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Find the minimal resonant wavelength at which saturation is reachable for eps_n >= $10^{-5}$ cm and realistic undulator technology, and whether lasing at photon energies above $100\\,\\mathrm{keV}$ is possible.","problem_ref":"cb0bad839d0d7d62952477778f20b1c7de116db2f973e1eb77266a8bca992ca0","references":"","settled_by":"An optimization over beam and undulator parameters including quantum diffusion and emittance growth, giving the minimal wavelength.","status_note":"","title":"Shortest wavelength at which a self-amplified FEL can 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