Scientists predict paradoxical laser effect

Apr 25, 2012 By Florian Aigner
Two coupled microlasers

New laser-effect, discovered by scientists from the Vienna University of Technology, Princeton, Yale and ETH Zurich: If coupled, lasers can switch each other off, leading to a "laser blackout".

Two are brighter than one. This simple truism does not necessarily apply to lasers, as a team of scientists, led by the Vienna University of Technology found out. When one laser is shining and next to it another laser is turned on gradually, complex interactions between the two lasers can lead to a total shutdown and no is emitted anymore. For technologies connecting the fields of electronics and , this result may be very important. The new findings have now been published in the journal .

“Imagine two light bulbs right next to each other, one of which is switched on. As you gradually turn on the second bulb by adjusting a dimmer switch, you expect the room to get brighter”, says Matthias Liertzer. He studied the behavior of coupled micro-lasers using computer simulations, together with Professor Stefan Rotter at the Institute for Theoretical Physics (TU Vienna). They were assisted by scientists from Princeton University, Yale University and the ETH Zurich.

To make a laser shine, it has to be “pumped” – it has to be supplied with energy, using light or electric current. If only one of two micro-lasers is pumped, only the pumped laser emits light. Surprisingly, pumping the second laser too does not necessarily increase the brightness of the coupled system. Supplying more energy can even reduce the brightness, until both lasers become dark. “When we saw that the two lasers can switch each other off completely, due to the coupling between them, we knew: either we made a mistake or this is a spectacular result”, says Stefan Rotter. In the meantime, the effect was confirmed in independent calculations by the co-authors from Yale.

Light consists of waves, and it is well known that waves can interfere and cancel each other out. The interplay between the two lasers, however, is more complicated than that: “This effect is not just about wave interference. It is a combination of interference and light amplification, which can lead to seemingly paradoxical effects”, says Matthias Liertzer. New methods, some of which were developed by mathematicians at TU Vienna, were necessary to solve the complicated equations which describe this problem. “The phenomenon is based on what mathematicians call exceptional points”, says Stefan Rotter. Exceptional points are special intersections of surfaces in complex spaces. “The appearance of such exceptional points in our laser equations can lead to a laser . In this way we could connect a rather abstract mathematical structure to a measurable phenomenon”, says Rotter.

Electrical engineers at the Vienna University of Technology are now working on experiments with micro lasers, in which the theoretical predictions should be verified. Laser effects like this one are especially interesting, as they show new ways to connect microelectronics and laser technology. In today’s computers, information is transmitted by electric signals. Adding light could open up exciting new possibilities.

Explore further: Symphony of nanoplasmonic and optical resonators produces laser-like light emission

More information: prl.aps.org/abstract/PRL/v108/i17/e173901 , Free arxiv version: arxiv.org/abs/1109.0454

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User comments : 18

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SoylentGrin
not rated yet Apr 25, 2012
Could this be used to reduce the emissions down to a single photon?
El_Nose
not rated yet Apr 25, 2012
why do it with two lasers when single photon sources are already effecient?
siouxie
not rated yet Apr 25, 2012
they are treating "two coherently coupled laser cavities", but the conventional term "external optical feedback" is not found in the arxiv's pdf. nor is the "saturable absorber". the results may be EP (exceptional point) for sure, but the phenomenon itself can be described by these two effects, i guess ...
stealthc
1 / 5 (3) Apr 25, 2012
quantum interferance pattern?
Eikka
5 / 5 (8) Apr 25, 2012
So that's why you're not supposed to cross the beams...
RealityCheck
1.1 / 5 (9) Apr 25, 2012
Could this side-by-side effect explain Olber's Paradox?

Given the long transit time from distant sources, all light we see from far away must eventually 'nuzzle up to each other along the trajectory/path that leads to any observer's localized view/detector.

So if light waves can affect other light waves not only by the well-known destructive interference phenomenon, but also by some sort of 'free-space-equivalent' of this recently observed phenomenon, could it be that 'space expansion' scenarios such as big bang 'recession' is not the reason why all the sky is not swamped (even at night) with light from 'infinity' in all directions?

Could this phenomenon, added to other interference phenomena, possibly exp[lain the 'increased wavelength' or 'redshift' also the further the light has come?

Any comments, info, anyone?

Cheers!

.
Jitterbewegung
1 / 5 (3) Apr 25, 2012
It will be interesting if the observation does not match the prediction. Let us know when they cross their swords.
axemaster
5 / 5 (1) Apr 25, 2012
In this way we could connect a rather abstract mathematical structure to a measurable phenomenon

Abstract?... Well, if you say so. Taking the absolute values and real parts of complex functions with non-infinite poles and branch points is kinda important in continuum optics, or so I'm told...
Vendicar_Decarian
0.1 / 5 (35) Apr 26, 2012
No. Olber's Paradox is nicely explained by general relativity.

"Could this side-by-side effect explain Olber's Paradox?" - RealityCheck
bluehigh
1 / 5 (4) Apr 26, 2012
GR doesn't explain Olbers Paradox. GR resolves the paradox in such a manner that there is no paradox. Whats with the No?

It is a combination of interference and light amplification


Never did like the term amplification. The original source never gets bigger. Though I guess, secondary flow modulation for signal reproduction from source, just doesn't has the same ring to it.

antialias_physorg
5 / 5 (3) Apr 26, 2012
Given the long transit time from distant sources, all light we see from far away must eventually 'nuzzle up to each other along the trajectory/path that leads to any observer's localized view/detector.

Light in the universe isn't laser light.

Well, if you say so. Taking the absolute values and real parts of complex functions with non-infinite poles and branch points is kinda important in continuum optics

In all of quantum mechanics I would add.

As for the article. Do I smell photonic transistors? If so (and if the switching is fast) then this could be the breakthrough we've been waiting for in photonic computing.
alfie_null
not rated yet Apr 26, 2012
What happens to the energy?
yks
1 / 5 (1) Apr 26, 2012
maybe they can create a hologram with these interfering lasers :)
DaFranker
1 / 5 (1) Apr 26, 2012
Light in the universe isn't laser light.


Laser light is light. Light is light. I fail to see the distinction. "Laser" light is merely "directed" light that has a short wavelength variance and is created with specific means as per the "Laser" definition.

As for the article. Do I smell photonic transistors? If so (and if the switching is fast) then this could be the breakthrough we've been waiting for in photonic computing.

It seems like the fact that they need to be side-by-side and near-parallel, along with the fact that these are coupled laser *emitters*, seems like it would make building transistors out of this a very difficult engineering problem. However, if the same thing can be reproduced within photonic "circuits" without the need for side-by-side emitters, then the rest is just math and design issues.

So yes, it really could be the breakthrough needed. There's just one more step and a few verifications to go through before it can be used by engineers.
antialias_physorg
5 / 5 (1) Apr 26, 2012
Laser light is light. Light is light.

Laser light is not merely 'directed light'. Shining a bulb through a pipe will not give you laser light at the other end.

Laser light has very distinct properties. It is (often) monochromatic, in phase and has a definite polarization.

Photons will not 'snuggle up' to other photons because that would require different speeds of light. For interference effects it also requires extraordinary frequency and polarization matching.
The conditions for the emission of laser light do not occur naturally.
SincerelyTwo
not rated yet Apr 26, 2012
Maybe a stupid reply but two equal waves with just the right offset in phase will cancel each other out ... how sure are they both lasers match equally?

Diagram; http://skullsinth...pg?w=640

Obviously they must know this. How exactly do they measure phase in a laser beam? Is it something you can guarantee? ... to have the right offset so the lasers don't cancel?
antialias_physorg
not rated yet Apr 26, 2012
How exactly do they measure phase in a laser beam? Is it something you can guarantee?

Yes, you can match phase for lasers of equal frequencies. The easiest way is to trigger one laser from the other, because all the photons that will come out of the inversion in the pumped medium will be in phase. then it's just a matter of getting your geometry to the interference point right.
But there are other methods:
- You can get the phase right by controlling when to pump the laser medium if the inversion has a very short decay time.
- You can do it by 'apodization' (which is shaping/retarding the beam after emission via optics - basically having media in between with tunable refraction index/speed of light
- you can do it via 'mode shaping' (e.g. by altering the geometry of the resonator cavity)

...and there are probably a few other ways I have forgotten (it's been a while since I had a lecture on lasers)
DarkHorse66
2 / 5 (3) Apr 27, 2012
@DaFranker: "Light in the universe isn't laser light.
Laser light is light. Light is light. I fail to see the distinction. "Laser" light is merely "directed" light that has a short wavelength variance and is created with specific means as per the "Laser" definition."

Antialias has already given a good answer. I'm merely providing this answer as food for thought, NOT a putdown & hope that you will take it in that light :). I have just one thing to add, that should be kept in mind when asking such questions; if a statement is true (ie all laserlight is light), does the reverse automatically hold true (ie all light is laserlight)? You actually gave yourself a partial answer when you described what laserlight actually was! That is PRECISELY why the the two types are being treated as different. When you think about the validity of such types of statements, you might want to use these tactics. Some people on these threads will tear shreds off you too easily otherwise. Best Regards, DH66