On the design of open resonators for quasi-optical gyrotrons

In the design of a 120 GHz 200 kW quasi-optical gyrotron, we have analyzed the influence of the open resonator geometry (two circular mirrors facing one another) on the electronic efficiency, the ohmic losses, the output coupling and the multimode behavior. The method we have used to optimized the resonator design will be presented. Mode selectivity is improved by using a resonator formed by two mirrors each of which has a central step. Numerical simulations show that single mode operation can also be attained in the more favorable situation of a magnetic field having a positive taper over the interaction region.     

Transient response of an open resonator in the time domain

In the present paper a time response of a quasi-optical open resonator when exciting it by a pulse signal with a radiofrequency filling has been investigated using an inverse Fourier transformation. The radiofrequency filling corresponds to millimeter wavelengths region. Fourier image of the time response of the resonator is calculated from a product of two frequency’s functions. One of these functions is the Fourier image of a pulse signal at the resonator input, and the second is a calculated or measured amplitude — phase characteristic of the resonator. When calculating the amplitude- phase characteristic of the resonator (a complex transfer coefficient) a plane — layered model of the resonator was used. Experimental investigation has been conducted in millimeter wavelengths with Fabry-Perot type open resonator. Amplitude- phase characteristic of the resonator were measured in “on passage“ regime in wide frequency band. It was shown that presence of weakly absorbing layer in the resonator leads to changing of the time response of the resonator. The obtained results can be used in the dielectric measurements, defectoscopy of stratiform materials, relaxometry, non-destructive control of materials and structures, etc.     

新型准光腔同轴虚阴极振荡器的研究

集合准光腔型虚阴极振荡器和同轴虚阴极振荡器的优点,设计了一种新型的准光腔同轴虚阴极振荡器。采用自由电磁振荡理论分析了3反射镜准光学谐振腔中的场分布,并用2.5维全电磁PIC程序对该器件进行了粒子模拟。在输入电压为600 kV,二极管电流为50 kA的条件下,得到主频为7.0 GHz,峰值功率超过6 GW的功率输出,其平均功率达2.5 GW,平均束波转换效率为8.3%。     

基于新型自耦合非对称阶梯阻抗谐振器的小型化三通带平衡滤波器

针对平衡滤波器的高集成度和高选择性的应用需求,基于一种新型自耦合非对称阶梯阻抗谐振器提出了一种具有高选择性的小型化三通带平衡滤波器。首先通过该平衡滤波器的差模和共模等效电路详细分析了其谐振器结构的谐振特性,并利用差模等效电路下的前三个谐振模式来分别实现三个通带。另外通过在电路对称面上加载电容和电阻元件来提高对共模噪声的抑制,且不影响差模频率响应特性。基于提出的多模平衡滤波器结构和设计方法,设计了一个通带频率为2.75/4.46/6.21 GHz的三通带平衡滤波器,并对其进行了加工和测试,结果表明,该结构可以实现紧凑的体积和高选择特性,并且具有很好的共模抑制特性。     

激光辐照下非稳腔镜变形对激光模式的影响

分析了正支虚共焦非稳腔中腔镜变形对激光模式的影响,采用时间离散化、快速傅里叶变换（FFT）和有限元分析(FEA)方法解决腔镜变形和激光模式两者之间的耦合问题。计算结果表明,随着激光器工作时间的增加,腔镜温升和变形相应增大,谐振腔模式变差,输出光场相位均匀性变差,呈现散焦现象,输出光束质量下降。实验验证了激光器输出光束质量随出光时间的延长而逐渐变坏。     

激光辐照下非稳腔镜变形对激光模式的影响

 分析了正支虚共焦非稳腔中腔镜变形对激光模式的影响,采用时间离散化、快速傅里叶变换（FFT）和有限元分析(FEA)方法解决腔镜变形和激光模式两者之间的耦合问题。计算结果表明,随着激光器工作时间的增加,腔镜温升和变形相应增大,谐振腔模式变差,输出光场相位均匀性变差,呈现散焦现象,输出光束质量下降。实验验证了激光器输出光束质量随出光时间的延长而逐渐变坏。     

Measurement of the electric field pattern of a Fabry-Perot resonator used in quasi-optical gyrotrons

The field pattern of the resonator used in a quasi-optical gyrotron operating in the millimetre wave range is measured. Two resonators are studied: one composed of a spherical mirror and an ellipsoidal grating and the other symmetric using two mirrors with annular slots. The measurements indicate that the electric field distribution is gaussian, in spite of the complex geometry of the resonator, and thus provide an experimental basis for the assumption often used to compute the efficiency of quasi-optical gyrotrons.     

高斯反射率镜单谐振光参量振荡器模式分析

采用高斯光束传输矩阵描述光参量谐振腔的行为,通过迭代计算模拟高斯光抽运高斯反射镜单谐振光参量振荡器的振荡过程,分析了谐振腔参数和抽运光口径对腔内输出模式的影响。报道了1 064μm脉冲抽运平 GRM腔单谐振非临界相位匹配KTP光参量振荡器的实验,其结果与理论分析相符。     

On classification of eigenmodes of an open resonator with spherical mirrors

A rigorous mathematical model describing eigenmodes of open resonators with spherical mirrors is proposed. Theoretical analysis of the spectral characteristics of an open resonator is performed for the case where the wavelength is comparable with the resonator size. Specification and significant generalization of eigenmode classification based on approximate open-resonator models are proposed. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 51, No. 12, pp. 1051–1060, December 2008.     

准光腔品质因数的标网测量与研究

 采用标量网络分析仪(SNA)对毫米波段的Fabry-Perot准光腔进行了品质因数测定。通过纵向半波数的测试确定了谐振峰对应的模式，给出了AV3617测量数据并计算了相应的外观品质因数和固有品质因数，详细分析了扫频测试的误差及其误差来源。分析表明，半功率点的频率测定误差是引起准光腔品质因数测量误差的主要因素；利用扫频源HP83630A较高的频率分辨率，结合参考频标使测试数据的有效位数增加，从而提高了测试准光腔品质因数的精度。     

热声谐振管品质因数的实验研究

回热器中填充了玻璃丝绵,在声驱动的热声谐振管中发生共振,通过测量谐振频率,分析热声谐振管的频率特性,辨识谐振管的品质因数,其测量结果能与理论计算值较好的吻合。实验证实,品质因数是评价热声谐振管工作性能的重要参数。     

Improved gyrotron cavity with high quality factor

For gyrotrons operating at the second harmonic of the electron cyclotron frequency cavities with high quality factors are needed. Up to now steep output tapers or abrupt output irises are used in order to provide a high reflection coefficient. Such circuits suffer from the problem of strong conversion to unwanted output modes. A promising possibility to achieve a high reflection at the cavity output (and thus a high quality factor) combined with high mode purity is the use of a rounded iris and an optimized nonlinear taper with very low unwanted mode conversion at the output of the resonator.     

Axisymmetric eigenmodes of magnetic type in an open resonator with spherical mirrors

We develop a rigorous mathematical model describing axisymmetric eigenmodes of magnetic type of open resonators with spherical mirrors. On the assumption that the spectrum of complex eigenfrequencies of an open resonator exists, it is proved that this spectrum is discrete and has finite multiplicity with a single accumulation point at infinity. Theoretical analysis of the spectral characteristics of an open resonator is performed in the case where the wavelength is comparable with the resonator sizes. The limits of applicability of the well-known asymptotic models of open resonators are established. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 49, No. 9, pp. 787–798, September 2006.     

准光腔品质因数的标网测量与研究

采用标量网络分析仪(SNA)对毫米波段的Fabry-Perot准光腔进行了品质因数测定。通过纵向半波数的测试确定了谐振峰对应的模式,给出了AV3617测量数据并计算了相应的外观品质因数和固有品质因数,详细分析了扫频测试的误差及其误差来源。分析表明,半功率点的频率测定误差是引起准光腔品质因数测量误差的主要因素;利用扫频源HP83630A较高的频率分辨率,结合参考频标使测试数据的有效位数增加,从而提高了测试准光腔品质因数的精度。     

非稳腔中调腔孔对光束质量的影响

在中、远红外波段的激光器中，组成谐振腔的反射镜基底材料多数是对可见光不透明的，采用在腔镜上开一小孔输入调腔光方法是最简便的。本文用Ｆｏｘ－Ｌｉ迭代法计算了无开孔及有开孔时正支非稳共焦腔空腔的模式，结果表明当调腔光开孔直径小于３ｍｍ时，对光束质量基本没有影响。     

Diffraction theory of an open resonator embedded in a uniaxial medium

A two-dimensional diffraction theory of an open strip resonator embedded in a umaxially anisotropic medium is presented. Applying the modified Kirchhoff approximation and a Green's function technique, the problem is reduced to the solution of a system of two coupled, homogencous integral equations for the unknown field distributions on the mirrors. The eigenvalues of this system of integral equations are related to the characteristic (complex) frequencies of the modes of the open resonator by an implicit relationship. The eigenvalues as well as the corresponding characteristic frequencies are calculated numerically. From the characteristic frequency of a mode, its resonance frequency, its diffraction loss and its quality factor follow immediatedly. For various resonator configurations the influence of the orientation of the optical axis of the uniaxial medium on the properties of the modes is studied in detail.     

基于轴棱锥带平面耦合输出镜的贝塞尔-高斯谐振腔

从较直观的概念出发,设计基于轴棱锥带平面耦合输出镜的贝塞尔-高斯谐振腔。应用Fox-Li数值迭代法对谐振腔横向光场模式进行较严格的分析,同时采用数值积分的方法,由输出镜面上光场采样点的数值直接模拟腔外输出光场分布情况。数值模拟结果与理论结果比较表明,该谐振腔的主模式与零阶贝塞尔-高斯光特征相似。针对实际中腔长可能并不严格地与最初设计腔长一致,讨论了腔长变化对谐振腔主模式分布的影响,发现当腔长变化较小时,谐振腔的横向模式特征基本保持不变。利用Nd:YAG激光器设计贝塞尔-高斯谐振腔进行实验,光束分析仪记录的输出光强横向分布与理论预期基本一致。     

Monofrequency excitation of open resonator with inclined comb grating

The theoretical and experimental analysis of the open resonator with the reflection diffraction comb grating has been presented. This resonator has excitation where is close to the monofrequency mode. This results may be used for the elaboration of mm-wave quasi-optical devices such as generators, mixer, converter, wavemeters and others.