Oepts, D., Bakker, R. J., Jaroszynski, D. A., van der Meer, A. F. G., & van Amersfoort, P. W. (1992). Induced and Spontaneous Interpulse Phase Locking in a Free-Electron Laser. Physical Review Letters, 68, 3543-3546. https://doi.org/10.1103/PhysRevLett.68.3543 (Original work published 1992)
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