A photodiode amplifier system for pulse-by-pulse intensity measurement of an x-ray free electron laser

What is it about?

We developed a high-precision measurement system to monitor the intensity of every single X-ray pulse from an X-ray Free Electron Laser (XFEL). Because XFEL pulses are incredibly fast and intense, we created a specialized amplifier and detector system that can handle a vast range of light levels—from very faint signals to extremely bright flashes—and transmit that data accurately over long distances (more than 100 meters) within a large-scale facility. X線自由電子レーザー（XFEL）から放たれる、極めて短く強力なX線パルスの強度を、一発ごとに精密に測定するシステムを開発しました。XFELの光は強度の変動が大きいため、微弱な光から非常に強い光まで（10の8乗倍という広い範囲）をカバーし、かつ大規模施設内の長いケーブル（100m以上）を通しても信号が劣化しない特殊な増幅器と計測手法を構築しました。

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Why is it important?

To conduct successful experiments with XFELs, researchers need to know the exact intensity of each pulse used to hit their samples. Our system provides a "ruler" that is both incredibly sensitive and robust. It played a crucial role during the development phase of the light source, capable of detecting the first weak glimmers of light, and continues to provide the high-accuracy data needed for cutting-edge science as the facility operates at full power. XFELを用いた実験を成功させるには、「今、サンプルに当たったパルスがどれくらいの強さだったか」を正確に知る必要があります。本システムはいわば、極めて感度が良く、かつ壊れにくい「光の物差し」です。施設の立ち上げ初期の微弱な光の検出から、フルパワー稼働時の強力な光の測定まで、一貫して高い精度（誤差0.1%程度）でデータを供給し、最先端科学の土台を支えています。

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