Yanqing Zheng

Characterization of high temperature piezoelectric crystals with an ordered langasite structure

Piezoelectric single crystals with the ordered langasite structure A3BC3D2O14, including Sr3TaGa3Si2O14, Sr3NbGa3Si2O14, Ca3TaGa3Si2O14, and Ca3TaAl3Si2O14 (CTAS), were studied as a function of temperature, up to 900 °C. The dielectric permittivity e11 and piezoelectric coefficient d11 of the ordered crystals were found to be on the orders of 12–16 and 4–5 pC/N, respectively, slightly lower than langasite (La3Ga5SiO14-LGS) or langanite (La3Ga5.5Nb0.5O14) crystals which possess a disordered structure. The mechanical quality factor Q and electrical resistivity ρ, however, were found to be greatly improved at elevated temperatures ≥500 °C, being one to two orders of magnitude higher, due to cation ordering. Of particular interest is the CTAS crystal, in which, the Ga cations are totally replaced by low cost Al cations. Together with its thermally stable piezoelectric properties and high electrical resistivity, CTAS crystals offer a competitive material for high temperature sensing applications.

Piezoelectricity of zinc-blende and wurtzite structure binary compounds

First-principles calculations were performed on binary compounds of zinc-blende and wurtzite structures to disclose the relationships between the piezoelectric performance and the microscopic structure. The authors defined the structure parameters P and θ to represent the degree of asymmetry in structure. They were found to be linear to piezoelectric constants e14 and e33 for zinc-blende and wurtzite structure binary compounds, respectively.

Experimental demonstration of joule-level non-collinear optical parametric chirped-pulse amplification in yttrium calcium oxyborate

In this Letter, we report on what is, to our knowledge, the first experimental demonstration of yttrium calcium oxyborate (YCOB) for joule-level and broadband non-collinear optical parametric chirped-pulse amplification centered at 800 nm. Based on a Ti:sapphire chirped-pulse amplification front end, an amplified signal energy of 3.36 J was generated with a pump of 35 J in the crystal. Compressed pulse duration of 44.3 fs, with a bandwidth of 49 nm, was achieved. The results confirm that YCOB crystal is another potential alternative as a final amplifier besides Ti:sapphire in a petawatt laser at 800 nm.

From ab initio forecast of piezoelectric properties to growth of piezoelectric single crystals

The piezoelectric properties of two langasite type compounds, Ca3TaAl3Si2O14 and Ca3NbAl3Si2O14, were predicted by first-principle calculation and single crystal of Ca3TaAl3Si2O14 was successfully grown by conventional Czochralski method. The complete elastic and piezoelectric properties of Ca3TaAl3Si2O14, measured by resonant-antiresonant method, indicated that Ca3TaAl3Si2O14 was a promising substitute for quartz in the surface acoustic wave application. The high veracity of calculated results compared with measured ones suggested that first-principle predictions could be considered as a pertinent tool for the development of new materials.

Molecular beam epitaxial growth, characterization and performance of high-detectivity GaInAsSb/GaSb PIN detectors operating at 2.0 to 2.6 μm

Abstract Molecular beam epitaxy has been employed to grow Ga x In 1− x As 1− y Sb y PIN detectors operating at 2.0 to 2.6 μm on (100)-oriented GaSb substrates. The epitaxial layers were characterized by X-ray double-crystal diffraction, Fourier transform infrared spectroscopy, electron microprobe analysis, and Hall effect measurements. The background hole concentration and mobility at room temperature are (4–5) × 10 16 cm −3 , 254 cm 2 /V·s and 9 × 10 15 cm −3 , 970 cm 2 /V·s for GaInAsSb and GaSb, respectively. For a PIN mesa front-illuminated photodetector, a maximum external quantum efficiency of 65% without anti-reflection coating and a peak detectivity D λ ∗ at 2.5 μm of 3.0 × 10 9 cm Hz 1/2 / W with a cut-off wavelength of 2.6 μm at room temperature have been achieved.

Piezoelectricity of A3BC3D2O14 structure crystals

First-principle calculations are performed to reveal the microscopic origin of piezoelectricity of ordered crystals with A3BC3D2O14 structure. The calculated piezoelectric constant e11 and atomistic piezoelectric contribution from every single atom type in a primitive cell of Sr3NbGa3Si2O14 (SNGS), Sr3TaGa3Si2O14 (STGS), Ca3NbGa3Si2O14 (CNGS), and Ca3TaGa3Si2O14 (CTGS) structures showed that the piezoelectricity comes mostly from one of three atoms in A positions. The percentages of the contributions from the A positions to the total internal piezoelectric constant exceed 69% in CNGS and CTGS and 81% in SNGS and STGS, respectively.

Comparison of thermal characteristics of antimonide and phosphide MQW lasers

The thermal characteristics of antimonide ridge waveguide MQW lasers have been investigated numerically and experimentally, and compared with phosphide lasers in detail. Using the finite-element method, the heat accumulation and dissipation process of the lasers under CW and pulse driving conditions have been simulated, and quantitative thermal time constants were introduced to describe the cooling efficiency of the lasers. The non-uniform temperature distribution inside the active core of the laser and its effects on lasing spectra have been discussed, and confirmed by the measurement of the broadening of the lasing spectrum towards the blue side. A way to improve the thermal property of antimonide lasers have also been proposed and discussed.

Quasi-parametric amplification of chirped pulses based on a Sm 3+ -doped yttrium calcium oxyborate crystal

One inherent characteristic of quadratic nonlinear interaction is that it allows both forward and backward energy transfer among the three interacting waves. This backconversion effect, universal in all the parametric processes, is detrimental when a unidirectional energy transfer is desired and limits the conversion efficiency. We report a family of quadratic nonlinear interactions, quasi-parametric amplification (QPA), in which the idler wave is depleted by the introduction of a material loss and only the signal is amplified. In contrast to optical parametric amplification (OPA), the QPA scheme can inhibit the backconversion effect and thus enable ideal chirped-pulse amplification with high conversion efficiency and broad gain bandwidth. We have numerically proved the feasibility of this new scheme, and experimentally realized it by using a Sm3+-doped yttrium calcium oxyborate crystal that is highly absorptive at the idler wavelength and transparent at the pump and signal wavelengths. Amplification of broadband chirped pulses, corresponding to a pump depletion of 70% and a signal efficiency of 41%, has been achieved in a typical Gaussian pump case, exceeding the results of the previously reported state-of-the-art OPA. The proposed QPA scheme will be a promising approach for efficiently amplifying chirped pulses to unprecedented powers.

First-principles Study of Microscopic Origin of Piezoelectric Effect in α-Quartz

Using a first-principles approach based on the density-functional theory, the piezoelectric properties of α-quartz are calculated. The computation is based on local-density approximation (LDA) and the density-functional perturbation theory (DFPT), directly yielding appropriate piezoelectric stress coefficients. The calculated results are in agreement with the experimental results. The internal piezoelectric coefficients e11,int and e14,int is decomposed into each ion and SiO4 tetrehedron in the primitive cell, respectively. In ionic decomposition, the ions most responsible for piezoelectric effects are Si14+, O22-, and O32-. In tetrahedral decomposition, the tetrahedra centered by Si24+ and Si34+ exhibit a higher piezoelectric coefficient than the tetrahedron centered by Si14+. The reason for these phenomena has been interpreted to be the difference between the geometric orientations of these two kinds of tetrahedra in α-quartz with respect to strain tensors.

Large CuI crystal growth by evaporation technique and its growth mechanism

Based on the negative temperature dependence of CuI solubility in acetonitrile solvent, a novel evaporation technique combined with increasing temperature programming was used to grow CuI crystals. It was found that the nucleation and growth of the CuI crystals can be adjusted by changing the temperature in the evaporation technique and a large transparent CuI single crystal of nearly 1 cm was first grown under a suitable temperature gradient. The growth process of the large CuI crystal in solution was then studied by measuring the evolution of the solute concentration with a spectrophotometer. The suitable temperature and solute concentration for the growth of large CuI crystals were in the range of 50–51.9 °C and 0.050–0.058 mol L−1, respectively. The variation of the CuI crystal growth mechanism at different stages was also discussed. These results could provide a useful clue to further optimize the experimental scheme to grow larger CuI crystals.