AI 中文总结
该研究提出一种基于6个布拉格反射晶体的非共面紧凑型可调谐X射线腔，其调谐范围优于平面蝴蝶结腔，可将CBXFEL的光子能量范围扩展至3~20 keV，为未来CBXFEL提供了可行的谐振器方案。
AI 中文摘要
基于腔的X射线自由电子激光（CBXFEL）需要可调谐X射线腔以拓宽其实际应用范围，使其能应用于更广泛的科学领域。我们提出并分析了一种紧凑型可调谐非共面X射线腔，该腔基于6个布拉格反射晶体，排列为两个由3个晶体组成的背散射单元。这种三维几何结构相比平面蝴蝶结腔提供了大得多的调谐范围，同时保持了紧凑的横向 footprint。我们推导了腔几何结构、晶体运动学以及本征和本征偏振基下与偏振相关的布拉格反射率的解析表达式。对于给定的布拉格反射，最终光子能量调谐范围为100%，从背散射时的E=E_H到布拉格角θ=π/6时的E=2E_H。实际的几何和偏振约束将直接可用的范围降低到约45%，而在腔本征偏振基下运行可将其扩展到约65%。通过结合基频和高次谐波金刚石反射，并利用不同晶面族的反射，可访问的光子能量范围可从约3 keV扩展到约20 keV。这些结果表明，非共面多晶体腔是实现未来CBXFEL所需的紧凑型、宽调谐X射线谐振器的可行途径。
英文摘要
Cavity-based x-ray free-electron lasers (CBXFELs) require tunable x-ray cavities to broaden their practical utility and enable access to a wider range of scientific applications. We propose and analyze a compact tunable non-coplanar x-ray cavity based on six Bragg-reflecting crystals arranged as two three-crystal backscattering units. The three-dimensional geometry provides a substantially larger tuning range than planar bowtie cavities while maintaining a compact transverse footprint. We derive analytical expressions for the cavity geometry, crystal kinematics, and polarization-dependent Bragg reflectivity both in the intrinsic and eigenpolarization bases. For a given Bragg reflection, the ultimate photon-energy tuning range is 100\%, from $E=E_{_{H}}$ at backscattering to $E=2E_{_{H}}$ at Bragg angle $θ=π/6$. Practical geometrical and polarization constraints reduce the directly usable range to approximately 45\%, while operation in the cavity eigenpolarization basis can extend it to approximately 65\%. By combining fundamental and harmonic diamond reflections, and using reflections from different crystallographic families, the accessible photon-energy range can be extended from about 3~keV to approximately 20~keV. These results establish non-coplanar multi-crystal cavities as a viable route toward compact, broadly tunable x-ray resonators for future CBXFELs.
Comments20 pages, 11 figures, 1 table
