Extended Data Fig. 9: Measured radiation energy at the exit of the undulator for various electron beam charges and relative energy spreads. | Nature

Extended Data Fig. 9: Measured radiation energy at the exit of the undulator for various electron beam charges and relative energy spreads.

From: Free-electron lasing at 27 nanometres based on a laser wakefield accelerator

Extended Data Fig. 9

The black diamonds represent cases with energy spreads larger than 2% (exponential gain is typically not available under such conditions), and the corresponding linear fitting curve (black dashed line) indicates the spontaneous emission. The radiation emitted by a low-energy-spread electron beam (<1%) typically has energy one to two orders higher than that in spontaneous cases, thus indicating the operation in the exponential-gain regime in the present scheme. The exponential gain of the radiation is illustrated with the orbit kick method in the main text.

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