Optical resonator for high-power transverse flow CO2 lasers

A new design of the U-type resonator is described. In this way, a laser beam with symmetrical intensity profile (regarding to a symmetry plane) can be extracted from an active medium that exhibits gain asymmetry along one of the transverse directions. The whole area of the active medium cross-section can be used, and consequently the laser efficiency will be increased. This resonator structure was applied for efficiency power extraction (as a low order TEM modes laser beam) from a DC excited transverse flow CO₂ laser with cylindrical geometry. Although the cross-section area of the discharge was entirely used (including the cathode fall region), a symmetrical intensity profile of the laser beam (regarding to the two orthogonal symmetry planes) was obtained in the near field as well as in the far field; the gain asymmetry along the flow direction was compensated by the gas circulation fluidodynamical circuit with two counterflowing discharge channels. A double-U optical resonator was introduced in order to provide a laser beam with axial symmetry.For the practical construction of these two types of optical resonators we have developed two new types of 90° deflection elements: the first one, which does not reverse the image (and which has the properties of the pentaprism), and the second one, which rotates the image with 90° angle. Both elements exhibit good focusability if they are equipped with two concave mirrors.     

HL-2A装置快速扫描气动探针的研制和运用

快速扫描气动探针已在HL- 2A 装置上用于对边缘等离子体参数的径向分布的测量, 特别是刮离层等离子体参数的特征长度和扰动的测量。该系统采用精密的气动气缸驱动带有探针组件的长驱动杆, 其最快速度可在60 ms 时间内水平扫描8 cm 的距离。探针信号测量具有1MHz 的快速时间响应和0. 04 mm 的空间分辨率。可靠地测量了HL- 2A 装置边缘电子温度和密度的时空分布。     

用于光纤拉曼放大器抽运源的单级光纤拉曼激光器

抽运光源是光纤拉曼放大器应用于密集波分复用系统的关键技术,设计了一种紧凑型的808nm激光二极管抽运的基于钒酸钇（Nd^3＋：YVO4）晶体1342nm固体激光器模块,提出利用上述1342nm固体激光器抽运基于光纤光栅的单级全光纤型拉曼谐振器获得1．4μm激光输出的光纤拉曼激光器,分析了固体激光器的阈值特性、性能优化方法和单级光纤拉曼谐振器的设计方法。上述1342nm固体激光器模块在抽运功率2W时获得了最大655mW的激光输出功率和42．6％的斜率效率,单级拉曼谐振器的1342nm到1．4μm光功率转换斜率效率达75％,在1425nm、1438nm、1455nm和1490nm处的输出功率达到300mW以上。最后给出基于1．4μm光纤拉曼激光器抽运的宽带平坦放大的光纤拉曼放大器的结构参量和性能测试结果。     

波导侧壁起伏对聚酰亚胺波导光学梳状滤波器串扰特性的影响及其改善方法

提出了一种结构模型来分析由工艺引起的波导侧壁起伏对于聚合物波导光学梳状滤波器的滤波特性的影响。含氟聚酰亚胺高分子聚合物制备多级马赫一曾德尔串联型光学梳状滤波器件的工作参量为中心波长1550nm,波长间隔为0．8nm,40通道的波长交错分离。模拟计算：表明,对由高分子聚合物材料制备的多级马赫-曾德尔串联型光学梳状滤波器件,其主要影响是增大了信道之间的串扰,中心波长1550nm处的信道串扰由理想情况下的-40dB降为-12dB,极大地影响了器件的性能。在此基础上,提出一种改善光学梳状滤波器串扰性能的新结构,该结构由多级马赫-曾德尔耦合器和微环共振滤波器串接构成,40个通道的串扰改善为-0dB以下。     

Electro–magnetic control of shear flow over a cylinder for drag reduction and lift enhancement

In this paper, the electro-magnetic control of a cylinder wake in shear flow is investigated numerically. The effects of the shear rate and Lorentz force on the cylinder wake, the distribution of hydrodynamic force, and the drag/lift phase diagram are discussed in detail. It is revealed that Lorentz force can be classified into the field Lorentz force and the wall Lorentz force and they affect the drag and lift forces independently. The drag/lift phase diagram with a shape of ＂8＂ consists of two closed curves, which correspond to the halves of the shedding cycle dominated by the upper and lower vortices respectively. The free stream shear （K 〉 0） induces the diagram to move downward and leftward, so that the average lift force directs toward the downside. With the upper Lorentz force, the diagram moves downwards and to the right by the field Lorentz force, thus resulting in the drag increase and the lift reduction, whereas it moves upward and to the left by the wall Lorentz force, leading to the drag reduction and the lift increase. Finally the diagram is dominated by the wall Lorentz force, thus moving upward and leftward. Therefore the upper Lorentz force, which enhances the lift force, can be used to overcome the lift loss due to the free stream shear, which is also obtained in the experiment.     

Tunable zeroth-order resonator based on a ferrite metamaterial structure

This paper proposes a tunable zeroth-order resonator on a composite right/left-handed transmission line consisting of a transversely magnetized ferrite substrate periodically loaded by microstrip inductors. Based on the propagation theory of edge guided modes, the analysis procedure of this structure is introduced. The numerical results demonstrate the tunability of the resonant frequency by changing the DC bias magnetic field applied to the ferrite. In contrast to previous work, the proposed structure is easy to design and fabricate and does not require a chip component.     

基于Add-drop型微环谐振腔的硅基高速电光调制器设计

相比于传统的All-pass型微环谐振腔硅基电光调制器, Add-drop型微环谐振腔可提供更多的设计自由度, 使调制器在不改变杂质掺杂浓度的情况下就能在调制带宽和消光比性能上获得均衡考虑. 本文设计了基于Add-drop型微环谐振腔的高速、且在低调制电压下实现大消光比的硅基电光调制器, 所用微环谐振腔的半径仅仅为20 μm. 重点分析了直波导与微环谐振腔的耦合对调制器性能的影响, 发现较小的Drop端耦合系数有利于消光比的提高, 但是不能同时达到最佳的调制带宽, 因此设计上存在一个带宽和消光比性能上的折中考虑. 根据优化设计的结果进行了实际器件的制作和测试. 静态光谱测试表明, 在3 V反向偏置电压的作用下, 调制器的消光比最大可达12 dB. 动态电光响应测试中, 在仅仅1.2 V的信号幅值电压下测得了8 Gbps数据传输速率的清晰眼图. 关键词： 电光调制器 绝缘体上的硅 微环谐振腔 载流子色散效应     

Study on the possibilities of controlling the laser output beam properties by an intracavity deformable mirror

The possibilities of controlling the laser beam properties by a deformable mirror introduced into the laser optical cavity were studied theoretically and experimentally. The experiments were performed under conditions of an industrial high power transverse flow cw CO₂ laser operating with a stable resonator of a folded configuration. A deformable bimorph mirror of a surface profile controlled by the voltage applied to the mirror electrodes is implemented to the laser system as a back cavity mirror or as a one of the inner folding mirrors. The near-and far-field characteristics of the laser beam versus the resonator configuration controlled by the changes of the focal length of the deformable mirror are discussed in the paper. The analysis reveals that the resonator with an inner deformable mirror is much more sensitive to the mirror curvature variations than the resonator in which the deformable mirror is used as a back cavity mirror. The presented results show that dynamic and controllable changes in the resonator properties result in the controlled modification and optimisation of the laser output power and spatial parameters of the laser radiation.     

Extension of the range of resonator scanning spectrometer into submillimeter band and some perspectives of its further developments

Extension of the working frequency of modern resonator spectrometers into submillimeter wave range is described. Experimental record of atmospheric absorption spectrum covering 45-370 GHz range is demonstrated for the first time, and measured water vapor J′_{ka′, kc′}-J_{ka, kc} = 5_1,5-4_2,2 at 325 GHz line parameters are presented. For the first time pressure lineshift for the 325-GHz water vapor line is measured. Further extension of working range is discussed. New estimations of physical limits of time needed for measurements of absorption in the whole Backward Wave Oscillator (BWO) range are given for phase continuous synthesizer regime. Basic schemes of fast broadband continuous phase synthesized sources are discussed. Verification of the previous measurements of water vapor 3_1,3-2_2,0 at 183 GHz line parameters is presented. Comparisons with ringdown resonator spectrometers are given.     

非谐振腔型KTP光参变振荡器

研究了双晶体走离补偿、非谐振腔型KTP光参变振荡器，利用一套膜片实现了KTP相位匹配所允许的全波段调谐，信号光调谐范围0.698μm-1.026μm，闲频光调谐范围1.105μm-2.237μm。5倍阈值处，信号光840nm最高输出能量53mJ，能量转换效率25.8%，量子转换效率40％，闲频光的量子郊率也达到32％。