photoemission (ARPES) studies on PdTe2 and Cu0.05PdTe2 single crystals, combined with the band structure calculations. We present in detail for the first time the complex multi-band Fermi surface topology and densely-arranged band structure of these compounds. By carefully examining the electronic structures of the two systems, we find that Cu-intercalation in PdTe2 results in electron-doping, which causes the band structure to shift downwards by nearly 16 meV in Cu0.05PdTe2. Our results lay a foundation for further exploration and investigation on PdTe2 and related superconductors. [ABSTRACT FROM AUTHOR]

We demonstrate an all-solid quasi-continuous-wave (QCW) narrow-band source tunable to sodium D2a 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 M2 = 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. [ABSTRACT FROM AUTHOR]

Optical superlattice Er:LiNbO[sub 3] was fabricated by inducing a periodic ferroelectric domain structure into the crystal during the growing process. Because of the combination of the nonlinear optical properties of LiNbO[sub 3] and the spectral properties of Er[sup 3+], the crystal can simultaneously emit the second harmonic light through quasi-phase matching and the green light through upconversion at room temperature. Pumped by infrared diode lasers, violet-and-green and blue-and-green light generation was demonstrated in two samples. The detailed absorption spectrum and emission spectrum of upconversion were measured. The possible physical mechanism was discussed. © 1998 American Institute of Physics. [ABSTRACT FROM AUTHOR]