Kainan Xiong

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.

Growth and characterization of SmxY1−xCa4O(BO3)3 single crystals for nonlinear optical applications

YCa4O(BO3)3 (YCOB) is a good candidate nonlinear optical crystal for optical parametric chirped-pulse application. In order to generate the suitable absorption of idler light near 1588 nm, Sm3+ ions with various concentrations are doped into YCOB crystals. SmxY1−xCa4O(BO3)3 (x = 0.05, 0.3, 0.5, 0.75, 1) crystals of high quality have been grown by the Czochralski method. The X-ray powder diffraction, high resolution X-ray diffraction, ICP-AES, density, absorption spectra, specific heat and thermal diffusion coefficient of as-grown crystals were measured. The results show that the as-grown crystals are isostructural with YCOB; the full width at half maximum (FWHM) of the rocking curve of the wafers with different Sm3+ concentrations are all lower than 30′′; the effective segregation coefficient of Sm3+ ion in this crystal is 0.773 with a Sm concentration of 5 at%; the crystals have absorption peaks in the 1400–1600 nm range.

Growth, characterization and piezoelectric applications of langasite-type and YCOB crystals

The research works of thirteen langasite-type crystals and YCOB crystal grown in SICCAS since 2002 were reported. Their piezoelectric properties at room temperature and high temperature up to 900°C were characterized in two cooperation universities and the product applications of SAW sensors and accelerometers in a German company were summarized here.

THE HIGH TEMPERTURE RESITIVITY OF LITHIUM NIOBATE AND RELATED CRYSTALS

Electrical property of lithium niobate crystals with various compositions from congruent to stoichiometric and Mg-doped and different crystal orientations are analyzed in the temperature range from 400 °C to 800 °C. The conductivity is found to decrease with increasinglithium concentration, and has little connections with the crystal orientations and Mg-doped. In addition, the activation energy of these lithium niobate related crystals are calculated based on the resistivities which have been linear fitted, and the mechanism of action work on the conductivity of lithium niobate and its related crystals at high temperature are analyzed.

Growth and characterization of Ca 3 NbGa 3 Si 2 O 14 crystal fibers for high-temperature applications

Ca₃NbGa₃Si₂O₁₄ crystal fibers along <;110> direction were grown by micro-pulling-down method with two different rates. The as-grown crystals were high transparent and had no crack. Due to the shape of die and crystal habit, the shape of as-grown crystals grown at 3 mm/h were approximately circular while they were approximately rectangular when grown at 1.2 mm/h. The center area of as-grown wafers perpendicular to the growth direction was free of second phase and low-angle boundaries. The second phase of Ca-Nb-O system was discovered in the peripheral area and was detected to have Ca₂Nb₂O₇ and CaNb₂O₆ phase and other phases. The as-grown crystals were also investigated to have great optical quality, high electric resistivity and high piezoelectric constant d_n. The research was benefit to the development of shaped-controlled crystals applied to high-temperature sensors.

Crystal growth and high temperature applications of 3” Langatate

Langasite (La₃Ga₅SiO₁₄, LGS) and its two isomorphs Langatate (La₃Ga_5.5Ta_0.5O₁₄, LGT) and Langanite (La₃Ga_5.5Ta_0.5O₁₄, LGN) belong to the same point group (32) as quartz. These LGS-type (LGX) crystals have attracted much attention over the past years and have been regarded as the new candidate materials for bulk acoustic wave (BAW), surface acoustic wave (SAW) and high temperature sensor devices, because of their outstanding properties. Firstly, the piezoelectric constants of the LGX are about two times larger than that of quartz, so they are expected to have higher electromechanical coupling coefficient than quartz; Secondly, they are reported have no phase transitions from room temperature to their melting points (about 1470°C); Thirdly, they have very low acoustic friction which is an indication of high Q factor, about twice of that of quartz; Finally, all of them can be grown by Czochralski and vertical Bridgman methods, and large size (about 3” ~4”) crystal has been obtained.

Pressure-induced enhancement of piezoelectricity of quartz-like single crystals

The piezoelectricity of same material is often affected by its form (such as bulk single crystals, low dimension materials, extension thin film and so on), pressure, stress and strain. In this paper, by first-principles calculation, the piezoelectricity of quartz-like crystals (synthetic quartz, AlPO4, GaPO4, GaAsO4 and GeO2) was investigated with virtual isostatic pressing. The virtual negative pressure makes its structure close to high temperature quartz phase with a higher symmetry, which lead to first-order phase transition and normal piezoelectric strain coefficient along a-axis disappearing eventually. The piezoelectricity is related closely with tetrahedral tilt angle which is used for characterizing the degree to divergence of centrosymmetry. Uniaxial stress or other non-isostatic pressing can also lead to this kind of increasing or declining, which is a general phenomenon. For a specific type of structure, piezoelectric coefficient can be represented as a simple function of pressure or order parameter. Furthermore, the contribution of piezoelectric effect can be divided into two parts, clamping ion and internal strain contribution. Then the internal strain is divided to each cell to get microscopic piezoelectric coefficient of every ions and oxygen tetrahedrons. By compared variation of tetrahedral tilt angle and microscopic piezoelectric coefficient of these five kinds of crystals, we get an explanation of the relationship between structure parameters and piezoelectric effect of quartz-like crystals in microcosmic level.