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I am trying to estimate the peak of a single photon signal in the oscilloscope by looking at the datasheet of the PMT (I am using Hamamatsu H7195 but the picture below is just for illustrative purposes). I started with the luminous of the Anode and estimate the flux（in lumen) using this. But I am stuck after that. Other data available are the impedance is 50\$\Omega\$, and the single-photon signal has a width around 1ns (estimated from Hamamatsu's HPD datasheet).enter image description here

Could anyone give me some hint on how to estimate from the data available here? Or it is just impossible to do that by looking at the datasheet?

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  • \$\begingroup\$ \$1.12 \times 10^{16}\$ photons/second = 1 lumen according to your link. Does that help? \$\endgroup\$
    – Andy aka
    Commented Jul 17, 2021 at 17:52
  • \$\begingroup\$ cZ, What exactly do you have to start with and what do you want to find? It's not really clear to me. What is your single-photon source? Or was that a rhetorical device? (You almost never want to allow ambient light near a PMT. You keep them in some very very dark place when you aren't using them. So I can't believe you are thinking of ambient light.) So what's the source? What kind of goal do you have for some as yet unknown calculation? \$\endgroup\$
    – jonk
    Commented Jul 17, 2021 at 18:08
  • \$\begingroup\$ cZ, also, I don't know what level of communication is appropriate. Do you know what a "work function" is, in this context? Are you familiar with electron-volts? Do you know how to calculate the energy of a photon in Joules or eV? It's important to know, because in considering an answer I don't know if I'd be "talking down," or not. The question sounds a bit "remedial" to me. But maybe that's not the case, at all. Could you disclose your level of knowledge, please? \$\endgroup\$
    – jonk
    Commented Jul 17, 2021 at 18:19
  • \$\begingroup\$ cZ, One final note before I walk off and do other things. PMT's are usually used with scintillators. For example, placed adjacent to sodium-iodide crystals so that they can pick up on faint light impulses resulting from energetic particles passing through the scintillating crystal. If you have some other application in mind, you should be very clear and say something about the application. If this is part of a study course, you should say something about the course and where you are in it. If this is just a matter of personal curiosity, then say that, too. All this matters for a useful answer. \$\endgroup\$
    – jonk
    Commented Jul 17, 2021 at 18:33
  • \$\begingroup\$ Hi @jonk, I am trying to estimate how efficient a blue LED can be used as a single-photon source. The LED light will be attenuated and I would like to measure the rate of single-photon production. I know the LED isn't a great source of single-photon but that's what I am assigned to do. Yes, I can understand the terminologies you used. But I am not quite familiar with the terms and concepts used in photometry. \$\endgroup\$
    – cZe99
    Commented Jul 19, 2021 at 3:52

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I started with the luminous of the Anode and estimate the flux（in lumen) using this.

You are making this much harder then you need to. Your datasheet gives you the radiant sensitivity in amps per watt, which gives you how many amps of current you get per watt of optical power. Knowing your wavelength, you can calculate how much energy each photon has and then convert that into amps of current per photon. Finally, once you know how many amps each photon (per second) gives you, you can multiply that times 50 ohms and divide by your rise time to get the approximate peak voltage.

Note that I say approximate because the peak voltage depends on the shape of your pulse (which is almost certainly not symmetric for a PMT), while the sensitivity in that datasheet is only the "typical" value, and for PMTs that can vary by an order of magnitude or more between devices. So at best you're going to get the peak value within a factor of maybe 3 or 4. When you buy a tube from Hamamatsu, usually it comes with measurements for that specific tube, from which you can more precisely calculate the expected amplitude.

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