User talk:Filou

From Wikipedia, the free encyclopedia

[edit] Controversy about some input: Expo.02 and financial problems

Your sentence about Expo.02 and taxpayer money has been removed for the second time on the Neuchâtel article. It is POV and does not belong to that article, so please stop adding it. However, you are welcome to edit the Expo.02 page and give us a little bit more information about the financial scandal side of the exhibition. But try to remain objective and cite your sources. I've already written a phrase or two on the subject, and if you have any precise figures, do not hesitate to share your information. Happy editing Glaurung 08:16, 21 January 2006 (UTC)

MY ANSWER:

Howdy, Glad someone watches carefully that NO OPINION is expressed. Don't go too far ! I'm afraid this belongs to a new social disease called "politically correct at any price", a behavior that can, in some instances, produce disasters. To the point: I would agree that the original phrasing was not appropriate. However, it is a fact that the event in 2002 did cost a large amount of TAX MONEY. Pointing this out enclines maybe some readers to start a mental process ... If you have a good link on the topic, why not add it ? I will think about phrasing it another way. Take care, Filou.

Even if I agree with you about the financial aspect of Expo.02, sentences like the one you introduced are not proper material for an encyclopedia. This is not really a question of being politically correct. But point-of-view statements do not belong to the aticle's pages, which must remain completely neutral on a subject. Unfortunately, I am not an Expo.02 expert, and don't have any precise figures to give nor any source, but it sure would be interesting material for the article. Glaurung 07:14, 23 January 2006 (UTC)

[edit] Detectors

In optical detectors, a single photon never excites more than one electron. Quantum physics prevents this. There are detectors, such as avalanche photodiodes and photomultiplier tubes, where the output signal is enhanced by electron amplification (an avalanche effect), but the initial photon still only excites one electron. The amplified signal is obtained by accelerating the electron with an electric field, so that it can excite other electrons by collision. Of course there are also detectors where the signal is amplified by conventional electronics.--Srleffler 01:27, 24 January 2006 (UTC)

You are right, but I disagree ! The photon indeed generates only ONE photo-electron. However, this photo-electron has energy and in a superconductor there is a cascade of effects, at the end of which phonons are generated. These phonons, (heat), can leak out (the system cools down) but a significant fraction of them can break Cooper pairs. Because the energy threshold for Cooper pair breaking is so much smaller than the energy required to generate a electron-hole pair in a semi-conductor, you end up having more than ONE electron available for some time to measure. They will recombine into Cooper pairs after a while. You can measure the number of excitations generated by the original photon as a deviation from the thermal equilibrium state using a superconducting tunneling junction (Josephson junction operated in as particular mode, see Josephson effect). Agree with me that this long story cannot be selled as such on the detector page !! I had wanted to mention this other (new) class of sensors, because they allow single photon counting AND yield information about the photon energy. There is no other device that gives you the color of a single visible photon. Maybe we can re-phrase this in order to avoid people to get confused about quantum mechanics. Regards, Filou 08:41, 24 January 2006 (UTC)

I don't know enough about superconducting detectors to argue the point. If you want to say that the photon excites multiple electrons in the superconducting detectors (but not the other types) I'm fine with that. I removed the reference to the photoelectric effect, though, since this is not the effect used in semiconductor detectors. They are based on simple absorption of photons in a band-gap material.

If you want to mention the micro-calorimeter that can measure photon energy, provide a reference where people can verify the claim and get more information. Speculative devices are not acceptable for Wikipedia articles, unless they have been published (ideally in the scientific literature).--Srleffler 13:00, 24 January 2006 (UTC)

P.S. Yes, a single-photon detector that can measure color is pretty cool.

Howdy, OK, I will add something about the micro-calorimeter, a thermal device, originally developped for soft x-ray work but sensitive enough to register visible photons as well. Something else: what makes you claim there is no photoelectric effect in the semiconductor detector ? The end result is indeed the creation of one or more electron - hole pairs by some energetic event. But at "time zero" there is absorption of a photon. Filou 14:36, 24 January 2006 (UTC)

The photoelectric effect is when absorption of a photon in a material causes the ejection of an electron from that material. When absorption of a photon raises an electron to a higher energy level, it's just "absorption" or "excitation" of an electron. It is literally "photo-electric", but it isn't the photoelectric effect. Photomultipliers use the photoelectric effect, but photodiodes and other semiconductor detectors do not. They all have the characteristic, though, that you excite one electron per photon.--Srleffler 15:41, 24 January 2006 (UTC)

Well, I'd like to dispute that. Maybe this is semantic, after all. I understand the (inverse)photo-effect as being the result of the (creation) annihilation of a photon by an electron. In the case you send light on a metal, we know from experiment that you do need a certain photon energy, say blue, to kick out an electron. You can shine in red light, as intensely as you want, no electron will gain sufficiently energy to compensate the work function etc. However, all the photons that are not reflected are absorbed and transfer their momentum to some electronic state. Because the photon is destroyed I'd advocate to call this the photo-electric effect. Filou 19:54, 24 January 2006 (UTC)

Yes, it's just semantic. The issue is the exact definition of "the photoelectric effect". I believe the conventional definition includes only the case where the photon causes an electron to be ejected from the material (which happens only when the photon's frequency is high enough, as you noted). Blue photons that excite an electron to a higher state within the material are, I believe, not participating in the photoelectric effect. I could be wrong. It also wouldn't surprise me if, say, semiconductor physicists used the term differently from other physicists.--Srleffler 23:39, 24 January 2006 (UTC)