Author: Halavanau, A.
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TU2A4
 A Low-loss 14 m Hard X-ray Bragg-reflecting Cavity, Experiments and Analysis  
 
  • R.A. Margraf, Z. Huang, R. Robles
    Stanford University, Stanford, California, USA
  • A. Halavanau, Z. Huang, J. Krzywiński, K. Li, J.P. MacArthur, G. Marcus, R. Robles, A. Sakdinawat, T. Sato, Y. Sun, D. Zhu
    SLAC, Menlo Park, California, USA
  • T. Osaka, K. Tamasaku
    RIKEN SPring-8 Center, Sayo-cho, Sayo-gun, Hyogo, Japan
  
  Funding: This work was supported by the Department of Energy, Laboratory Directed Research and Development program at SLAC National Accelerator Laboratory, under contract DE-AC02-76SF00515.
Bragg-reflecting cavities on the 10 s or 100 s of meter scale are a core component of proposed Cavity-Based X-ray Free-Electron Lasers (CBXFELs). While CBXFELs promise improved longitudinal coherence and spectral brightness over single-pass self-amplification of spontaneous radiation (SASE) FELs, construction and alignment of large Bragg-reflecting cavities can be difficult technical challenge. Our collaboration recently demonstrated stable operation of a low-loss 14 m 9.831 keV X-ray cavity of four Bragg-reflecting diamond mirrors*, a significant step towards a CBXFEL-scale cavity. We in-coupled X-rays from the Linac Coherent Light Source (LCLS) into our cavity via a transmission grating, then measured round-trip efficiencies approaching 88%, or >96% when neglecting losses on in-coupling and focusing optics. Additionally, we characterized transverse oscillations in the cavity, demonstrating the effectiveness of our cavity focusing. We will discuss these results, additional new analysis and consider implications for future CBXFEL projects.
* R. Margraf et al., ‘Low-loss Stable Storage of X-ray Free Electron Laser Pulses in a 14 m Rectangular Bragg Cavity’, In Review, preprint, 2023. doi: 10.21203/rs.3.rs-2465216/v1. 		 
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WE2C1
 Population Inversion X-ray Laser Oscillator at LCLS and LCLS-II  
 
  • A. Halavanau, A. Aquila, U. Bergmann, C. Pellegrini
    SLAC, Menlo Park, California, USA
  • A.I. Benediktovitch
    DESY, Hamburg, Germany
  • N. Majernik
    UCLA, Los Angeles, California, USA
  • N. Rohringer
    Max Planck Institute for the Physics of Complex Systems, Dresden, Germany
  • N.B. Welke
    UW-Madison/PD, Madison, Wisconsin, USA
  
  The advancement of X-ray Free Electron Lasers (XFELs) has created revolutionary new research opportunities, owing to their high peak and average power, transverse coherence, and short pulse duration. Despite their remarkable capabilities, XFEL pulses lack longitudinal coherence and are not transform-limited, which limits their utilization, e.g. in quantum optics and precision interferometry. We explore the development of coherent, transform-limited pulses through alternative strategies, namely, X-ray lasers based on population inversion. We propose a novel approach relying on the principle of stimulated emission in the hard X-ray regime, using the XFEL as a pump. We will specifically discuss the case of the X-ray Laser Oscillator (XLO) at the LCLS copper linac and the planed LCLS-II-HE. Our recent work has shown the feasibility and performance characteristics of these systems, which can operate over a broad wavelength range from 5 to 12 keV. Future applications at LCLS-II-HE might allow for transform-limited XLO pulses with repetition rates up to tens of kHz. We show that XLO is experimentally feasible and discuss its projected performance and photon pulse properties operating at the Copper K-alpha1 line. Finally, we discuss possible first experiments with XLO.  
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