Zhaojie Zhu

Spectroscopic investigations of highly doped Er3+ : GGG and Er3+/Pr3+ : GGG crystals

Heavily Er3+-doped and Er3+/Pr3+ co-doped Gd3Ga5O12 (abbreviated as Er : GGG and Er,Pr : GGG, respectively) laser crystals were synthesized by the Czochralski method. The synthesized laser crystals were characterized by absorption, up-conversion fluorescence, near-infrared (NIR) and mid-infrared (Mid-IR) fluorescence, and luminescence decay measurements. The optical parameters related to absorption and emission cross-sections and fluorescence lifetimes were evaluated and compared. It was found that the up-conversion and NIR fluorescence weaken, at the same time Mid-IR fluorescence intensity strengthens with the increment of Er dopant concentration or co-doping with Pr3+ in Er : GGG crystals. Furthermore, the self-termination bottleneck was broken successfully in the Er,Pr : GGG crystal, and the energy transfer efficiencies of Er3+ : 4I11/2 → Pr3+ : 1G4 and Er3+ : 4I13/2 → Pr3+ : 3F4 were determined.

Internal friction study on oxygen vacancies and domain walls in Pb(Zr, Ti)O3 ceramics

The internal friction of Pb(Zr0.52Ti0.48)O3 ceramics was measured above room temperature at low frequencies by using an inverted torsion pendulum. Two obvious relaxation peaks were observed at 420 and 560 K, respectively, on the internal friction versus temperature curves. The activation parameters were calculated by means of the peak shift method. The activation energy of the peak around 420 K was equal to 1.04 eV, and its relaxation mechanism was attributed to the stress-induced migration of oxygen vacancies, which would make it possible to determine the concentration of oxygen vacancies by the peak height of this peak. The peak around 560 K was related to a complex mechanism including the viscous motion of domain walls and the interaction between domain walls and point defects.

Red–green–blue generation from a lone dual-wavelength GdAl3(BO3)4:Nd3+ laser

We demonstrate the simultaneous generation of the three basal red–green–blue colors from a lone GdAl3(BO3)4:Nd3+ bi-functional laser and optical nonlinear crystal. The laser works in a dual-wavelength operation in the two 4F3/2→4I11/2 (near 1062 nm) and 4F3/2→4I13/2 (near 1338 nm) channels, under a fixed wavelength pumping (at 744.7 nm) and with a fixed crystal orientation. Red and green results from self-frequency doubling of the two laser channels, blue results of self-sum frequency mixing of the pump and the 1338 nm laser.

Self-frequency tripling from two cascaded second-order nonlinearities in GdAl3(BO3)4:Nd3+

We combine inside a single noncentrosymmetric laser crystal, GdAl3(BO3)4:Nd3+, a stimulated emission and two second-order nonlinearities in cascade. The first one self-doubles the 1062.8 nm Nd3+ laser emission corresponding to the 4F3/2→4I11/2 channel, despite the fact that it is not phase-matched. The second one can be phase-matched or not and mixes the laser wave and its second harmonic (SH) in order to produce the third harmonic (TH) at 354.3 nm.

Structural perspectives on the elastic and mechanical properties of metallic glasses

The flow units of glasses are generally perceived to be a local rearrangement of atoms that are microstructural origin for plastic deformation and relaxations in metallic glasses. We find a relationship of the effective concentration of flow units and some properties such as elastic moduli, micro-hardness and plasticity of metallic glasses. The relationship helps in understanding the softening phenomenon, structural heterogeneous, evolution process of flow units, and widespread mechanical behavior of metallic glasses and can reveal the essential structural mechanism of the Poissons ratio criterion for plasticity in metallic glasses. The relationship also indicates that the flow unit is a key structural parameter for understanding and controlling the properties and the performance of metallic glasses.

Spectroscopic properties of Er3+ transitions in SrWO4 crystal

Er3+:SrWO4 crystal of good optical quality was grown by Czochralski technique method. Polarized absorption and emission spectra of Er3+ ions in SrWO4 crystal have been investigated. The Judd-Ofelt (JO) theory was applied to the polarized absorption spectra of Er3+:SrWO4 to obtain the three JO parameters: Ω2=7.41×10−20cm2, Ω4=0.25×10−20cm2, and Ω6=1.71×10−20cm2. The radiative probabilities, radiative lifetimes, and branch ratios of Er3+:SrWO4 were calculated. The stimulated emission cross sections of the potential laser transitions at 1535nm were determined using the reciprocity method and the Fuchtbauer-Ladenberg formula, and the potential laser gain versus wavelength for the I13∕24→I15∕24 transition has been estimated and discussed.

Optical properties of Dy3+ ion in GGG laser crystal

High optical quality Dy3+-doped Gd3Ga5O12 (abbreviated as Dy : GGG below) crystal was grown by the Czochralski technique along the (1 1 1) orientation. The absorption spectrum, fluorescence spectrum and fluorescence decay curve of Dy : GGG have been recorded at room temperature. Based on the Judd–Ofelt (J–O) theory, the intensity parameters from the measured line strengths were determined. The J–O parameters were used to predict radiative transition probabilities, radiative lifetime and branching ratios for various excited levels of the Dy : GGG crystal. In the visible region, one intense fluorescence band was observed at 581 nm, corresponding to the 4F9/2 → 6H13/2 transition. The room-temperature fluorescence lifetime of this transition of Dy3+ ion in the GGG crystal was measured to be 0.79 ms, and the luminescent quantum efficiency of the 4F9/2 level was evaluated to be 71.4 %. The emission cross-sections of the 4F9/2 → 6H13/2 transition were estimated by the use of the Fuchtbauer–Ladengurg method. The research on the emission at 581 nm indicates the possibility of using a commercially available laser diode of 353 nm as a pumping source for a solid-state yellow laser.

Benefit of Pr 3+ ions to the spectral properties of Pr 3+ /Er 3+ :CaGdAlO 4 crystal for a 2.7 μm laser

The spectra of Er3+:CaGdAlO4 and Pr3+/Er3+:CaGdAlO4 crystals were measured under the same conditions. With the presence of Pr3+ ions, the intensities of the green, red upconversion and near-infrared emissions are dramatically reduced to 1/20, 1/150, and 1/8.5 of those for Er3+:CaGdAlO4. Furthermore, the lifetimes of 4I11/2 upper and 4I13/2 lower laser levels fall from 450 and 982 μs to 84.8 and 74.3 μs. It is obvious that the self-saturation for Er3+ 2.7 μm laser is effectively suppressed. The energy transfer efficiencies and coefficients of Er3+→Pr3+ are also calculated. These results indicate that Pr3+ codoping is beneficial in achieving 2.7 μm laser in Pr3+/Er3+:CaGdAlO4 crystal.

Diode pumped passive Q switching of Yb3+-doped GdAl3(BO3)4 nonlinear laser crystal

The authors report the passive Q switching of a diode pumped Yb:GdAl3(BO3)4 (Yb:GAB) laser. The slopes of the average output power are 25% and 39.5% under different experimental conditions. The repetition rates occur in the 1–4.5kHz range and pulse energies of 125 and 165μJ with about 30ns duration are obtained. An experimental comparison with passively Q-switched Nd:GAB laser is provided. A theoretical analysis is performed. It is in reasonable agreement with the experimental data and it is shown to be a useful tool for predicting the optimization of the cavity parameters.

Positron Lifetime as a Nanoprobe for Free Volume Distribution in High Density Polyethylene–Carbon Black Conducting Composites

The room-temperature electrical conductivity of High Density The room-temperature electrical conductivity of High Density