宽线宽Cr∶LiSAF受激布里渊散射相位共轭谐振腔的实验研究

将受激布里渊散射(SBS)相位共轭镜置于谐振腔中,构成宽线宽Cr∶LiSAF相位共轭激光器,对其输出特性进行了初步研究. 由于宽线宽激光的受激布里渊散射阈值较高,所以Cr∶LiSAF相位共轭激光谐振腔的形成比较困难.为了提高起始腔中的激光能量密度,我们将起始腔输出镜的透射率减小,后腔镜为高反镜,在SBS池的两端分别用透镜将腔内激光聚焦到池中,选用适当的SBS介质.实验中观察到相位共轭腔的输出脉冲,其脉冲宽度约为80 ns,实现了相位共轭腔的自调Q输出.与共轭腔未形成时的静态输出光束相比,光束质量得到明显提高. 我们还在起始腔中放置了三个色散棱镜.由于腔内棱镜所造成的损耗较大,单靠起始腔中的静态激光无法达到相位共轭腔的启动阈值.为此,借助电光调Q来增大起始腔中的激光能量密度,即以动态激光启动相位共轭腔.实验表明,这种相位共轭腔不仅能进一步压缩激光脉冲,达到30 ns左右,更重要的是能够有效地提高输出光束的质量,并能在一定的波长范围内调谐激光输出.(OB5)     

环形激光谱振腔的分析

本文采用光束传输矩阵方法和高斯光束的透镜变换方法导出了由一个,两个,三个和四个球面反射镜组成的环形激光谐振腔的稳定性判据,G参数表达式以及腔内高斯光束和球面波光束以谐振腔参数表示的解析式。     

具有非对称高斯反射率相位共轭光腔的基模

由高斯光束泵浦的四波混频相位共轭反射镜(PCM)具有横向高斯分布的反射率.这种分布是空间非对称的.本文给出这种PCM(包括自泵浦情况)的光束变换矩阵,把它用于自泵浦相位共轭光腔的分析;得出腔内振荡是椭圆高斯光束的结论.     

具有两个瑞利长度三镜折叠腔的设计

为了提高倍频效率、分析倍频晶体内束腰位置对倍频效率的影响,根据基模高斯光束传输特性,结合稳定三镜折叠腔中端镜处等相位面曲率半径与腔镜曲率半径相等这一特点,在激光光束传输的合适位置上,放入与等相位面曲率半径相同的腔镜,构成倍频晶体内具有两个瑞利长度的三镜折叠腔,提高了倍频效率。对比了相同端镜构成的具有一个瑞利长度和两个瑞利长度谐振腔,相对于分臂长度变化的稳区范围。结果表明,使用5W光纤耦合880nm激光二极管,端面抽运3mm×3mm×5mm的Nd:YVO₄,采用10mm×2.1mm×0.5mm的PPMgOLN为倍频晶体,使用具有两个瑞利长度的谐振腔比具有一个瑞利长度的谐振腔,整体提高倍频效率约18%,两种腔型的光束质量相同,倍频光与基频光偏振方向一致,输出稳定的低噪声绿光,验证了谐振腔设计的有效性。该研究对腔内倍频效率的提高是有帮助的。     

几何光学近似区的相位起伏和幅度起伏

研究了几何光学近似区的相位起伏和幅度起伏.分三种模型:平面波、球面波和高斯光束,Tatarskii给出了平面波的结果,本文进一步给出了球面波和高斯光束的结果.对于平面波和球面波,考虑了在几何光学近似区,发射端的相位扰动如何影响接收端的幅度起伏;对于高斯光束,考虑了发射端自适应光学共轭相位对接收端的幅度起伏的影响.结论是:对于平面波,只有折射率不均匀媒质的相位起伏的曲率项对幅度起伏有贡献,只有发射端的相位扰动的曲率项能影响总体的幅度起伏;对于球面波,折射率不均匀媒质相位起伏的倾斜项和曲率项共同对幅度起伏有贡献,只有发射端相位扰动的曲率项能影响总体的幅度起伏;对于高斯光束,折射率不均匀媒质相位起伏的倾斜项和曲率项共同对幅度起伏有贡献,发射端的自适应光学共轭相位的倾斜项和曲率项共同作用于总体的幅度起伏.     

掺杂铌酸锂双相位共轭镜光学谐振腔的温度特性

用带导模型和耦合波方程在强泵浦条件下建立了能反映温度特性的光折变双相位共轭镜光学谐振腔的稳态强度公式,研究了这种光腔的温度特性.相位共轭镜的温度相对于输出光功率来说存在着一个最佳值,在此温度值下输出光功率最大.不同温度下两个相位共轭镜的最佳泵浦比不同.用Ce:LiNbO3单晶和He-Ne激光构成了光折变双相位共轭镜光学谐振腔.测得的实验值与理论值基本吻合.     

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。     

弱高斯光阑近似和相位共轭腔

本文证明了在弱高斯光阑近似下,相位共轭腔中不存在确定模,只有当非弱高斯光阑处于腔中或相位共轭镜之前,相位共轭腔才具有确定的模。     

望远相位共轭激光腔

考虑到相位共轭腔和望远镜谐振腔的一些良好特性,本文提出了一种新的激光腔型结构——望远相位共轭谐振腔,以此提高激光输出功率和改善输出光束质量。 本文分析了该型的调Q原理,探讨了该激光     

高斯输出镜对平凹腔模式影响研究

运用边界元法数值计算了平凹谐振腔具有高斯反射镜情况下的场强分布和相位分布,考察了高斯反射镜谐振腔的模鉴别规律和增大模半径的规律.高斯反射率镜平凹腔可扩大模式本征值差,具有模鉴别能力,中心反射率大小对选模能力也有影响,但对基模半径无影响.同时,高斯镜具有对输出光束整形的功能.     

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。     

高斯和超高斯型随机相位调制的光腔模式

本文利用空间－频率域相干模式理论对内置高斯或超高斯类型的随机相位调制的腔内模式进行了数值分析。结果表明：在这种随机相位片调制下,通过控制参数,可以在一腔镜上得到部分相干的类超高斯分布的光束,且类超高斯阶次可由相位参数控制;本文还引入新的参量－平整度来描述光束的整体强度分布的特征。     

Radiation characteristics and performance of millimeter-wave horn-fed Gaussian beam antennas

Radiation characteristics and performance of Gaussian beam antennas (GBAs) are studied theoretically and experimentally in the 60 GHz band. A GBA consists of a plano-convex half-wavelength Fabry-Perot (FP) resonator excited by a guided source with a metal flange. Two reflecting metal mesh mirrors are formed on both faces of the cavity. After a review of the principles and quasi-optical performance of plano-convex FP resonators illuminated by a plane wave, a new formulation is proposed to compute the radiation patterns of GBAs: the usual expression of the waist radius inside open resonators is modified to account for the horn aperture and for the grid parameters of the plane mirror. Standard closed-form relations of vector Gaussian beams are then used to compute the radiated copolar components. In particular, it is shown that the plane mirror is not an equiphase surface, due to the metal flange of the horn. The true phase distribution is approximated by a spherical wavefront. As a result, the directivity of the antenna becomes lower than its quasi-optical value. Experimental data obtained at 60 GHz with several pyramidal horns and various cavities agree very well with the theory. Sidelobes are lower than -25 dB, and the cross-polarization level is the same as that of the primary radiator. Universal curves showing the variations of resonant frequency, -3 dB bandwidth, gain, and radiation efficiency as a function of mirror reflectivity are very useful for the design of GBAs.     

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.     

Nonparaxial eigenmodes of stable resonators

A method to determine the nonparaxial eigenmodes of stable resonators is presented. The method is based on the perturbation theory of Lax et al. For calculating nonparaxial components of the electric field. A matrix formalism which uses a mode expansion into paraxial Hermite-Gaussian modes is applied to describe the nonparaxial propagation and the phase shift at a parabolic and a spherical mirror. Expressions for these matrices are derived analytically. Multiplying all matrices corresponding to a round trip, a matrix for the resonator is obtained. Eigenmodes of the resonator are numerically found by solving the eigenvalue problem. In the special case of paraxial propagation and parabolic mirror profiles, the standard Hermite-Gaussian modes result analytically. Nonparaxial modes of a given resonator are compared for different mirror profiles. It is found that, in the nonparaxial domain, spherical mirrors do not change the mode profile and the frequencies of the transverse modes, in contrast to parabolic mirrors which aberrate the beam profile and cause frequency shifts     

热不灵敏激光谐振腔补偿特性研究

为了实现热容激光器远场可聚焦性的实时控制,采用角锥棱镜阵列作为准相位共轭反射镜对光束波前进行被动式实时补偿。详细研究了阵列角锥棱镜谐振腔的光学特性,通过优化谐振腔的构型,进行腔内滤波,抑制角锥之间的共轭模式,获得了在保持90%输出能力条件下的单模输出,中心主斑能量集中度提高了约4.5倍,远场可聚焦性与传统的平-凹腔比提高约10倍。结果表明,角锥棱镜阵列谐振腔具有热不灵敏的特性,可显著提高热容激光器的远场聚焦能力。     

Determination of the thermal lens in solid-state lasers with stablecavities

A useful method to determine the thermal lens in a thermally loaded material inside a laser resonator under operation is presented. The laser beam emitted is focused with a lens placed exactly at the distance of its focal length behind the output mirror. For stable spherical resonators this focusing is not astigmatic even for an astigmatic cavity. This fact is used to experimentally determine the thermal lens including the beam quality factor (beam propagation factor) M² of the laser beam. Measurements are presented for an end-pumped rod and a longitudinally pumped slab laser serving as an example for an astigmatic cavity     

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     

What is the confocal parameter?

A novel derivation is presented of the Gaussian beam as a limit of the solution to the full wave equation. Usually, the functional form of the Gaussian beam is found by a two-step process. First, the Green's function of the paraxial wave equation is identified. Then, since the paraxial wave equation is invariant under translation, the z-axis variable is replaced by z+jb. It is shown that when starting with a solution of the full three-dimensional Helmholtz equation in spherical coordinates, performing the transformation z→z+jb corresponds physically to causing the phase fronts of the solution to become ellipsoids. The separation of the foci of the ellipsoids is 2b, where b is the confocal parameter of the beam. In the paraxial limit the ellipsoidal solution becomes a Gaussian beam. Adopting this approach to Gaussian beams allows a simple, geometrical interpretation of the optical resonator stability criterion