An alternative approach to determine the spot-size of a multi-mode laser beam and its application to diode laser beams

An alternative approach is suggested to determine the spot-size of a multi-mode laser beam. It has been shown by simulations that the suggested approach can give the beam quality factor and characteristic radius with less than 5% error. Unlike the power content method, the proposed method is applicable to the beams even with diameter one tenth of the CCD size. The new approach has been applied to a multi-mode diode laser output and it is shown that the ABCD matrix analysis can be used for beam propagation, with the measured parameters of the laser.     

高功率激光器腔镜热变形对输出光束质量的影响

利用有限元分析法结合Fox-Li迭代法,考虑腔内本征模式与腔镜热形变的相互耦合作用,计算模拟了正支共焦非稳腔的本征模式分布,定量分析了高功率激光器腔镜热变形对输出光束质量的影响,重点讨论了腔镜热变形所引起的腔内本征模式相位特性的变化,并从波前功率谱密度、Zernike像差系数及光束质量值等角度对腔镜发生热形变前后的激光器输出光束的光束特性进行比较分析。研究结果表明：高功率激光器腔镜热形变对输出光束的光束质量会产生一定的影响,且随着激光输出功率的增大,镜面热形变引起的输出光束波前相位高频比例及Zernike高阶像差均会有所增大,波前畸变程度也明显变大,光束质量逐渐变差。     

抽运光分布对二极管抽运激光器振荡光光束质量的影响

研究了二极管抽运激光器（DPL）中抽运光的空间分布对振荡光光束质量的影响.通过对端面 抽运情形下光场运动方程的研究，发现不均匀的空间增益分布会影响激光振荡的模式，并且 使得基模振荡光偏离高斯分布.引入一个称之为抽运光影响因子参数，来判断这种影响的程 度.研究表明，这个参数计算方便而且实用.在对基模调Q脉冲激光的研究中发现，由于抽运 光的影响，脉冲前沿的场分布将由远离高斯分布向接近高斯分布变化，称之为脉冲前沿的场 倏变现象. 关键词： 激光二极管 二极管抽运激光器 光束质量     

高斯涡旋光束的光束传输因子和峭度参数

基于强度二阶矩定义, 导出了高斯涡旋光束光束传输因子即M² 因子的解析表达式, 高斯涡旋光束的M² 因子唯一取决于拓扑电荷数n. 数值计算表明, 高斯涡旋光束的M² 因子随着拓扑电荷数n的增大而增大. 基于强度高阶矩, 还导出了高斯涡旋光束经傍轴ABCD光学系统传输时峭度参数的解析表达式, 高斯涡旋光束的峭度参数取决于拓扑电荷数n、参数δ、矩阵元A和矩阵元D. 在自由空间传输时, 高斯涡旋光束的峭度参数仅取决于拓扑电荷数n和参数δ. 自由空间传输时, 高斯涡旋光束峭度参数的变化规律为: 峭度参数随参数δ的增大先减小而后趋向于一最小值, 随拓扑电荷数n的增大而减小. 这一研究有助于高斯涡旋光束的实际应用.     

Measurement of beam quality factor (M) by slit-scanning method

Beam quality factor (M²) and far-field scattering angle of LD end-pump Nd : YVO₄ laser were measured by slit-scanning method. The experimental results showed that the laser operated on a multi-mode state. The corresponding analytical treatments for slit-scanning method and M² factor measurement also were presented in this paper.     

光束控制系统热效应与球差对激光光束质量的影响

采用Strehl比、桶中功率、β参数和束宽描述远场光束质量，研究了光束控制系统热效应和球差对远场激光光束质量的影响.用四维仿真程序作了详细计算，给出了数值计算结果并进行了物理分析.研究表明，传输通道的热效应和正球差会使远场光强分布扩展，可聚焦能力下降，光束质量变差.有意义的是，当激光发射功率达到一定值时，合适选取负球差会在几何焦面得到比无球差时更高的峰值光强和更好的可聚焦能力.但在以前的工作中，由于焦移，类似的结论是在实际焦面上得出的.非线性热晕的存在是其物理原因，对此用数值计算例子作了说明. 关键词： 高功率激光 热效应 光束控制系统 球差     

The beam quality of nonparaxial Hermite-sine-Gaussian beam

Based on the theory of the second intensity moment of nonparaxial scalar beam and the method of angular spectrum, the expressions for the far-field divergence angle, waist width and M² factor of nonparaxial Hermite-sine-Gaussian (HSiG) beams are derived. Calculation and analysis show the dependence of the far-field divergence angle of nonparaxial HSiG beams on the parameter w₀/λ, as well as on order m, And it with even and odd orders approach 73.898° and 63.435° as w₀/λ → 0. With increasing order m and the parameter w₀/λ, the waist width increase monotonously, which is same as paraxial case. But nonparaxial M² factor is different from paraxial case, it cannot only less than 1, but also approach 0 as w₀/λ → 0.     

锥形太赫兹量子级联激光器输出功率与光束特性研究

针对锥形太赫兹量子级联激光器, 利用有限差分波束传播法和速率方程法, 建立了准三维的太赫兹有源器件仿真模型, 能够对具有轴向非线性波导结构的激光器进行模拟. 利用此模型, 研究了锥角大小对激光器输出光功率及光束质量的影响. 仿真结果表明, 考虑到器件之间的光耦合效率, 为了达到最大的有效输出光功率, 锥形太赫兹量子级联激光器的锥角存在一个最优值.     

高功率激光器腔镜热变形对输出光束质量的影响

利用有限元分析法结合Fox-Li迭代法,考虑腔内本征模式与腔镜热形变的相互耦合作用,计算模拟了正支共焦非稳腔的本征模式分布,定量分析了高功率激光器腔镜热变形对输出光束质量的影响,重点讨论了腔镜热变形所引起的腔内本征模式相位特性的变化,并从波前功率谱密度、Zernike像差系数及光束质量值等角度对腔镜发生热形变前后的激光器输出光束的光束特性进行比较分析。研究结果表明:高功率激光器腔镜热形变对输出光束的光束质量会产生一定的影响,且随着激光输出功率的增大,镜面热形变引起的输出光束波前相位高频比例及Zernike高阶像差均会有所增大,波前畸变程度也明显变大,光束质量逐渐变差。     

厄米-高斯光束的M2因子矩阵

提出了厄米-高斯光场的M²因子矩阵.引入束半宽平方的交叉项、M²因子的交叉项,理论推导出了在同一坐标系下光场旋转一定角度后的M²因子矩阵,数值模拟了与M²因子矩阵有关的各参数随光场旋转角度变化的规律,给出了光场的M²因子矢量点随光场旋转角度变化的轨迹曲线.计算结果与理论推导结果相符,证实了利用M²因子矩阵可以将旋转前后的二维厄米-高斯光场用旋转矩阵统一起来.该方法可推广到对一般的二维高阶高斯光束的光束质量的理论分析上,具有普适性,对光束质量的实际测量有重要的理论指导意义. 关键词： M²因子矩阵')" href="#">M²因子矩阵 厄米-高斯光束 非对称激光束 矩阵光学     

Does the beam width affect the generalized M factor of hard-edged diffracted beams?

A detailed study of the generalized M² factor of hard-edged diffracted beams based on the truncated second-order moments method, asymptotic analysis and self-convergent beam width approach is performed. The dependence of the generalized M² factor on the parameters characterizing the spatial profile, and beam truncation, etc. is analyzed.     

Thermal lens determination of LD end-pumped solid-state laser with stable resonator by slit scanning method

A simple method to determine the thermal focal length of LD end-pumped solid-state laser with stable resonator is presented. The M² factor describing the quality of the beam can be obtained by scanning a slit through the multi-mode Gaussian beam field. The waist width of the beam and the corresponding TEM₀₀ under the same parameters of laser are then deduced through the law of multi-mode Gaussian beam propagation. Based on the standard matrix theory of stable resonator, the thermal focal length of the gain medium can be easily achieved. To show the application of this approach, the thermal focal length of an LD pumped Nd:YVO₄ laser is measured and the experimental results are in agreement with the theoretical prediction.     

Propagation characteristics of the Yb-doped fiber lasers after spectral beam combining by the VBGs

The propagation model for the spectral beam combining system of five Yb-doped fiber laser beams by the volume Bragg gratings (VBGs) has been built up. Considering the surface distortion by thermal effect, the intensity of an individual beam passing through the spectral beam combining system by the VBGs with deformation has been analyzed numerically and iteratively by using finite-different and sparse matrix methods, and the intensity of combined beam has been studied by the principle of incoherent superposition. Consequently, according to the intensity second-order moments method, the M²-factor of the combined beam has been calculated. The effects of deformation of the VBGs on the intensity, the combining efficiency, the M²-factor and the power in the bucket of the combined beam have been analyzed quantitatively. It can be shown that the effects of the deformation of the VBGs on the intensity distribution of combined beam become more and more obvious with the increasing of the deformation of the VBGs. The results show that the surface distortion of the VBGs due to high-power lasers dramatically degrades both the beam quality of the combined beam and the combining efficiency of the spectral beam combining system.     

Irradiance-moments characterization of off-axis Gaussian beam combinations by means of the Wigner distribution function

The irradiance-moments characterization of off-axis Gaussian beam combinations is presented in use of the Wigner distribution function (WDF). Analytical expressions for the propagation through an optical paraxial ABCD system, beam propagation factor (M² factor), beam width, far field divergence angle and kurtosis parameter of the resultant beam are derived and illustrated with specific numerical examples. It is reexamined that a flat-topped irradiance profile of the resultant beam can be achieved at a certain plane by appropriately choosing beamlet parameters. As compared with previous work, our results show the advantage of using the WDF and irradiance-moments methods.     

Electron-beam-excited lasers based on A2B6 compounds (review)

The literature on electron-beam-pumped semiconductor lasers (EPSLs) based on A²B⁶ compounds is reviewed. Recent advances in the development of EPSLs in the Nineties are reflected. The literature data on the output parameters of these EPSLs are systematized. Basic parameters and characteristics of EPSLs their hardware realization, the properties of active media, and the mechanisms of amlification and degradation are discussed. The works on the use of EPSLs for pumping of other active media are reviewed. Institute of Semiconductor Engineering RWTH, 55, Templergraben, Aachen, D-52056, Germany (permanent address: B. I. Stepanov Institute of Physics, National Academy of Sciences of Belarus, 68, F. Skorina Ave., Minsk, 220072, Belarus). Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 66, No. 5, pp. 601–618, September–October, 1999     

The beam propagation factor and far-field distribution of Bessel-modulated Gaussian beams

The explicit expressions for the beam propagation factor (M ² factor) and far-field distribution of Bessel-Modulated Gaussian beams with quadratic radial dependence are derived. The results are analyzed with numerical example.     

Modeling the cw lasing regime for diode-pumped solid state lasers

In terms of a system of balance equations, we propose a model for describing the operation of lasers based on solid-state quasi-three-level active media in the cw lasing regime with longitudinal pumping by emission from diode lasers, taking into account the spatial distribution of the pump and lasing light beams. We model the operation of lasers based on the active crystals Yb³⁺:NaLa(MoO₄)₂ and Yb³⁺:YVO₄, taking into account the proposed spatial distribution function of the intensity and the emission spectrum of the pump. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 1, pp. 55–60, January–February, 2007.     

环状球差透镜对超高斯光束光束质量的影响

以桶中功率及β值为光束质量评价参数,分析了环状球差透镜的球差系数、遮拦比等参数对超高斯光束光束质量的影响。研究表明,在几何焦面和实际焦面的桶中功率曲线是不同的,选用适当参数的负球差环状透镜, 可获得比无球差环状透镜更高功率/能量集中度的光束。     

光束自聚焦的矢量理论研究

基于矢量非傍轴非线性Schr-dinger方程,利用调制理论研究了光束的自聚焦特性,比较了非零电场散度项和非傍轴项在消除自聚焦崩塌方面的贡献。结果表明,引入两项之一都可使光束聚焦到一有限宽度后开始散焦,然后又自聚焦,如此作聚焦-散焦的周期性循环。但是,在光束自聚焦点附近,非零电场散度项的作用要强于非傍轴项。