New FIR laser lines and frequency measurements in CD3OD

Twenty-four new submillimeter laser lines in fully deuterated methyl alcohol (CD₃OD) in the wavelength range from 52 to 328 m have been obtained in a Fabry-Perot FIR resonator by optically pumping the methanol with a cw CO₂ laser. We have made accurate wavelength measurements and have determined the relative polarization of most of the known CD₃OD laser lines. The frequencies of 13 of the strongest lines were also measured.Contribution of the U.S. Government, not subject to copyright.     

Overall values of conventional discrepancy indices for related and unrelated models of a non-centrosymmetric crystal with a centrosymmetric group

Theoretical expressions for the overall values of the conventional discrepancy indicesR(F) andR(I) are derived for a non-centrosymmetric crystal with a centrosymmetric group by taking the centrosymmetric group and a part of the other atoms in the unit cell as the trial structure. These results are used to obtain tables of values of these indices in terms of the parameter σ _1c ² and σ ₁ ² which define the fractional contribution to the local mean intensity from the centrosymmetric group and all the known atoms respectively. Contribution No. 561     

圆柱型正交各向异性圆形薄板的非线性非对称弯曲问题(Ⅰ)

本文利用“两变量法”[1]研究了圆柱型正交各向异性圆形薄板在非均布横向载荷作用下的非线性非对称弯曲问题,并得到在周边为可移夹支条件下的本问题的一致有效渐近解。     

强度解调型光纤光栅温度传感实验

光纤光栅在工程上应用广泛,但由于存在解调系统复杂、成本高,尤其是需要使用光纤光谱仪等波长解调仪器,使得光纤光栅很难走入本科教学的实验课堂.本文提出了一种基于窄线宽DFB激光器的强度解调方案,极大地简化了光纤光栅传感器的解调系统,完全满足较高分辨率和实时检测的系统要求.合理安排的温度传感实验可以非常直观地展示光纤光栅的线性传感性能,使得工程化的光纤光栅传感技术轻松走进本科教学课堂,具有极高的推广和应用潜力.     

六方相LaOF∶Er,Yb的上转换发光及温度传感特性

氟氧化物兼有氧化物优异的稳定性和氟化物的低声子能量,是上转换发光材料的一种热点基质材料,因而研究六方相LaOF∶Er,Yb的上转换发光性能及其温度特性具有重要意义。本文采用水热法制备了六方相LaOF∶Er,Yb荧光材料,通过X射线衍射(XRD)、扫描电镜(SEM)和荧光光谱对其结构和上转换荧光性能进行表征。实验结果表明,水热法120℃得到六方相LaF₃,经800℃和1 000℃退火后分别形成四方相LaOF和六方相LaOF。980 nm激发下,六方相LaOF∶Er,Yb中Yb³⁺与Er³⁺存在能量传递,通过双光子吸收产生绿光和红光的上转换荧光,并且Yb³⁺与Er³⁺的最佳浓度分别为3%和1%。最后研究了六方相LaOF∶Er,Yb在温度传感方面的应用,其在150～400 K温度范围的相对灵敏度和绝对灵敏度分别为0.037 K^-1和0.004 3 K^-1。该材料具有优异的温度传感特性,对荧光温度传感器件的设计和应用具有指导意义。     

三色圆偏振激光组合脉冲驱动氦原子产生椭圆偏振的阿秒脉冲

我们提出利用频率为ω,3ω和强度较弱的2ω组成的三色圆偏振激光组合脉冲驱动氦原子能够得到椭偏率较大的阿秒脉冲链的一种方法.通过强场近似方法,计算了氦原子在两色和三色圆偏振激光组合脉冲驱动下发射高次谐波谱及其合成阿秒脉冲链,比较了氦原子(初态为s态)在这两种情况下发射高次谐波谱的特点及其合成阿秒脉冲链椭偏率的大小,结果发现,在反旋的两色ω,3ω激光脉冲基础上加入了频率为2ω的第三色激光脉冲联合作用到氦原子上,所得到的阿秒脉冲链的椭偏率相对于双圆场情况下有所增加,通过调整ω,3ω激光的强度比,并且选择适当的第三色激光的强度,对初态为s态的原子,仍能够得到具有较大椭偏率的阿秒脉冲链.     

一种用以提高强度型光纤传感器稳定性的新方法

本文描述了一种Beheim的改进型方案,用以提高强度型光纤传感器的稳定性,可用于多种物理量的测量.给出了应用于相对位移测量的实验结果.     

On the measurement of electron tunnelling time

A suggestion to experimentally measure the electron tunnelling time by observing the tunnelling current cut-off as a function of the magnetic field intensity in semiconductor pn tunnel junctions, when they are placed in a crossed electric and magnetic field configuration, has been made in this paper. A simple and a rigorous quantum mechanical analysis to justify the above proposition have been presented. An order of agreement between the tunnelling time values derived from the published experimental data and our theoretical prediction has been noticed.     

In search of the Griffiths shield region

The van der Waals equation of state for binary mixtures has been used to determine the location and shape of the Griffiths shield region (where three tricritical lines intersect). If one takes the geometric mean fora ₁₂, the arithmetic mean forb ₁₂, and the configurational free energy as ideal, the center of the Griffiths shield region is found only when the ratio of molecular sizes is infinite. When the Flory equation for the configurational free energy for mixtures of chain molecules is substituted for the ideal form, the results appear to be somewhat different. However, for all the cases studied, with systems which approach geometric mean behavior one finds the shield region only when the ratio of molecular size is very large and when the internal pressure of the small molecule is very much greater than that of the long-chain molecule.This paper is dedicated to our colleague Howard Reiss on the occasion of his 66th birthday.