ENEA C.R. Frascati, Via E. Fermi, 45 00044 Frascati, Roma, Italy.
Phys Rev Lett. 2011 Nov 25;107(22):224801. doi: 10.1103/PhysRevLett.107.224801. Epub 2011 Nov 22.
The injection of a seed in a free-electron laser (FEL) amplifier reduces the saturation length and improves the longitudinal coherence. A cascaded FEL, operating in the high-gain harmonic-generation regime, allows us to extend the beneficial effects of the seed to shorter wavelengths. We report on the first operation of a high-gain harmonic-generation free-electron laser, seeded with harmonics generated in gas. The third harmonics of a Ti:sapphire laser, generated in a gas cell, has been amplified and up-converted to its second harmonic (λ(rad)=133 nm) in a FEL cascaded configuration based on a variable number of modulators and radiators. We studied the transition between coherent harmonic generation and superradiant regime, optimizing the laser performances with respect to the number of modulators and radiators.
在自由电子激光（FEL）放大器中注入种子可以减少饱和长度并提高纵向相干性。级联 FEL 在高增益谐波产生模式下运行，可使我们将种子的有益效果扩展到更短的波长。我们报告了首例采用气体中产生的谐波进行种子注入的高增益谐波产生自由电子激光的运行情况。钛宝石激光器的三次谐波在气体池中产生，在基于可变数量调制器和辐射器的 FEL 级联结构中被放大并上转换为其二倍频（λ（rad）=133nm）。我们研究了相干谐波产生和超辐射之间的转变，通过调整调制器和辐射器的数量来优化激光性能。
