Date: Fri Jun, 27 2008 – 8:26am From: Henry Frisch frisch@hep.uchicago.edu To: Jean-Francios Genat genat@lpnhep.in2p3.fr, Lionel De Sa lionel@hep.uchicago.edu Lionel, Anatoly has pointed out that the electrons are (probably) kicked out at 90 degrees to the photon's direction, as that's where the Efield points. Can you try finding references to this? (googling photoelectric effect etc. may be the way) One quick embarrassing question- can you plot dN/dtheta for your present simulation? -Henry Date: From: Jean-Francios Genat genat@lpnhep.in2p3.fr To: Henry Frisch frisch@hep.uchicago.edu Can't believe that... -JF Date: Sun, 29 Jun 2008 - 01:59pm From: Henry J. Frisch frisch@hep.uchicago.edu To: Jean-Francios Genat genat@lpnhep.in2p3.fr, J. Va'vra jjv@slac.stanford.edu Jean-Francios, Absolutely. BUT, we need to find out what the real story is...- I can imagine that there are competing effects- the momentum transfer from the photon is in the photon direction; the force from the lattice could include a component from the E field. (howevr, are the time scales right? The E field for 400 nm radiation oscillates at ~10^{15} Hz, if I did it right, which is femto-seconds, while the electron takes some time I don't know to leave the surface- something like a few 100 Angstroms I would think (10^{-8}m)- perhaps they ARE comparable. -Henry Date: Mon, 30 Jun 2008 - 11:33am From: J. Va'vra jjv@slac.stanford.edu To: Henry J. Frisch frisch@hep.uchicago.edu Henry, My intuition, which can be easily wrong, says that the process is entirely isotropic. The photoelectrons then do a random walk within the photocathode and when they escape it; i think that they still retain the isotropic angular distribution. I was not able to find the direct proof of this guess. I did find a reference, which does indicate that it is not a simple matter to simulate the process. The time response of the photocathode tau is governed by time spread between photo-excitation and subsequent emission of electrons. The paper indicates that for the bi-alkali and the multi-alkali photocathodes, the time response is 10^-13 < tau < 10^-12 sec, and for GaAs photocathodes it is longer 2x10^-4 < tau < 10^-9 sec. Higher QE, longer tau. Metals, with the lowest QE, have smallest tau. I do include this reference. It is clear that one cannot do these simulations with a pedestrian knowledge, such as I have, and it requires a deep knowledges. I am guessing the manufacturers do have more knowledge, but not necessarily better theoretical understanding. My guess. -Jerry