Power Density Distribution Simulation and Relevant Heat Effect Calculation of a High-power CO2 Laser with Low Order Modes

The vertical excitation axial-flux kilowatt CO2 laser is an equipment widely used in the high-power laser heat treatment industrial applications. The experimental measurements indicate that the power density distribution of laser beam is generally of ring distribution with a sunken at the center, therefore the laser beam cannot be simply regarded as base mode Gaussian beam. In this paper, such laser beam is regarded as the non-interference superposition of TEM00 and TEM01 mode beams, the method to determine the simulation parameters is discussed, and the relevant heat effect calculation equation is deduced.     

激活介质热效应对振荡模式的影响研究

理论分析了激活介质热效应对端面泵浦固体激光器激光振荡模式分布的影响,并以光纤耦合半导体激光器端面泵浦Nd∶YAG激光器实验研究了激活介质热效应对激光振荡模式的影响。实验结果表明：由于热效应,基模的模体积随泵浦功率的增加而变大,基模在模式竞争中占优;在泵浦光轴线偏离几何腔轴时,基模光斑中心位置朝泵浦光轴线所在位置移动,偏离量与泵浦光轴线的偏离量近似成线性关系。利用实验结果指导腔调节,可使泵浦光轴线与几何腔轴精确重合,获得了椭圆率为0.98、M2因子为1.01的基模输出。     

有横向分布为TEM10模的信号注入的环形腔激光器的双稳性

本文假设注入环形腔激光器的信号的横向场分布为TEM_(10)模.利用平均场近似方法得到了单横模共振时的定态方程,并进行了线性稳定性分析.结果表明,对优质腔来说,与Lugiato等讨论的注入信号为平面波光束及高斯光束(TEM_(00)模)的情况不同,注入光场横向分布具有TEM_(10)模的横式时,环形激光器的输出呈现双稳性.     

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。     

Intracavity coherent addition of single high-order modes

We report on efficient intracavity coherent addition of several single high-order mode distributions in a multichannel laser resonator. The phase locking and coherent addition is achieved by using an intracavity interferometric beam combiner. The principle, configuration, and experimental results with pulsed Nd:YAG Laguerre-Gaussian TEM01 and TEM02 laser beam distributions are presented. The results reveal more than 95% combining efficiency with a nearly pure high-order mode output beam distribution in both free-running and Q-switched operation.     

Femtosecond diode-pumped Nd:glass laser with more than 1 W of average output power

We have demonstrated 175-fs pulses with 1 W and 300-fs pulses with 1.2 W of average output power at a pulse repetition rate of 117 MHz from a Nd:phosphate (Schott LG 760) glass laser pumped by a 1-cm-wide, 20-W diode laser bar. Stable soliton mode locking was achieved by use of an intracavity semiconductor saturable absorber mirror. We obtained more than 2 W of average power without mode locking. Using cylindrical cavity mirrors, we adapted the laser mode inside the Nd:glass to the highly elliptical pump beam in both dimensions (tangential and sagittal axes) while maintaining a nearly ideal circular TEM(00) output beam with M(2) approximately 1.2 . Overpumping the laser mode in the tangential plane and efficient unidirectional heat removal in the sagittal plane using a 0.8-mm thin Nd:glass also contributed to the good output-beam quality.     

用SF6气体作SBS相位共轭镜的激光谐振腔

利用高压SF_6气体中的受激布里渊散射作相位共轭镜,将其用于Nd:YAG激光谐振腔,得到了能量在100mJ左右的脉冲激光输出.与利用液体介质的受激布里渊散射相位共轭腔的激光输出相比,其光斑的空间模式大大改善,基本达到TEM_(00)模,功率密度在150MW/cm~2输出能量的稳定性也有所提高.     

光学补偿LD侧向非均匀泵浦全固化激光器

采用定向棱镜谐振腔、半圆柱面LD阵列交错侧向泵浦两根串接NdYAG激光棒、热传导冷却结构,研制出了一台工程实用的全固化激光器.定向棱镜腔内振荡光线平行于光轴的对称位置交换穿行,匀化了增益,降低了模序数;同时,定向棱镜准相位共轭特性和自准直作用在一定程度上修正波前畸变、热光楔以及热致双折射,保证了大的动态范围内热稳定性,改善了光束质量.激光器采用Cr4+YAG被动调Q,在室温条件下,工作电流为53 A、频率10 Hz时,1.06 μm单脉冲激光能量高于150 mJ、脉宽9 ns、输出稳定度±3%、束散度2.5 mrad且光轴指向稳定,远场分布近似相干平顶高斯光束.     

High-power Er:YAG laser with quasi-top-hat output beam

A simple method for simultaneously exciting the fundamental (TEM00) transverse mode and first order Laguerre-Gaussian (LG01) donut mode in an end-pumped solid-state laser to yield a quasi-top-hat output beam is reported. This approach has been applied to an Er:YAG laser, in-band pumped by an Er,Yb fiber laser, yielding 9.6 W of continuous-wave output at 1645 nm in a top-hat-like beam with beam propagation factor (M2)<2.1 for 24 W of incident pump power at 1532 nm. The corresponding slope efficiency with respect to incident pump power was 49%. The prospects of further scaling of output power and improved overall efficiency are considered.     

强激光照射下受预内压作用的球壳的热力响应

分析受强激光照射和预内压联合作用的球壳的热力效应。在光强相对较低的情形,激光照射处理为壳体表面热流输入。推导了瞬态热传导解析解;并选取一组典型的几何及材料参数,针对一系列激光光强情形用大型有限元程序对热传导和热弹塑性变形作了数值计算,得到了热传导的清晰的物理图象,讨论了壳体结构变形的空间分布和随时间的演变规律以及对激光光强和照射时间的依赖关系。     

The dynamic stability resonant cavity design of two rod Nd:YAG laser

The stability of the higher output power with high-quality beams is very important parameter in material processing. This paper presents using the S parameter and Gauss beam parameters matching to design efficient resonant cavity of two-rod Nd:YAG. The fundamental mode beam radius in rod, fundamental mode beam radius on the mirror, beam quality factor, and the value of the degree of the symmetry of the TEM00 mode volume as a function of the between neighbor rods distance, laser rod end face to mirror distance, and input power are simulated. The design method of resonant cavity is illustrated and compared with previously published experimental measurements for different pump power and the length of the cavity parameters and a good agreement has been found.     

Output beam analysis of high power COIL

As the output power of a chemical oxygen iodine laser (COIL) increases, the output laser beam instability appears as the far-field beam spot drift and deformation for the large Presnel number unstable resonator. In order to interpret this phenomenon, an output beam mode simulation code was developed with the fast Fourier transform method. The calculation results show that the presence of the nonuniform gain in COIL produces a skewed output intensity distribution, which causes the mirror tilt and bulge due to the thermal expansion. With the output power of COIL increases, the mirror surfaces, especially the back surface of the scraper mirror, absorb more and more heat, which causes the drift and deformation of far field beam spot seriously. The initial misalignment direction is an important factor for the far field beam spot drifting and deformation.     

激光二极管端泵微片固体激光器的研究

本文介绍了一种用波长为809nm的激光二极管(LD)端面泵浦厚度为1mm的微片Nd:YVO4全固化固体激光器。器件结构上采用了一种独特的光学系统,该系统由分别用于LD激光束的耦合和聚焦的两部分组成。由Nd:YVO4的一个平面与一个曲率半径为21mm的球面镜组成半共焦腔,以获得高的转换效率。文中详细讨论了单横模运转时的泵浦光与激光腔模之间的匹配问题。当泵浦光功率为400mW时,获得152mW的1064nm波长的TEM00模激光输出。器件阈值功率为48.3mW,总的光-光转换效率为38%,斜效率为43%.     

Output beam drift and deformation in high-power COIL

During the operation of a chemical oxygen iodine laser (COIL) with an unstable resonator of a large Fresnel number, as the output power increases, an instability of the output laser beam will appear, behaving mainly as far-field beam spot drift and deformation. In order to interpret this phenomenon, thermal expansion analysis on the scraper with finite element analysis method and a simulation of the output beam mode of this kind of laser by the method of Fast Fourier Transform were developed. From the experimental measurement and the calculation, we proposed that the presence of the nonuniform temperature distribution of scraper causes the front surface of the scraper to tilt and bulge due to thermal expansion. As the output power is increasing, all the mirror surfaces, especially the scraper's, will absorb more and more heat, causing thermal expansion of the mirror front surface to occur more seriously, thus resulting in the tilting and deformation of the far-field beam spot. The initial misalignment of the direction is also an important factor leading to the far-field beam spot drift and deformation.     

热透镜控制激光光束质量技术研究

在端面抽运固体激光器中,就如何改善在高抽运功率时输出激光的光束质量,提出一种激光器的设计方法。在激光器谐振腔中放入多根掺杂浓度不同的激光介质,利用激光介质内部产生的热透镜控制抽运光和基模振荡光的空间分布,并且最大限度地使抽运光的分布区和基模振荡光分布区重叠,实现抽运光与基模振荡光在空间上高度匹配,进而提高抽运光能量的利用效率和振荡光的光束质量。实验表明,在不同抽运功率下,抽运光和基模振荡光在晶体内部的光斑的空间分布可通过热透镜加以控制。在端面抽运功率200 W附近时,实现了抽运光与基模振荡光较高程度匹配,光束质量因子M2由14.7改善为4.1。     

Laser Diode Pumping High-stability 1047 nm TEM00 Mode CW Nd:YLiF4 Laser

A laser diode (LD) pumping high-stability 1047 nm TEM00 mode Nd: YLiF4 (Nd: YLF) continuous wave (CW) laser is reported in this letter. The laser output power of 5.83 W with optical to optical effidency of 27% and slope efficiency of 30% has been achieved The instability of output power is 0.36% and spike caused by relaxation oscillation has not been observed in the laser beam. The transverse cross section of laser beam is an ellipse, the diameters of laser beam at output mirror in both directions are 0.97 mm and 1.07 mm, respectively. The divergent angles are 0. 936 mrad and 0. 774 mrad, and the values of M2 are 1.37 and 1.24, respectively. The polarization degree of laser beam is better than 237:1.     

超高斯光束抽运调Q固体激光器仿真模型研究

仿真计算一直是研究激光器的重要手段,而激光理论是仿真计算的基础.虽然半经典激光理论能够精确地描述激光的产生过程,但是其复杂性导致仿真需要庞大的计算资源和计算时间.为了能够更加高效地对激光器进行仿真,提出了一种调Q固体激光器的仿真模型.基于此模型,研究了影响主动调Q激光产生过程的因素.这些因素包括抽运功率、抽运光分布和模式竞争.仿真计算结果与对照实验测量数据相符合,说明了模型的有效性.     

Conversion of a high-order mode beam into a nearly Gaussian beam by use of a single interferometric element

We present a new, compact, and practical optical mode converter that efficiently transforms a high-order Hermite-Gaussian (HG) laser beam into a nearly Gaussian beam. The mode converter is based on coherently adding different transverse parts of the high-order mode beam by use of a single planar interferometric element. The method, configuration, and experimental results obtained with a pulsed Nd:YAG HG TEM10 laser beam are presented. The results reveal that the efficiency of conversion of a HG beam to a nearly Gaussian beam can be as high as 90%.     

Operation of electro-optically Q-switched Nd:LuAG laser at 1064 nm

We present the operation of a diode-pumped high-power electro-optically Q-switched 4 W Nd:LuAG laser operating at 1064 nm. At an absorbed optical power of 20 W, the laser described provides a maximum output of 3.5 W average power at a repetition rate of 50 Hz. The output varies up to a factor of 1.3% for about 1 h operation with a peak power of 280 kW, with the laser beam quality in the TEM00 mode.     

Efficient improvement of laser beam quality by coherent combining in an improved Michelson cavity

The efficient improvement of laser beam quality is demonstrated by coherent combining of two Nd:YVO4 lasers in an improved Michelson cavity. When the two lasers are separately operated with beam qualities of M(x)2 = 1.74 and M(y)2 = 1.34 for laser 1 and M(x)2 = 1.53 and M(y)2 = 1.39 for laser 2, by coherent combining of the two lasers, a single beam output exceeding 2 W with a nearly perfect TEM00 mode (M(x)2 = 1.08, M(y)2 = 1.04) is obtained. Moreover, it can withstand environmental perturbations with no change in beam quality or output power and has the potential for scaling to much higher output power with high beam quality by coherent addition of multiple lasers in this configuration.