A nice, touching story about a physicist

You all are probably aware of this story, but it just so nice and touching that I thought I would share it here. Over at r/physics, Reddit's main physics channel, physicists chat about the end of the universe, dark energy, quarks and whatnot. But then this popped up last night. A non-physicist posted this, asking for help:
My grandfather, Juan Maldonado, was a physicist. He’s dying and I want to understand his work. Can someone put this in laymen’s terms?  
Hi r/physics. My grandfather is Juan R Maldonado. He’s a physicist who worked for Bell Labs and Stanford, and from what I understand, did some important and interesting research. Unfortunately, every time he talked about his work, it went completely over my head. He now has final-stage dementia, so I can’t ask him to clarify. I’m hoping someone here can summarize what his work was about? Obviously he did a lot of things in his long career, but instead of asking you to summarize the whole thing, I’ll focus on one of his more recent publications: High gradient rf gun studies of CsBr photocathodes. What does this mean? What was he working on and what are the implications?

Thank you in advance. His time is limited, and he can no longer talk to me about his work. I’d like to know a little more about what he did and what his impact was as I try and come to terms with his condition.
A couple of responses:

1. My suggestion is to reach out to one of his co-authors. It appears Piero Pianetta is still active at Stanford: https://profiles.stanford.edu/piero-pianetta?tab=bio  He almost certainly knows your grandfather quite well, and I bet he would be happy to give you both a layman explanation of his work and probably some stories about working together.

2. If you go to the patent section of the page the poster above sent you, you'll see that your grandfather was first author of the second patent! That is so awesome! What a small world. I attended Stanford, majored in physics and worked at SCA/FEL at Hanson Labs. I, unfortunately, did not know of your grandfather when I was there. It's very nice of you to want to connect with him like that. Best wishes.


Then a physicist valiantly but foolishly tried to answer the question. That's when things went downhill.

4. High Gradient RF Gun: essentially a super bright beam of electrons. High Gradient refers to the act of accelerating the beam to a higher energy to prevent RF breakdown, which is the lowering of the beams brightness due to inter-electron Coulomb forces. Versions of these are used in particle accelerators, for electron diffraction and for electron microscopy.

Photocathodes are like light detectors. When photons hit the detector (the layer of CsBr in this case i believe), enough energy is absorbed by the surface to eject some electrons. Those ejected electrons form a measurable current, which we can interpret to mean that light is hitting the sensor. In the paper referenced below, these photocathodes are being used as electron sources: "Here a spatially modulated laser illuminates a photocathode, producing a structured beam of electrons."

You'll also see the word "coherence" often. Coherence is effectively a measure of the stability of certain wave properties & it comes in two flavors: Temporal Coherence - the amount of time the beam will remain coherent after being emitted by a source. A wave is "temporally coherent" if we see even separation in time between peaks of the wave.

Etc., ect. 🤨 Huh?

Another physicist responded:

5. Parts of this reply interpret his work incorrectly. Most notably, the work on photo-cathodes are intended as an electron source for particle accelerators, not as a detector. Compared to copper cathodes the CsBr cathodes can have increased quantum efficiency and reduced mean thermal energy. This leads to high brightness electron beams for use in electron microscopy and as a driver for "next" (current) generation free electron lasers (FELs).

Etc., ect. 🤨 Huh?


Ain't all of that just adorable?


🤨 Huh?


By Germaine: The physicist ultra-light (a/k/a/ non-physicist)

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