Archive for the 'Optics' category

"Liveblogging" What's Hot in Optics at Frontiers in Optics 2009

Oct 11 2009 Published by under Optics, Science news

Each year, Frontiers in Optics has a session entitled "What's hot in optics".  I thought I'd "liveblog" it (type it up on my computer and post it later) like I did last year; hopefully the comments make sense, considering I got up at 4 a.m. to fly to San Jose.

There were some very interesting things discussed, though I always feel that these talks lack a certain amount of energy.  If you're going to label a session "hot", I would think that the speakers should bring some enthusiasm to the podium!  Then again, people may be a little gloomy due to the economy, which has hit optics like everything else.

The blogging:

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The first paper on invisibility? (1902)

Oct 02 2009 Published by under Invisibility, Optics

When discussing the history of invisibility physics, I typically cite Ehrenfest's 1910 paper on radiationless motions as the first publication dedicated to the subject.  Ehrenfest's paper, which attempts to explain how electrons could oscillate in a classical atom without radiating, is a direct precursor to the long history of nonradiating sources and nonscattering scatterers that I've been chronicling on this blog.

However, it turns out that Ehrenfest was not the first author to discuss some form of invisibility!  I recently stumbled across an article in an early issue of the Physical Review: "The invisibility of transparent objects," by R.W. Wood, 1902.  It is not an earth-shattering paper, but it presents some intriguing ideas and suggests that visions of invisibility may go even further back in the sciences... Continue Reading »

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Lord Rayleigh vs. the Aether! (1902)

Jul 09 2009 Published by under History of science, Optics, Relativity

(Note: This is an attempt to get myself rolling on my long-ignored series of posts explaining Einstein's theories of relativity.  It's also a really cool experiment in the history of science.)

One of the most fascinating aspects of 19th century physics is that many remarkable ideas and ingenious experiments were motivated by a physical hypothesis which we now know to be incorrect: namely, the aether.   When light was demonstrated to have wavelike properties in the early 1800s, it was natural to reason that, like other types of waves, light must result from the excitation of some medium:  after all, water waves arise from the oscillations of water, sound waves arise from the oscillation of air, and string vibrations are of course the oscillations of string.  The hypothetical medium which carries light vibrations was dubbed the "aether", due to its unknown, "aetherial" nature.

A lot of scientists speculated on the physical properties of the aether, and sometimes this speculation produced lasting results in other fields; for instance, Earnshaw's theorem was originally conceived to try and describe the forces involved in the aether's oscillation.

By the late 1800s, however, more and more research cast doubt on the very existence of the aether, notably the Michelson-Morley experiment (to be discussed below).  In response, theoreticians produced more and more "patches" to the aether theory, until at last Einstein published his special theory of relativity, which eliminated the need for an aether and in fact suggested that the idea of an aether was incompatible with the experimental evidence.

Before this happened, however, at least one brilliant researcher took up the challenge of testing one of the "patches" to the aether.  Lord Rayleigh (1842-1919), distinguished physicist and eventual Nobel Prize winner, conceived of and carried out a very clever optical experiment to see whether objects shrink in the direction of motion, a phenomenon known as length contraction.

As is often the case, even though the experiment was unsuccessful, we can still learn many useful lessons about the workings of science from it!

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Some musings on negative refraction

Jul 04 2009 Published by under Optics

For a part of this past week I was at a workshop in California, and a lot of excellent theoretical and experimental researchers of metamaterials were present.  One of the points stressed by many of them is the difference between the idea of 'negative refraction' and a 'negative refractive index'.  I had been vaguely aware of the issue, but it was really driven home by some of the discussion.  I thought I'd share my musings on the subject in a post.

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Invisibility physics: Hiding and seeking, all at once!

Jun 19 2009 Published by under Invisibility, Optics

When the first papers on the idea of a "cloaking" device came out in 2006, lots of people were immediately worried that the CIA would soon be peering right over their shoulder from the shelter of invisibility cloaks.  Many scientists, including myself, pointed out the flaw in that reasoning: a "perfect" cloak would direct all light around the outside of the cloak.  This meant that, although the spy couldn't be seen in the cloak, he couldn't see anything from inside!


An illustration of one of the original cloaking concepts from J. B. Pendry, D. Schurig, and D. R. Smith, Science 312, 1780 (2006): rays of light are guided around the interior region, which sees no light.

A recent paper in Physical Review Letters, however, suggests that this "mutual invisibility" can be overcome.  The research described suggests that a different type of cloaking device could be used to enclose a sensing device, and that the sensor would not only be (almost) invisible, but it would be able to detect radiation just as well as when outside the cloak!  The research is intriguing (though it still won't help the CIA quite yet), and it illustrates a different, earlier, technique for making something "not be seen".

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The National Naval Aviation Museum and a cute optical illusion

May 25 2009 Published by under Optics, Travel

Bleah!  I'm back from my trip to the Flora-bama area, but didn't make any jumps -- we were essentially weathered out Friday and Saturday, and by Sunday I'd had enough.  Most of my jump friends had already bailed, and though the weather looked like it might be better, I missed my wife and couldn't stand to sit around another day without jumping.  If they did jump Sunday, it would be quite ironic, because the complete 10-hour drive once we left the beach was nothing but low clouds and rain.

On Saturday, once it was clear we wouldn't be jumping earlier in the day, we hit the nearby National Naval Aviation Museum.  It was a pretty neat place, and it also contained one interesting (intentional) optical illusion.  Some pictures and description below...

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What does negative refraction LOOK like?

May 19 2009 Published by under Optics

My friend Personal Demon recently forwarded me an article that deals with a rather cute idea: Photorealistic ray tracing aids understanding of metamaterials.  "Metamaterials" may be described roughly as materials with a man-made structure on the scale of nanometers which gives them unusual optical properties not to be found in nature.  With that in mind, the rest of the article title, though rather technical-sounding, simply refers to computer simulations which can answer the following question:

Suppose you have constructed a piece of metamaterial of "everyday" size.  What does it 'look' like to the unaided human eye?

This to me is an interesting question for a number of reasons.  For one, it is not yet within our power to construct metamaterials which are larger than microscopic size (though, as I've noted previously, we're getting closer).  Being able to simulate the materials gives us a head-start in developing possible applications.  Second, we already know that metamaterials have the potential to produce interesting visual effects -- including, possibly, invisibility!  Finally, it can be very difficult, and intellectually stimulating, to try and make the connection between what light is doing in an optical system and how the system would appear to a person looking at it.

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Optics in the Haunted Mansion!

May 12 2009 Published by under Entertainment, Optics

During our visit to Walt Disney World, the new wife and I made sure to hit all the classic rides in the Magic Kingdom: Pirates of the Carribean, The Tiki Room, The Haunted Mansion, even It's a Small World (though, alas, not Space Mountain, which is under renovations until November).  The Haunted Mansion is one of my favorites, with its classic Gothic ghost story atmosphere and dark sense of humor.  As a child, I was terrified of the essentially harmless attraction.  This trip, as a professor of optics, I was delighted to not only see the clever special effects, but deconstruct them -- to "peek behind the curtains", so to speak.

I suppose some would think that this peek would "ruin the magic" or "unweave the rainbow".  For me, though, I find it a joy to see how people's ingenuity can lead to wonderfully fun, even beautiful, attractions.  The Haunted Mansion is filled with clever applications of very simple optics, and I can't resist explaining one of them.


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Optics basics: Young's double slit experiment

Mar 28 2009 Published by under Optics, Optics basics

As I've so far been restricting my 'optics basics' posts to discussions of fundamental concepts related to optics, it might seem strange at first glance to dedicate a post to a single optical experiment.  What will hopefully become clear, however, is that Young's double slit experiment is connected to so many basic concepts in optical physics  (and still provides surprising new results to this day) that one post is hardly enough to describe all the interesting insights that can be gained by studying the experiment and its implications.

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Faraday brings light and magnetism together (1845)

Mar 02 2009 Published by under History of science, Optics, Physics

The more I read of Michael Faraday's work, the more I am in awe  of the scientist's insights and abilities.  As evidence of the remarkable intuition he had regarding the forces of nature, consider the following passage:

I have long held an opinion, almost amounting to conviction, in common I believe with many others of natural knowledge, that the various forms under which the forces of matter are made manifest have one common origin; or, in other words, are so directly and mutually dependent, that they are convertible, as it were, one into another, and possess equivalents of power in their action.  In modern times the proofs of their convertibility have been accumulated to a very considerable extent, and a commencement made of the determination of their equivalent forces.

Faraday wrote this as the introduction to the nineteenth series of his "Experimental Researches in Electricity," published in the Philosophical Transactions (vol 136, pp. 1-20) in 1846!  It is an eloquent and remarkably timeless statement which could very well have been written by any modern physicist working on the foundations of a grand unified theory of forces.

As he himself notes in the passage above, Faraday was not alone in envisioning a single theory encompassing all physical phenomena.  Indeed, once Ørsted discovered that a magnetic compass needle could be deflected by an electric current, the relationship of electricity and magnetism, as well as other forces, was very much on the minds of physicists.  Faraday, however, led the charge in actually demonstrating these relations.  As I have noted in previous blog posts, Faraday demonstrated experimentally that magnets could induce electric currents (Faraday induction) around 1831, and also compiled evidence demonstrating that the diverse sources of electricity were different manifestations of the same electrical phenomena around 1833.

Because of these discoveries (and other hugely important ones that I haven't had time yet to discuss), by 1845 Faraday was one of the most prestigious and famous scientists in England.  He was by no means done with his research, however, and in that year he presented a paper describing his observations that a magnetic field can indirectly influence the behavior of a light wave.  This was the first definitive evidence that light and electromagnetism are related, and helped pave the way for Maxwell's brilliant theoretical demonstration of the existence of electromagnetic waves, and their identity with light.

The effect that Faraday observed is now known as Faraday rotation, and we take a look at the experiments, and their reception, in this post.

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