Xiaoniu Tu

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.

Laser damage threshold and nonlinear optical properties of large aperture elements of YCOB crystal

Large size of YCa4O(BO3)3(YCOB) crystals were grown both by Czochralski and Bridgman methods. Large size elements as large as 60 mm clear aperture were cut and polished with surface flatness of 1/5 wavelength. Optical homogeneity of YCOB crystal was found in the order of 10-6. Laser damage thresholds of several YCOB crystal elements were tested using different laser facilities with different pulse widths or wavelengths, with thresholds varied from 0.8 GW/cm2 to more than 1 TW/cm2. One SHG and two optical parametric chirped-pulse amplification (OPCPA) experiments were executed to characterize the nonlinear optical properties of YCOB crystals and the quality of the crystals. The results shown that YCOB had good performance in OPCPA application, especially with low content of parameter florescence. Combined with good NLO performance and possibility to grow large size crystals, YCOB crystal was a good choice for high power OPCPA applications.

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.

Advances in design, growth and application of piezoelectric crystals with langasite structure

Crystals with langasite structure consist of more than one hundred compounds. Only about 20 compounds are grown and characterized. In this work, we first use first-principles calculation to simulate the crystal structure of 29 ordered langasite compounds and then forecast their piezoelectric related properties including dielectric constants, elastic constants, piezoelectric coefficients and electromechanical coefficients. Four known ordered crystals including SNGS, STGS, CTGS, CNGS, and several novel crystals including BTGS, CTAS, CNAS were grown by Czochralski method and characterized at room temperature and at high temperature from 400 to 900°C. The experimental results of piezoelectric properties verified the validity of theoretical forecast and that errors between experimental and theoretical results were in reasonable range. Gallium-free crystals shown good prospect in application of piezoelectric sensors, combining the advantages of low cost of raw materials and high performance. More efforts should be paid to the growth of these novel crystals.

Piezoelectric acceleration sensors based on LGX and ReCOB crystals for application above 645ºC

In the field of aviation and aerospace engine, monitoring of the vibration of the engine in situ directly in the high temperature part is of great importance for the safe and performance of the engine. So there is demanding for sensors that can stand for high temperature of 645^oC or above temperature. Recently, the crystals of langasite and ReCOB family are found to be good candidate for this application through the study of basic properties of crystals at high temperature. But there is few reports about the acceleration sensors made of these crystals. In this work, the single crystals of La₃Ga₅SiO₁₄ (LGS), La₃Ga_5.5Ta_0.5O₁₄ (LGT), YCa₄O(BO₃)₃ (YCOB) and SmCa₄O(BO₃)₃ (SmCOB) were grown by Czochralski method respectively, and the basic properties of these crystals were characterized. The acceleration sensors with LGT as sensitive components were successfully made and characterized up to 700^oC. The results show that sensors made by these crystals can be used at the high temperature circumstance above 645^oC and under the vibration with frequency in the range of ten Hz to several thousands Hz.

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.

Growth and characterization of several piezoelectric crystals with an order langasite structure

STGS (Sr 3 TaGa 3 Si 2 O 14 ), SNGS (Sr 3 NbGa 3 Si 2 O 14 ), CTGS (Ca 3 TaGa 3 Si 2 O 14 ) and CTAS (Ca3TaAl3Si2O14) were grown by using the Czochralski method. Selecting a suitable growth direction for the growth of large crystals is very important. STGS and CTGS is easily grown along the X-axis direction, and SNGS is easier to be grown along Y-axis direction than along X-axis direction. CTAS can be pulled along X-axis direction, but there was a serious opaque growth core defect. The measured piezoelectric stress coefficient and dielectric coefficient of crystals showed STGS, SNGS, CTGS and CNAS have similar piezoelectric performance, and the values of e 11 are about 2 times than that of the quartz. In addition, the cost of CTAS is lower than that of other three crystals, which make CTAS become a more promising piezoelectric material.