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23-11-2011, 08:06 AM
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Unpredictable
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Join Date: Jul 2010
Location: Australia
Posts: 3,023
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Counterintuitive Light
Take a look a this …
Blocked holes can enhance rather than stop light going through
Quote:
Conventional wisdom would say that blocking a hole would prevent light from going through it {a thin metal film}, but Princeton University engineers have discovered the opposite to be true. A research team has found that placing a metal cap over a small hole in a metal film does not stop the light at all, but rather enhances its transmission.
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How much more light ?
70 percent more !
Try predicting that from 'first principles' !
I suppose once it is known that this is how it works, it can then be 'predicted' from theory … chuckle, chuckle …
How does it happen ? (Here comes the theoretical 'prediction' …)
Quote:
Chou said the metal disk acts as a sort of "antenna" that picks up and radiates electromagnetic waves. In this case, the metal disks pick up light from one side of the hole and radiate it to the opposite side. The waves travel along the surface of the metal and leap from the hole to the cap, or vice versa depending on which way the light is traveling.
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Talk about counterintuitive !! And this time, the unanticipated result has been exposed via experimentation.
I wonder how many 'intuitive' expectations end up being incorporated into theoretical predictions, entirely due to unconscious/unchallenged/unsupported (empirically) 'intuition'?
.. Great stuff !

Cheers
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23-11-2011, 09:15 AM
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Seriously Amateur
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Join Date: Sep 2009
Location: Brisbane
Posts: 1,279
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so what would happen if you have a series of these holes with each enhancing the output from the previous? or does it only work with coherent light, and the output is a bit scrambled?
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23-11-2011, 09:39 AM
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Unpredictable
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Join Date: Jul 2010
Location: Australia
Posts: 3,023
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Hi Adam;
I'll have to confess that in spite of the views expressed in my OP, I think I'd have to guess that this effect is more a function of clever engineering, than necessarily an unexpected fundamental property of light.
It looks as though the interference patterns around the hole/cap interface acts constructively, provided the ratio of hole diameter/cap diameter, gap size, and hole spacing, are all engineered specifically to get the increased light levels. They could probably engineer these dimensions to obtain the opposite effect .. ie: increased blockage of light.
What you question … seems to be about altering the dimensions even more, altering the light coherency/source, and aligning the holes/caps specifically to maybe amplify the effect even more. I guess this could be done .. but it would have to be a matter of tuning the device to get the desired effect (whatever that may be).
I guess my point about the thread, is that one usually expects that if a light gap is plugged, it will block out the light. At this level of granularity of detail, the results seem almost inconceivable. I think the level of detail is the difference maker here.
Microscopic details can make the macroscopic world seem counterintuitive.
… A very easy factor to forget in science !
Cheers
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23-11-2011, 10:22 AM
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Registered User
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Join Date: Jun 2007
Posts: 2,926
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There are are lot of unanswered questions.
For example did they experiment with different frequency lasers?
Did the transmitted light undergo a frequency change?
Why are electrical engineers dabbling in science (sorry only kidding.  )
The answer to the second question in particular might provide hints as to what is going on here.
Regards
Steven
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23-11-2011, 10:58 AM
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Registered User
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Join Date: Jan 2006
Location: Sydney
Posts: 753
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I can not see anything about this counterintuitive, but it may be that my intuition is bit funny. If the light is an electromagnetic radiation it should be possible to design antenna for it that exhibits a gain (same as with all lower frequency electromagnetic radiation). I agree with Craig it is engineering solution.
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23-11-2011, 11:00 AM
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avandonk
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Join Date: Aug 2005
Location: Melbourne
Posts: 4,786
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They have just discovered plasmons I think. It has been known since the 1930's that the transmission of visible light and its colour is due to small spherical grains of gold in thin films less than 100nm. Thin films are made of these discrete grains as they grow from the first atoms to 'stick' to the substrate. The red colour in red glass comes from gold particles in the glass.
You are correct sjastro they should better specify what wavelength etc is involved.
A cursory search revealed this old gem
http://www.jstor.org/pss/95606
Bert
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23-11-2011, 11:01 AM
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Unpredictable
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Join Date: Jul 2010
Location: Australia
Posts: 3,023
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Quote:
Originally Posted by sjastro
There are are lot of unanswered questions.
For example did they experiment with different frequency lasers?
Did the transmitted light undergo a frequency change?
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Hmmm … their website says:
Quote:
The researchers published their findings Oct. 7 in the journal Optics Express, and it quickly became one of the most downloaded papers.
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Haven't found the paper yet .. but 'twould be an interesting one.
Quote:
Originally Posted by sjastro
Why are electrical engineers dabbling in science (sorry only kidding.  )
The answer to the second question in particular might provide hints as to what is going on here.
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See my new avatar …
Actually, I'd say the answer to the third question is that they want answers .. not more questions !
Cheers
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23-11-2011, 11:14 AM
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Registered User
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Join Date: Jan 2006
Location: Sydney
Posts: 753
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Quote:
Originally Posted by sjastro
There are are lot of unanswered questions.
Why are electrical engineers dabbling in science (sorry only kidding.  )
Regards
Steven
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Because if they did not all of you scientists would be still using pencil and paper for your calculations (that is if you could manufacture it)
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23-11-2011, 11:17 AM
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Unpredictable
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Join Date: Jul 2010
Location: Australia
Posts: 3,023
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23-11-2011, 11:23 AM
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Registered User
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Join Date: Jun 2007
Posts: 2,926
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Yeah, like the electric universe provides the answers.
It's good to see electrical engineers putting Euler's equation to good use.
Regards
Steven
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23-11-2011, 11:33 AM
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Unpredictable
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Join Date: Jul 2010
Location: Australia
Posts: 3,023
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Quote:
Originally Posted by sjastro
Yeah, like the electric universe provides the answers.
It's good to see electrical engineers putting Euler's equation to good use.
Regards
Steven
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Just kidding around with the Avatar …. 'twas "gimmick" infringement so I've reverted back to the Lorentz Attractor !
Looking at the paper, figure 4 shows the comparison of transmittance vs wavelength .. its an interesting relationship.
They definitely say its due to the 'antenna effect' which enhances Raman scattering:
Quote:
In developing a new plasmonic architecture, termed “disk-coupled dots on pillar antenna array” (D2PA) [13], for significantly enhancing Raman scattering signals, we needed to understand the effects of the metal disks (a key element in D2PA) on the light transmission through the subwavelength holes in a metal film, which were covered by these disks.
We observed that even though the holes are fully blocked by the disks and there are no geometrically open light paths, the light transmission through the blocked holes is much larger than the holes unblocked [14]. We attributed this counterintuitive observation to the antenna effect of the blocking metal disks [14].
In this letter, we report the details of our experiments, observations, simulations and potential applications of enhancing and tuning the light transmission through subwavelength holes by blocking them with metal disks.
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Interesting.
Cheers
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23-11-2011, 11:49 AM
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Unpredictable
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Join Date: Jul 2010
Location: Australia
Posts: 3,023
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Quote:
Originally Posted by avandonk
They have just discovered plasmons I think. It has been known since the 1930's that the transmission of visible light and its colour is due to small spherical grains of gold in thin films less than 100nm. Thin films are made of these discrete grains as they grow from the first atoms to 'stick' to the substrate. The red colour in red glass comes from gold particles in the glass.
You are correct sjastro they should better specify what wavelength etc is involved.
A cursory search revealed this old gem
http://www.jstor.org/pss/95606
Bert
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Yep .. you're right here Bert.
They're playing around with the tunable parameters to optimise the retransmittance and reflectance amplitudes (by wavelength).
They vary the hole and gap size and provide simulations showing what happens if other structures (like a bar) is introduced (under one end of the 'cap').
All engineering stuff. Very interesting. Has military applications also, I notice … (like enhancing sensitivity to sniffing out explosive molecules).
Cheers
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23-11-2011, 02:30 PM
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Registered User
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Join Date: Jun 2007
Posts: 2,926
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Quote:
Originally Posted by CraigS
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Very interesting paper Craig which incorporates ideas from quantum physics (Raman scattering), solid state physics (dielectric breakdown or antenna effect) and plasma physics (plasmons).
And all compiled by electrical engineers.
Regards
Steven
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23-11-2011, 02:36 PM
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Registered User
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Join Date: Jun 2007
Posts: 2,926
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Quote:
Originally Posted by Karls48
Because if they did not all of you scientists would be still using pencil and paper for your calculations (that is if you could manufacture it) 
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If we scientists didn't provide you with the necessary tools such as the equations, you engineers would be as useful as a screen door on a submarine.
Regards
Steven
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