Friday, June 22, 2012

Catching photons

The Germans have a great history of telling tales, most of which are supposed to teach some type of lesson. One series of such tales is about the citizens of Schilda, the "Schildbürger," who in each story excel in stupidity. One of the best known stories is the construction of a new city hall. Unfortunately, the Schildbürger forget the windows, and then try to carry light into the building with buckets. 


I forgot which lesson one was supposed to learn from that, maybe that the photon number is not a conserved quantity, more likely though that you better don't forget the windows if you build a house. I recall however that I was bugging my poor grandmother with that story over and over again because it wasn't really clear to me exactly why one can't catch light in a box. Surely you could just put mirrors on the inside and visible light would bounce around till you left it out again? 

Well, leaving aside that it's easier to bring light into a dark room by flipping a switch, the problem is that mirrors are imperfect, that is, they don't actually always bounce back photons. The typical mirror in your bathroom, glass with aluminium coating, only reflects about 90% of the infalling light in the visible spectrum, so this wouldn't help the citizens of Schilda very much. (This isn't obvious if you look into a mirror but if you hold two mirrors opposite to each other, you might notice the reflection getting weaker, also, probably getting a little blue/green tint which is from the glass not being perfectly transparent.)

The Schildbürger were on my mind when I came across this paper by a group of French physicists around Serge Haroche who is known for a series of quantum optics experiments. They developed "diamond-machined copper mirrors coated with superconducting niobium."

If you shape the mirrors suitably and arrange them opposite to each other, you can use them to capture photons. And the mind-boggling number that you should take away from here is that the typical decay time of light bouncing back between these mirrors is 0.129 seconds, which corresponds to about 39,000 km light travel time back and forth between the mirrors that have a distance of about 3 cm (a quality factor of more than 1010).

So they would have to run a little, the citizens of Schilda, but they might finally be able to carry light into the city hall. They would also have to cool their buckets to 0.8 K and it would only work in the infrared, but at least it's a start.

The two mirrors of the photon box at ENS
Photo Credits: Photothèque/LKB/Michel BRUNE
Image Source

14 comments:

Zephir said...

From dense aether model at last two effects follows here: the long wavelength radiation should exert an attractive force instead of repulsive pressure of radiation to both mirrors and the superconducting electrons should should induce drag to quantum fluctuations.

Phil Warnell said...

Hi Bee,

Interesting as I thought of a similar scenario when I was a child about capturing photons in a completely mirror lined room as to when one turned off the lights the room wouldn’t go dark. Actually though when we think about it since the big bang the universe has been awash in light if one considers that to extend to the entire EM spectra. That is even here with this experiment a large part of the trick is maintaining the wave length you want to have observed while omitting the others.


”If the whole universe has no meaning, we should never have found out that it has no meaning: just as, if there were no light in the universe and therefore no creatures with eyes, we should never know it was dark. Dark would be without meaning.”

-C.S. Lewis

Best,

Phil

Uncle Al said...

"try to carry light into the building with buckets" Copper-doped zinc sulfide little buckets. Plumb light in via total internal reflection (light pipes, fiberoptics) or go hollow mirror tubes,

http://gemini.cems.umn.edu/research/macosko/papers_n_shows/gbo.pdf
3M nanolayered PEN/PMMA or pat. pend. WO 2010/078105 A1 / US #2009283133

"the typical decay time of light bouncing back between these mirrors is 0.129 seconds" If the plates were flat, Casimir etalon! As is, add an excited (and who wouldn't be? Assuredly not Rydberg atoms) atom for vacuum Rabi oscillation. Go big casino with a BEC.

http://arxiv.org/abs/1205.7061
http://arxiv.org/abs/0904.1618
http://arxiv.org/abs/1012.1014
Get naughty!

If the windows were installed backwards, the building would be impossible to internally light, re first comment.

Bee said...

Hi Phil,

Well, household mirrors might not be very efficient in capturing photons, but they are certainly efficient in capturing the imagination. The other household item that I was fascinated by as a kid were magnets of all type. And, to a lesser extend, our pitchfork. Best,

B.

Phil Warnell said...

Hi Bee,

Ditto with the magnets, yet regarding the pitch forks I don’t get your point; sigh ;-)

Best,

Phil.

Arun said...
This comment has been removed by the author.
Arun said...

Sorry for the digression, but this caught my eye: "If the whole universe has no meaning, we should never have found out that it has no meaning".

The only way to make this statement correct without doing major violence to it is "If the whole universe has no meaning to us, we should never have found out that it has not meaning" - and the nonsensical nature of this sentence is clear.

What C.S. Lewis is really saying is

"If the whole universe has no meaning [to God; i.e., if there is not God], we should never have found out that it has no meaning".
Another way of claiming that it is beyond human capacity to prove the non-existence of God.

Phil Warnell said...
This comment has been removed by the author.
Phil Warnell said...

Hi Arun,

In being familiar with C.S. Lewis’ personal convictions I would agree this is what it meant for him, yet for me it simply means the universe itself has meaning as our minds with its sensors is able to have it so perceived. That is for me one can maintain the spiritual sense of that statement without insisting there being a god.


“But there is a third stage of religious experience which belongs to all of them, even though it is rarely found in a pure form: I shall call it cosmic religious feeling. It is very difficult to elucidate this feeling to anyone who is entirely without it, as there is no anthropomorphic conception of God corresponding to it.”


-Albert Einstein, “Ideas and Opinions”, Crown Publishing (1954)


Best,

Phil

Arun said...

Can these mirrors be usefully used in LIGO?

Plato Hagel said...
This comment has been removed by the author.
Plato Hagel said...

There are mirrors being used in LIGO yes.

If you understand how Grace satellite system is being used it paves the way for how one might look at the earth(Isostasy) differently as well. Isostatic formation of planets as well.:)Nothing like crashing a object into the moon's surface

Best,

Plato Hagel said...

Arun,

See: Core Optics

Best,

Bee said...

Hi Arun,

I doubt it. I don't think the main source of error they have comes from imperfect mirrors. I believe the light runs the arms of the order 100 times or so, which you could improve on by better mirrors without going to the extremes of the mirror I wrote about. Best,

B.