Inverse symmetric Dammann gratings

Inverse symmetric Dammann grating is a special grating, whose transition points are reflection symmetric about the midpoint with inverse phase offset in one period. It can produce even-numbered or odd-numbered array illumination when the phase modulations are pi or a specific value. Numerical solutions optimized by the steepest-descent algorithm for binary phase and multilevel phases with splitting ratio from I x 4 to 1 x 14 are given. Fabrication of 1 x 6 array without the zero-order intensity and 1 x 7 array with the zero-order intensity are made from the same amplitude mask. A 6 x 6 output without the crossed zero-orders was achieved by crossing two one-dimensional 1 x 6 inverse symmetric Dammann gratings. This grating may have potential value for practical applications. (C) 2008 Elsevier B.V. All rights reserved.

Influence of electron irradiation on hydrothermally grown zinc oxide single crystals

The resistivity of hydrothermally grown ZnO single crystals increased from similar to 10(3) Omega cm to similar to 10(6) Omega cm after 1.8 MeV electron irradiation with a fluence of similar to 10(16) cm(-2), and to similar to 10(9) Omega cm as the fluence increased to similar to 10(18) cm(-2). Defects in samples were studied by thermally stimulated current (TSC) spectroscopy and positron lifetime spectroscopy (PLS). After the electron irradiation with a fluence of 10(18) cm(-2), the normalized TSC signal increased by a factor of similar to 100. A Zn vacancy was also introduced by the electron irradiation, though with a concentration lower than expected. After annealing in air at 400 degrees C, the resistivity and the deep traps concentrations recovered to the levels of the as-grown sample, and the Zn vacancy was removed.

微波网络分析仪的校准

对微波网络分析仪和测试夹具的校准方法和校准过程经常出现的问题进行了介绍.从提高校准精度的角度,针对不同的测试端口和相应的校准标准,提出了选取校准方法和运算方法的准则,同时给出了解决这些问题和提高校准精度的具体建议.发现并通过实验验证直通标准得到的4个方程能够同时使用,并可以获得精确的结果.实验中,观察到对同一校准方法,采用不同的运算方法可能导致频率限制问题的出现.