HGHG自由电子激光时间相干性研究

A study on temporal coherence of HGHG FEL

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)FEE具有的重要优势之一。利用自制的迈克尔逊干涉仪测量了600 nm(二次谐波)和400 nm(三次偕波)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600 nm和400 nm HGHG自由电子激光的相干长度,分别为119±6.7 fs和112±16.9 fs。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。

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.