猫眼谐振腔氦氖激光器理论分析

猫眼逆向器作为谐振腔镜与一个凹面镜构成猫眼激光谐振腔.精确计算了三种猫眼逆向器(即理想猫眼逆向器和两种存在误差的猫眼逆向器)的逆向平行反射性，并对应用这三种猫眼逆向器的谐振腔中高斯光束的各项参数进行了深入分析，得出结论：对于高斯光束，凸透镜的焦距、凹面镜曲率半径、凸透镜与凹面镜间距三者相等的猫眼逆向器为理想逆向器，其逆向平行反射性最好，此时猫眼谐振腔处于理想状态，基模模体积最大，远场发散角最小，稳定性最好；在猫眼谐振腔的设计中，要尽量减小猫眼逆向器中凸透镜的焦距，增大凹面输出镜的曲率半径；猫眼逆向器存在误差时谐振腔的各项性能将受到影响.为猫眼谐振腔激光器的设计提供了理论依据.     

猫眼激光谐振腔横模选择特性研究

将猫眼逆向器作为激光谐振腔的一个腔镜组成猫眼谐振腔。介绍了猫眼逆向器的结构,阐述了猫眼逆向器中凸透镜和凹面镜的间距改变时猫眼曲率半径的相应变化,并通过有效地控制该间距来选择激光横模,从而保证基横模输出。在激光谐振腔衍射积分方程的基础上,运用牛顿柯特斯数学方法,对不同参量下的猫眼激光谐振腔的横模状况进行分析,得出了各阶横模对应的特征值和功率损耗,计算出保证基横模输出的参量,并与实验对比,得到了一致的结论,为激光器的横模选择和控制提供了一种简便易行的新方法。     

Modeling of vertical external cavity semiconductor laser with MQW resonant structure

Numerical model is developed for modeling pulsed operation of a vertical external cavity semiconductor laser (VECSEL) with a resonant gain structure. Properties of optical modes for compound resonator formed by Bragg reflector, chip boundary and external spherical mirror were studied. For above threshold operation carrier density in each of quantum wells (QW) obeys non-linear diffusion equation with a source supplied by electron-hole pairs generated in barrier layers by pump radiation or fast electron beam. A new iteration procedure for round-trip operator evaluation was developed, which provides linear growth of computation time with the number of QWs. Results of numerical simulations are reported for a VECSEL comprising 25 QW in resonant configuration and the output spherical mirror with curvature radius 3 cm. Variation of distance to the external mirror is found to result in notable changes in power and optical quality of the output beam. The decisive role of gain and index non-linearity in these changes is identified. A range of values of distance to external mirror is found where iterative procedure does not converge. In another range, the resulting solution depends on the initial conditions for the iteration procedure.     

Control of transverse mode pattern in a helium-neon laser using the cat’s eye cavity

This paper introduces an innovative method to control and select transverse mode pattern in a He-Ne laser. The cat’s eye cavity is established by using a cat’s eye reflector as the reflecting mirror. Laser transverse mode pattern varies continuously when the distance between the convex lens and the concave mirror is changed, which form the cat’s eye reflector. By Newton-Cotes method, the numerical solution of two-dimensional diffraction integral equation in the cat’s eye cavity is obtained, the laser operating modes under various parameters are analyzed, and the eigenvalue η_mn and diffraction power loss corresponding with every transverse mode are calculated. The parameters assuring fundamental transverse mode output are figured out, which match the experiment results well. Therefore, a new convenient real-time means for the control and selection of the laser transverse mode is realized.     

Feedback coupling loss in single mode fiber lasers

Based on the expansion of the fundamental mode LP₀₁ in single mode fiber in terms of Laguerre-Gaussian free space modes, the feedback coupling losses for two different types of cavity mirror, i.e., a curvature mirror and a combing mirror of a lens and a plane mirror, are numerically calculated for the first time. The results show that, for the curvature mirror, the lowest coupling loss is obtained when its curvature radius matches the wavefront curvature. In particular, if a plane mirror is used as the cavity mirror, it has to be placed close to the fiber end to obtain the low coupling loss. For the combing mirror, the lowest coupling loss can be obtained when the plane mirror is placed at the back focal plane of the lens, and the variation of the coupling loss is insensitive to the mirror positions for the lens with longer focal length. Finally, the plane mirror and the combing mirror of a lens and a plane mirror are suggested to be the cavity mirror in the practical construction of the high power fiber lasers.     

输出环状光束的新型激光谐振腔

提出一种输出环状光束的新型激光谐振腔,即在稳定激光谐振腔中采用外环耦合方式得到环状光束的输出。利用For-Li数值迭代算法求解此类激光谐振腔的积分方程,通过计算机编程计算了平面一凹球面稳定谐振腔的输出端平面镜在不同半径的情况下,谐振腔镜面上和衍射耦合输出场基模的振幅和相位分布。计算结果预示了当输出端平面镜半径小于通常的稳定腔的基模半径时,衍射耦合输出场有稳定的环状光束输出。实验中TEA CO2激光器采用印刷电路板预电离结构,增益长度90cm,腔长5m,球面全反射镜曲率半径20m,输出端平面镜半径4．5mm,得到了内环半径为4．5mm、外环半径为5．5mm的基模环形光斑输出。从而在理论上和实验上证实了该方案产生环状光束的可行性。     

Laser beam brightness of apertured optical resonators

We model the fundamental mode of a circularly symmetric plano-concave resonator where one mirror is apertured by a super-Gaussian aperture, while the other is apertured by a π/2 phase aperture. The aim of the paper is to find the best values of the apertured cavity parameters allowing the highest output beam brightness. For that we take into account loss level, fundamental mode volume and beam quality factor M². We demonstrate that for a given loss level, the phase aperture is able to increase the laser beam brightness, with a rate of about 60% when its diameter is properly chosen.     

Improvement of the operation parameters for a Cr:LiSAF ultrashort-pulsed laser

The optimization of the pumping power that is focused on a gain medium inside an optical cavity is fundamental for increasing the efficiency of the power transferred inside a crystal, in this way increasing the output power of the laser. Nevertheless, in the case of pumping with a highly astigmatic laser diode, an undesirable form of the beam is focused on the cavity and the process to improve the cross section and sizes of the beam produce a notable reduction in the effective pump power ultimately focused in the crystal. The cavity design improvements for a Cr:LiSAF laser pumped with a 200 um × 1 um laser diode emission is presented for three different configurations, Z, V, and ring. The pump power is introduced in the cavity through a simple optical array, coupling more than 83% of the laser-diode power. The design requirements for the resonant cavity are reviewed in order to improve the coupling between the fundamental mode of the cavity and the cross-section form of the pumping beam. The stability limits of the cavities and Kerr sensitivity region are presented.     

Optical losses in dielectric apertured terahertz VCSEL

The resonant wavelength and mode radius of the fundamental modes supported by an oxide apertured terahertz vertical surface emitting laser are determined from Gaussian resonant theory and scalar variational method. The reflectivity of the Bragg mirror is calculated for the lowest modes and it decreases as the aperture size decreases. The aperture radius, thickness, and axial position in the cavity are shown to be an important factor for high efficiency vertical cavity surface emitting lasers and single mode operation. When the aperture size is much larger than the emitting wavelength, the optical loss is negligible. However, the optical loss strongly depends on the aperture size and thickness when aperture size is similar to or smaller than emitting wavelength.     

Efficient High-Power Ho:YAG Laser Pumped by Dual-End-Diode-Pumped Tm:YLF Laser

We report a Ho:YAG (Ho-doped yttrium aluminum garnet) laser pumped by a dual-end-diode-pumped Tm:YLF (Tm-doped yttrium lithium fluoride) laser to obtain an efficient experimental device with high output-power characteristics. We study the influence of the specific values of the output coupling mirror transmittance, the resonant cavity length, and the radius of curvature of the output coupling mirror on the Ho:YAG laser output characteristics. Under optimum experimental conditions, under which the output coupling mirror transmittance was 30%, the resonant cavity length was 25 mm and the output coupling mirror radius of curvature was 300 mm, and the maximum pumping power of the dual-end-diode-pumped Tm:YLF laser was 15.2 W. We obtain an efficient high-power 2.122-μm laser output of 7.98 W from the Ho:YAG laser. The optical-to-optical conversion efficiency is 52.5%, and the beam quality factor figures are M _x ² ?=?2.89 and M _y ² ?=?2.97.     

LD端面泵浦Cr4:YAG被动调Q激光器输出特性研究

对激光二极管端面泵浦Cr⁴⁺:YAG被动调QNd:YAG激光器输出特性进行了实验研究.实验研究发现,激光器输出功率及脉冲重复频率随谐振腔长度增大而增大.为解释这一实验现象,测量了泵浦光斑在激光晶体内尺寸,同时计算了激光晶体及Cr⁴⁺:YAG晶体内的基模激光光斑半径随谐振腔长度变化.分析结果表明:激光晶体内泵浦光斑尺寸远小于激光晶体内基模光斑半径,腔模间交叠效率较低;当腔长增加时,激光晶体内的基模激光光斑减小,腔模间交叠效率增加,从而导致输出功率及脉冲重复频率随腔长增加而增加;另外,Cr⁴⁺:YAG晶体内光斑半径也随谐振腔长度减小,引起Cr⁴⁺:YAG晶体漂白时间缩短,导致脉冲重复频率随腔长增加而增加.     

LD端面泵浦Cr~4∶YAG被动调Q激光器输出特性研究

对激光二极管端面泵浦Cr4+∶YAG被动调Q Nd∶YAG激光器输出特性进行了实验研究.实验研究发现,激光器输出功率及脉冲重复频率随谐振腔长度增大而增大.为解释这一实验现象,测量了泵浦光斑在激光晶体内尺寸,同时计算了激光晶体及Cr4+∶YAG晶体内的基模激光光斑半径随谐振腔长度变化.分析结果表明:激光晶体内泵浦光斑尺寸远小于激光晶体内基模光斑半径,腔模间交叠效率较低;当腔长增加时,激光晶体内的基模激光光斑减小,腔模间交叠效率增加,从而导致输出功率及脉冲重复频率随腔长增加而增加;另外,Cr4+∶YAG晶体内光斑半径也随谐振腔长度减小,引起Cr4+∶YAG晶体漂白时间缩短,导致脉冲重复频率随腔长增加而增加.     

磁控管衍射输出结构的π模特性

 磁控管结构以及类磁控管结构（无阴极）是具有衍射输出结构的磁控管最基本的组成单元,分析这两种结构的色散关系是研究具有衍射输出结构的磁控管模式转换和传输特性的基础。在基于场匹配法得到类磁控管结构的色散关系的同时,利用数值计算定量分析了6腔和2腔磁控管结构以及类磁控管结构中的π模谐振点随结构参数的变化关系。分析结果表明：对于磁控管结构,当阴阳极间距一定时,π模谐振波数随谐振腔半径的减小而增大;当谐振腔半径一定时,π模谐振波数随阴阳极间距的增大而增大;对于类磁控管结构,π模谐振波数随谐振腔深度的减小或提取腔半径的减小而增大。     

新型无线局域网双频段微带贴片天线设计

 新型无线局域网双频段微带贴片天线采用50 Ω微带线进行馈电,采用在贴片切槽设计方式,实现了微带天线在双频段工作的要求。其中心工作频率分别为2.44 GHz和5.20 GHz,相应的工作带宽分别达到了200 MHz和1.20 GHz。该天线具有小尺寸、结构简单、制作简单,低成本和在各工作频点处具有良好的方向性等优点,而且只需简单修改辐射贴片上的缝隙尺寸参数,就可以实现对天线高频段和低频段的调节。     

Ku波段径向线相对论速调管放大器的仿真与设计

高频段相对论速调管放大器(RKA)是近年来高功率微波领域的研究热点之一,其发展主要受限于模式竞争、相位抖动和效率偏低等问题。设计了一种径向线RKA,主要由输入腔、两组非均匀双间隙群聚腔和三间隙提取腔等四部分构成。通过比较单双间隙群聚腔与电子束互作用的耦合系数,说明了非均匀双间隙群聚腔具备对电子束较强的调制能力。前端加载TEM模式反射器的非均匀双间隙群聚腔的工作在TM01-π模式,Q值较大,有利于谐振腔之间的能量隔离。采用两组非均匀双间隙群聚腔级联的方式,在注入功率仅10 kW情况下,实现短漂移管长度下电子束深度群聚达110%。粒子模拟结果表明,该器件具有效率高的优点,在电子束电压400 kV,电流5 kA,磁场强度0.4 T条件下,得到功率825 MW,频率14.25 GHz,效率41%的微波输出。     

200兆赫高功率CW锁模YAG激光泵浦源研究

本文报导一台200MHz 12W平均功率的CW锁模Nd:YAG激光泵浦源,输出脉宽约100ps,能够可靠地长期稳定运转。     

Photonic crystal fiber for fundamental mode operation of multicore fiber lasers and amplifiers

A mode-selection method based on a single-mode photonic crystal fiber (PCF) in the multicore fiber (MCF) lasers is presented. The designed PCF has a central core region formed by a missing air-hole, and three air-hole rings. With an appropriate choice of the design parameters of the PCF, the power coupling between the fundamental mode (FM) of the PCF and the fundamental MCF mode can be much higher than those between the FM and the other supermodes. As a result, the fundamental MCF mode has the maximum power reflection coefficient on the right-hand side of the MCF laser cavity, and dominates the output laser power. Since the maximum power of the fundamental MCF mode will lead to the desired laser beam profile, higher the fraction of the fundamental MCF mode power contained in the total output power contributes to higher beam quality. The numerical simulations show that the effectiveness of the fundamental MCF mode-selection is higher in the MCF lasers with the PCF as a mode-selection component than in the MCF lasers based on the free-space Talbot cavity method. Additionally, for the MCF amplifiers, an approach is presented to decrease the sensitivity of the amplifier performance to the variation of Gaussian beam waist utilizing the coupling between the Gaussian beam and the FM of the PCF. The numerical results show that this method can effectively increase the design flexibility for a broad range of the Gaussian beam waist.     

Comprehensive modeling of vertical external cavity surface emitting laser with resonant periodic gain

One of the promising laser constructions having much attention in the past years is thin-disc semiconductor lasers with the resonant periodic gain in a form of multiple quantum wells. The 3D numerical model is developed based on combining bi-directional beam propagation method with the round-trip operator technique. The standing wave effect in resonant gain structure and diffraction in the external laser cavity are taken into account explicitly. Characteristics of optical modes are found numerically for cylindrical vertical extended cavity surface emitting laser with above-threshold pumping. Variation of distance to the external mirror is found to result in notable changes in power and optical quality of the output beam. The decisive role of gain and index non-linearities in these changes is identified.     

外腔共振和频系统中阻抗匹配的理论研究

外腔共振是提高和频效率的有效方法. 实现外腔共振高效和频需要基频光高效地耦合到外部谐振腔中, 因此系统要达到阻抗匹配. 本文分别建立了双波长和单波长外腔共振和频系统的理论模型, 分析了腔增强因子与耦合腔镜反射率、入射基频光功率等参数的依赖关系, 通过数值模拟获得最优化的共振光耦合腔镜反射率, 使系统达到阻抗匹配, 提高和频效率. 研究表明, 无论双波长还是单波长外腔共振和频系统, 共振基频光的最佳耦合腔镜反射率只会随着另一束共振或者不共振的基频光入射功率的增加而减小, 而其本身的入射功率变化则影响较小; 进一步分析表明, 若共振基频光的耦合腔镜反射率超过阻抗匹配值, 和频光功率将会迅速减小, 而小于阻抗匹配值时, 和频光功率减少速度相对较慢, 因此实验过程中要尽量避免过耦合的情况出现. 本文的理论分析过程将对外腔和频实验有一定的指导意义.     

3 mm波段回旋速调管放大器设计与粒子模拟

设计了一支3 mm 波段基波回旋速调管,该回旋速调管工作在低损耗的TE01模式,包含四个谐振腔。首先使用线性理论确定工作参数的大致范围, 然后采用HFSS软件设计单个谐振腔,通过调整谐振腔尺寸和腔壁介质层参数使谐振腔的谐振频率和Q值符合设计要求, 最后使用粒子模拟程序优化设计了回旋速调管的互作用电路,研究了谐振腔参差调谐方案, Q值对回旋速调管性能的影响, 互作用电路的稳定性以及电子注参数变化对注-波互作用性能的影响。PIC粒子模拟结果表明,在电子注电压65 kV, 电流6 A, α(V⊥/V∥)1.5, 工作磁场3.6 T时,回旋速调管的3 dB带宽约为600 MHz,在93.7 GHz获得139 kW 的峰值输出功率,效率为35.6%,增益为28.4 dB。模拟中没有考虑电子注速度零散的影响。