色散透镜系统中宽带厄米-高斯光束的焦移

为了了解带宽对厄米-高斯光束的聚焦特性和焦移的影响,采用衍射积分推导了TEM₁₁模和TEM₂₂模厄米-高斯光束通过受光阑限制色散透镜的传输公式,并利用数值计算对聚焦光强分布进行了研究,分析了带宽对两种模式焦移的影响。结果表明,TEM₁₁模和TEM₂₂模厄米-高斯光束的焦移量都会随带宽增大而增大,但两者的大小依赖相对带宽;当相对带宽小于0.25时,TEM₂₂模焦移量大于TEM₁₁模焦移量,然而相对带宽大于0.25时,后者会稍大于前者;带宽变化使TEM₂₂模轴上光强主极大和次极大发生消长,从而引起轴上光强极大位置发生跃变。该研究结果对宽带厄米-高斯光束的应用具有一定的参考价值。

Focal shift of polychromatic Hermite-Gaussian beams in dispersion lens system

In order to know effect of bandwidth on the focused properties and focal shift of Hermite-Gaussian (H-G) beam, propagation formula of H-G beams passing through a dispersion lens system with polychromatic TEM₁₁ mode and TEM₂₂ mode was obtained by using diffraction integral. The focused intensity distribution was studied by numerical calculation. The effect of bandwidth on focal shift of both modes were analyzed. The results show that the focal shifts of H-G beams with TEM₁₁ mode and TEM₂₂ mode increase with the increase of the bandwidth and depend on the relative bandwidth. Focal shift of TEM₂₂ mode is greater than that of TEM₁₁ mode when relative bandwidth is smaller than 0.25 whereas the latter is somewhat greater than the former when relative bandwidth exceeds 0.25. The principle maximum intensity and the secondary maximum intensity of TEM₂₂ mode on the axis compete each other with the vary of bandwidth and then the axial primary maximum intensity transits from one place to another. The results are helpful for further application of the polychromatic H-G beams.