B How much space does a single photon occupy?

[Peter Mason]

Questions.
I have some (2) pdf files of papers that I have found that I think would be useful references that I would like to upload here. Is that legal? Possible? Desirable?

 

[davenn]

Questions.
I have some (2) pdf files of papers that I have found that I think would be useful references that I would like to upload here. Is that legal? Possible? Desirable?

are they peer reviewed papers ? if so, put them on some site and link to them :)

 

[mfb]

photons as objects like they are ball bearings

But that is precisely how the literature describes the photon just after it shows line of electric charge sitting in a line holding hands like a flock of swallows on an overhead cable.

That is how bad pop-science articles describe photons. This is not "the literature".

Modern cameras are sensitive to individual photons (where necessary).

Further the problem eluded to in my sketch is solved with a star shader.

For a 1 meter telescope and Proxima Centauri b as target, this star shade has to be at a distance of more than 5000 km (as rough estimate: (distance to star * telescope size)/(distance between star and planet)). Completely impossible on Earth, and with a space-based telescope you have to steer your shade around with a precision of centimeters, while keeping thousands of kilometers of distance to the telescope. Not impossible, but extremely challenging, especially if you want to observe objects in different sky directions.
With a pinhole you don't collect enough light to see anything interesting, and a 1 mm pinhole would still need 5 km distance.

See the example numbers I calculated in an earlier post. You need telescopes to get enough light.

Questions.
I have some (2) pdf files of papers that I have found that I think would be useful references that I would like to upload here. Is that legal? Possible? Desirable?

Link to them, or write the reference here if there is no proper online version available. Don't upload copyrighted material here.

 

[Peter Mason]

Andromeda galaxy

Oops. For Andromeda read Milkyway.

The Corpuscular Theory of Light dies hard

For a considerable part of my time on the planet I have been assuring people that I have been searching for the truth and when I tell them that the only reliable source of the truth is physics this seems to find resonance. Now you inform me that I have to choose a variation of the truth.

masking the central maximum of the star's image

This is theoretically highly mathematical
https://www.google.fr/url?sa=t&rct=...6/meta&usg=AFQjCNGUQJ-oo8sbxobLsh50Uc8pe_h78w

and why the petals are not a prime number, the answer is always a prime number, is probably more to do with engineering expediency than anything else.
I will also take a pragmatic view of the occulter position and probably use two pin holes, 1,0μm and 12,μm. The local astronomy group has a summer open evening next week. I will go and attempt not to frighten and confuse them.
How to point the arrangement, I have no idea what is achievable with current positioning systems. A question for my astronomer. The reviews talk of having the image nearly in the centre of view so probably not good enough, though I suppose repeatable would suffice.

 

[mfb]

With a 12µm pinhole you might get a few photons per second from the brightest stars. You will get a photon every few years from the brightest planets. And you have no way to distinguish this from all the background sources, even if you could collect data for years to get 1 or 2 photons.
With a 1µm pinhole you get a photon every few centuries.

 

[Drakkith]

The proposal is for a single photon sensor probably an avalanche diode because I have not found a SPAD device that is not connected to a piece of specialised electronics and presumed to cost a lot. That signal I can see on an oscilloscope although counting individual photons to produce rate signal is probably the final destination. I Know that if I receive a photon at the detector it can be counted I was more concerned that the rate of photon collection from a remote planet would be too low to be meaningful. Is there any data on photon data rates from these objects? Answer in Hz/m^2 at the aperture of the device before the glass, mirror, pin hole, fibre, or what ever please :-)

The main issue isn't with detecting the faint signal from the planet, it's with being able to distinguish the signal from the noise. Noise comes in many forms. Background light from the parent star, scattering and emission in the atmosphere, background stars, thermal noise in your sensor, and more. Professional setups typically have cooled sensors (reducing thermal noise), operate in very dark locations away from major cities (reducing background noise from light pollution), and block the light from the parent star (reducing the dominant source of noise, which is the star itself).

This is all in addition to having large apertures (increasing resolving power/resolution), high-precision guiding (to keep the image centered on the sensor), and some may have adaptive optics (to correct for atmospheric blurring of the image).

In light of all of those issues, having a sensor capable of detecting each and every photon should be the least of your concern. In fact, going from an efficiency of ~100% to ~20% isn't that big of a problem. It means you have to take more/longer exposures, but it also means that the noise from all of those sources except thermal noise is also reduced by the same ratio.

 

[Peter Mason]

Professional setups typically have cooled sensors (reducing thermal noise), operate in very dark locations away from major cities (reducing background noise from light pollution), and block the light from the parent star (reducing the dominant source of noise, which is the star itself).

This is all in addition to having large apertures (increasing resolving power/resolution), high-precision guiding (to keep the image centered on the sensor), and some may have adaptive optics (to correct for atmospheric blurring of the image).

All of that makes it interesting.

I looked at the photoelectric effect and the explanation that I found needed intense reading and was in the end unhelpful but I did get the idea that a photon is a quanta of energy. People here do not like the idea of thinking of photons as little bullets but will not have a continuous wave front either. The concept of an energy quanta described as a 2 dimensional wave E and H does at least provide a reason for it arriving here unattenuated after a long journey. I assume it can be influenced by gravity and other fields and what happens if two photons meet, Elastic collision or are we into quantum mechanics.

Then I have another problem with "field". We can describe much about the force effect but I have not found a description as to why two massive bodies attract each other, simply descriptions of distortions in space down which they seem to like to "fall".

I have done some crude calculations.
For a planet 0,123 Jupiter radius, 4,2 ly distant, radiating 1000W/m^2 @ 800 nm, I receive 207 photons/s/m^2. I finally found a sensor for a high gain diode to convert this in 62 pico Amps but this is pA/m^2. The surface of the sensor is small, 1 mm^2, I now feel somewhat justified in the original question though it should probably be what is the probability of 207 photons/s/m^2 hitting a 1 mm^2 sensor.

 

[weirdoguy]

People here do not like the idea of thinking of photons as little bullets

It's not about people here, it's about physics. And physically, thinking that way about photons is so far from the truth that it can't get further. There were a lot of discussions about that issue here, use "search" button.

but I did get the idea that a photon is a quanta of energy

There is no quanta of energy, like there is no quanta of velocity or any other quantity used to describe matter. But photons have energy, velocity, momentum, and other thing used to describe them.

 

[sophiecentaur]

For a planet 0,123 Jupiter radius, 4,2 ly distant, radiating 1000W/m^2 @ 800 nm, I receive 207 photons/s/m^2. I finally found a sensor for a high gain diode to convert this in 62 pico Amps but this is pA/m^2. The surface of the sensor is small, 1 mm^2, I now feel somewhat justified in the original question though it should probably be what is the probability of 207 photons/s/m^2 hitting a 1 mm^2 sensor.

The problem with thinking in terms of a 'shower of' photons is that you are instantly into statistics and probability. If you just talk in terms of Power Flux, you need not concern yourself with this problem. You have a signal and you have a noise / interference level. That will tell you the uncertainty in your measurement for a given bandwidth. Photons just do not help; let's face it, you have had nothing but trouble here by sticking with the little devils. Why do you think communications Engineers do not muck about with them in their calculations?

 

[sophiecentaur]

It's not about people here

Yes. Not people 'here' or anywhere else, when they know the business. Things have changed greatly in the last hundred years. One can't hold on to outmoded ideas just because they appeal to intuition.

 

[Lord Jestocost]

I looked at the photoelectric effect and the explanation that I found needed intense reading and was in the end unhelpful but I did get the idea that a photon is a quanta of energy. People here do not like the idea of thinking of photons as little bullets but will not have a continuous wave front either.

One should not think of a light beam as a particle current. Quantization of electromagnetic radiation means that the field energy can only be changed by integer numbers of „energy portions“ (called photons) of amount hν, where ν is light frequency and h Planck's constant.

 

[mfb]

I now feel somewhat justified in the original question though it should probably be what is the probability of 207 photons/s/m^2 hitting a 1 mm^2 sensor.

They don't - unless you have optics to focus them. That's what telescopes do. You need a telescope with a diameter of more than a meter to collect the light of one square meter.

I assume it can be influenced by gravity and other fields and what happens if two photons meet, Elastic collision or are we into quantum mechanics.

Electromagnetic waves pass through each other without interaction for all practical purposes. There are tiny effects, you can measure the interaction in dedicated experiments, but it does not play a role in astronomy.

 

[Peter Mason]

Quantization of electromagnetic radiation means that the field energy can only be changed by integer numbers of „energy portions“ (called photons)

That is what this has taught me and what was difficult to get from the wikipedia article.

You need a telescope

I would like a recommendation. I would like to to be able to see Venus, Mars, Saturn and Jupiter. I would like software access to control of the drive in real (Sidereal) time so that I can track the target more accurately. I would like to be able to split the optics so that I can view with a camera and my sensor optics at the same time. Is it necessary to replace the eye piece with a camera or is there a separate camera mount on current telescopes?.

I have tried to find the data for Venus and the first iteration shows 8,7E13 photons/s/m^2, That sounds like enough if I use a telescope. Presumably I get (Photons at the aperture)*sensor size/image size . I also searched "single photon venus" and found three non relevant results .

 

[mfb]

Well, the planets within the solar system are very bright compared to exoplanets... to see the planets you mentioned you don't need any equipment.

 

[sophiecentaur]

I also searched "single photon venus" and found three non relevant results .

Lets hope that search helps give you the message about the reality of things. You surely can't be thinking that you will revolutionise Astronomy with an approach that you think is new. You are ignoring some very relevant factors (mentioned all through this thread) in your determination to see things your way. Just consider that you could possibly have got hold of the wrong end of the stick. Look up the term Irradiance, which is used to describe the brightness of an astronomical object. The word "photon" doesn't come into it. You can't expect textbooks to be specially written in your terms. We talk in terms of Watts of Energy received over a given area.

 

[Drakkith]

If anyone is saying that thinking of light as photons is a bad idea in this situation, I respectfully disagree. I do astrophotography and photons are integral to understanding the details of SNR and image processing. My book on astronomical image processing is several hundred pages thick and goes into detail about photon statistics.

 

[sophiecentaur]

and photons are integral to understanding the details of SNR

Yes - but the interest is the interaction within the sensor, surely, and not in the optics. The quantum size will be relevant there, of course.

 

[Paul Colby]

People here do not like the idea of thinking of photons as little bullets

The example I posted using a CCD shows that thinking of them as little bullets gives the wrong answer to a trivial correlation experiment. Wrong is wrong. Game over.