J Wang

Flocculation behavior and mechanism of an exopolysaccharide from the deep-sea psychrophilic bacterium Pseudoalteromonas sp. SM9913

Flocculation behavior and mechanism of the exopolysaccharide secreted by Pseudoalteromonas sp. SM9913 (EPS SM9913), a psychrophilic bacterium isolated from 1855m deep-sea sediment, has been studied in this paper. EPS SM9913 showed a peak flocculating activity of 49.3 in 1g/L kaolin suspension with 4.55mmol/L CaCl2 and the optimum pH range of 5-8. It appears that the flocculating activity of EPS SM9913 was stimulated by Ca2+ and Fe2+. This study found that EPS SM9913 showed a better flocculation performance than Al2(SO4)3 at salinity of 5-100 per thousand or temperatures of 5-15 degrees C. In addition, this EPS was effective to flocculate several other suspended solids. The measured zeta-potentials, the size of flocs formed during the flocculation process and the surface profile of flocs revealed by scan electron micrograph suggest that bridging is the main flocculation mechanism of the studied EPS. Deacetylation of EPS SM9913 resulted in a significant decrease in its flocculating activity indicating that the large number of acetyl groups in EPS SM9913 played an important role in its flocculation performance.

Passively Q-switched fiber laser based on graphene saturable absorber

A passively graphene Q-switched Erbium doped fiber laser around 1.5 μm is demonstrated in this paper. The graphene saturable absorber was fabricated by sandwiching a thin graphene film produced via chemical vapor deposition between two FC fiber connectors. Stable pulse trains were obtained with the pulse repetition rate varying between 34.72 and 53.2 kHz and the average output power ranging from 0.504 mW to 0.926 mW. The achieved shortest pulse duration and highest pulse energy were 3.2 μs and 17.41 nJ, respectively.

Tunable femtosecond laser based on the Nd3+:BaLaGa 3O 7 disordered crystal

We demonstrate clear inhomogeneous linewidth broadening for the disordered laser crystal Nd:BaLaGa3O7 (Nd:BLG), which is very promising for the replacement of Nd:glass for ultrafast sources in multiwatt power applications. A Nd:BLG laser oscillator passively mode-locked and pumped by a Ti:sapphire laser generated pulses of 316-fs duration at 1060?nm, whose spectrum completely fills the fluorescence peak at such wavelength. More interestingly, sub-picosecond pulses were smoothly tunable in a 20-nm range, from 1070 to 1090?nm. The shortest pulses achieved were 290?fs long, centered at 1075?nm.

378 fs pulse generation with Nd3+:SrLaGa3O7 (Nd:SLG) disordered crystal

In this work we present femtosecond pulse generation with a disordered Nd:SLG crystal. By pumping with a Ti:sapphire laser tuned at 808 nm, we obtained pulses as short as 378 fs in a single-dispersive prism resonator employing a semiconductor saturable absorber mirror (SESAM) for mode-locking. Furthermore, sub-picosecond pulses were generated in the 1060–1083 nm spectral range.

Stimulated Raman scattering spectroscopy of Y0.4Gd0.6VO4 crystals with partly disordered zircon-type structure—observation of new χ(3)-nonlinear optical interactions

This letter presents the results of stimulated Raman scattering (SRS) spectroscopy of tetragonal Y0.4Gd0.6VO4 vanadate crystals having a partly disordered zircon-type structure. Picosecond laser pumping revealed previously unexplored χ(3)-nonlinear interactions comprising the generation of an almost two-octave spanning Stokes and anti-Stokes frequency comb, self-third harmonic generation as well as cross-cascaded processes involving four different Raman-active modes. The recorded spectral lines have been assigned to the participating molecular vibrational modes of the (VO4)3− structural units of the studied crystal. In addition, this work provides a brief review of all known SRS-active tetragonal and monoclinic vanadates of the form REVO4 including their χ(3)-nonlinear properties and steady-state Raman gain coefficients for first Stokes generation.

Investigation of pulse splitting behaviour in a dissipative soliton fibre laser

Pulse splitting in a dissipative soliton fibre laser taking the nonlinear polarization evolution (NPE) rejection port as the output is investigated. Both numerical and experimental results show that with enhancement of the NPE effect, the pulse and its spectrum from the rejection port will split into two parts, which are the wings of the intra-cavity circulating pulse. It is consistent with what we expect from nonlinear polarization rotation acting on the pulse. However, to the best of our knowledge, this is the first systematic report on this phenomenon. Numerical simulation results show that when the output pulse splits into two sub-pulses, the evolution of the intra-cavity pulse is totally different from the case in which the rejected pulse has a high-quality intensity profile.

Monoclinic m-LaVO4—a novel high Raman gain SRS-active crystal

Monoclinic m-LaVO4, having a monazite-type structure and being known as a host crystal for Nd3+-lasants, is an attractive χ(3)-nonlinear optical material for Raman laser converters. This paper presents the stimulated Raman scattering (SRS) spectroscopy of m-LaVO4 in the visible and near-IR spectral range using picosecond laser excitation. High-order SRS and Raman-induced four-wave parametric mixing processes result in an almost two-octave-wide Stokes and anti-Stokes frequency comb. All the measured spectral lines were assigned to the participating molecular vibration modes of the studied vanadate. Finally, an estimation of the steady-state Raman gain coefficient for first Stokes generation in near-IR was performed.

Monoclinic β-BaY2F8—a novel crystal simultaneously active for SRS and Ln3+-ion lasing

This paper presents the first investigation of stimulated Raman scattering (SRS) in the monoclinic fluoride crystal β-BaY2F8, which is known as a promising host-material for trivalent lanthanide (Ln3+) lasant ions. Picosecond laser excitation in the visible and near-IR spectral range at room temperature revealed the manifestation of nine SRS-promoting phonon modes, which are related to Ag and Bg vibrations of the crystal. Besides multi-phonon Stokes and anti-Stokes generation, we observed cross-cascaded χ(3) ↔ χ(3) processes involving different pairs of SRS-active phonons. A comparative estimation of the first Stokes steady-state Raman gain coefficients, both in the visible and near-IR region related to the most active SRS-phonon mode ωSRS1 ≈ 208 cm−1 of β-BaY2F8, was also performed. Furthermore, a brief review of the pioneering papers on laser action of Ln3+-ions doped in β-BaY2F8 single crystals and other known SRS-active fluoride crystals is given in tabular form.

Continuous-wave laser performance of Tm:LuVO4 under Ti:sapphire laser pumping

We investigate the cw laser performance of Tm:LuV O4 crystals pumped with tunable polarized source and report a roughly twofold improvement to their efficiency with 1 W of output power and broad tunability at room temperature.

Preparation and characteristics of gelcast RBSC–B4C composite

Abstract The preparation and mechanical properties of silicon infiltrated SiC–B4C composite were studied in the present work. Gelcasting process was adopted to obtain green bodies with uniformity and compaction. The gelation behaviour of the slurry was controlled by introducing the polymerisation inhibitor mixture and the gelation reaction was delayed to about 10 min with increasing B4C content from 20 to 40%. Mechanical properties of the SiC–B4C sintered samples were tested and the results showed that increasing B4C content led to an increase in bending strength, fracture toughness and hardness. Microstructure investigation revealed that the SiC–B4C composites showed less content of free silicon and finer grains comparing to RBSC ceramics.