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.     

An unstable resonator Nd-YAG laser

The operating characteristics of an unstable resonator Q-switched Nd-YAG laser are reported and its suitability for a number of applications has been tested. At repetition rates up to 50 Hz, output energies of 150–200 mJ are obtained with a beam divergence of 0.25 mrad half-angle. Single longitudinal mode operation has been achieved either with passive Q-switching or with an active slow Q-switch.     

Experimental studies of an unstable confocal resonator alexandrite laser

The effects of excited converging wave in an unstable confocal resonator onthe properties of an alexandrite laser are investigated experimentally.The results show thatexciting the converging wave inside the resonator is an effective method to reduce the diver-gence of the laser beam for low gain laser medium.     

The mode-locked unstable resonator YAG laser

Experimental results on mode-locked action of a polarization coupled unstable resonator YAG laser are reported. The main features of this oscillator are ～ 20 mJ per pulse, good spatial profile and high focusable energy.     

球面角锥棱镜非稳腔钕玻璃激光器

为了将虚共焦非稳腔输出光束质量高和角锥棱镜谐振腔具有免调试的优点结合到一起,提出了用球面角锥棱镜构成虚共焦非稳腔的方案。利用已有虚共焦非稳腔钕玻璃激光器,设计加工了一球面角锥棱镜非稳腔钕玻璃激光器。模拟计算了两谐振腔输出光束的模式分布,然后对两钕玻璃激光器进行了实验对比研究。结果表明:实验得到的模式分布与模拟计算结果相吻合,球面角锥棱镜非稳腔钕玻璃激光器与虚共焦非稳腔钕玻璃激光器分别获得了最大2 176.9 J和2 340.6 J的能量输出,二者的电光效率与束散基本相同,分别为4.3%,0.30 mrad和4.6%,0.26 mrad。     

A long-pulse TE CO2 laser with a negative-branch unstable resonator

Summary A long-pulse (>3 μs) CO₂ laser has been built using a negative-branch, frequency-selective, unstable resonator. The results obtained with this device are shown. The authors of this paper have agreed to not receive the proofs for correction.     

球面角锥棱镜非稳腔钕玻璃激光器

为了将虚共焦非稳腔输出光束质量高和角锥棱镜谐振腔具有免调试的优点结合到一起,提出了用球面角锥棱镜构成虚共焦非稳腔的方案。利用已有虚共焦非稳腔钕玻璃激光器,设计加工了一球面角锥棱镜非稳腔钕玻璃激光器。模拟计算了两谐振腔输出光束的模式分布,然后对两钕玻璃激光器进行了实验对比研究。结果表明:实验得到的模式分布与模拟计算结果相吻合,球面角锥棱镜非稳腔钕玻璃激光器与虚共焦非稳腔钕玻璃激光器分别获得了最大2176.9J和2340.6J的能量输出,二者的电光效率与束散基本相同,分别为4.3%,0.30mrad和4.6%,0.26mrad。     

非稳腔输出环状激光束的传输特性

本文从菲涅耳衍射积分公式出发研究了激光器非稳腔输出环状光束在空间的传输规律.由轴上光强的极值点位置给出了划分非稳腔传输空间的近场、中场和远场区域公式.理论计算结果表明,非稳腔输出端环状光束在中场区域激光能量逐渐向轴心方向转移,而在远场变为爱里型圆盘状光束的过程.在非稳腔脉冲TEA CO_2激光器上测得的实验结果与理论计算结果很好地符合.     

Operation of an unstable resonator TE CO2 laser with large electrode spacing using additives

A study of a pulsed transversely excited (TE) CO₂ laser using an unstable resonator configuration is reported. It is shown that a large aperture (4.75 cm) wire-triggered device can successfully operate at pressures of up to 650 torr with undoped gas mixtures whose molecular gas concentration exceeds 35%. These results are utilised for a comparative study of the influence of an organic additive on the performance of the system. It is observed that the addition of traces of tri-n-propylamine leads to significant improvements of the laser output characteristics even under conditions where a glow discharge could be obtained without the additive. With the doped TE CO₂ laser employed using a relatively low magnification unstable resonator (M = 1.45) near diffraction-limited performance has been achieved and a peak radiance of 4.5 × 10¹³ W cm⁻² sr⁻¹ has been obtained with a peak power of 65 MW.     

Low gain laser with an unstable cavity

A neon 633 nm laser with an unstable cavity was made to lase in the negative unstable region. The characteristic parameters were measured. The loss calculated by using both the geometric approach and the diffraction integral is higher than the gain of the gas mixture, it contradicts the experimental results. If the radial dependence of the gain is taken into account then the calculated loss fits the experimental results satisfactorily.     

The behaviour of the negative-branch unstable resonator with an aperture inside

The negative-branch unstable resonator with an aperture inside the cavity at one conjugate image point is studied. The analysis shows that there is only one unique wave existing. The behaviour of the cavity depends only on the magnification and Fresnel numberN ₁.     

高功率TEA CO2激光器非稳腔实验研究

为了提高光束质量、压缩光束发散角,利用现有高功率稳定腔TEA CO2激光器进行了非稳谐振腔的技术改造及激光输出试验,非稳谐振腔采用正分支虚共焦型非稳腔方案。为充分研究谐振腔结构参数及激光振荡模体积对输出能量和光束发散角的影响,共设计加工了包含4种放大率、5种模体积的20组非稳腔腔镜组合。在其它参数都相同的试验条件下,进行了非稳腔镜的单脉冲输出对比试验,得到的最大输出能量为14 J,是原平凹稳定腔的70%,而光束发散角只是原平凹稳定腔的1/4。     

大功率TEACO2非稳腔激光器的远场传输特性

针对大功率激光器的远场传输特性,提出了一种测量TEACO,远场光束传输特性的新方法,该法采用相对测量和绝对测量相结合的方式来获得高能激光器的绝对空间光强分布。利用该方法测试了2kW脉冲TEACO,非稳腔激光器在500m处的光强分布,并对测试结果进行了分析讨论。实验结果表明,此方法简单、易行,准确度较高,而且测量过程中考虑了大气湍流的影响,光斑强度相对分布上出现了平顶、破碎并出现旁瓣现象,实测大气透过率为81．5％,最大功率密度为1．59W／cm^2,光束的横向远场发散角达到0．64mrad,基本与理论计算结果相吻合。本研究将为评估激光系统的应用效果及系统的优化设计提供重要的参考。     

The application of an unstable resonator to a high-pressure CW CO2 laser

Unstable resonators provide high quality beams of high output power needed for material processing. We have developed a CO₂ laser of over 5 kW for material processing with an unstable resonator of positive confocal configuration under high-pressure, sealed condition. High quality beams with high extraction efficiency of the power were obtained and deep pentration was attained in welding tests.     

Estimation of output beam characteristics of laser with unstable resonator and turbulent active medium

In this paper we present calculations of the three-dimensional mode structure and output beam characteristics of unstable resonator with turbulent active medium. The calculations of the output beam are carried out in the Fresnel approximation using the well-known iterative method [1]. The active medium is modeled as a series of phase screens with Kolmogorov statistics. The dependence of output radiation parameters of the gas flow laser with unstable resonator on the strength of turbulence in active medium and parameters of resonator is under consideration.     

Diffraction losses of an asymmetric stable laser resonator using an equivalent resonator

An asymmetric stable laser resonator with one large mirror and the other mirror apertured is considered. An equivalent symmetric resonator is derived which enables the determination of the theoretical diffraction losses from Li's computations. Experiments are done to test the validity of the predictions. The experimental diffraction losses agree very well with the theoretical values and the usefulness of the concept of equivalent resonator is therefore confirmed.     

High-quality lowest-loss-mode lasing in GaAs quasi-stadium laser diodes having unstable resonators

We obtained high-quality lowest-loss-mode lasing in quasi-stadium laser diodes having unstable resonators that consisted of two curved end mirrors and two straight sidewall mirrors. The laser diodes were fabricated by applying a reactive ion etching technique to a metal-organic chemical-vapor deposition-grown graded-index separate-confinement heterostructure single-quantum-well GaAs/AlGaAs structure. The electrode contact area of the laser diodes was formed along unstable periodic orbits, along which the optical beams are localized. Highly directional fan-out beams corresponding to the numerically obtained lowest loss mode were emitted from the end mirrors under CW operation at room temperature.