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Ask any question you want about Physics

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posted on Aug, 26 2015 @ 02:31 PM
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a reply to: pfishy
In a way the previous reply was part of the explanation, about virtual particles that aren't really particles and you can never find them alone. The quantum foam is the idea that you get more of those at small scales, but we don't understand the vacuum very well (see vacuum catastrophe). As relativity has space time as the fabric of the universe, quantum mechanics has this speculative "foam", but without a theory of quantum gravity our description of the universe has gaps at certain scales and that's one of them, so we don't really know. A good theory of quantum gravity would hopefully provide a better understanding.




posted on Aug, 26 2015 @ 04:23 PM
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a reply to: Arbitrageur

Thank you, once again.



posted on Aug, 26 2015 @ 09:03 PM
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originally posted by: Arbitrageur
You know a lot more about photon detectors than I do. I noticed those photon detectors you linked to had detection efficiencies from 25% to 40% which is not bad considering how small they are. I didn't see any cryogenics shown in the photos. I saw someone from NIST saying they had single photon detectors with much higher detection efficiency but it was a huge apparatus which had cryogenics, I suppose to cool things down and lower the background? I didn't really look into the details of how it worked but that was my guess.


Well Quantum efficiency (QE) is an interesting thing, because it is possible to create a device with a very high efficiency. Photodiodes can have up to 80%, but often the design of them, and operation means they are small, or maybe they are low gain, or the 80% is only over a narrow wavelength range.

For these diodes, the way the pn junction is structured changes things a-lot! often very efficient devices have terrible noise problems, and to reduce that, they are cooled, sometimes to cryogenic temperatures as you mention, it reduces the effect of random thermal excitation of the junction, without drastically altering the junction structure (it can, LEDs for example can change colour when cooled) So cooling can be for several reasons...
Noise reduction
Band gap modification
specific application testing

most likely the cryogenics where for the first two options... but not really sure unless i know what kind of device it was.

For MPPCs what is really interesting is not QE, but Photon detection efficiency (PDE) which is an exact conversion between photons in and pixel triggers.

It is important because 1) the pixels themselves can have 80% QE but 2) the whole surface of the device is not active, 3) the probability that when a photon is absorbed, it is absorbed near the junction and results in a avalanche. Factor 3 is important because hole induced avalanches have about a 0-20% chance of forming a full avalanche and electrons 0-60%

So if depending if you are forward or reverse structured, you can change your performance massively... so lets say we have electrons as the majority carrier,

So roughly we have something that looks like 80% x 60% = 48%

but then what about factor 2? well for MPPCs looking under a microscope, i found that the Geometrical efficiency is of the order of 64%

So the real performance expected is around
0.8*0.6*0.64 -> 30%

Which is roughly what i measured for my PhD... and was included in earlier versions of that catalogue


These operate at room temperature, have noise rates (single pixel triggers) of the order of 100-200kHz but have gains of the order of 10^5-10^6 which is very good, this being said iv seen devices with noise in the MHz range !!! which is terrible

Today, the modern MPPCs, 6 years after my PhD are vastly improved

This is really cool because it allows the development of more compact medical imaging equipment such as PET scanners, or the possibility of producing combined NMR-PET scanners at lower cost, and lower power consumption.
edit on 26-8-2015 by ErosA433 because: (no reason given)



posted on Aug, 26 2015 @ 10:24 PM
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originally posted by: ErosA433
Well Quantum efficiency (QE) is an interesting thing, because it is possible to create a device with a very high efficiency. Photodiodes can have up to 80%, but often the design of them, and operation means they are small, or maybe they are low gain, or the 80% is only over a narrow wavelength range.

For these diodes, the way the pn junction is structured changes things a-lot! often very efficient devices have terrible noise problems, and to reduce that, they are cooled, sometimes to cryogenic temperatures as you mention, it reduces the effect of random thermal excitation of the junction, without drastically altering the junction structure (it can, LEDs for example can change colour when cooled) So cooling can be for several reasons...
Noise reduction
Band gap modification
specific application testing
Yes the noise reduction was my guess, I'm not sure about that. Here's a picture of the equipment followed by the video it came from. You can see the apparatus is huge compared to the smaller devices in the catalog, and shows the cryogenic apparatus in the top right.




I'm not sure if this is the same apparatus or not, but it might be...where they claim 99 percent efficiency but then admit there's not really an accurate way to measure that 99% so it's only approximate.

NIST Detector Counts Photons With 99 Percent Efficiency
That was months before the video and they are both from 2013 so it might be the same thing.


This is really cool because it allows the development of more compact medical imaging equipment such as PET scanners, or the possibility of producing combined NMR-PET scanners at lower cost, and lower power consumption.
Yes I can certainly see advantages to the small size devices that operate at room temperature! That NIST device may have great performance but more than is needed for many applications and the cryogenics is a complexity most end users would probably rather live without unless they really need that level of accuracy.

By the way the video might be boring to many people but there's an interesting "avalanche" demo starting at 49 minutes in the video which many people might enjoy and it's only just over a minute long, where they set up dominoes of larger and larger size and talk about how a millimeters high domino can knock over a domino the height of the empire state building if there are something like 27 dominoes in between. For the demonstration he's limited to the size of the room he's in but he still makes the point.

The demonstration shows how mechanical action can be amplified, and of course it's a little harder to visualize how we do something similar electronically for photon detectors, but it's a similar effect using electronics.


originally posted by: pfishy
a reply to: Arbitrageur

Thank you, once again.
You're welcome.

edit on 2015826 by Arbitrageur because: clarification



posted on Aug, 27 2015 @ 09:35 AM
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a reply to: Arbitrageur
Cool - so the lower part of the apparatus is a DAQ and controller, the upper part if its cryogenic looks like a dark box and small cryostat, It looks to me like an ISO type O-ring sealed vacuum canister, which would suggest, cryostat anyway.

Oh neat, so just flicking through, the slides they talk about transition edge sensors. These are really neat, you basically have a super conductor sit at the edge region between normal and super conducting. You then can measure a huge difference in resistance depending upon the temperature of the device. This is important because at the mili-Kelvin level, photons can be absorbed by the material and impart a noticeable temperature change.

Its really quite neat technology, the Dark Matter search called CDMS (Cryogenic Dark Matter Search) uses cold germanium and silicone crystals with phonon sensors (thermometry) and charge read out in a very similar operating regime

Really awesome technology!



posted on Aug, 27 2015 @ 07:35 PM
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originally posted by: Bedlam

originally posted by: darkorange
If I shoot highly concentrate pulse with water gun under the water? The pulse would live as defined 'bullet' for a time being. Eventually it would dissipate into surrounding water body.

That's what photon does on emission.


No?


No. UNDER the water, you'd have to have a longitudinal wave. No soliton for YOU.


This, by the way, is a reason you can't have aether. If "luminiferous aether" were everywhere all the time, any EM wave that depended on "aether" in which to propagate would HAVE to be longitudinal also, like a Bearden scalar wave.

However, we know it's not, because the LCD screen in front of you works. Therefore, light is transverse, and there is no aether. Sim, salabim!


Not sure how LCD tech fits into this but I got you drift. On the other hand CRT screen works because of close proximity of the gun and the screen. If you place CRT gun away enough, try getting that picture on the screen. No matter how accurate your gun is no picture for you. You will have to crank shooting power to it.
If you agree then what does it tell you?


cheers, bud.
edit on 27-8-2015 by darkorange because: (no reason given)

edit on 27-8-2015 by darkorange because: (no reason given)



posted on Aug, 27 2015 @ 07:38 PM
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and there is no aether. The aether for light (energy) is light (energy) that fills our cosmos. Technically it is not aether when it is being itself.


edit on 27-8-2015 by darkorange because: (no reason given)



posted on Aug, 27 2015 @ 07:39 PM
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originally posted by: darkorange

Not sure how LCD tech fits into this but I got you drift.


LCDs work because light can be polarized. You can't polarize longitudinal waves. Light is polarizable, thus it's transverse.

Aether would have to have longitudinal waves, like sound in air.



posted on Aug, 27 2015 @ 07:42 PM
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originally posted by: darkorange
and there is no aether. The aether for light (energy) is light (energy) that fills our cosmos. Technically it is not aether when it is being itself.



I agree that there's no aether, light needs nothing to "wave" in at all. It's a combination of electric and magnetic fields.

You can pick out the individual components with the right sorts of probes.

Or with a polarizer.



posted on Aug, 27 2015 @ 08:05 PM
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originally posted by: Bedlam

originally posted by: darkorange
and there is no aether. The aether for light (energy) is light (energy) that fills our cosmos. Technically it is not aether when it is being itself.



I agree that there's no aether, light needs nothing to "wave" in at all. It's a combination of electric and magnetic fields.

You can pick out the individual components with the right sorts of probes.

Or with a polarizer.



I think NO. You dismissing complexity of this world. You also dismissing something that contributes to space expansion. Sure to keep theory alive another particle will be found to contribute to space expansion. I think space time is bubble being driven by excess energy pressure upon BB released it. Still no aether? May be?

Otherwise please advice what keeps photon as isolated particle when it travels in space.



posted on Aug, 27 2015 @ 08:21 PM
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everything is this cosmos works under pressure. This cosmos is one big explosion into something that has resistance to the volume. Hence entropy concept. We are all exist because everything around us applies some sort of pressure to us.

The reader of your posts might assume that space is dry static place where particles are zipping by. As Paoli said, there is not much left to discover in physics. He felt sad about that fact.



posted on Aug, 27 2015 @ 08:21 PM
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originally posted by: darkorange

Otherwise please advice what keeps photon as isolated particle when it travels in space.


Why would it need something to do that?



posted on Aug, 27 2015 @ 08:24 PM
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I don't know. How do define photon for example?

actually you don't have to answer this.



edit on 27-8-2015 by darkorange because: (no reason given)



posted on Aug, 27 2015 @ 08:29 PM
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originally posted by: darkorange
Otherwise please advice what keeps photon as isolated particle when it travels in space.
What keeps a car "isolated" from other things as it drives around? If the driver is careful the car isn't crashing into anything like other cars, or bridge supports, so it can keep going without any "interactions" such as "car crashes".

If a photon is traveling though mostly empty space, there's not a whole lot for it to crash into, but if a bunch of photons pass through say a gas cloud, a few of them will interact with the matter in the gas cloud. That's the photon's equivalent of a car crash. So, the photon either interacts with something, or it doesn't.



posted on Aug, 27 2015 @ 09:40 PM
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originally posted by: Arbitrageur

originally posted by: darkorange
Otherwise please advice what keeps photon as isolated particle when it travels in space.
What keeps a car "isolated" from other things as it drives around? If the driver is careful the car isn't crashing into anything like other cars, or bridge supports, so it can keep going without any "interactions" such as "car crashes".

If a photon is traveling though mostly empty space, there's not a whole lot for it to crash into, but if a bunch of photons pass through say a gas cloud, a few of them will interact with the matter in the gas cloud. That's the photon's equivalent of a car crash. So, the photon either interacts with something, or it doesn't.


so, what keeps the car isolated? You do not imply same thing that keeps photon isolated? It has to be a joke.


cheers


now you are going to blast telling me to go else where to ask my questions and stop hi jacking your thread. Am I right?



edit on 27-8-2015 by darkorange because: (no reason given)



posted on Aug, 27 2015 @ 11:27 PM
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a reply to: darkorange
Obviously I'm not saying a car and a photon are the same thing.
What I am saying is that they seem to have something in common, which is that if they don't interact with any obstacles, (crash into something), they can keep going.

But there are differences, of course. You don't have to put gasoline in the photon to keep it going.

However if you launched the car into space, it would also be closer to having that in common with a photon, or look at Voyager spacecraft as more real example than a car. What keeps Voyager isolated?

If you think I'm joking, don't assume that, it means you need to clarify your question. Maybe it's not clear to me what you mean by "isolated".



posted on Aug, 28 2015 @ 01:32 AM
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originally posted by: darkorange
I don't know. How do define photon for example?

actually you don't have to answer this.




I generally define it as the gauge particle for the electromagnetic force.



posted on Aug, 31 2015 @ 05:47 PM
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originally posted by: ErosA433
On photons its always about how we understand wave-particle duality

There are a few different experiments that we can perform using the setup i had and the devices i had available.

Firstly my photon source was an LED pulser, it would give me a sharp picosecond rise time flash of light, with a width of about 2.5ns, each flash, when the LED is operated at full intensity was giving around 10^9 photons with about 5% pulse to pulse variation.

So what does this look like in a detector?

Well at full intensity you get a rediculously large pulse, for us I was using a high bandwidth current to voltage pre-amplifier and when we saturate it, we basically get a huge 5 volt spike, and then a decay time related to the discharge of the photo-diode capacitance. So for photon counting, thats not so useful.

Interesting question is this... can you see it with the naked eye? A single shot, no you cant. Iv tried... and iv never been able to see it over ambient. Dark adapted, you can just about see it... the reason is that the pulse is very fast, and it doesnt activate the retina for long enough for your brain to register it.

OK so what do we do? We have two options, you run the LED at its threshold voltage (this is when the voltage is just enough to make it shine) OR you use neutral density filters.

I used calibrated filters to give me a 10^9 reduction in light, to the eye, there is no light coming from the filter. To the Avalanche Photodiode (In my case a multi-pixel one) with each flash of the LED it will see occasionally a single photon, sometimes two, sometimes three.

This is significant because the MPPC operates in Geiger mode, which means once a pixel activates it discharges and gives you a fixed charge output... doesn't matter if you hit the pixel with 1 or 50 photons, you see a binary 1.

So for a filtered LED flasher with a mean number of expected photons of 1, seeing 3 pixels fire, does mean that the device was activated by 3 separate photons.

The energy of the photon is used to create an electron-hole pair in the semi-conductor, the energy required to do this depends upon the p-n junction, doping materials and if it is standard or reverse structured. Basically the minimal energy required for this device is a few electron-volts, which means infra red wavelength light. So the device is sensitive to I-R, and in the blue it is limited by the absorption of blue and UV light by the silicon (basically blue light gets absorbed by the surface layers and doesnt reach the p-n junction)

So the activation of 3 random pixels on the device, means that 3 'things' separated in physical space, imparted energy in the device. these 3 'things' where all of roughly the same energy (and thus wavelength), they also arrived within a few picoseconds of each other.

So that doesn't really separate things right? is it a wave or is it a particle. you might say 3 different waves came out of the LED and struck the sensor in 3 different locations.

My point is that 1) im not making this stuff up, i know quite a lot about photon counting and characterizing sensors and 2) if the photon was a long wave that stretched out until it his something, you would not expect quantized observations like this. the sensor would activate fully as a wavefront hit it, the wavefront here being when the flash starts. The device behaves exactly like a low numbers counting system, it is Poisson distribution.

Wave particle duality does also require that photons can be split into distinct energies or wavelengths, we can observe how the device behaves differently when different wavelenghts activate it.

in the case on an MPPC, the avalanche can produce Infra red radiation due to electron-hole re-combination, why does it matter you ask? Well because with an IR camera it is possible to see which pixels activate. You can also do something cleaver which is to use two LEDs to give you two different wavelengths, and observe how the pixels activate differently, and yet still maintain a binary like activation.



Now thats a long of text, but the point here really is, that the image of light emanating from a source as some nice ripple wave out like waves on a lake, just isn;t how light is. If it was that way, we would NOT observe what we do in the above experiment. if you filtered the light down, you would expect to see the whole detector activate, or nothing, your wave will pass through the filter, or it wont. If photons however are quantized... the filter may let single ones through. The intensity being set by the number of single photons... and not the imaginary 'height' of the wave front, which is how some people want to see it or propose it is


so... all the electrons in all of those "detectors" were synchronous ?
because then an only then a point like force would kick just one of them at the time.
otherwise... well, wave comes in and strike all of them at the same time, but only those in "comfortable" position would interact and make the readings you did.



posted on Aug, 31 2015 @ 05:54 PM
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a reply to: dragonridr



Now a warning be careful going to websites like electric universe. They like to attack the standard model without ever truly offering any counter point other than to say we can explain it, of course they dont. As far as the electric believing gravity is tied to electricity? They can't even explain a simple test done by Apollo astronauts. They dropped a hammer and a feather and we watched them hit the ground at the same time(also performed in vacuum chambers on earth). With electricity causing gravity this feat would be impossible, And here's why it shows us objects always fall at the same rate regardless of their charge. Electric universe also has no explination for gravitational lensing be impossible if gravity was just electric interactions.


look...
hammer + moon
feather + moon

it's not JUST the hammer or JUST the feather .

start thinking about rethinking your thinking !!

I don't even bother to explain it any more...



posted on Aug, 31 2015 @ 06:17 PM
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originally posted by: KrzYma
start thinking about rethinking your thinking !!
We have thought through the electric universe model and evaluated evidence for or against it. The conclusion:

Testing the Electric Universe

So never let it be said that an astro-scientist has never considered the electric universe model with an open mind. The Electric Universe model is wrong. Provably, clearly and ridiculously wrong.

We’ve put the Electric Universe to the test. Final Grade: F-



I don't even bother to explain it any more...
Is that because you can't? I noticed you didn't touch the gravitational lensing issue. You can't explain away all the other tests EU fails as mentioned in the above article, either.



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