Creating Photonic BEC: What Possibilities & Applications Arise?

[sanman]

Researchers have for the first time managed to create a Bose-Einstein Condensate from photons:

http://www.nature.com/news/2010/101124/full/news.2010.630.html

What possibilities then arise from such a creation? What practical applications can be made from this work? I'd really like to know.

Can the local space around a "super-photon" be considered a region of altered spacetime, having different properties from normal space?

 

[sanman]

Furthermore, if an atomic BEC can be used to create an "atom laser" - then what is the analogous counterpart for a photonic BEC?

 

[sanman]

So whereas a classical laser uses population inversion to create the stream of synchronized photons, this new approach uses statistical dynamics to create a stream of synchronized photons. So it sounds like the end product is the same, with just the origin being different. You don't seem to need a crystal or a lasing material with this new method.

Or do you? It does seem that they used a green laser as the photon source to begin with, although they amplified beyond its power.

Could this then be used for laser-ignition fusion?

Can you make a more powerful laser through this method than you'd be able to using the classical population inversion method?

 

[Cthugha]

I am not quite sure, whether I actually buy all the stuff Weitz claims. There are actually some features considered as "smoking guns" for identifying BEC, but all they show is the redistribution and pile-up in the ground state of the cavity. I suppose we will see experiments clearing up this point during the next few years: Renormalization of the excitation spectrum towards Bogoliubov-Goldstone modes or not, measurements of coherence time and second-order coherence, vortices and half-vortices and all that stuff. As the photons leaving the cavity are also part of the BEC wavefunction, all of these points should be pretty straight forward to test. I expect similar experiments to what has already been done on microcavity polariton BECs as these are rather similar systems.

 

[sanman]

But I thought the characteristic telltale sign was that the BEC "laser" formed at the particular photon density.

I'm curious - are the 2 approaches mutually exclusive, or can they complement each other?

 

[Cthugha]

Well, the transition happening at the predicted density sure is a good hint, but it does not completely rule out other predictions. But as I said before, I am quite sure that point will become clear in the following years.

If you mean laser and BEC with "the 2 approaches" they are mutually exclusive at a given excitation power, but I suppose it should be possible to go from normal thermal emission to photon BEC to photon lasing with increasing excitation density. However, I do not exactly know whether the mode structure of the dye they use would allow for easy lasing, but most dyes do. The molecules forming the dye between the mirrors are used to cool the photon gas down. If you send enough photons into keep the molecules excited most of the time, cooling should become inefficient and lasing should become possible. I guess seeing two thresholds at different excitation levels would also be a very good indicator that this is really some kind of BEC.

 

[physalpha]

Can we say this condensate state?
Fast phase changed state like laser?

 

[sanman]

I notice that many news articles are saying that this 'photonic BEC' discovery may help to produce better UV lasers. Is there something particular about this BEC approach to making lasers that aids in UV/X-ray/high-energy laser production, or are people just saying this because high-energy lasers are hot right now?

 

[physalpha]

What is the attraction force to attach the photon?

Very fast photon --------------> slow down.
E=hv = 1/2 m c^2 + m c^2, m;photon mass

So captured photon
E=hv -1/2 m c^2 = m c^2
v_captured = m c^2 / h = (hv -1/2 m c^2) / h
always constant

How to remove 1/2 m c^2 energy?
For example electron
electron ----------------------> kinetic energy lower
....photon emission(UV or visual ray)

Reemit 1/2 m C^2 energy required.
Energy transfer method?
If it were true, it would be the candidate for Nobel Prize.

 

[Cthugha]

The approach of the Weitz group relies on cooling the photons by interaction with the dye or whatever material is placed inside the cavity. However, differing from common lasers, the cavity mirrors allowing for high reflectivity are not the main reason for the effect of interest to occur. By improving the setup and choosing ideal materials and such it might be possible to reduce the influence of the mirror and get efficient cooling without the need for photons to be reflected back and forth very often.

As most materials have a refractive index near or even slightly below 1 in the far UV, there are no really good mirrors in the far UV (there are some approaches using distributed Bragg reflector-like structures or metamaterials, but they are not good enough at the current stage to create really good lasers) and a method for creation of coherent light in that region without the need for very good mirrors would be a major step towards efficient uv light sources. At the moment, the SASE process which can occur in free electron lasers in synchrotrons is about the closest thing to a coherent far UV light source. However, these have great spatial coherence, but large shot-to-shot fluctuations and therefore pretty bad temporal coherence.

@physalpha
I think you misunderstood the experiment slightly. The photons are not really captured, slowed down or such. They just slightly interact with atoms and will finally almost all be in the lowest energy state the cavity can support.

 

[physalpha]

So the experiment is like this.

hv photon speed =c ---------------------------------> hv photon speed= c-c'
......Atomic interaction reduce to 1/2 m(c-c');photon kinetic energy- How to?
......light traveling pass->more longer ; Yes
......No time delay by photon absorption and emission

Is this condensate state?
interaction?

 

[Cthugha]

Sorry, I do not even understand your post. Are you familiar with cavity photons and the fact that they can be described as having an effective mass depending on the curvature of the energy vs. wavevector dispersion?

 

[physalpha]

Is photon-photon attraction force existence?
It represents a wave property.
Then photon-electron case.
The case when photon collide with surface electron, electrons are emitted.
..... " ...... with gas, electron orbital is more high than before, or emitted.
Photon-neutron or photon-proton case
-->Fusion. Its difficult in general case because of external orbit electron interaction is high.
photon wave is electromagnetic wave.
The paper is very excellence, but BEC theory for photon is required more theoretical approach, Its for next paper, I suppose.

 

[Cthugha]

You do not need an attractive photon-photon force.
All you need is some reason for photons being predominantly emitted into one mode. In lasers this is caused by stimulated emission of an inverted ensemble of emitters. Already in common lasers you get a huge number of photons inside one mode without an attractive force being present.