Equivalent circuit parameters of an aperture coupled open resonatorcavity

In this paper, we use modified form of Bethe's small hole coupling theory to compute equivalent circuit parameters of an aperture coupled open resonator cavity. The open resonator cavity is composed of spherical mirrors of circular cross section. The cavity is coupled to a rectangular waveguide by means of a common hole in the mirror and the shorted end wall of the rectangular waveguide. Closed form expressions have been obtained for the equivalent circuit parameters. Experiments conducted in the W-band frequency range show good agreement with theory when an experimentally estimated correction to the transmission coefficient is applied for the thickness of the coupling holes     

3kW射频板条CO2激光器抛物面非稳波导腔研究

为了提高传统球面镜腔3kW射频板条CO2激光器光束质量,设计了新型抛物面镜负支非稳-波导混合腔;结合标量光束的瑞利-索末菲衍射理论与特征向量法,研究了大菲涅耳数下镜面类型对非稳波导混合腔光场传输特性的影响;利用矩形波导理论、1维近似分析得出了波导传输损耗及偏振情况。结果表明,将非稳方向输出镜和尾镜改为与光轴交点处曲率半径为R1=951.32mm和R2=1088.68mm的抛物镜面,能够避免尾镜漏光,可有效改善模式鉴别特性;常用波导电极镀膜材料中,镀铝电极内波导方向传输损耗最小,传输光场为x偏振的EH1模。采用电极镀铝的抛物面非稳波导腔能够降低损耗、提升光束质量。     

高斯镜平凸非稳腔本征模场的有限元数值计算

为了研究激光在高斯镜平凸非稳腔中的模式和相位特征,在SIEGMAN分析多元件非稳腔的理论基础上,采用有限元数值方法计算耦合输出镜镜面反射率为高斯分布的圆镜平凸非稳腔本征模场分布。将光场在腔内一次往返的ABCD系数代入惠更斯-基尔霍夫衍射积分方程,可以写出光场往返一次的衍射积分方程。将镜面分割成若干个等宽圆环,把衍射积分方程转化成矩阵相乘形式,经过数值计算,得到理想空腔和非共轴空腔优先起振的光场本征模式分布结果与相位特性。计算结果表明,当合适选择输出镜半径与高斯反射率分布,可以得到光斑半径为0.3cm的基模高斯光束输出,此计算结果与实验结果相符。同时也讨论了耦合输出镜对光束质量的影响。     

A tilted mirror unstable resonator laser cavity

A simple unstable resonator cavity using flat optics which provides a nonannular low-divergence output beam from a large mode volume is described. The resonator uses as output the "spillover" from a walkoff mode established between a pair of tilted flat mirrors; this also allows continuous adjustability of the output coupling. An extra pass of this spillover output through the gain medium helps to provide a saturated output. Results obtained using this resonator on a CO2oscillator are described.     

电子束轰击半导体偏转调制放大器带状层流电子束的设计

本文给出了用于电子束轰击半导体器件的带状层流电子束的设计考虑、计算机分析和实验结果。采用特殊校正透镜获得了截面为1×3mm~2的带状层流束。校正透镜的使用对于有限宽度带状束的实现是一个重要措施,可推广应用于其他场合。     

Attenuation of a shielded rectangular dielectric rod waveguide

The attenuation coefficient of a rectangular dielectric line enclosed by a rectangular shield is obtained by the use of a rigorous mode-matching method to calculate the required mode field intensity. The cross section of the waveguide is overlaid by a grid, and numerical integration is used to determine the power flow, dielectric, and conductor losses and respective attenuation coefficients. To obtain experimental verification, a length of waveguide was made into a resonator, and measured and calculated Q factors were compared. The results for the E/sup y//sub 11/ mode show how the influence of the shield decreases with distance. This is relevant to the design of dielectric waveguide structures and in filter applications where dielectric resonators are used.     

Gaussian-beam open resonator with highly reflective circularcoupling regions

A high-Q open resonator with quasi-optical coupling regions is described. The resonator consists of a pair of spherical mirrors, on each of which a highly reflective, partially transparent circular region is fabricated with a diameter larger than several wavelengths. The signal is coupled in and out as a Gaussian beam by means of these regions. Both very weak coupling and very efficient mode conversion are simultaneously achieved. This results in a Q-factor over 2×10⁵ and a high signal-to-noise ratio at 105.9 GHz. The Q-factor of the open resonator can be varied by rotating the output mirror to change the angle between the directions of the conducting stripes on the two mirrors     

考虑波导壁影响开放腔孔耦合品质因数的计算

本文计算了矩形波导壁孔耦合球面开放腔的孔耦合品质因数。计算运用了偶极子近似模型，考虑了波导壁对偶极子磁极化率张量的影响。计算结果和文献（２）中实验值吻合得很好。     

Method of Synthesizing Nonuniform Waveguides

A method is proposed for the synthesis of continuous nonuniform waveguides with rectangular cross section so that they show desired electromagnetic properties for discrete frequencies when excited by the TE/sub 10/ mode. Starting from a uniform structure with known properties, the shape of the nonuniform waveguide is attained step by step by small systematic deformations. To show the feasibility of the method proposed, the mathematical formalism and numerical results are presented for reactive one-ports and filters with simple properties. In these cases, the problem is reduced to the solution of an equivalent resonator problem, i.e., a nonuniform waveguide resonator is developed for which a certain set of resonance modes occur at desired frequencies.     

高斯变反镜改善板条激光器光束质量的研究

在实验中对比研究了稳腔和高斯变反镜非稳腔两种腔型。采用尺寸为66.7 mm×11 mm×1.7 mm板条Nd∶YAG增益介质,泵浦功率860 W条件下,稳腔获得196 W的激光输出,Mx2=2.47,My2=38.6;高斯变反镜非稳腔获得102 W激光输出,Mx2=2.34,My2=6.48。实验结果表明高斯变反镜非稳腔明显改善了板条激光器宽度方向的激光输出光束质量。     

Experimental investigation of extinction cross-section of single vegetation elements using open resonator

The experimental results of investigation of the total cross — section of scattering and absorption (extinction cross — section) σ_t of stalks and strip leaves of grass in millimeter waves range are presented. The investigation was carried out using open quasioptical resonator with spherical mirrors. Measirements were carried out as by absolute method as using the relative method. Experimental results obtained by two different methods showed that in spite of some data differences obtained by absolute and relative methods the latter may be used for estimation of the extinction cross — section σ_t of vegetation elements.     

The advantages of a negative branch unstable resonator for use with free-electron lasers

The sensitivity to misalignment of an almost concentric stable resonator is compared to that of a negative branch confocal unstable resonator, with specific applications to free-electron lasers. The practicability of both resonators is examined for both grazing and normal incidence configurations within the constraints of maximum feasible length, finite angular stability of resonator mirrors, size (determined by cooling requirements) of laser beam on mirrors, and minimum electron beam spot size in the wiggler. For the examples presented, a numerical fast Fourier transform propagation code was used.     

Effects of hard apertures on mode properties of resonators with gaussian reflectivity mirrors

The effects of hard apertures on the energy distribution, the far-field beam quality, the mode volume, and the discrimination against high-order modes in Cassegrain resonators with Gaussian reflectivity mirrors have been investigated both theoretically and experimentally. It has been shown that, in the far field, the fraction of energy in the secondary lobes remains small as long as the ratio of the design beam waist to the radius of the gain mediumw_{b}/ais <0.40. Forw_{b}/a > 0.7, deterioration of the beam quality and diffraction losses counterbalanced a more efficient filling of the gain medium to limit the resonator efficiency. At low magnifications, resonators with Gaussian mirrors out perform resonators with Standard mirrors.     

Explicit formulas for the fundamental mode of a linear resonator with elliptic mirrors and construction of higher order modes

A linear resonator bounded by elliptic (hyperbolic) mirrors with noncoinciding principal curvature directions is considered. Explicit analytic formulas describing the fundamental mode of such resonator are derived in the principal approximation. A procedure of constructing higher order modes is developed. The potentialities of the technique are exemplified by considering a resonator with mirrors whose shapes are close to spheres and a resonator with elliptic mirrors whose shapes are close to each other.     

虚共焦非稳腔腔内失调因素分析及实验研究

在腔内失调理论分析基础上,采用Hartmann?蛳Shack波前传感器实验研究了无源正支共焦非稳腔失调后输出光束像差特性,结果表明,腔内倾斜像差对光束强度分布有显著的影响,但小的腔内倾斜扰动不会使输出光束的相位分布中的高阶像差发生变化。当腔镜垂轴移动偏离光轴时,可能引起某些Zernike高阶像差,如彗差和像散的增大,但首先带来的是Zernike倾斜像差,类似于引入腔内倾斜扰动时的结果。因此在做腔内像差自适应校正时,应首先考虑腔内倾斜像差的校正。该方法为腔内像差特性的研究和像差校正提供了一定参考。     

Properties of an unstable confocal resonator CO2laser system

The results of an experimental and theoretical study of the properties of a confocal unstable resonator used with a conventional CO2-N2-He laser operating at 10.6 μ are presented. Measurements were made of the near- and far-field intensity distribution of the aligned resonator for Fresnel numbers of 3.7, 6.1, and 7.1. Fundamental mode operation was achieved in all cases. Beam steering and mode degradation associated with mirror misalignment were also studied experimentally. Suitable geometric models have been developed to account for 1) the sensitivity of the resonator output coupling and center far-field intensity to variations in the resonator length and mirror curvatures, and 2) the sensitivity of the beam direction and power to angular misalignment of the mirrors.     

Beam properties of AlGaAs power lasers with high-quality etched mirrors

High-quality etched mirrors for AlGaAs/GaAs power lasers for applications in optical storage have been fabricated by chemically assisted ion-beam etching (CAIBE). In order to ensure flat mirror facets of the ridge-waveguide lasers, a flared-waveguide end section is used. This results in a very slight mirror roughness of approximately 20 nm across the beam cross section, and yields excellent beam properties allowing diffraction-limited focusing up to 50-mW output power.<>     

A rectangular beam waveguide resonator and antenna

A closed microwave resonator is derived from the beam waveguide of rectangular symmetry. The resonator is essentially a metal box with one curved wall and approximate dimensionslambda/2bylambda/3by20lambda, wherelambdais the free-space wavelength. Each beam waveguide mode is shown to resonate at a distinct frequency. When apertures are cut in one wall of the resonator a line source antenna is formed. Since then = 0andn = 1beam modes have field distributions which are, respectively, a Gaussian and the derivative of a Gaussian, the radiation patterns produced are of interest in monopulse radar and tracking. A 9 GHz resonator antenna was built, and its measured radiation patterns confirm the theory.     

Method for excitation of a high-order spatial mode in the input cavity of gyroklystron

Microwave-power input devices for a multimegawatt pulsed gyroklystron that works in the centimeter-wavelength range using a relativistic electron beam are considered. A device representing a supply waveguide with rectangular cross section that is tangentially interfaced with the side wall of a hollow cylindrical cavity is proposed for the excitation of a high-order rotating spatial mode as the working mode of the input cavity. The efficiency of the device is numerically optimized and measured to be 70% at a low power level using a broadband Bragg reflector for the input variant that provides the excitation of the TE_6,1,1 mode.     

High-power CO2 laser with coaxial waveguide anddiffusion cooling

A diffusion-cooled CO₂ laser using a coaxial waveguide is analyzed theoretically and experimentally. The resonator used for extracting the laser beam consists of two annular plane mirrors enclosing the two ends of the waveguide. The beam exits through an aperture in one of these annular mirrors. The mirror tilt is shown to provide efficient beam extraction through this aperture. A theoretical resonator model based on the vector modes of propagation in a dielectric coaxial waveguide is presented. Experimental data show the feasibility of coaxial waveguide lasers and their ability to supply beams of high power and quality. Experimental data are discussed with respect to the presented theory