中文摘要：

时间相干性是外种子型自由电子激光（FEL）对于自发辐射自放大（SASE）FEL具有的重要优势之一。利用自制的迈克尔逊干涉仪测量了600nm（二次谐波）和400nm（三次谐波）高增益谐波放大（HGHG）FEL的时间相干性，分析不同延迟时间处的干涉图样条纹可见度，得到了600nm和400nmHGHG自由电子激光的相干长度，分别为119±6．7fs和112±16．9fs。通过与光谱测量和理论计算结果进行比较，进一步验证了实验测量的准确性。结果表明HGHG自由电子激光继承了种子激光的相干性特点，这与理论预测结果相一致。

英文摘要：

Good temporal coherence is a significant advantage of the seeding free electron laser （FEL） compare with FEL of the self-amplified spontaneous emission （SASE） type. The temporal coherence properties of HGHG （high-gain harmonic generation） pulses on the Shanghai Deep Ultra-violate FEL at Shanghai Institute of Applied Physics are measured at 600 nm and 400 nm （the wavelength of seed laser is 1200 nm） by a Michelson interferometer with sub-femto second time resolution. At zero delay visibilities of 0.88±0.02 at 600 nm and 0.66±0.06 at 400 nm are measured. The delay of one partial beam reveals coherence time of 119±6.7 fs at 600nm and 112± 16.9 fs at 400 nm.