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Whether hard X-ray lasers can reach that limit shot after shot is open.","posed_since":"","precise":"Determine whether a seeded or cavity-based XFEL at photon energy $> 5\\ \\mathrm{keV}$ can deliver pulses with time-bandwidth product within 1.5 times the transform limit and pulse-to-pulse energy fluctuation below a few percent, given shot noise and microbunching in the electron beam.","problem_ref":"ddbcf58dba29987b52040846a8919e7d28820e1dd68c04906a50239e4f63fa1e","references":"","settled_by":"Single-shot spectral and temporal measurements of a hard X-ray FEL meeting the stated criteria over many shots.","status_note":"","title":"Can XFELs produce stable transform-limited hard X-ray 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