Practical single-mode fibre-horn beam expander

A new design and implementation technique for the single mode fibre-horn beam expander is outlined. This new design is more practical, both in its fabrication technique and in its application, than the previous approach. The field evolution along the beam expander has been measured and the fundamental limits to the rate of tapering examined     

Large-time-bandwidth-product surface-wave pulse compressor employing reflective gratings

A novel dispersive delay line with a time-bandwidth product in excess of 1500 has been developed. The device uses the reflection of elastic surface waves from sputter-etched gratings on LiNbO3. This reflective-array compressor is relatively free of the spurious signals which limit the performance of inter-digital transducer arrays.     

Time-domain reflective beam propagation method

A time-domain reflective beam propagation method (TD-RBPM) is presented for the analysis of optical pulse propagation and reflection in waveguide structures with multiple discontinuities. By utilizing an implicit scheme, the method allows relatively large time steps and, therefore, is highly efficient. The accuracy of the method is verified by simulating a time-domain Gaussian pulse reflected and transmitted from a multiple period grating and a four-layer antireflection coating structure.     

Polarization properties of a reflective fiber amplifier employing acirculator and a Faraday rotator mirror

We present a detailed study of the polarization properties of a reflective fiber amplifier composed of a circulator, a normal single-mode Er-doped fiber and a Faraday rotator mirror. The amplifier can preserve an arbitrary input state of polarization regardless of any external perturbations, and is completely free from polarization effects. The effect of imperfections of the Faraday rotator mirror is also discussed. Finally, we demonstrate experimentally the polarization-stability of the amplifier and its ability to compensate polarization mode dispersion both in the circulator and in the single-mode Er-doped fiber     

用于染料激光器的柱面透射式光束扩展器

本文提出了一种新颖的拄面伽里略透射望远系统。该系统用于染料激光器中作为光束扩展器，具有调整简便，光能损耗小等优点，可提高染料激光器的转换效率和输出功率。     

Space charge effects in a gyrotron employing a solid electron beam

The influence of space charge forces on the performance of a single cacity gyrotron oscillator which uses a solid electron beam was investigated. It was found that space charge effects cause a large efficiency degradation as the beam current is increased, if the other experimental parameters are unchanged. A small increase in the magnetic field, however, can restore the efficiency to higher values.     

Unstable ring resonator with an intracavity prism beam expander

A type of unstable ring resonator that includes a prism beam expander is proposed. Neither lenses nor curved mirrors are used, and transverse mode discrimination is achieved, despite the one-dimensional beam expansion, by configuring the cavity mirrors to cause 90° image rotation during a round-trip pass. The output beam has a filled-in rectangular cross section, and the cross section of the resonator mode is also rectangular.     

Fibre-optic polarising beam splitter employing birefringent-fibre coupler

An in-line fibre-optic polarising beam splitter, consisting of a fused birefringent-fibre coupler, is reported. Splitting of the orthogonally polarised lights was accomplished by increasing the difference of coupling ratios for the two polarisation modes. When a light at 1.402 ?m wavelength was coupled to the input lead, each polarisation was split on to different output leads, showing extinction ratios of more than 17 dB in both leads.     

Ion beam switching magnet employing HTS coils

This paper describes the design, construction, and testing of an ion beam switching high-temperature superconducting (HTS) magnet installed at Institute of Geological and Nuclear Science (IGNS) in New Zealand. It was designed by a consortium comprising American Superconductor Corporation (ASC), ISYS, Applied Engineering Technologies (AET), the New Zealand Institute for Industrial Research and Development (IRL), and Alphatech. The work was also supported in part by New Zealand Foundation for Research and Technology-Technology for Business Growth Programme. The magnet generates 0.72 T in the airgap between two 410×700 mm warm iron poles. The Bi-2223 HTS coils are conduction-cooled with a single stage Gifford-McMahon (G-M) type cryocooler for steady-state operation. The magnet was fully tested at ASC during the fall of 1996. This represents the first large-scale fully operational HTS physics magnet announced so far. The successful operation of this magnet has verified maturation of HTS magnet technology employing conduction cooling techniques with G-M type cryocoolers. Long term operation of this magnet in continuous use will prove the reliability of HTS magnet systems in critical applications and is expected to open future opportunities for HTS in other related areas     

Equivalent generators for a cavity with a bunched charged beam

Equivalent generators are developed to represent a conducting cavity of arbitrary size and shape through which a periodically bunched beam of charged particles passes. This development is reminiscent of the Lorentz reciprocity theorem. Three circuits are developed: a Norton's theorem generator, a Thevenin's theorem generator, and an equivalent wave generator.     

Local beam deflector interated in a diode laser cavity

Deflection of a diode laser beam using a local deflector monolithically integrated in the cavity near an output facet is demonstrated. The index distribution in the deflector is adjusted by controlling the injection currents, and the laser beam is scanned over 9° by the prism effect of the deflector.     

Eccentricity of the electron beam in a gyrotron cavity

Dependence of the coupling of the electron beam and RF field in a gyrotron cavity on eccentricity of the electron beam is studied.     

大口径哈特曼扩束系统的设计和研制

论述了用于哈特曼波前探测系统的透射式光学扩束器的研制.以三级像差理论为基础,分析了传统扩束器没能很好校正轴外像差的原因,在推导计算出初始结构参数后,通过ZEMAX光学设计软件,设计出轴上和轴外像差都得到很好校正的、大口径、大相对孔径、视场可增大的新型扩束器.并根据此哈特曼扩束系统的实际使用要求,考虑支撑受力与热变形等因素,为光学元件配以相应的结构设计,给出了具体的设计实例.介绍了加工过程与调整方法,提供了检验方式.最终验收得到波前PV值为λ/4.     

AC space charge effects on beam loading of a cavity

A calculation of the loading of a resonant cavity by an electron beam is presented. This calculation is the first to include all effects of ac space-charge. The fields in the cavity are determined in the presence of the beam, including the effects of higher order structure modes. The formulation also explicitly includes Ramo's space-charge waves of all ranks. The result reduces to the conventional ballistic beam loading result for low beam current. Comparison of the complete theory developed here with the ballistic result demonstrates that the ballistic theory is sufficiently accurate, typically accounting for the quality factor to within 5%, and the resonant frequency to within 1%. In addition, the theory is shown to agree well with particle-in-cell simulations.     

Using cavity ring-down to test laser high reflective thin film's loss

光学薄膜的损耗类型主要涉及吸收和散射,精确测定其数值是制备具有高品质和灵敏度指标激光薄膜的前提.本文以薄膜光学和激光技术为背景,介绍了谐振腔衰荡检测高反射薄膜的原理、特性以及测试方法.以1064 nm和1311 nm的高反射膜层为例,利用Losspro激光测试装置,对于二氧化锆( ZrO2)、五氧化二钽(Ta2O5)材料获得百万分(ppm)量级精度的损耗数据后,针对不同薄膜材料和工艺方法进行了对比检测,分析认为速率控制和离子束能量对于相同材料的激光高反射薄膜具有明显的影响,进而为薄膜样品的制备奠定了技术基础.     

1.064μm测风激光雷达扩束系统的设计

根据三级像差理论,提出了单片物镜与单片目镜的像差共轭的扩束器设计方法,设计了带有非球面的两片式扩束系统,从设计的结果看出,整个系统的像差被很好地校正.为解决1.064 μm不可见波长扩束系统发散角测试问题,提出了利用线列CCD和示波器结合检验光束发散角的方法,此检验方法简便,容易实现,检测精度高.     

基于衍射/反射光束整形系统的高密度泵浦源

利用二元光学元件微型化和对波面进行任意整形的特点,将二元光学衍射器件用于高功率激光二极管阵列光束的快、慢轴准直,并结合空心导管设计一种衍射/反射混合型光束整形系统,用于实现高密度、高均匀性LD泵浦源.应用时域有限差分法(FDTD)的严格矢量分析表明:所设计的二元光学准直器性能优良,准直后光束发散角在误差范围内接近衍射极限,慢轴方向衍射效率为82.21%,快轴方向为75.76%.模拟设计的结果表明:采用这种衍射/反射光束整形技术的高密度泵浦源能获得高功率密度和高均匀性的抽运光束,在空心导管出射端面附近光强起伏RMS<1%,并且在光束的准直性能和系统紧凑性方面优于传统整形方法.     

Effects of a finite axial magnetic field on the beam loading of a cavity

The effect of a finite axial magnetic field on the beam loading of a cavity is evaluated. The calculation extends Branch's classic paper on ballistic bunching in that both the conductive and susceptive components of the beam-loaded admittance are computed, for general values of axial magnetic field. Also included is a comparison of the analytic formulation with a two-dimensional particle-in-cell simulation. This paper suggests that the finite axial magnetic field used in linear beam tubes (typically exceeding 1.5 /spl times/ the Brillouin field) would only modify the beam-loaded admittance by about 20%, from that computed under the assumption of an infinite axial magnetic field.     

A UHF traveling-wave amplifier tube employing an electrostatically focused hollow beam

The increasing importance of beam-type microwave devices has stimulated interest in focusing methods other than the usual uniform magnetic field. One such method applicable to hollow cylindrical beams, proposed by L. A. Harris, utilizes a radial electric field acting on a spinning beam to counterbalance the space-charge divergence forces. A traveling-wave amplifier operating in the 300 to 600 mc region, employing this focusing method, was designed and constructed. Experimental results obtained with this tube are presented. Beam transmissions as high as 90 per cent and net gain over 15 db were obtained. Practical considerations and tube design factors are discussed. The primary advantage of this kind of focusing is in the elimination of the solenoid, and consequent reduction in power supply requirements and weight, accessibility of rf connections to the tube, and elimination of capsule and aligning adjustments. This focusing method appears to have great potential usefulness in hollow-beam applications, and particularly in devices where the spiral motion of the beam can be made to interact with a spirally traveling wave.