The absolute frequency of 87Rb 5S1/2 （F=2）→5D5/2 （F＂ = 4） two-photon transition at 778nm is measured in an accuracy of 44kHz. A home-made erbium-doped fiber laser frequency comb with frequency stability of 5.0 ...The absolute frequency of 87Rb 5S1/2 （F=2）→5D5/2 （F＂ = 4） two-photon transition at 778nm is measured in an accuracy of 44kHz. A home-made erbium-doped fiber laser frequency comb with frequency stability of 5.0 × 10-13@1 s is employed for the light source. By using a periodically poled lithium niobate, the femtosecond pulse operating in 1556 nm is frequency-doubled to 778 nm to obtain the direct two-photon transition spectroscopy of thermal rubidium vapor. Through sweeping the carrier envelope offset frequency （fceo）, the 5S1/2 （F=2）→5D5/2 （F＂ = 4） two-photon transition line is clearly resolved and its absolute frequency is determined via the peak-finding of the fitting curve. After the frequency correction, the measured result agrees well with the previous experiment on this transition. The entire potential candidate of optical frequency standard for system configuration is compact and robust, providing a telecommunication applications.展开更多
为研究真空等离子喷涂Si/Yb_(2)Si_(2)O_(7)/Yb_(2)SiO_(5)环境障涂层试样在涂层受压、涂层受拉时的室温弯曲强度及失效原因,采用超景深三维显微镜、SEM(Scanning Electron Microscope)等方法对喷涂后的试样进行了表征,并测量了涂层孔隙...为研究真空等离子喷涂Si/Yb_(2)Si_(2)O_(7)/Yb_(2)SiO_(5)环境障涂层试样在涂层受压、涂层受拉时的室温弯曲强度及失效原因,采用超景深三维显微镜、SEM(Scanning Electron Microscope)等方法对喷涂后的试样进行了表征,并测量了涂层孔隙率;采用拉伸法测试了涂层的结合强度,并采用三点弯曲试验测试了裸材、涂层受压和涂层受拉时的室温弯曲强度。结果表明:Si/Yb_(2)Si_(2)O_(7)/Yb_(2)SiO_(5)涂层与SiC_(f)/SiC复合材料的结合强度为10.13 MPa,拉伸断裂主要在复材表层发生。计算涂层厚度时,涂层受压样的弯曲强度(503.21 MPa)与裸材(506.79 MPa)基本一致;不计算涂层厚度时,涂层受拉样的弯曲强度(499.77 MPa)与裸材一致;EBC涂层整体具有一定的压缩强度,其整体抗拉强度比复材自身抗拉强度小很多。压涂层时,在载荷增加至接近最大载荷时,复材层间发生破坏,并逐步失效,随后涂层发生飞崩,载荷迅速下降,试验停止;拉涂层时,在载荷很小时(约64 N)涂层就被拉开,随着载荷增加,直至接近最大载荷时,层间发生破坏并逐步失效。弯曲试验时复材的主要失效模式是SiC纤维断裂、复材的SiC基体开裂和复材层间撕裂,复材受拉面产生复材厚度方向的纵向裂纹;复材表层沉积的SiC膜层失效模式主要是开裂和剥落;EBC涂层在受压时的主要失效模式是整体飞崩和开裂,在受拉时,涂层在最大应力处断裂为2部分。本研究对含EBC涂层的SiC_(f)/SiC复材的最大弯曲载荷设计具有参考意义.展开更多
F-B co-doped TiO_(2)nanosheets with exposed anatase(001)facets were synthesized via a one-pot solvothermal method,and their photocatalytic hydrogen evolution performance was investigated.Characterization results confi...F-B co-doped TiO_(2)nanosheets with exposed anatase(001)facets were synthesized via a one-pot solvothermal method,and their photocatalytic hydrogen evolution performance was investigated.Characterization results confirm that this method effectively promotes the growth of the highly active anatase(001)facets and enhances visible and infrared light absorption while inducing oxygen vacancies.Under optimal conditions,the hydrogen evolution reaches 20.57μmol after 10 h of ultraviolet-visible(UV-Vis)light irradiation,exceeding the commercial TiO_(2)nanoparticles Degussa P25 by more than 10 times.These findings highlight the potential of F-B co-doped TiO_(2)nanosheets for efficient photocatalysis.展开更多
基金Supported by the National Natural Science Foundation of China under Grant Nos 61405002,91336103,10934010,61535001 and 61078026
文摘The absolute frequency of 87Rb 5S1/2 （F=2）→5D5/2 （F＂ = 4） two-photon transition at 778nm is measured in an accuracy of 44kHz. A home-made erbium-doped fiber laser frequency comb with frequency stability of 5.0 × 10-13@1 s is employed for the light source. By using a periodically poled lithium niobate, the femtosecond pulse operating in 1556 nm is frequency-doubled to 778 nm to obtain the direct two-photon transition spectroscopy of thermal rubidium vapor. Through sweeping the carrier envelope offset frequency （fceo）, the 5S1/2 （F=2）→5D5/2 （F＂ = 4） two-photon transition line is clearly resolved and its absolute frequency is determined via the peak-finding of the fitting curve. After the frequency correction, the measured result agrees well with the previous experiment on this transition. The entire potential candidate of optical frequency standard for system configuration is compact and robust, providing a telecommunication applications.
基金National Natural Science Foundation of China(No.81861138040)。
文摘F-B co-doped TiO_(2)nanosheets with exposed anatase(001)facets were synthesized via a one-pot solvothermal method,and their photocatalytic hydrogen evolution performance was investigated.Characterization results confirm that this method effectively promotes the growth of the highly active anatase(001)facets and enhances visible and infrared light absorption while inducing oxygen vacancies.Under optimal conditions,the hydrogen evolution reaches 20.57μmol after 10 h of ultraviolet-visible(UV-Vis)light irradiation,exceeding the commercial TiO_(2)nanoparticles Degussa P25 by more than 10 times.These findings highlight the potential of F-B co-doped TiO_(2)nanosheets for efficient photocatalysis.
