宽频带激光自由空间传输的调制特性研究

基于惠更斯-菲涅耳衍射积分公式,研究了宽带光束在菲涅耳衍射区的自由空间传输特性,得到宽带光束传输的调制深度与光束带宽Δλ及菲涅耳数F的变化关系。结果表明:一定的带宽对光束的均匀性有适当的改善;当光束的带宽Δλ<2λ0/F时,带宽越大,光束越均匀;当带宽满足条件Δλ=2λ0/F时,菲涅耳衍射完全消失;在一定的菲涅耳数范围内,宽带光束的调制深度随菲涅耳数振荡变化,振荡曲线的主极大值和次极大值分别出现在菲涅耳数为奇数和偶数处,而极小值则出现在菲涅耳数F=2k±1/3(k=1,2,3,…)处,在极小值处光束的均匀性最好。

Study on Modulation Property of Broadband Laser Propagation in Free Space

The free space propagation property of broadband laser beam in Fresnel diffraction area is studied based on Huygens-Fresnel diffraction integral. The relationship between modulation depth, bandwidth Δλ and Fresnel number is obtained. It is found that the uniformity of the beam is improved to a certain extent for an appropriate bandwidth. The bandwidth is widened, and the beam is more uniform, for Δλ > 2λ0/F. Fresnel diffraction disappears completely when Δλ = 2λ0/F is fulfilled. For Fresnel number in a certain range, the modulation depth of broadband laser beam oscillates with the Fresnel number, with the main and secondary maximums of the oscillating curve appearing for odd and even Fresnel number respectively. Its minimums exist for Fresnel number F=2k±1/3 (k=1, 2, 3 …), and meanwhile the uniformity of the laser beam is the best.