射频板条CO2激光器输出光束的光学变换

射频激励板条CO2激光器输出激光近场光斑近似为一条线,远场光斑为O形图样。在垂直于光束传输方向的平面内,光束在一个方向发散很大,无法用于激光加工。根据激光器不同的激光功率级别及光束尺寸,分别采用了圆柱面镜、滤波光阑、扩束望远镜等不同组合的方法,将200 W激光器输出光束变换成远场光束为Φ6、近似TEM00模的圆形光束,500 W激光器远场光束为Φ10的低阶模的圆形光束。成功用于激光切割。     

Hybrid optical resonator type laser proposed for direct coupling into optical fiber

Combining one stable resonator with a concave mirror and a coupling-hole plane mirror, and another unstable resonator having a concave mirror and a convex mirror, a new hybrid optical resonator type laser has been proposed by overlapping the concave mirror as a common one and fitting the convex mirror exactly to the coupling-hole. Using theABCD law, the so-called g-parameters are first found for beam confinement. Then, based on the eigen-equation, the field distribution on the plano-convex mirror is obtained with the g-parameters above. Knowing this field distribution results in an effective transmittanceG _{e e}. Finally, the ratio of the inner convex to outer plane mirror radii can be determined for an optimum coupling in both the limiting cases of homogeneously and inhomogeneously broadened gain media. Some numerical examples will also be given for a CO₂ laser having the proposed hybrid resonator.     

A simple positive-step alignment technique for a ring resonator

A quick and simple technique is presented for the alignment of a ring resonator of any configuration and any number of mirrors, given that a laser power source of variable gain is available. The method used ensures that the resonator is known to be aligned—a distinct advantage over former techniques.     

Numerical Simulation and Analysis on Deflection of Silicon Mirrors Irradiated by High Power Laser

ＮｕｍｅｒｉｃａｌＳｉｍｕｌａｔｉｏｎａｎｄＡｎａｌｙｓｉｓｏｎＤｅｆｌｅｃｔｉｏｎｏｆＳｉｌｉｃｏｎＭｉｒｒｏｒｓＩｒｒａｄｉａｔｅｄｂｙＨｉｇｈＰｏｗｅｒＬａｓｅｒＸＩＡＪｉｎａｎ；ＣＨＥＮＧＺｕｈａｉ；ＱＩＵＪｕｎｌｉｎ（ＮａｔｉｏｎａｌＬａｂ...     

Design and Cold Tests of Asymmetric Quasioptical Resonators

This paper presents the design and test of asymmetric quasioptical resonators for gyrotron applications, where most of the diffraction output coupling comes from the smaller of two mirrors. A computer code based on scalar diffraction theory is used to calculate the resonator losses and the electric field near the mirrors. Resonators with mirror separations approaching confocal have reduced side lobes in the diffraction patterns, which should allow for better power transmission and focusing. Cold tests have been performed at 94 and 141 GHz to measure the quality factor of the asymmetric resonators as a function of mirror separation and mirror misalignment. Typical resonator parameters include 65 cm mirror separation, 1-3% output coupling and 85% of the losses from the small mirror. A half-symmetric resonator with one flat and one curved mirror has also been investigated. The calculated values of Q are in reasonably good agreement with the cold test measurements.     

同轴放电环形增益区谐振腔镜面的场分布

 对几类环形增益区谐振腔进行了比较，得出利用谐振腔两镜之一的全工作面输出的新型环形增益区谐振腔是适合的谐振腔。提出了一种计算全工作面输出的同轴放电环形增益区谐振腔镜面场分布的方法，利用几何方法对腔镜镜面进行划分,得出了基于菲涅尔-基尔霍夫衍射积分定理的积分区域，并对该区域进行了有限元划分，应用计算机编程计算出了同轴放电环形增益区谐振腔镜面处的光场分布和相位分布。近场分布在环形区中央部分近似地呈高斯分布，且沿径向出现高阶模场分布特点，沿角向无差别。     

Deep penetration welding using a CO laser with an unstable resonator

An unstable resonator (M = 2) has been applied to reduce the beam divergence of a gas-dynamically cooled supersonic CO laser operating at 105 K in a semiclosed gas cycle. A 4.7 kW laser beam with a total divergence of 2.5 mrad is obtained with an efficiency of 9.4%. The results of welding experiments are compared with those using a CO₂ laser. The weld depths obtained with the CO₂ laser are drastically reduced using argon as the assist gas, whereas the results with the CO laser are independent of the assist gas because of the lower plasma absorption coefficient for the shorter CO laser wavelength.     

Study on the possibilities of controlling the laser output beam properties by an intracavity deformable mirror

The possibilities of controlling the laser beam properties by a deformable mirror introduced into the laser optical cavity were studied theoretically and experimentally. The experiments were performed under conditions of an industrial high power transverse flow cw CO₂ laser operating with a stable resonator of a folded configuration. A deformable bimorph mirror of a surface profile controlled by the voltage applied to the mirror electrodes is implemented to the laser system as a back cavity mirror or as a one of the inner folding mirrors. The near-and far-field characteristics of the laser beam versus the resonator configuration controlled by the changes of the focal length of the deformable mirror are discussed in the paper. The analysis reveals that the resonator with an inner deformable mirror is much more sensitive to the mirror curvature variations than the resonator in which the deformable mirror is used as a back cavity mirror. The presented results show that dynamic and controllable changes in the resonator properties result in the controlled modification and optimisation of the laser output power and spatial parameters of the laser radiation.     

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。     

Theoretical analysis of broad-area semiconductor lasers with laterally shifted modal reflectors

Broad-area (BA) semiconductor lasers enable the achieving of high output power. However, the beam quality is low because of the vast number of lateral modes supported by the wide structure. A solution to this problem can be to produce BA lasers with modal reflectors. In this paper a theoretical analysis of the near-threshold behavior of such lasers is provided. The emphasis is put on the geometrical precision of producing of the inhomogeneous mirror. Consequences of asymmetry, with regard to the low-ohmic contact center, and localization of the reflecting part of the mirror on laser operation is discussed.     

Laser beam patterns of an optical cavity formed by two twisted cylindrical mirrors

Propagation of an elliptical Gaussian beam in a multiple-pass optical cell formed by two twisted cylindrical mirrors has been described by means of complex curvature tensors. Using the ABCD tensor approach various light patterns were computed for the use in tunable laser absorption spectroscopy with a multiple-pass optical cell. Light patterns with high beam-spot density can be also defined for a cavity formed by two twisted cylindrical high-reflectivity mirrors. In order to achieve higher cavity output intensity, a high-reflectivity cylindrical mirror cavity with at least one mirror that has a central transparent spot for laser beam injection has been described for applications in non-resonant cavity enhanced absorption spectroscopy. The author was with TDL Sensors Ltd., when the experimental part of this work was performed.     

太阳光抽运激光器抽运系统优化

太阳光抽运激光器中,抽运系统提供的太阳抽运光与激活晶体之间的耦合决定了激光输出的总体效率。使用Tracepro软件,建立了菲涅耳透镜、锥形抽运腔二级抽运系统模型,并对该系统进行优化。通过分析菲涅耳透镜焦斑能量沿轴线的分布,得到了锥形腔入射窗口的口径和窗口距菲涅耳透镜的距离。通过改变锥形抽运腔的腔长和锥度,分析晶体棒轴向抽运功率密度分布,得到了锥形腔的最佳结构,并对镜面反射腔和陶瓷腔进行了详细的介绍。     

反射式激光扩束器的切换变倍技术

反射式扩束常用于大功率的激光发射装置,但在离轴状态下,仅仅控制多组镜片之间的相对距离并不能像透射式扩束一样顺利实现变倍。从扩束望远镜系统的失调状态得到启发,提出一种两片次镜切换变倍的光学方案,针对一束CO2激光器发出的直径为54mm的激光束,完成了离轴工作时1.5倍和3.0倍两个档位的扩束光学设计。仿真结果证明了扩束功能的正确性,而且与主次镜相同曲率半径下同轴使用的失调望远镜系统的调制传递函数(MTF)曲线基本吻合,对离焦量进行补偿之后的成像效果能够达到衍射极限。     

Influence of spherical aberrations on the performance of dynamically stable resonators

Spherical aberrations of thermal lens of the active media are severe when the solid state lasers are strongly pumped. The aberrations influence the mode profile, the diffraction loss, the output power and other laser beam properties, especially for a dynamically stable resonator with large TEM₀₀-mode volume. Self-consistent modes in a resonator with aberrations are calculated using Fox-Li diffraction iterative algorithm. There are side lobes with the fundamental mode when the spherical aberration is introduced, hence the beam quality is deteriorated. The calculated results agree well with the experimental data. The beam filling factor plays an important role in the design of a laser system. The optimum value of the beam filling factor should be determined by the experimental results according to the spherical aberration effect.     

High power 1.3414 μm Nd:YAP cw laser

The eigen-oscillation mode of the Nd:YAP cw laser has been analysed. The influence of thermal effects arising from the pumping process on the output character of the 1.3414 μm Nd:YAP cw laser has been discussed. The crack problem of the reflective film at a 1.34 μm dielectric mirror has been solved. Based on the aforementioned work, we have been able to achieve an 82.8 W laser output at 1.3414 μm with a nearly polarized beam from a 5.8 mm diameter by 111 mm Nd:YAP rod. The overall efficiency and the slope efficiency are 1.15% and 2.02% respectively, and the fluctuation of the output power at 62 W is less than 1% during continuous operation for 45 min.     

变耦合率法测量化学激光器小信号增益

为了评价化学激光器增益发生器模块的性能,采用变耦合率法对化学激光器的小信号增益系数进行了研究。实验中采用的稳定光学谐振腔由2块全反射平面镜、1块全反射凹面镜及1块输出耦合镜组成。将测量结果中存在的饱和光强、非输出损耗和小信号增益的三元拟合问题转化为二元数值问题。通过数值拟合得到了满足工程需求的数据结果,并对该结果进行了误差分析。应用数学方差分析发现平均值二对应的拟合曲线与实验测量结果符合得更好,化学激光器的输出功率存在极大值。     

Heating by Optical Absorption and Cooling of High Power Laser Mirrors

In high power laser system, laser mirror is the core and the most sensitive optical component, which influences the increase of laser power and the quality of laser. Absorption of light at mirrors causes wavefront distortions through the thermal deformations of substrates. The analytical solutions of the two-dimensional transient thermal theory of high power laser mirrors are developed, copious graphical results in our case are presented, and the predicted results are compared with those of the experiment.     

High beam quality in a HyBrID copper laser operating with an unstable resonator made of a concave mirror and a plano-convex BK7 lens

This paper presents a very simple unstable resonator, made of a concave mirror (total reflector) and a bare plane–convex BK7 lens working as a convex coupling mirror, which is quite efficient for HyBrID copper laser. In addition to a good quality factor (M²=4.9), experimental results showed that it is possible to control the laser output power by introducing a variable aperture iris inside the cavity, close to the coupling lens, without spoiling beam quality. A rough theoretical model helped to explain these results as a combined effect of unstable resonator plus radial gain distribution.     

Quartz CO2 waveguide laser with a separated diffraction grating

A quartz CO₂ waveguide laser with external totally reflecting mirrors and a NaCl plate for the output power coupling is described. The output power was measured as a function of the distance of the mirrors from the waveguide aperture. Using a diffraction grating instead of one of the mirrors the output power at the 10 P(20) line was measured as a function of the mirror position. The results sustain the assumption of a multimode waveguide structure.     

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].