All the hot-hydrogen and other stuff was really crappy, though, whereas apparently the formate stuff is stable more or less forever--you can just build it into the emulsion, and bye-bye reciprocity failure.
The Belloni et al. paper is a good read.
That's because the black was made with dyes, most of which are transparent past about 850ish nanometres. It's amusing when people try using black felt with a SWIR camera. ;)
Carbon black is a good absorber at all wavelengths of interest.
Cheers
Phil Hobbs
--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics
160 North State Road #203
Briarcliff Manor NY 10510
hobbs at electrooptical dot net
http://electrooptical.net
Some MCP tubes intended for fast time gating have a grid between the photocathode and the MCP. You could probably measure the axial component of the primary photoelectron momentum that way.
Of course, you'd need a very thin photocathode to prevent scattering from dominating the results.
Cheers
Phil Hobbs
--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics
160 North State Road #203
Briarcliff Manor NY 10510
hobbs at electrooptical dot net
http://electrooptical.net
I've never done the relevant experiments myself, so I don't know how clear-cut all these statements are. It seems to me that it's singularly unhelpful to simplify the situation by saying that beyond some particular wavelength, *no* emission occurs, whatever the light intensity. Surely photo-emission doesn't behave like the perfect brick-wall filter! We don't have perfect mono-chromatic light, noise-free detectors and infinite time to dedicate to an experiment.
I say that since these experiments are systematically at the limit of what's detectable, it's important to avoid sweeping the inevitable imperfections under the rug. In the end, it's all statistics. If you look for longer, you'll be able to see smaller signals.
Well, you can't prove a negative experimentally, it's true. Also there's thermal activation and surface reconstruction, which will put some spread into the Fermi level.
Well, if you're looking for phlogiston or aether wind, you'll be looking for a long time. Not all effects exist.
Cheers
Phil Hobbs
--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics
160 North State Road #203
Briarcliff Manor NY 10510
hobbs at electrooptical dot net
http://electrooptical.net
Did anyone ever notice that phlogiston is similar to the well-tested magic smoke theory of how electronics work? Maybe those 17th C guys were just ahead of their time. ;)
Cheers
Phil Hobbs
--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics
160 North State Road #203
Briarcliff Manor NY 10510
hobbs at electrooptical dot net
http://electrooptical.net
It seems to me that you're setting off on a wild goose chase. If, as seems likely, light is not classical, then any experimental setup is only going to be able to exclude classical light down to some particular intensity, beyond which the experimental results will be indistinguishable from noise.
So it will always be possible to speculate that some more sensitive experiment would show a classical light effect, and you'll never have your answer.
Turning it around, one could seek to send other people off on a wild goose chase by challenging them to provide experimental evidence that light is not classical below some particular intensity. They would be foolish to accept such a challenge, for the same reason.
I suppose in extremis you are right - at least if you count say a NdYAG pulsed IR laser focussed onto a tiny spot so that the material of the target is instantly turned into a plasma by the incident light flux.
These days they actually use even heftier NdYAG to pump a frequency doubler to go from 1066nm down 532nm (green laser pointer) then to UV
266nm - you can still see some residual green light in the beam. The finer spot size allow better resolution of the target doping.
For clean metals with a simple Fermi surface and work function and incoherent but monochromatic light photo emission of electrons is to a very good approximation a brick wall filter. Any slope being due to imperfections of monochromatic light and the cleaving of the crystal planes. A Fabry-Perot etalon can make pretty good monochromatic light.
If the intensity of the light is sufficient to trigger thermal emission of electrons from the surface or to make the sample resonate internally with stored lattice energy in phonons then all bets are off.
I find the photon approximation very cumbersome and hard to understand in the radio wavelengths where everything is conventionally done as coherence functions using the Van Cittert-Zernicke theorem (sp?).
? Or at least a threshold spectrometer to reject photoelectrons below a thr eshold energy. I guess that might be an neat invention to have a fully fun ctioning photoelectric spectrometer that is sensitive to single photons :)
se height is proportional to incident photon energy. That's why, on an osc illoscope, you can easily see doubles and triples.
Only PMT's with high gain at the first dynode would do that. The only one I know of was the RCA 8850. You can see it on page 4 of the data sheet.
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which has GaP first dynode surface, which offered a first stage gain of abo ut 40. The square root of 40 is about 6 which means that the size of your s ingle photon pulse has standard deviation of 15%. Of course that meant if y ou had drawn more than 200uA at the anode for more than 30 seconds, you had boiled enough caesium off the last dynode to poison the first dynode. Dead expensive and easy to wreck.
If the noise can be removed by using a photocathode with no dark current then the experiment could be done I think. Even if the quantum efficiency is low, the main thing is to have zero noise. I think this is possible as there are some detectors with zero noise already in operation ie this detector designed to detect neutrino decay didn't generate a single pulse for over several years:
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from the page: "The EXO-200 experiment has searched for these decays over several years. From the fact that not one of these decays has been detected..."
The main problem with a low sensitivity detector might then be getting rid of the noise in the electrical amplifier part of the circuit too so that it is still sensitive to single photons. I'm not saying the experiment is possible but it is still interesting to think about.
I think the best chance for a zero noise detector is to use a relatively high frequency light source and reject all photoelectrons (ie. with an electric field) that don't have enough kinetic energy. Even if most of the photoelectrons are rejected due to low kinetic energy and/or their scattering angle, as long as some of them are detected then some of them will continue to be detected as the light intensity approaches zero. This still requires a detector with zero noise, but I think requiring higher photoelectron energies as well as a high work function photocathode could reduce the noise to zero maybe.
My only idea for measuring big G, (which I must have mentioned here before, I got an email wanting me to build it.) Is to replace sphere next to sphere, with sphere inside sphere... and then just put a sphere through a wall.. (well if you can afford all that mass.) in the "traditional" torsion oscillator.
The trick it to separate the noise from the signal by combining different techniques until the noise is below the required detection signal. But it may also be possible for some experiments noise is never an issue too, ie. ones that require so much sensitivity they are put deep underground. There is still electrical noise in the circuitry, but the environmental background noise is attenuated to a level that effectively reduces it to zero.
I think you will find that the detectors saw quite a few pulses, but no combinations of pulses that could be attributed to the mode of decay being looked for.
Thanks, ya that is a way to reduce "meta noise". For the photoelectron experiment I guess it is good to define a valid photoelectron emission in this way so that the noise while still there can hopefully be made irrelevant and also then effectively there is zero "meta noise" :)
combinations of pulses that could be attributed to the mode of decay being looked for.
But only when the experiment lends itself to that sort of discrimination. T he one you are contemplating doesn't.
Cute idea, but impracticable. Your photocathode is going to produce backgro und photons by several mechanism - cosmic rays hitting it is the obvious on e, good for about one photoelectron per second for a 50mm diameter photocat hode at sea level, and there's always "quantum mechanical tunneling" for wh ich I don't know the numbers - Phil Hobbs probably does.
Oh sorry, I'm starting by thinking of a Cavendish balance. So the first "improvement" is to put a hole in a big sphere, and then "drop" another smaller test sphere, through the hole. (Of course you can't drop it so it's gotta oscillate back and forth. with some very small additional torque from the big mass with a hole in it.) I'd have to check my note book, but this gives (something like) a factor of two increase in the force/ torque. You can then gain a bit more... (? 25-50%..I don't recall the exact numbers.) by making the big sphere into an infinite wall of mass (but still with a hole in it to let the test mass "fall" through it.) (Hmm all just Gauss's law problems.)
Oh, and then of course make the whole thing out of gold... or osmium. George H.
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