WE2A1
ANL, Lemont, Illinois, USA
Observations of stimulated emission in atomic media pumped by X-ray FELs have shown that X-ray lasers may be possible using the physical process referred to amplified spontaneous emission(ASE). The coherence and stability of an ASE-based X-ray laser can be improved in an X-ray laser oscillator (XLO)* by employing an X-ray cavity as in the X-ray FEL oscillator (XFELO). We present a Hamiltonian-based, 3D theory in paraxial approximation. Assuming factorization of operator products, the ensemble-averaged Heisenberg equations become Maxwell-Bloch equations which provide a correct description of the stimulated emission. The spontaneous emission is accounted for by adding a random noise term to the atomic coherence, which is uniquely determined from the fact that factorization does not apply for products of operators associated with the same atom. Our theory reproduces the results of the previous 1D theory ** and extends it in including the 3D diffraction effects, in including the seed field, and in incorporating the noise in more versatile way***. It provides a sound numerical framework to evaluate an X-ray laser, either in single pass or oscillator configurations.
*A. Halavanau, et al., PNSA 117, 27 (2020).
**A. Benediktovitch, et al., Phys. Rev. A 99, 013839 (2019)
*** J.-W. Park, K.-J. Kim, and R. Lindberg, Phys. Rev. Lett., submitted
TH3B3
University of Chicago, Chicago, Illinois, USA
ANL, Lemont, Illinois, USA
The X-ray free-electron laser oscillator (XFELO) has the potential to greatly surpass current SASE-FELs in terms of peak power and photon coherence. Although a large, 4th generation storage ring (4GSR) is promising as a diver for an XFELO operation, meeting the requisite electron energy spread remains a challenge. The transverse gradient undulator (TGU) is a potential solution to this issue*. Using low-gain TGU theory, we derive optimal beam parameters for a hypothetical XFELO in a straight section of PETRA-IV and discuss potential implementation challenges associated with the ring-FEL coupling, namely FEL beam degradation and gain modulation. The need for a by-pass and fast kickers is obviated by equipping a higher charge (4 nC) to sixteen equidistant electron bunches for XFELO interaction. RF is used to control the FEL duty cycle and allow the XFELO bunches to damp before resuming the FEL interaction. Detailed multi-stage numerical simulation was used to compute the projected performance**.
* T. I. Smith, L. R. Elias, J. M. J. Madey, and D. A. G. Deacon, J. Appl. Phys. 50, 4580 (1979).
** Y. S. Li, R. R. Lindberg, and K.-J. Kim, Phys. Rev. AB 26, p. 030702 (2023).