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Comment by eslaught | Hacker News Reader

I don't work on this directly, but I do adjacent stuff in the computer science research group at SLAC.

Feel free to ask me questions, I guess? (I will not be able to say much about the physics.)

Incredible stuff. I can't imagine the undulators are perfectly efficient at extracting all the energy from the electron beams. What do you guys do with the leftovers?

Neat! Wouldnt powerful xrays change the reaction to be filmed?

Again, not a physicist. But my understanding is that on a femptosecond timescale (the duration of the x-ray pulse generated by LCLS-II), effectively no reactions occur. The pulse destroys the sample, so that means you have to pump through a steady stream of sample particles to image. So for any given experiment, you'll get a stream of what are effectively snapshots of the reaction occurring at a given moment in time, and then it's up to software post-processing to figure out what you're looking at in a given snapshot and how far progressed the chemical reaction is at that point.

I helped with similar experiments at LCLS-I and the first half of this comment is correct. The chemical reaction is carefully timed on the order of milliseconds, so they get a series of snapshots of the reaction at a specific known state (but previously unknown structure). There isn't enough information in individual snapshots for the processing software to do very much with besides combine it with other snapshots (thousands of them).

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