Study on Production of Coherent Light by SASE

我们利用L波段直线加速器在红外波段对有望实现X射线激光的自放大自发辐射进行了研究，该加速器可以加速电荷高达91 nC的单束团电子束。在11-32 MeV的宽能量范围内，测得电子束的特性为相对能散1.1~4%，每束电荷20 nC，束长20-30 ps，归一化发射率150~250πmm mrad。利用这些测量参数和基于一维模型的SASE理论对SASE的预期性能进行了估算。对于电子能量为11 MeV，摇摆器K值为1.47时，自由电子激光参数为0.022，增益长度为0.128 m。发现该理论适用于峰值电流&gt；1kA和电子能量&lt；20 MeV。我们测量了12.6 MeV的电子束通过周期为6厘米的32个周期的摇摆器时所发出的强光。随着K值的增大，被观测光的峰值功率从1W增加到1kW。由于功率对K值的依赖关系与理论的预测符合得很好，因此得出结论：观察到的光是由SASE引起的。我们用单色仪测量了SASE在80-180μm范围内的波长光谱。基峰的光谱宽度为2-3%，略大于理论预测的2.2-2.3%。我们首次观测到了SASE的二次谐波峰。我们正在定量测量SASE的特性，并使用三维FEL模拟程序分析实验结果。

We have conducted research on SASE (Self-Amplified Spontaneous Emission), which is expected to be a promising candidate for realizing X-ray lasers, in the infrared region using the L-band linac, which can accelerate a single-bunch electron beam with charge up to 91 nC.The characteristics of the electron beam have been measured over the wide energy range of 11-32 MeV to be the relative energy spread 1.1〜4%, charge per bunch > 20 nC, the bunch length 20-30 ps, and the normalized emittance 150〜250 π mm mrad. The expected performance of SASE has been estimated using these measured parameters and SASE theory based on the 1-dimensional model. The FEL parameters is 0.022 and the gain length is 0.128 m for the electron energy 11 MeV and the K value of the wiggler 1.47. It has been found the theory is applicable for the peak current > 1kA and the electron energy < 20 MeV.We have measured strong light emitted when the electron beam of 12.6 MeV passes through the wiggler with 6 cm period length and 32 periods. The peak power of the observed light increases from 1 W to 1 kW as the K-value increases. Since the K-value dependence of the power agrees quite well with the prediction of the theory, it is concluded that the observed light is due to SASE.We have measured wavelength spectra of SASE over the range of 80-180 μm using a grating monochromator. The spectral width of the fundamental peak ranges 2-3 %, and this value is slightly larger than 2.2-2.3 %, predicted by the theory. We have observed the second harmonic peak of SASE for the first time. We are quantitatively measuring characteristics of SASE and analyzing experimental results using 3-dimentional FEL simulation codes.