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。     

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.     

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     

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。     

内含热薄透镜四镜环形腔的光束特性

二平二凹四镜8字型环形腔是色心激光、激光陀螺等研究经常采用的谐振腔。本文采用热薄透镜模型,运用等效腔方法,分析了四镜环形腔的光束特性。详细讨论了热效应对谐振腔基本特性的影响,给出了四镜环形腔的热不灵敏条件。这些结果对谐振腔的设计和应用具有一定的指导作用。     

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.     

External design freedom for optimization of resonator originatedbeam shaping

Modern fabrication techniques like electron beam lithography allow the use of resonator mirrors with sophisticated surface modulation. We use this flexibility to realize a resonator with a beam the intensity distribution of which is specified in the focal region. The phase in the focal region is used as a freedom to homogenize the beam in the active medium and by that to allow the satisfaction of the laser gain condition. This is possible by a decoupling of the beam propagation characteristic of the beam inside and outside of the cavity. The design concept is described and experimentally demonstrated in a Nd:YAG laser     

Design of a 2.5 THz submillimeter wave laser with optical pump beam guiding

A ring resonator design using the same set of mirrors for pump beam and submillimeter wave (SMMW) beam guiding is introduced. Optimal design is discussed on the example of a 2.5 THz methanol laser. It turns out that due to refocussing of the pump beam on the pinhole certain focal lengths of the focussing mirror, which mainly is responsible for the beam guiding, should be avoided. Diffraction losses and pinhole losses determine optimalg-parameters for which the pump beam guiding losses of the resonator are minimum, and optimal pump beam waist radii. The setup of an experimental laser with the optimized resonator and the experimental setup to measure laser performance are described, and results concerning laser output power, beam quality and efficiency are discussed.     

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     

Design of SMMW Laser Resonators with On-Axis Signal and Pump Beam Guiding in a Mirror Ring

A ring resonator design for optically pumped submillimeter wave (SMMW) lasers using the same set of four mirrors (including one focussing mirror) for pump beam and SMMW beam guiding is introduced. The optimum design is discussed on the example of a 2.523 THz methanol laser. It turns out that the focal length of the focussing mirror has to be adapted to the resonator perimeter. Eleven well suited focal length - resonator perimeter ratios, defining eleven standard resonator configurations, can be distinguished. The setup of an experimental laser with the optimized resonator and the experimental setup to measure laser performance are described, and results concerning laser output power, beam quality and efficiency are discussed. This paper is the extended version of the paper presented on the 23rd International Conference in Colchester [1] and continues a former article presented in this journal [2].     

内含介质的正交柱面一柱面镜象散腔

本文用矩阵光学的方法研究了内含介质的正交柱面一柱面镜象散腔。给出了显示象散作用的腔稳定图和稳定腔模参数公式，并作了数值计算。本文还研究了其光束传播特性，并讨论了其象散补偿问题     

Spherical Mirror Fabry-Perot Resonators

An experimental investigation of the Fabry-Perot interfometer (FPS) using spherical mirrors is reported. The FPS was operated as a microwave resonant cavity at 60 to 70 Gc. Measurements were made of the loss and coupling as a function of mirror spacing. The electric field variation within the resonator was also measured. Other characteristics of the spherical Fabry-Perot resonator were observed and are discussed. A qualitative discussion of the behavior of a spheroidal cavity resonator is presented and its relation to the FPS and beam waveguide is demonstrated.     

Compact free-electron laser resonators utilizingelectron-transparent mirrors

The potential advantages and the physical properties of several electron-transparent mirrors (e.g., metal meshes, thin foils, pierced mirrors, and Bragg reflectors) to be used in infrared free-electron laser resonators are reviewed. The conditions under which the effect on the electron beam quality can be kept small are discussed, and experimental results on the angular spread produced by a 2.5-μm-thick metal mesh on a 5 MeV electron beam are presented. The experimental test of a resonator with two different electron transparent output couplers is reported     

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.     

用于连续高功率YAG激光器的高斯镜稳定腔的设计

本文通过对高斯镜热透镜稳定腔(GRMSR)内光束特征的分析,提出了设计该类激光谐振腔的一般原则,并设计了平平腔型高斯镜稳定腔。实验结果与理论分析相符,并得到高输出功率、高光束质量的连续YAG激光输出。     

环形腔内光束的传输特性

本文以四面镜8字形稳定环形腔为代表,利用传输矩阵法、等效厚透镜法和腰斑处为参考面展开等三种方法,对环形腔内光束的传输特性作了详细的计算和分析,并与驻波腔的结果进行了比较。对象散的影响亦作了讨论。     

The tilt sensitivity of a grazing incidence confocal unstable resonator with applications to free-electron lasers

The paraxial sensitivity to tilt misalignments of a four-element grazing incidence unstable resonator is calculated in terms of the beam displacement both at the center of a free-electron laser (FEL) wiggler and on the tilted component. A convenient representation of the resonator is made by splitting the diverging elements such that the resonator is modeled as three afocal telescopes. This formulation simplifies the round-trip system matrix and yields terms that are physically meaningful. The grazing incidence resonator is then compared with an equivalent nongrazing incidence two-element resonator. For a tilt misalignment of the small-angle-of-incidence components, the resulting beam displacement at the center of the FEL wiggler is calculated to be equivalent for both types of resonators and is found to be a function of the wavelength, the round-trip magnification, the fractional allowable beam displacement at the center of the FEL wigglers and the beam size On the small-angle-of-incidence components.     

Tests of a grazing-incidence ring resonator free-electron laser

The authors describe operational experience of the first free-electron laser (FEL) using a grazing-incidence ring resonator. The Boeing FEL optical cavity was changed from a simple concentric cavity using two spherical mirrors to a larger grazing-incidence ring resonator. Initial tests showed that poorly positioned ring focus and unreliable pointing alignment resulted in reduced and structured FEL output. Later efforts concentrated on improving the resonator alignment techniques and lowering the single-pass losses. FEL performance and reliability have significantly improved due to better ring alignment. The alignment procedure and recent lasing results are described. The effect the electron beam has on lasing is also discussed. Measurements are presented showing FEL temporal output and wavelength are sensitive to electron beam energy variation     

多元件光学谐振腔的公式化分析方法

本文使用“混合”等价腔的变换技巧,将含热透镜的望远镜腔最后化为[1]、[2]中的两种基本类型,从而可对光腔的模参数,包括两腔镜处的光斑半径、各腰斑的大小和位置给出公式化的解析结果.解决了一般多元件腔模参数的公式化表述问题.数值计算不仅证实了解析结果的正确性.而且给出了整个腔内的光束分布图,光斑尺寸随热焦距的变化关系等数据.     

Quasi Optical Resonator for Measuring Surface Resistance and Its Distribution of High Temperature Superconductor Film

A quasi optical resonator consisting of two spherical mirrors and a new calibration technique were developed to measure the surface resistance Rs and its distribution of high temperature superconductor (HTS) at 94GHz. The Q factor of the open resonator is greater than 1.4×10⁵, and the radius of Guass beam waist is 2.53mm. This method has advantage of being nondestructive, high sensibility, convenient experiment setup.