Wavefront measurement of double-clad pulsed ytterbium fiber laser

Because of high efficiencies, compact structure, and excellent heat dissipation, high-power fiber lasers are extremely useful for applications such as cutting, welding, precision drilling, trimming, sensing, optical transmitter, material processing, micromachining, and so on. However, the wavefront of the double clad fiber laser doped with ytterbium is still unknown. In this paper, wavefront of a fiber laser is measured and the traditional Hartmann-shack wavefront sensing method is adopted. We measured a double clad fiber laser doped with ytterbium which produces pulse wave output at infrared wavelength. The wavefront shape and contour are reconstructed and the result shows that wavefront is slightly focused and not an ideal plane wavefront. Wavefront measurement of fiber laser will be useful to improving the lasers' performance and developing the coherent technique for its applications.

Transport phenomena in radial flow MOCVD reactor with three concentric vertical inlets

Transport phenomena in radial flow metalorganic chemical vapor deposition (MOCVD) reactor with three concentric vertical inlets are studied by two-dimensional numerical modeling. By varying the parameters such as gas pressure, flow rates combination of multi-inlets, geometric shapes and sizes of reactor and flow distributor, temperatures of susceptor and ceiling, and susceptor rotation, the corresponding velocity, temperature, and concentration fields inside the reactor are obtained; the onset and change of flow recirculation cells under influences of those parameters are determined. It is found that recirculation cells, originated from flow separation near the bend of reactor inlets, are affected mainly by the reactor height and shape, the operating pressure, the flow rates combination of multi-inlets, and the mean temperature between susceptor and ceiling. By increasing the flow rate of mid-inlet and the mean temperature, decreasing the pressure, maintaining the reactor height below certain criteria, and trimming the bends of reactor wall and flow distributor to streamlined shape, the recirculation cells can be minimized so that smooth and rectilinear flow prevails in the susceptor region, which corresponds to smooth and rectilinear isotherms and larger reactant concentration near the susceptor. For the optimized reactor shape, the reactor size can be enlarged to diameter D = 40 cm and height H = 2 cm without flow recirculation. The susceptor rotation over a few hundred rpm around the reactor central axis will induce the recirculation cell near the exit and deflect the streamlines near the susceptor, which is not the case for vertical reactors. (c) 2006 Elsevier B.V. All rights reserved.

Impacts of the embedded windings to the field quality of dipole

Cooler Storage Ring (CSR) of Heavy Ion Research Facility in Lanzhou (HIRFL) consists of a main ring (CSRm) and an experimental ring (CSRe). Two particular C-type dipoles with embedded windings are used in the injection beam line of CSRm. They also act as the prototype dipoles of CSRe. The windings are designed to improve the field quality by their trimming current. The current impacts on field homogeneity and multipole components are investigated by a hall sensor and a long coil, respectively. The experiment shows that a field homogeneity of +/- 1.0 x 10(-3) can be reached by adjusting the trimming currents, though the multipole components change correspondingly. In our case, the quadrupole component is decreased to a low level with the octupole, decapole and 12-pole ones increased slightly when the trimming current is optimized.

ECR离子源高真空微调针阀控制系统

本论文首先介绍ECR（电子回旋共振）离子源的基本原理及其发展，在此基础上讲述了近物所的14.5GHzECR离子源的结构和特点。本论文主要内容是介绍所研制的适用于30KV高压端的ECR离子源高真空微调针阀控制系统。此系统被控对象是位于ECR源上的高真空微调针阀，它与地面之间有20～30KV的电位差。论文中首先阐述此控制系统研究的背景，并对ECR离子源电气参数控制的特点进行了说明。根据被控对象的情况以及对系统提出的指标，详细讲述了此控制系统的软、硬件实现。硬件包括步进电机、步进电机驱动器、轴编码器等。软件包括译码编程。然后从总体介绍此控制系统的功能结构，再分步讲述发射器、接受器、译码等各功能模块的实现过程。此控制系统的最大特点是使用光路实现高压绝缘，这为解决位于ECR离子源高压端器件的控制问题提出新思路。本系统的光路采用红外线发射接收系统，以空气为传输介质，依据光信号的有无接收控制信息，此方式效果好、易于实现。在系统中，使用光路传输装置定位，聚集透镜聚集，增加信号强度，提高抗干拢能力。而且此光路传输系统价格便宜，易于实现，可靠性好。在整个控制系统方案调研期间，对各种控制方式进行了比较和实验，在此基础上，确定了一个比较经济实用和具有高可靠性的方案。经过设计电路原理图、绘制印制线路板、加工印制线路板、购买元器件、组装电路后，首先成功地进行了离线调试，最后，将整个系统模拟实际环境进行调试实验。整个系统实现了稳定可靠的工作，达到了预期的设计指标，精度好于要求的千分之一。由于时间紧张和条件的限制，该系统还未在现场设备上进行实验。因此，在今后的工作中，此控制系统还需要在条件具备时，在现场设备上进行实验和考验。此外，为满足国家大科学工程兰洲重离子冷却储存环的要求，我参与了在14.5GHz ECR离子源上进行afterglow工作模式的实验，首次产生了高电荷态脉冲束流Ar~(11+)和Ar~(12+)。论文最后一部分给出了初步实验结果，并对结果进行了分析和解释。