Recent content by xxfzero

I can understand what you addressed that it is possible for PMT to employ higher gain without increasing applied voltage, hence without increasing dark current. Meanwhile for APD, this is limited by numbers of electron-hole pairs that can be generated. I find one ambiguity in our discussion is...

Could you please give a qualitative picture why PMT has a better SNR, with respect to APD? Many thanks.

Thank you, tech99. My confusion is that electrons due to thermal or field emission (dark current, when no light incidents) from cathode will also be amplified, in other words, generation of secondary electron does not discriminate whether the origin is signal photoemission or thermal/field...

Thank you ZapperZ. Maybe my expression on noise was unclear. Actually, for simplicity, I consider two kinds of noise: 1) shot noise of incident photon, meaning that even the power of incident light is exactly constant, the number of photon still fluctuates over time, 2) dark durrent of PMT. If...

Thank you, Marcusl. Are you talking about excess noise (ratio) of gain of either PMT or APD? Indeed, some material (maybe from website of Hamamatsu Co. , I remember) mentioned that PMT wins in this aspect. But this seems to be a put-in-number problem, while I want to firstly get a qualitative...

Empirically, photomultiplier tube (PMT) is said to present better signal-to-noise ratio (SNR) than avalanche photodiode(APD). Some materials say that it is attributed to the higher gain and lower dark current of PMT. The benefit of higher gain is confusive for me, since I suppose that noise (of...

OK, thank you. I'll firstly read group theory, esp. representation part, and then return.

I asked this question somewhere else and got a similar answer that real/complex field comes from real/complex representation (just experiment not mentioned), is this answer OK? And, still, I want to know what the correlation between real field/complex field and real/complex representation is...

Oh, thank you very much, too Could you please recommend me some book/chapters where systematically discuss the correlation between real field/complex field and real/complex adjoint representation?

Oh, thank you very much. So if I can roughly speak that when someone gives me a kind of particle, I should check if it has any kinds of Noether charge, then decide either write it as real field or complex field? Another question is could you please recommend me some book/chapters where...

Oh, sorry, field is a loose statement. I just refer to plane wave or other eigenfunctions by "field" (please see the attached figures, both from Scully's Quantum optics, one from pp5, the other pp27). A complete statement should be that photons are always described by real function when...

Why are photons described by real field, while electrons by complex field?

Thank you, Cthugha. I can understand your meaning. My previous picture is atoms at ground state absorb some amplitude of "positive frequency part" and transit to excited state, and then the amplitude of positive frequency part of light field is weaker than negative frequency part, and as a...

Thank you, Timo. Actually, I am haunted by another problem for long time. This one is also in such a "an atom probably absorbs photon" situation. When incident light is resonant with transition, usually we use rotation wave approximation (RWA), which says that positive frequency part mainly...

Thank you for your answer first. I have understood what you say about atom state after measurement, but if I do not care these atoms, and measure the unabsorbed photons, what will happen? For simplicity, I suggest 1 photon impinge on 1 atom, and cross section is large enough so that this atom...