The highest extraction efficiency (9.4%) of a free electron laser (FEL) oscillator has been achieved at the midinfrared FEL facility of Kyoto University. Because of the interaction between the electron beam and FEL electromagnetic field, a maximum electron energy decrease of 16% was observed. The measured energy decrease was consistent with the measured FEL spectrum. An FEL micropulse energy of ∼100μJ with the expected few-cycle pulse duration at a wavelength of 11μm was observed. This result is an important milestone for the high-extraction-efficiency FEL oscillator and will contribute to the strong-field physics of atoms and molecules.

自由电子激光 (FEL) 振荡器的最高提取效率 (9.4%) 已在京都大学的中红外 FEL 设施中实现。由于电子束和 FEL 电磁场之间的相互作用，观察到最大电子能量降低了 16%。测得的能量下降与测得的 FEL 光谱一致。观察到FEL 微脉冲能量约为 100 μJ ，在 11 μm波长处具有预期的几个周期脉冲持续时间。这一结果是高提取效率 FEL 振荡器的一个重要里程碑，并将有助于原子和分子的强场物理。