Shikai Wang

Compositional dependence of the 1.8 μm emission properties of Tm3+ ions in silicate glass

The compositional dependence of the 1.8 μm emission properties of Tm3+ ion-doped lead silicate glasses is investigated. Judd–Ofelt parameters are calculated and their variation with different glass modifier ions is obtained. The Judd–Ofelt parameters increase with decreased modifier ionic radius. A large spontaneous emission probability and a large emission cross-section are found to be related with the strength of the modifier ion. Fluorescence spectra are analyzed using rate equations and compared with recorded data. The results are very close, indicating the reliability of this method. Non-radiative probability is deduced by fitting the fluorescence decay curve; it becomes smaller with increased ionic field strength. Energy transfer processes are studied using the extended overlap integral method.

Dermorphin-like immunoreactivity in guinea pig and rat stomach

Dermorphin is an opioid peptide containing one D-amino acid isolated from amphibian skin. We examined the presence of dermorphin-like immunoreactivity (DMP-IR) in mammalian brain and tissues using an antiserum developed in our own laboratory which works at a dilution of 1:120,000 for Radioimmunoassay (RIA) and can detect 2.1 pg of dermorphin. We were unable to find DMP-IR in guinea pig, rat and toad brain and rat and toad spinal cord either extracted with methanol or with HCl. The guinea pig and rat stomach contained significant amounts of DMP-IR (228.9 pg/mg protein and 97.5 pg/mg protein respectively) when extracted with HCl but not with methanol. The DMP-IR we detected in the stomach is not dermorphin per se. A single peak of DMP-IR was found on Sephadex G-25 gel filtration. When re-chromatographed on reverse phase HPLC, this peak of DMP-IR gave rise to three peaks of DMP-IR.

Watt-level Yb-doped silica glass fiber laser with a core made by sol-gel method

A Yb-doped silica glass fiber laser with a core made by sol-gel method is reported. The maximum power of 1.14 W is obtained with a pump power of 5.46 W at a wavelength of 976 nm. The slope efficiency is 34%. The refractive index fluctuation across the core is below 5×10-4 at a doping level of Yb 0.15 mol%, A2O3 4.0 mol%, and P2O5 2.0 mol%. High background attenuation of 6 dB/m at 1 053 nm limites the slope efficiency and maximum output power.

Ion-redistribution induced efficient upconversion in β-NaYF_4:20%Yb^3+,2%Er^3+ microcrystals with well controlled morphology and size

We develop an efficient green upconversion (UC) β-NaYF₄:20%Yb³⁺,2%Er³⁺ microcrystal with well controlled morphology and size by hydrothermal method using two different chelating agents of CIT and EDTA-2Na via a simple ion-exchange reaction. Importantly, the UC emission efficiency of newly developed CIT and EDTA-2Na β-NaYF₄:20%Yb³⁺,2%Er³⁺ microcrystals is almost as strong as that of commercial counterpart by solid-state method. A proof-of-concept β-NaYF₄:20%Yb³⁺,2%Er³⁺ microcrystal waveguide is demonstrated to extend their applications in modern micro-optoelectronics. The local ion-redistribution process during the ion-exchange reaction, which effectively disperses the locally clustered Yb³⁺, accounts for the enormously enhanced UC emission in β-NaYF₄:20%Yb³⁺,2%Er³⁺ microcrystals.

50 μm core diameter Yb³⁺Al³⁺/F⁻ codoped silica fiber with M²<1.1 beam quality.

This paper reports, for the first time to our best knowledge, a nearly diffraction-limited output in a Yb(3+)/Al(3+)/F(-) codoped double cladding silica fiber with a 50 μm core diameter and 0.02 core NA. The core glass with a diameter >6  mm was fabricated through solgel process combined with high temperature sintering. Laser performances of this fiber at different bend diameters were studied. The mean M2<1.1 in this 50 μm core diameter fiber was achieved at a bend diameter of 0.35 m. The core glass with the refractive index nearly equal to pure silica glass is suitable for the fiber design, such as large-mode-area photonic crystal fiber.

2 μm laser properties of Tm 3+ -doped large core sol-gel silica fiber

Tm3+-doped 0.1Tm2O3-1Al2O3-98.9SiO2 (mol%) silica glass with good uniformity was prepared by sol-gel method combining with high temperature sintering. The core glass sized Φ3.2 × 50 mm with Δn of 5 × 10−4 was obtained after gelation, heat treatment, melting and polishing. Its spectroscopic properties were evaluated according to the detected absorption and fluorescence spectra. The maximum emission cross-section of Tm3+ ion in this glass is 6.2 × 10−21 cm2 and tested fluorescence lifetime is 836 μs at 1806 nm. Large core double cladding fiber with core NA of 0.102 was prepared by rod-in-tube and high temperature drawing. Its tested optical loss is 1.1 dB/m at 1333 nm. 1.11 W fiber laser output centered at 1969 nm with M2 factor of 1.99 was obtained from a 140 cm length double-cladding fiber with core diameter of 38 μm. The quasi-single mode laser with M2 factor of 1.33 was achieved in the fiber with core diameter of 19 μm.

Monodisperse β-NaYF4:Yb3+,Tm3+ hexagonal microplates with efficient NIR-to-NIR up-conversion emission developed via ion exchange

Monodisperse β-NaYF4:Yb3+,Tm3+ (NYF) hexagonal microplates with efficient near-infrared (NIR)-to-NIR up-conversion (UC) developed via a new ion-exchange modified hydrothermal method are reported. Ion exchange modification (IEM) not only significantly increases the UC intensity by up to 1000 times and prolongs the emission lifetimes of Tm3+ and Yb3+, but also enables the monodisperse morphology and size of hexagonal microplates to be maintained. A high UC quantum efficiency (QE) of 3.1% is obtained for IEM β-NaYF4:20%Yb3+,1%Tm3+ when excited with 980 nm light at a power density of 10 W cm−2. The UC emission properties can be finely tailored by changing the NaF/NYF molar ratio (NYF represents lanthanide doped β-NaYF4) and the doping concentration of Tm3+. The two photon NIR UC emission centered at ∼803 nm (arising from Tm3+: 3H4 → 3H6) dominates the UC emission spectrum and high concentrations of Tm3+ favor NIR UC further. A proof-of-concept optical image of printed patterns is demonstrated to verify their applications in security. These results suggest the promising applications of the newly developed monodisperse β-NaYF4:Yb3+,Tm3+ hexagonal microplates in security, luminescent labels, solid-state lasers, amplifiers, and biomedicine.

Optical and laser properties of Yb 3C - doped Al 2 O 3 -P 2 O 5 -SiO 2 large-mode-area photonic crystal fiber prepared by the sol-gel method

Yb 3C , Al 3C and P 5C co-doped silica glass with the composition of 0:05Yb2O3‐2:0Al2O3‐ 1:0P2O5‐96:95SiO2 (mol%) was prepared by the sol‐gel method. Using this glass as the fiber core, the corresponding large-mode-area (LMA) photonic crystal fiber (PCF) was drawn by the stack-capillary-draw technique. Spectral properties of the silica glass chip and LMA PCF are discussed. Pumped with a 976 nm laser diode, the PCF fiber achieved the highest laser output power of 34.6 W at 1040 nm, with a slope efficiency of 62%. To the best of our knowledge, this is the highest laser output power report on Yb 3C -doped silica LMA PCF prepared by the sol‐gel method. (Some figures may appear in colour only in the online journal)

Spectroscopic and laser properties of Al-P co-doped Yb silica fiber core-glass rod and large mode area fiber prepared by sol-gel method

A large-size (∅5 mm) Yb3+-doped silica fiber core-glass rod with an Al-P co-doped composition: 0.035Yb2O3-1.0Al2O3-1.0P2O5-97.965SiO2 (mol%) was prepared by the sol-gel method combined with high-temperature melting technology. We successfully solved the doping homogeneity problem caused by the volatility of P2O5. The doping homogeneity of the glass rod was very high with the maximum refractive index fluctuation Δn < 2 × 10−4. The refractive index of the glass rod was very low because of the equimolar amounts of Al and P co-doping, which yielded an AlPO4 structure. A large-mode-area single cladding fiber (LMA SCF) and photonic crystal fiber (LMA PCF) with core diameters of 35 and 50 µm, respectively, were drawn from this glass rod. Owing to the low refractive index of the core-glass rod and the corresponding low numerical aperture (NA, 0.033) of the core, the LMA SCF exhibited a high laser beam brightness with M2 = 1.3-1.4. The LMA PCF exhibited the maximum output power, which was limited by the available pumping power, of 46 W and the slope efficiency of 61%.

Fabrication and Laser Amplification Behavior of Yb 3+ /Al 3+ Co-Doped Photonic Crystal Fiber

Yb³⁺/Al³⁺ co-doped silica glass with the composition of 0.1Yb₂O₃-1Al₂O₃-98.9SiO₂ was prepared by sol-gel method combined with high-temperature sintering. Using this glass as active core, a photonic crystal fiber (PCF) with 105-μm core was fabricated by the stack-capillary-draw technology. The refractive index fluctuation of this core rod is as low as 2 × 10-4, implying that highly homogenous silica preform can be realized in this method. Furthermore, this PCF achieved a maximum amplified power of 255 W, with a slope efficiency of 65.7%. It indicates that Yb³⁺-doped silica preform prepared by the sol-gel method can be employed in the field of high-power laser.