Mode-locking fiber laser with dual wavelength continuous-waves-induced resonant spectral sidebands.

The optical spectrum of mode-locked lasers can exhibit multiple peaks resulting from different mechanisms such as modulation instability, dispersive waves (DWs), and coupling between continuous waves (CWs) and DWs. The latter was recently reported in a mode-locked fiber laser. Here we show that besides the coupling between single-wavelength CW and DWs, dual-wavelength CWs can also couple with DWs giving rise to quite different spectral peaks in a mode-locked fiber laser. In particular, we find that the sidebands of one CW can couple with the other CW, leading to an enhancement of the CWs.

Improved dispersion of SiC whisker in nano hydroxyapatite and effect of atmospheres on sintering of the SiC whisker reinforced nano hydroxyapatite composites.

In order to improve the mechanical properties of nano hydroxyapatite (HA), silicon carbide whisker (SiCw) with excellent mechanical and biological properties was used as the reinforcement for SiC whisker reinforced nano hydroxyapatite (SiCw/HA) composites. Hydrothermal synthesis method was adopted to prepare the uniformly dispersed SiCw and HA composite powders, and SiCw/HA composites were fabricated by pressureless sintering. The interfacial bonding state and mechanical properties of SiCw/HA composites in different sintering atmospheres (air and N2) were systematically investigated. The results show that the uniformity of the composite powders decreases with the increase of SiCw content, and the cross-section of SiCw/HA composites gradually changes from glossy and smooth to rough and undulate. When the content of SiCw is 15 wt%, the maximum bending strength and fracture toughness of the composites sintered in air atmosphere (HAW15) are 40.85 MPa and 1.82 MPa·m1/2 respectively, which are higher than those of pure HA. Compared with those of the SiCw/HA composites sintered in N2 atmosphere, the bending strength and fracture toughness of the HAW15 composites are increased by 154.2% and 10.3%, respectively. Moreover, Simulated body fluid (SBF) and in vitro cell behavior tests indicate that the SiCw/HA composites still have excellent bioactivity. The possible strengthening and toughening mechanisms of SiCw/HA composites are that the dispersion of SiCw in HA matrix is improved by hydrothermal process, and the interfacial bonding property is enhanced because of the reaction fusion on interface of SiCw/HA composites during sintering in air atmosphere. The adoption of hydrothermal process improves the dispersion uniformity of SiCw in HA matrix. When sintering in air atmosphere, the interfacial bonding property of SiCw/HA composite is enhanced via the reaction fusion (SiO2 is formed by the oxidation of SiCw). Both of them lead to the increase of strength and toughness of the composites. This study would provide additional insights into the feasibility of SiCw/HA composites as load-bearing implant materials in orthopedic applications.

Design and fabrication of carbon fibers with needle-like nano-HA coating to reinforce granular nano-HA composites.

Carbon fibers (CFs) with needle-like nano-hydroxyapatite (nHA) coating were first used as reinforcing materials named nHA-CFs to improve the mechanical properties of pure HA. A powder mixture containing nHA-CFs and granular nano-HA (gHA) was directly sintered by hot pressing at appropriate sintering pressure and temperature. A three-phase nHA-CFs/gHA composite was designed, fabricated, and used as an artificial bone. Results show that the bending strengths of the nHA-CFs/gHA composite are approximately 41.1% and 59.2% higher than those of CFs/gHA composite and pure HA, respectively. The possible reinforcing mechanism of nHA-CFs in the composite is also proposed at the end. When nHA-CFs are applied for preparation of nHA-CFs/gHA composites, the internal stress on its phase boundary with gHA matrix generated during cooling of sintered is significantly reduced due to the presence of the nHA coatings. It infers that nHA coatings on CFs might act as a bridge to control the forming of interfacial gaps between the gHA matrix and the CFs effectively. Our work provides additional insights into the feasibility of nHA-CFs/gHA composites as load-bearing implant materials in clinical applications.

Controllable preparation of a nano-hydroxyapatite coating on carbon fibers by electrochemical deposition and chemical treatment.

A nano-hydroxyapatite (HA) coating with appropriate thickness and morphology similar to that of human bone tissue was directly prepared onto the surfaces of carbon fibers (CFs). A mixed solution of nitric acid, hydrochloric acid, sulfuric acid, and hydrogen peroxide (NHSH) was used in the preparation process. The coating was fabricated by combining NHSH treatment and electrochemical deposition (ECD). NHSH treatment is easy to operate, produces rapid reaction, and highly effective. This method was first used to induce the nucleation and growth of HA crystals on the CF surfaces. Numerous O-containing functional groups, such as hydroxyl (-OH) and carboxyl (-COOH) groups, were grafted onto the CF surfaces by NHSH treatment (NHSH-CFs); as such, the amounts of these groups on the functionalized CFs increased by nearly 8- and 12-fold, respectively, compared with those on untreated CFs. After treatment, the NHSH-CFs not only acquired larger specific surface areas but retained surfaces free from serious corrosion or breakage. Hence, NHSH-CFs are ideal depositional substrates of HA coating during ECD. ECD was successfully used to prepare a nano-rod-like HA coating on the NHSH-CF surfaces. The elemental composition, structure, and morphology of the HA coating were effectively controlled by adjusting various technological parameters, such as the current density, deposition time, and temperature. The average central diameter of HA crystals and the coating density increased with increasing deposition time. The average central diameter of most HA crystals on the NHSH-CFs varied from approximately 60 nm to 210 nm as the deposition time increased from 60 min to 180 min. Further studies on a possible deposition mechanism revealed that numerous O-containing functional groups on the NHSH-CF surfaces could associate with electrolyte ions (Ca(2+)) to form special chemical bonds. These bonds can induce HA coating deposition and improve the interfacial bonding strength between the HA coating and NHCH-CFs. The results of this study and the proposed preparation of uniform and dense nano-HA coating provide theoretical and practical guidance for future investigations of active HA coatings on fiber materials for medical products and implants. This work also lays the foundation for the wider use of HA-coated CFs/HA composite implants in clinical application.