Liu X, Lu X-Y, Tian Q-L, Pan Z-L, Deng X-J, Yan L-X, Li R-K, Huang W-H, Tang C-X, Chiche R, Dupraz K, Martens A, Zomer F
Department of Engineering Physics, Tsinghua University, Beijing 100084, China.
Université Paris-Saclay, CNRS/IN3P3, IJCLab, 91405 Orsay, France.
Rev Sci Instrum. 2024 Oct 1;95(10). doi: 10.1063/5.0222951.
The innovative mechanism of steady-state microbunching (SSMB) promises a potent light source, featuring high repetition rate and coherent radiation. The laser modulator, comprising an undulator and an optical enhancement cavity, is pivotal in SSMB. A high-finesse prototype optical enhancement cavity for SSMB with an average power of 55 kW is described in this paper. Preliminary design of the laser modulator, experimental setup, and methods to address frequency degeneracy and power coupling issues are discussed. D-shaped mirrors are utilized to successfully suppress the modal instability. This study is the first to illustrate the finesse reduction caused by high-order mode damping during experiments. The experimental and simulation results match closely. A cavity power coupling model is established, and the experimental results verify the correctness of the coupling model. A method for estimating the absorption coefficient through thermal-induced evolution of cavity mode has been implemented. Experimental results demonstrate a high-average-power enhancement cavity with a finesse of 16 518 ± 103 and an estimated average absorption coefficient of 12 ppm for the cavity mirrors. The findings contribute to the advancement of SSMB by providing insights into the design and operation of high-power optical enhancement cavities.
稳态微聚束（SSMB）的创新机制有望成为一种强大的光源，具有高重复率和相干辐射的特点。由波荡器和光学增强腔组成的激光调制器在SSMB中起着关键作用。本文介绍了一种用于SSMB的平均功率为55千瓦的高精细度原型光学增强腔。讨论了激光调制器的初步设计、实验装置以及解决频率简并和功率耦合问题的方法。利用D形镜成功抑制了模式不稳定性。本研究首次说明了实验过程中高阶模阻尼导致的精细度降低。实验结果与模拟结果紧密匹配。建立了腔功率耦合模型，实验结果验证了耦合模型的正确性。实现了一种通过腔模热致演化估算吸收系数的方法。实验结果表明，该高平均功率增强腔的精细度为16518±103，腔镜的估计平均吸收系数为12 ppm。这些发现为高功率光学增强腔的设计和运行提供了见解，有助于推动SSMB的发展。
