Ultralow power continuous-wave frequency conversion in hydrogenated amorphous silicon waveguides

We demonstrate wavelength conversion through nonlinear parametric processes in hydrogenated amorphous silicon (a-Si:H) with maximum conversion efficiency of -13 dB at telecommunication data rates (10 GHz) using only 15 mW of pump peak power. Conversion bandwidths as large as 150 nm (20 THz) are measured in continuous-wave regime at telecommunication wavelengths. The nonlinear refractive index of the material is determined by four-wave mixing (FWM) to be n(2)=7.43×10(-13) cm(2)/W, approximately an order of magnitude larger than that of single crystal silicon.     

基于Stark展宽的TIG焊接电弧三维电子密度测量研究

焊接电弧三维电子密度的测量对于焊接质量控制具有重要意义,通过光谱仪采集电弧弦方向特征谱线轮廓,利用多项式拟合对径向采集数据进行降噪及平滑处理,通过Abel逆变换法重新构建径向光谱发射系数谱线轮廓,采用傅里叶变换从重建光谱轮廓中分离出Lorentz线形,获得Stark展宽,最终计算了TIG焊电弧等离子体电子密度的三维空间分布。     

Enhanced photocatalytic activity of TiO2 thin film coating on microstructured silicon substrate

Photocatalytic TiO2 thin film is prepared by sol–gel technique on microstructured silicon substrate produced by femtosecond laser cumulative irradiation. The photocatalytic activity is evaluated by the degradation of methylene blue (MB) solution under ultraviolet (UV) irradiation. For 6-ml MB solution with initial concentration of 3.0×10~-5 mol/L, the degradation rate caused by TiO2 thin film of 2-cm~2 area is higher than 70% after 10-h UV irradiation. Microstructured silicon substrate is found to enhance photocatalytic activity of the TiO2 thin film remarkably. The femtosecond laser microstructured silicon substrate is suitable to support TiO2 thin film photocatalysts.     

Growth, Characterization and Theoretical Study of a Novel Organometallic Nonlinear Optical Crystal: CdHg(SCN)4(C2H5NO)2

A novel potentially useful second harmonic generation (SHG) organometallic nonlinear optical (NLO) crystal: cadmium mercury thiocyanate bis(N-methylformamide), CdHg(SCN)₄(C₂H₅NO)₂ (CMTN), has been prepared, and large high-optical-quality single crystals with dimensions up to 30 ×27×9 mm³ have been grown by the temperature-lowering method. Its structural, physicochemical and optical properties are characterized by elemental analyses, X-ray powder diffraction, Fourier transform infrared and Raman spectroscopy, thermal analysis, powder SHG measurements and UV/Vis/NIR transmission. The specific heat has been determined to be 515.5 J?mol^?1?K^?1 at 300 K. CMTN possesses good physicochemical stability up to 128.5^°C, exhibits powder SHG efficiencies 0.8 times that of urea and its UV transparency cutoff is 358 nm. By the use of the DFT/B3LYP/6-31G(d) method, the microscopic second order NLO behavior of CMTN has been investigated by computing the first-order hyperpolarizability together with that of CdHg(SCN)₄ (CMTC) and CdHg(SCN)₄(C₃H₈O₂) (CMTG) crystals. The results have been explained based on their crystal structures.     

Diode pumped active-mirror Yb:YAG ceramic lasers

Lasers from Yb:YAG ceramic at different temperature were reported in this paper. The Yb:YAG ceramic laser with active-mirror structure was end-pumped by a laser diode whose central wavelength was 940 nm. At 80 K, with doping concentration of 5 at % Yb:YAG ceramic slab, output energy of 0.68 J at 10 Hz repetition rate was obtained under the pump energy of 2.49 J, corresponding to a slope efficiency of 40% and a conversion efficiency of 27.3%, respectively.     

Resonantly pumped continuous wave Er:YAP laser

A continuous wave Er:YAP laser pumped by Mgo:PPLN laser locked at 1535 nm was reported. 170 mW of 1609 nm output was achieved under total incident pump power of 7 W at 77 K. The slope efficiency were 5.0 and 3.1% with the cavity length 75 and 140 mm.     

纤锌矿结构AlInN电子及光学性质的第一性原理研究

本文通过基于密度泛函理论的第一性原理,研究了纤锌矿结构Al1-xInxN在不同In浓度下的稳固结构,以及电子和光学性质的变化规律。研究表明,AlInN不同In浓度的晶格结构都很稳定,说明AlInN的兼容性很好。晶格常数随In浓度的增大不断增大,而混晶的带隙则不断减小。并且随In浓度的增大,混晶在紫外光区的吸收系数、反射系数及折射率增大,吸收边、吸收峰和反射峰蓝移,且这两个峰的峰值减小。AlInN的吸收、反射和折射率曲线在Eg处出现峰值行为,此Eg处的峰值大小随In浓度的增加而增大。当In浓度达到87.5%时,混晶AlInN在紫外光区的吸收、反射和折射能力均达到最强,表明此时的掺杂效果最好。     

Characteristics of xenon-lamp pumped pyrromethene 567-doped dye laser based on polymethylmethacrylater

The solid-state medium containing pyrromethene 567 (PM567) in a polymethylmethacrylate polymer host is shown to lase under the flash lamp excitation. The experimental setup is an ordinary industrial product without special design. The bulk transmission losses, the output energy, and the other lasing properties are compared. The medium with the lowest transmission loss, measured to be 0.392 %/cm at 633 nm, gives a laser output of 130 mJ with a slope efficiency of 0.082%.     

Room-temperature direct-bandgap photoluminescence from strain-compensated Ge/SiGe multiple quantum wells on silicon

Strain-compensated Ge/Si_0.15Ge_0.85 multiple quantum wells were grown on an Si_0.1>Ge_0.9 virtual substrate using ultrahigh vacuum chemical vapor deposition technology on an n⁺-Si(001) substrate. Photoluminescence measurements were performed at room temperature, and the quantum confinement effect of the direct-bandgap transitions of a Ge quantum well was observed, which is in good agreement with the calculated results. The luminescence mechanism was discussed by recombination rate analysis and the temperature dependence of the luminescence spectrum.     

Phase-dependence of inversionless gain in a Doppler broadened open four-level system

The effect of the relative phase (?) between the probe and driving fields on the gain without inversion (GWI) in a Doppler broadened open quasi Λ-type four level atomic system with vacuum induced coherence (VIC) for both co- and counter-propagating probe and driving fields cases is studied. It is shown that: (1) GWI and the probe detuning region in which GWI exists are very sensitive to variation of the relative phase; when values of the other parameters keep unvarying, by adjusting value of ?, the largest GWI can be obtained. (2) The Doppler width (D) also has dramatically modulation role on the phase-dependent GWI. When value of D is smaller, the value of ? which corresponds to the largest value of GWI is about π, when value of D is large enough, it is about π/2. (3) GWI varies periodically with ? varying, the period is 2π, but the concrete variation rule is closely related to value of D. (4) In the co-propagating case we can obtain much larger GWI than that in the counter-propagating case.