Jeong Tae Moon, Weber Stefan, Le Garrec Bruno, Margarone Daniele, Mocek Tomas, Korn Georg
Opt Express. 2015 May 4;23(9):11641-56. doi: 10.1364/OE.23.011641.
The focusing property of a focal spot of a femtosecond laser pulse is presented under tight focusing conditions (below f-number of 1). The spatial and temporal intensity distributions of a focused electric field are calculated by vector diffraction integrals and coherent superposition method. The validity of the calculation method is examined by comparing the intensity distribution obtained under a high f-number condition to that obtained with the fast Fourier transform method that assumes the scalar paraxial approximation. The spatial and temporal modifications under tight focusing conditions are described for a focused femtosecond laser pulse. The calculation results show that a peak intensity of about 2.5x10(24) W/cm2 can be achievable by tightly focusing a 12-fs, 10 PW laser pulse with a f/0.5 parabolic optic. The precise information on intensity distributions of a femtosecond focal spot obtained under a tight focusing condition will be crucial in assessing a focused intensity and in describing the motion of charged particles under an extremely strong electric field in ultra-relativistic and/or relativistic laser matter-interaction studies.
在紧聚焦条件下（f数小于1），给出了飞秒激光脉冲焦斑的聚焦特性。通过矢量衍射积分和相干叠加方法计算聚焦电场的空间和时间强度分布。通过将高f数条件下获得的强度分布与采用标量傍轴近似的快速傅里叶变换方法获得的强度分布进行比较，检验了计算方法的有效性。描述了紧聚焦条件下聚焦飞秒激光脉冲的空间和时间变化。计算结果表明，通过使用f/0.5抛物面光学元件对12飞秒、10拍瓦的激光脉冲进行紧聚焦，可实现约2.5×10²⁴W/cm²的峰值强度。在超相对论和/或相对论激光与物质相互作用研究中，在紧聚焦条件下获得的飞秒焦斑强度分布的精确信息对于评估聚焦强度以及描述超强电场中带电粒子的运动至关重要。
