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Author Topic: What is the duration of a single photon?  (Read 1045 times)

Offline hamdani yusuf

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What is the duration of a single photon?
« on: 17/06/2016 11:25:36 »
http://phys.org/news/2008-04-world-shortest-photon-pulse.html
Quote
The Oxford team can create individual photons that are 65 femtoseconds in duration: thatís approximately fifty times shorter than any single photon previously produced.
Doesn't that mean that previous single photon is actually 50 photons in a row?
If in the future someone comes up with even shorter photon pulse, it would make this newly created single photon merely a series of photons?
« Last Edit: 17/06/2016 23:53:32 by chris »


 

Offline Colin2B

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Re: what is the duration of single photon?
« Reply #1 on: 17/06/2016 14:31:43 »
Doesn't that mean that previous single photon is actually 50 photons in a row?
No it's the pulse duration from beginning to end?
 

Offline hamdani yusuf

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Re: what is the duration of single photon?
« Reply #2 on: 17/06/2016 15:02:20 »
No it's the pulse duration from beginning to end?
so if they have same frequency then long duration photons will have less power (energy per unit time) than shorter one?
 

Offline evan_au

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Re: what is the duration of single photon?
« Reply #3 on: 17/06/2016 20:37:21 »
Quote from: phys.org
every photon this source produces is identical to the previous one.
When you try to control or measure the exact time or position of a particle, it becomes more uncertain in momentum or energy. This is a product of Heisenberg's uncertainty principle.
https://en.wikipedia.org/wiki/Uncertainty_principle

In theory, if you take a stable laser beam which is running for a long time (like the one in LIGO), it can generate many photons of (almost) a single frequency. But as soon as you chop the light into pulses (as is done in telecommunications), the frequency spreads out more. In the extreme, a single photon should have an extremely wide bandwidth (ie frequency uncertainty≡energy uncertainty≡momentum uncertainty).

You could balance this uncertainty by controlling the frequency more closely, and allowing more uncertainty in the time at which the single photon is emitted.

It seems that they are trying to get closer and closer to the limits dictated by Heisenberg.

Quote from: hamdani yusuf
if they have same frequency then long duration photons will have less power (energy per unit time) than shorter one?
This description of average power may apply to a source generating repeated photons. But:
  • The energy of a photon is dictated by its frequency.
  • A single photon is either detected, or it is not.
  • The photon is detected at a certain time (with some uncertainty), or it is not.
  • IMHO, the concept of power is not directly applicable to a single photon.
     

    Offline hamdani yusuf

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    Re: What is the duration of a single photon?
    « Reply #4 on: 21/06/2016 04:24:25 »
    Light pulses have wide spread frequencies, as shown clearly when we convert the signal from time domain into frequency domain using Fourier transformation.

    If we assume that the wavelength is 600 nm (red), then the 56 femtosecond pulse will contain 28 waves, since in 1 femtosecond light travels approximately 300 nm.
    What is the justification for the claim that the 56 femtosecond light pulse is indeed a single photon? What about previous experiment with 50 times longer pulse?
     

    Offline Colin2B

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    Re: What is the duration of a single photon?
    « Reply #5 on: 21/06/2016 08:27:57 »
    MOD NOTE:

    Some of the threads relating to GR and its interpretation have been moved to http://www.thenakedscientists.com/forum/index.php?topic=67283.0

    Sorry if this has left the thread a little lumpy.
     

    Offline Hans van Leunen

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    Re: What is the duration of a single photon?
    « Reply #6 on: 03/10/2016 12:13:29 »
    The current mainstream physical interpretation of a photon is in conflict with behavior of these photons. Photons can travel billions of light years through nearly empty space and after that trip they still have sufficient energy left in order to be detected by a suitable photon detector that has a limited size. Electromagnetic waves cannot perform that trick. Their amplitude quickly diminishes with increasing distance from the emission source. In addition the EM field relies on the nearby existence of electric charges. The EM field does not stretch uniformly over ranges that cover billions of light years. On the other hand like EM waves the photons are constituted from solutions of a homogeneous second order partial differential equation. But apart from waves the homogeneous second order partial differential equations offer other solutions and  in odd participating dimensions they offer solutions that are shape keeping fronts. In one dimension those solutions also keep their amplitude. Thus these one-dimensional solutions can travel huge ranges without losing their integrity. I call such solutions WARP's. The problem is that these warps do not feature a frequency. However, if the emitter spouts these warps at equidistant instants and if the warps travel with light speed, then the emitted strings feature a frequency. If all photons feature the same emission duration and each warp carries a standard bit of energy, then the energy-frequency relation E=h v is fulfilled. At least locally the emission duration, the absorption duration and the passage duration must be a fixed constant. The existence of redshift indicates that this constant may vary with distance or with clock time. You may see more details at docs.com/hans-van-leunen .
     

    Offline Hans van Leunen

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    Re: What is the duration of a single photon?
    « Reply #7 on: 03/10/2016 12:50:20 »
    Quite probably the duration of the emission, the absorption and the passage of photons is the same and is the same for all photons. If that is the case, than the emission of photons during particle annihilation becomes interesting. The duration of that photon must be equal to the regeneration cycle of elementary particles. If elementary particles can be represented by a hopping path and a corresponding hop landing location swarm, then the number of the swarm elements must equal the number of shape keeping fronts (warps) in the emitted photon.
    Thus, knowledge of the duration of photons is essential for understanding more of elementary particles.
     

    Offline alancalverd

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    Re: What is the duration of a single photon?
    « Reply #8 on: 03/10/2016 15:21:04 »

    If we assume that the wavelength is 600 nm (red), then the 56 femtosecond pulse will contain 28 waves, since in 1 femtosecond light travels approximately 300 nm.


    Thanks for doing the arithmetic - I kept mislaying powers of 10!

    Now if 56 fs corresponds to 28 cycles at 600 nm then it corresponds to 1 cycle at 600 x 28 = 16,800 nm. There are CO2 and CF4 lasers operating in this range so a bit of clever optics may well produce a single cycle of electromagnetic field.
     

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    Re: What is the duration of a single photon?
    « Reply #8 on: 03/10/2016 15:21:04 »

     

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