By means of the Huygens-Fresnel diffraction integral, the propagation expression of a laser beam passing through a hard-edged aperture is derived. The effects of the bandwidth on the transverse intensity distributions of the beam in the near and far fields are analyzed. It is found that, in the near field, the beam uniformity is improved with increasing the bandwidth and the broader the spectrum, the smoother the transverse intensity distribution is. Intensity spikes produced by low-frequency diffraction are eliminated in the diffraction patterns and the transverse intensity distribution near axis tends to smooth when the bandwidth increases. The intensity spikes produced by high-frequency diffraction still exist with increasing the bandwidth, but the amplitudes and numbers of them decrease. In the far field, there are only a few differences among the transverse intensity distributions of the beams with different bandwidthes. However, The secondary maximum intensity still presents for the beam with small bandwidth, and it decreases with increasing the bandwidth and is eliminated with large bandwidth.

针对激光加工大功率激光功率密度分布测量的要求,采用空心探针扫描采样测量法,提出并建立了被测激光经探针小孔、探针内通道传输的数学物理模型,经计算,给出了包括探针微孔孔径、探针内通道尺寸、系统采样点数等系统参数,设计了新的测量系统,实现了对大功率激光光束、聚焦光斑功率密度分布的直接测量,测量结果与理论计算相吻合.测量仪能对CO2激光和YAG激光进行直接测量,测量的功率大于10 kW,功率密度大于107 W/cm2,测量激光光束的最大直径为60 mm,激光聚焦光斑的直径小于0.5 mm.

提出了一种实时测量大功率激光照射下聚焦镜产生的像差的新方法。 该方法利用混合模激光束在传输过程中光束横截面能量分布的变化来进行测量。 首先通过计算混合模激光束的光学参数来模拟其在传输过程中的光束横截面能量分布的变化, 然后计算其通过聚焦镜后在焦点位置的光束横截面能量分布, 通过对比计算所得的光束横截面能量分布和实际测量的焦点位置的光束横截面能量分布的差异, 得到聚焦镜的像差。

根据大功率CO2混合模激光束横截面强度分布的变化规律,任选两个横截面的强度分布,采用数值迭代方法,精确计算出混合模传输的光学参数。