Deutsches Elektronen-Synchrotron DESY, Notkestrasse 85, D-22607 Hamburg, Germany.
Phys Rev Lett. 2013 Jul 19;111(3):034802. doi: 10.1103/PhysRevLett.111.034802. Epub 2013 Jul 17.
We present measurements of second- and higher-order intensity correlation functions (so-called Hanbury Brown-Twiss experiment) performed at the free-electron laser (FEL) FLASH in the non-linear regime of its operation. We demonstrate the high transverse coherence properties of the FEL beam with a degree of transverse coherence of about 80% and degeneracy parameter of the order 10(9) that makes it similar to laser sources. Intensity correlation measurements in spatial and frequency domain gave an estimate of the FEL average pulse duration of 50 fs. Our measurements of the higher-order correlation functions indicate that FEL radiation obeys Gaussian statistics, which is characteristic to chaotic sources.
我们呈现了在自由电子激光（FLASH）的非线性操作模式下进行的二阶和更高阶强度相关函数（所谓的汉布利·布朗-特威斯实验）的测量结果。我们用约 80%的横向相干度和数量级为 10^9 的简并参数证明了 FEL 光束的高横向相干特性，使其类似于激光源。空间和频率域的强度相关测量给出了 FEL 平均脉冲持续时间约为 50fs 的估计。我们对高阶相关函数的测量表明，FEL 辐射服从高斯统计，这是混沌源的特征。
