He polarization for ISIS TS2 phase I instruments

Here we report on the development of polarization analysis (PA) techniques to be employed at the ISIS pulsed neutron source second target station. Both spin exchange optical pumping and metastability exchange optical pumping techniques are being developed at ISIS to produce polarized neutron spin filters for use as neutron polarizers and analysers. We focus on the developments of a polarization solution on the LET spectrometer, including the updated design of the PASTIS XYZ coil set and single crystal silicon analyser cell. We also report on the construction of a combined polarizer/analyser solution for the WISH diffractometer.     

光磁共振设计性实验思路和教学效果

结合光磁共振实验的物理图像，提出测量朗德因子耵和地磁场的实验方案设计思路，并总结该实验近年教学的效果。     

不同泵浦光下Nd:GdVO4晶体输出特性

为研究808 nm和879 nm两种泵浦光对Nd:GdVO4晶体激光输出特性的影响,并比较两种不同波长泵浦所得连续输出光的效率高低,分析了Nd:GdVO4晶体的能级结构和两种泵浦光作用下的激光输出特性,发现在879 nm也有较强的吸收峰.用808 nm和879 nm两种不同波长泵浦Nd:GdVO4晶体的过程是不同的,808 nm泵浦是一种间接方式能量转移的过程,在此过程中有明显的热负载产生.而879 nm泵浦是将粒子直接激励到激光辐射上能级,降低无辐射弛豫过程产生的热量.从理论上可知,879 nm的泵浦量子效率要高于808 nm的泵浦量子效率,对减少晶体的热产生有很强的优势.实验中采用激光二极管端面泵浦Nd:GdVO4晶体直腔方案,研究了两种不同泵浦光泵浦Nd:GdVO4晶体以获得1 063 nm的连续光,得到了两种光抽运时的斜效率,发现在同样实验条件下,879 nm泵浦的输出光斜效率在小功率泵浦时略高于808 nm|而在大功率泵浦的情况下明显高于808 nm,最高达到38%.同时,在808 nm抽运时,实验上获得了1 341 nm波长的激光,为光通讯的应用提供了一种光源.     

Abnormal spin-pumping effect at Pt/NiFe interface by an oxidation of ferromagnet

The Inverse Spin Hall Effect (ISHE) voltage induced by spin-pumping was measured in Pt/[nonoxidized or oxidized NiFe] samples. The spectrum shape of the DC voltage signal was well-reproduced by simple Lorentzian functions, which were consistent with the prediction of ISHE in Pt/nonoxidized NiFe sample. On the other hand, the voltage signal from the Pt/oxidized NiFe was significantly decreased in accordance with abnormal ferromagnetic resonance (FMR) behavior. The origin of the ISHE voltage degradation was investigated by the FMR spectrum and X-ray photoelectron spectroscopy (XPS) analyses. The spin-pumping was suppressed by the oxidation of NiFe layer and deficient Pt/NiFe interface. The well-defined ferromagnet and clear interface with a normal spin mixing conductance were experimentally demonstrated to be reasonable spin-pumping.     

Laser performance and thermal lens of diode-pumped Nd,Y-codoped:SrF_2 single crystals

We demonstrate the laser performances of Nd, Y：SrF2 crystals with Nd＇3＋ concentrations of 0.15 and 0.43 at.%. The sample with 0.43 at.% Nd3＋ concentration yields a maximum output power of 1.023 W at 1056.9 nm with a slope efficiency of 53%. The focal length of the thermal lens is analyzed for the 0.15 at.% Nd3＋-doped crystal sample. An improved cavity is designed considering the thermal lens. The maximum output power is 464 mW at 1056.9 nm, with a slope efficiency of 36.1%. The wavelength is tuned within the range of 1049.74-1059.13 nm.     

双包层稀土掺杂光纤抽运吸收特性的分析

建立了复折射率纤芯结合有限差分束传播法的双包 层稀土掺杂光纤抽运吸收效率数值模型,利用该模型对几种常 用内包层外边界结构下双包层稀土掺杂光纤的抽运吸收系数进 行了详细的分析,得出相应双包层光纤的抽运吸收特性. 分析结果对双包层稀土掺杂光纤的优化设计具有重要的指导意义.     

56 MHz重复频率端泵SESAM连续波锁模Nd∶YVO4激光器

为了增大皮秒注入种子激光的能量,获得较高的激光放大效率和信噪比,关键是要在保持较高的平均锁模激光功率下实现连续波锁模激光器的低重复频率运转。通过选取五镜折叠激光谐振腔腔型和参数设计,克服了随着腔长增加损耗加大而导致的激光锁模不稳定的困难。分析了较长腔长条件下工作物质和SESAM光斑尺寸的大小和变化,及其对激光器稳定性的影响。由于SESAM饱和工作和稳态条件的能量要求,在激光谐振腔调整过程中,对应臂长的光程互补变化。实验中采取腔长和晶体热控制方式,优化了激光谐振腔的工作参数,实现了脉冲能量10.7 nJ,重复频率56 MHz,平均功率1.2 W的SESAM连续波锁模激光输出。     

流气条件下表面放电光泵浦源重复频率运行的稳定性

以高纯度Al2O3陶瓷作为放电基底,研制了重复频率表面放电光泵浦源模块,详细地讨论了流气条件下泵浦源的放电抖动和辐射强度波动,并采用高速相机拍摄了泵浦源的放电等离子体图像,研究了等离子体的空间稳定性。研究发现:在流气状态下,泵浦源的重复频率为1～5 Hz时,泵浦源的放电抖动与放电等离子体的空间稳定性受充电电压和气体流量的影响较大,随运行频率的变化较小;辐射强度波动主要与充电电压相关,基本不受气体流量和重复频率变化的影响;在大流量条件下,提高充电电压,可以有效降低混合气体流动对泵浦源放电抖动的影响,减小辐射强度波动,改善放电等离子体的空间重复性;当充电电压达到26.8 kV时,气流量在60～300 L/min范围内,泵浦源的放电抖动可以小于45 ns,辐射强度波动小于2%,放电等离子体有很好空间稳定性。研究结果表明该表面放电光泵浦源模块在流气条件下具有良好的重复频率运行稳定性。     

Influence of pumping laser bandwidth on the quantum fluctuation chracteristic of a non-degenerate optical parametric amplifier

Usually the quantum fluctuation characteristic of a non-degenerate optical parametric amplifier is analysed under the assumption of monochromatic pumping. However, in experiments, a driving beam with finite bandwidth is used to obtain the non-degenerate signal and idler beam amplifications. On account of that, we derive an analytical solution for the non-degenerate optical parametric amplification system with finite bandwidth laser pumping, and evaluate the associated quantum fluctuation. Finally, the application of the V1 criterion to bipartite entanglement is discussed.