Laser Smackdown

The Most Amazing Laser Application of All Time Is...

drorzel — Mon, 03 May 2010 08:27:39 +0000

The Most Amazing Laser Application of All Time Is...

Voting has closed on the Laser Smackdown poll, with 772 people recording their opinion on the most amazing of the many things that have been done with lasers in the fifty years since the invention of the first working laser (see the Laserfest web site for more on the history and applications of lasers). The candidates in the traditional suspense-building reverse order:

Lunar laser ranging 22 votes
Cat toy/ dog toy/ laser light show 41 votes
Laser guide stars/ adaptive optics 46 votes
Holography 47 votes
Laser eye surgery 53 votes
Optical storage media (CD/DVD/Blu-Ray) 60 votes
Laser frequency comb/ spectroscopy 65 votes
LIGO 68 votes
Optical tweezers 74 votes
Telecommunications 91 votes
Laser ignited fusion 95 votes

That means that the winner, and The Most amazing Laser Application of All Time is:

Laser cooling/ BEC 110 votes

And there you have it. The people have spoken, and it doesn't get any more amazing than laser cooling, which is hereby awarded bragging rights over all other fields of laser-related physics.

Thanks to everyone who voted. And even if you missed your chance to vote, I hope you'll take a little time to look over the posts explaining the various applications, and appreciate the many amazing things being done with lasers today.

drorzel Mon, 05/03/2010 - 04:27

and now they are making rain clouds with laser:

http://www.engadget.com/2010/05/03/swiss-scientists-create-dark-clouds-…

Weird outcome, likely has more to do with the fact that Chad does ultracold physics then with anything else (people here are not representative).

By far the most amazing application is telecom, without it there would be no internet as we know it and no poll, second is optical storage, the impact of those two technologies is hard to overestimate.

Telecom did lead the poll for a long time though the results changed significantly near the end (link ended up somewhere?).

BEC/cooling is nice but still a fringe application with more hype then useful results.

Oh. You wanted aMAZing. I read aMUSing, which is why I voted for "cat toy". Lula holding a claw somewhere tender had NO effect on my vote.

Last Call for Laser Smackdown Voting

drorzel — Sun, 02 May 2010 16:00:37 +0000

Last Call for Laser Smackdown Voting

With over 700 votes cast in the Laser Smackdown poll in honor of the 50th anniversary of the laser, laser cooling has opened a commanding 20-vote lead in the race to be the Most Amazing Laser Application of All Time. If you prefer one of the other options, you have only six hours left to change the final outcome:

Which of the following is the most amazing application of a laser?Market Research

Voting will remain open until midnight, with the ultimate winner announced on Monday, May 3rd. So get reading, and get voting. One vote per computer per user, please-- this is Serious Science.

drorzel Sun, 05/02/2010 - 12:00

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Damn it! I voted for spectroscopy like 30 times and it still got clobbered!

Laser Smackdown: Final Days of Voting for the Most Amazing Laser Application

drorzel — Fri, 30 Apr 2010 07:06:48 +0000

Laser Smackdown: Final Days of Voting for the Most Amazing Laser Application

We're just over 600 votes in the Laser Smackdown poll in honor of the 50th anniversary of the laser, as of early Friday morning. I notice that it has moved off the front page of the blog, though, so here's another signal-boosting repost, just so we have as many votes as possible, to establish maximum scientific validity when we declare the winner the Most Amazing Laser Application of All Time

Which of the following is the most amazing application of a laser?Market Research

Voting will remain open until next Sunday, May 2, just two days from now, with the ultimate winner announced on Monday, May 3rd. So get reading, and get voting. One vote per computer per user, please-- this is Serious Science.

drorzel Fri, 04/30/2010 - 03:06

Maybe it's because I'm an EIT (EE), but it absolutely shocks me "Laser cooling/BEC" is winning out over telecommunications and optical storage.

red spotty chasey thing FTW! gimmie a treat?

Reminder: Vote for the Most Amazing Laser Application of All Time

drorzel — Mon, 26 Apr 2010 11:52:56 +0000

Reminder: Vote for the Most Amazing Laser Application of All Time

As of 1:45 Monday, 217 people have cast votes in the Laser Smackdown poll. That's not bad, but it's currently being handily beaten by the 271 people who have voted for a favorite system of units.

The nice thing about using actual poll services for this sort of thing, though, is that I can re-post the poll to boost signal a little. So, here it is again, a list of the twelve most amazing laser applications suggested by my wise and worldly readers, with links to short explanations of the pros and cons of each:

Which of the following is the most amazing application of a laser?Market Research

Voting will remain open until next Sunday, May 2, with the ultimate winner announced on Monday, May 3rd. Whereupon everybody will have to acknowledge the winning application as the Most Amazing Laser Application of All Time. Because, you know, that's how these things work.

So get reading, and get voting. One vote per computer per user, please-- this is Serious Science.

drorzel Mon, 04/26/2010 - 07:52

Where is the "sharks with friggin laser beams attached to their heads"???

Yesterday, I got Wii shoulder after playing baseball for the first time. Now my muscles get tense whenever I write or move my arm in general. Good thing I don't own a Wii myself.

What, no optical stimulation of neurons in the brain (after the neurons have been genetically modified by viruses to express genes that cause them to be light-sensitive)?

Or two-photon microscopy?

I'm gonna have to stick with making popcorn - real genius style.

Our best measurements of supermassive black holes come from Nature's own lasers. And the lasing material is water.

Cat toy FTW. gimmie a treat.

Laser eye surgery saved my father's eyesight (and will probably save mine one of these days), so I'm going to go with that one.

I vote for big lasers on satellites to shoot down ICBMs in their boost phase, because without them, we'd all be helpless against a nuclear attack...

What, it has to be something that WORKS? Damn, you're a tough crowd here...

Laser Smackdown: Vote for the Most Amazing Laser Application

drorzel — Fri, 23 Apr 2010 08:42:22 +0000

Laser Smackdown: Vote for the Most Amazing Laser Application

In 1960, the first working laser was demonstrated, and promptly dubbed "a solution looking for a problem." In the ensuing fifty years, lasers have found lots of problems to solve, but there has been no consensus about which of the many amazing applications of lasers is the most amazing.

Now, in 2010, as we celebrate the anniversary of the laser, we finally have the technology to definitively answer the question: radio-button polls on the Internet!

Which of the following is the most amazing application of a laser?Market Research

Each of the choices above links to a post I wrote here giving you the basic information about that application (I'll reproduce the list below), so you can make an informed decision as to what the most amazing application of the laser is. Voting will remain open until next Sunday, May 2, with the ultimate winner announced on Monday, May 3rd. Whereupon everybody will have to acknowledge the winning application as the Most Amazing Laser Application of All Time. Because, you know, that's how these things work.

So get reading, and get voting. One vote per computer per user, please-- this is Serious Science.

The list of application posts, in chronological order:

drorzel Fri, 04/23/2010 - 04:42

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Hey, what about barcode readers, those ubiquitous devices seen in almost every retail store nowadays? Besides allowing customer to check out their own groceries, consider how cool it is to be able to do inventory with a wave of a wand instead of slogging through it item by item? Heaven!

I wrote another chapter in my latest Hard SF novel about quantum combs, but what happened to laser propulsion? I wish I'd gotten it in writing (and not just Project Manager Jordan Kare) that Edward Teller praised my equations on propellant mixed with chopped up IR fibers so as to optimize the thermal gradient in the block of solid hit by the ground-based humongous laser, ablating the propellant, and rocketing the payload into orbit or beyond. P^3. Propellant, Payload, Period.

Argh, and libraries! Mustn't forget how important barcoding of books has become for library inventory and control.

What about "putting on the heads of sharks as a means of execution", huh?

Voting for "most amazing" is difficult. Optical tweezers, quantum combs, and BEC are all pretty mind-boggling. I'll go with BEC because it is so counter-intuitive at first glance.

A separate poll of most "significant" application might be neat.

What about the Boeing ALTB? http://www.boeing.com/defense-space/military/abl/index.html

It was a tossup between BEC and tweezers, mainly because so many of the others were ideas that were already being popularized (if not realized) in my youth. But playing with individual atoms and/or manipulating them into a macroscopic quantum state?

Remember, atoms did not become "real" until about a century ago. Last year was the centennial of the Rutherford experiment, and next year is the centennial of his explanation that led to the Bohr model and a physical basis for chemistry. Quite a jump from that to a BEC.

I was going to vote, but it was too difficult. Can I really put the frequency comb over LIGO?

After having worked on laser systems for many years, I have to plug my own nickel. Nowhere in the list is LISA. Why ?
In 1984 myself & colleagues at NASA-Goddard & JPL explored LISA's predecessor: A Mars Laser, with an orbiting lasing path thru the Martian CO2 atmosphere, sampling at anytime of the day, two active gain regions pumped by the sun.
The laser beam was calculated to produce several hundred watts of directed, coherent, infrared energy, which would then sweep a narrow band `lighthouse' beam, once around the solar system per Martian day, and out to the stars.
No practical application except advancing Dyson-like technology. As fallout, it would be a narrow band beacon, broadcasting Mar's intelligent civilization, which would stand out amidst the broadband, noisy, IR background like a sore thumb, and hence be easily detectable by ETI.
Don't tell Hawking: He is terrified of aliens finding out about Earth. Now he can sleep easier at nite !

Amazing Laser Application 12: Laser Guide Stars!

drorzel — Thu, 22 Apr 2010 08:12:15 +0000

Amazing Laser Application 12: Laser Guide Stars!

What's the application? Producing artificial "stars" to serve as a reference for telescopes using adaptive optics to correct for atmospheric turbulence. This allows ground-based telescopes to produce images that are as good as those from the Hubble Space Telescope.

What problem(s) is it the solution to? "How can I make this giant telescope produce even more impressive pictures?"

How does it work?The basic problem with ground-based telescopes, as anyone who has ever looked at the stars or listened to nursery rhymes can tell you, is that stars "twinkle." They appear to fluctuate in brightness from one moment to the next, and if you look at them closely enough, they appear to shift position very slightly. This is caused by turbulence in the atmosphere-- as the light from a distant star passes through the air above us, it encounters shifting patches of slightly different density and temperature, which bend the light onto slightly different paths. The overall effect is to "smear" the image of the star over a wider area. This isn't too awful when you're just looking at a star (a point just becomes a slightly fuzzier point), but it's fatal if you'd like to see the details of a galaxy or some such object.

"Adaptive Optics" is a technique for fixing this problem by adjusting the mirror of the telescope to compensate for the blurring in the atmosphere. The idea, shown in the figure (and explained at the CTIO site) is to use the telescope to image two objects, one of them something like a single star that we know should be a single point source, the other something like a galaxy with lots of fine detail. You split up the light from those two objects, and use a deformable mirror to correct the image of the star so that it appears as a single sharp point, rather than a blurred mess. If the star is close to the target object you'd like to see in detail, then the correction used to get the star back to a single image will almost certainly fix most of the blurring in the object you care about, as well, giving you a much sharper image.

This system can produce dramatic results-- see the images below with and without adaptive optics corrections, taken from the Center for Adaptive Optics. It requires constant small adjustments to the mirror to keep correcting the focus, as the atmospheric disturbances shift around and change, but that's something that can be automated, and run by a computer during the lengthy image runs that astronomers need to pick up details.

Why are lasers essential? You might notice that the above description doesn't mention lasers at all. What do lasers have to do with this?

The maddening thing about stars is that they're scattered fairly randomly across the sky, and there's never one right where you want it. Depending on what object you'd like to view, there may or may not be a star in the same region of the sky that can serve as a point source for adaptive optics correction. That limits the applicability of the technique.

With lasers, though, you can make your own "stars," wherever you need them. You just use a telescope to project a laser beam up into the sky, illuminating a tiny spot in the upper atmosphere, above most of the problematic distortion. That spot then serves as the reference "star" for the image correction, and you proceed as described above. This can have really impressive results, as in these really spiffy pictures of the Orion Nebula (this also includes a shot of the laser beam shooting up into the sky, like they're blasting alien invaders...).

For this to work, you need to project a very small spot onto the sky fifty-odd miles above the surface of the Earth. While you could do this with the Bat-Signal and a great big lens, this is really a job for a laser.

Why is it cool? Dude, look at those pictures! Or this one, comparing ground-based telescopes with adaptive optics to the Hubble:

You can't say that isn't cool...

Why isn't it cool enough? The basic technique doesn't require lasers per se; lasers just make it more convenient. Also, the laser correction isn't always enough, because there's still a bunch of atmosphere above the layer where they project the laser spot.

Also, you could argue that the technology that enables adaptive optics isn't the laser, but the computer-- what makes this a practical tool is the ability to do real-time corrections of the mirror to adjust the focus, which is a formidable computing problem.

drorzel Thu, 04/22/2010 - 04:12

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Amazing Laser Application 11: Frequency Combs!

drorzel — Wed, 21 Apr 2010 09:55:27 +0000

Amazing Laser Application 11: Frequency Combs!

What's the application? An optical frequency comb is a short-duration pulsed laser whose output can be viewed as a regularly spaced series of different frequencies. If the pulses are short enough, this can span the entire visible spectrum, giving a "comb" of colored lines on a traditional spectrometer. This can be used for a wide variety of applications, from precision time standards to molecular spectroscopy to astronomy.

What problem(s) is it the solution to? 1) "How do I compare this optical frequency standard to a microwave frequency standard?" 2) "How do I calibrate my spectrometer well enough to detect small planets around other stars?" 3) "How can I do precision molecular spectroscopy really quickly?" 4) "How can I do qubit rotations faster in my ion trap quantum computer?" among others.

How does it work? The key idea is that in order to make short pulses of light, mathematically, you need to add together large numbers of waves at different frequencies. I talk about this a little in the book, from which I'll lift this figure:

From bottom to top, this shows a single frequency, the sum of two different frequencies, then three different frequencies, then five. As you can see, adding mroe frequencies gets you a shorter pulse (where the waves are obvious) with a larger gap between pulses.

When you do this with the right sort of laser, you can generate a pulse whose length is given in femtoseconds (10^-15s, or 0.000000000000001s). That kind of ridiculously short length requires an extremely broad range of frequencies to make it up, which can be pictured as a "comb" of lines of different frequencies, corresponding to the different colored lines seen in this figure lifted from the group of Theodor Hänsch, who shared the 2005 Nobel Prize for developing the technique:

The lines of the comb are separated by a frequency that is determined by the repetition rate of the laser, which can be controlled extremely precisely. If the "comb" is broad enough (the technical term is "octave-spanning") it's possible to find high-frequency lines that are at double the frequency of some of the low-frequency lines, which lets you nail down most of the systematic effects that would otherwise plague the measurement. And if you arrange things right, you can get one of the lines to line up with a line from an atomic standard (a rubidium atom, say, or a mercury ion), and lock the frequency of that line to the frequency of the atomic standard to the sort of precision that people expect from atomic clocks-- a few parts in 10¹⁶ or so. That gives you a collection of regularly spaced lines spanning more or less the entire visible spectrum, with all of their frequencies known to fifteen or so digits.

This is an incredible resource for all sorts of physics. For one thing, it gives you a way to make direct comparisons between atomic clocks running in very different regions of the spectrum. This is a huge issue, because atomic clocks based on visible or ultraviolet transitions offer a lot of advantages over traditional microwave clocks when it comes to accuracy, but it's very difficult to get an optical frequency down to something useful in the lab. The frequency comb lets you do that.

It can also be applied to spectroscopy in areas like astronomy. The figure above is from the Hänsch group's experiment using a frequency comb to calibrate a spectrometer for astronomical observations, and we had a very nice talk last week by Dr. Chih-Hao Li, who's doing similar work with Ron Walsworth's group at Harvard. The idea is that the comb gives you a way around one of the limitations in spectroscopy of stars, which is that the calibration of the instruments is difficult, and tends to change over time. That leads to an uncertainty in Doppler shifts measured for astronomical objects. The comb provides a nearly perfect calibration source, with atomic-clock precision over a huge range of wavelengths-- the Walsworth group's tests spanned almost 100nm in wavelength, and they think this could allow them to measure Doppler shifts of stars at levels corresponding to a few centimeters per second. That's about the size of the shift Earth would cause in the Sun's spectrum as we orbit, so that level of precision could allow the detection of Earth-like planets through Doppler shift measurements.

You can also apply the comb directly to spectroscopy, as Haänsch's co-laureate Jan Hall has done in spectroscopic experiments at JILA in Colorado. They use the comb to detect trace amounts of particular gases, based on the way they absorb some lines and not others. (If you click on the picture on the page linked, there's a spiffy animation to go with the press release.)

Even more recently, Chris Monroe used a frequency comb to drive transitions in a trapped ion, which could be a faster way of doing the operations needed for quantum computing, where you often need widely separated frequencies that are controlled with extreme precision.

Frequency comb sources are a relatively new technology, so people are still coming up with amazing things to do with them. It's one of the most exciting areas in AMO physics right now.

Why are lasers essential? The entire comb generation method depends on using a laser. There's absolutely no way to make this sort of source without the laser principle-- it's not just a really bright light, it's a really bright light with very special frequency and phase properties.

Why is it cool? Dude, ultra-precise spectroscopy at essentially any wavelength! Extrasolar Earth-like planets! Fast qubits! What more do you need?

Why isn't it cool enough? Only great big nerds really get excited about ultra-precise spectroscopy and all that other stuff. Sadly, many ordinary people are bereft of the soul needed to appreciate the utter coolness of frequency comb sources.

drorzel Wed, 04/21/2010 - 05:55

Amazing Laser Application 10: Surgery!

drorzel — Tue, 20 Apr 2010 07:51:51 +0000

Amazing Laser Application 10: Surgery!

What's the application? Using lasers to cut and/or cauterize tissue during surgical procedures, instead of the traditional very small very sharp knives.

What problem(s) is it the solution to? 1) "How can we do surgery without touching the tissues being operated on?" 2) "How can I get rid of these annoying glasses/contact lenses?"

How does it work? First, you strap a device to your head that lets you shoot laser beams from your forehead, like one of the X-Men. then you use a magnifying glass to focus it to where it needs to be. Like so:

(I'm not sure exactly what sort of procedure that is, but I really hope that's not how they do the surgeries where they re-shape the cornea...)

The basic idea of laser surgery is sort of similar to the previous application, namely, if you focus a laser beam down to a very small spot, it will deliver a great deal of energy to that spot. If that spot happens to be on a bit of human tissue, it can get hot enough to blast the target cells into vapor.

This allows you to make extremely precise cuts in human tissue, with the bonus effect of keeping everything involved nice and sterile, as there is no contact between a physical device that might carry microbes and the tissue in question-- just light. The heat involved also tends to kill harmful microscopic critters that are already hanging around, and sometimes to cauterize blood vessles, keeping everything much cleaner.

The default sort of laser surgery that people think of is LASIK vision correction, which is explained in slightly gross detail with step-by-step images here. The idea is to use a powerful laser to blast away bits of the cornea, reshaping it so as to move the focal point to a location closer to the retina, thus improving the patient's vision.

There are a bunch of other non-LASIK eye surgeries done with lasers, as well. It's also used for surgeries on other parts of the body, but it's damnably difficult to sort those applications from the nine billion pages about laser eye surgery. A partial and not very detailed list can be found here, which gives you the basic idea.

Why are lasers essential? Once again, the key to the whole thing is getting a very intense pulse of light directed to a very small point. While I suppose it's theoretically possible to do this sort of thing with a great big lens on a sunny day, lasers are really the way to go. Especially if you're in a climate where it's often cloudy.

Why is it cool? Dude, surgery with lasers!

As noted above, laser scalpels offer a number of nice properties that help reduce the chance of serious complications-- reduced bleeding, lower risk of infection, greater precision, etc. And, as a bonus, when you're done with surgery you can breathe some ether, crank up the Pink Floyd, and enjoy a homemade light show.

Why isn't it cool enough? Surgical applications of lasers are still kind of limited, and mostly reproduce things that can also be done with a regular scalpel. Also, the radio and tv spots run by some LASIK doctors are pretty annoying.

drorzel Tue, 04/20/2010 - 03:51

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I got laser surgery for retina reattachment in the 80's (not knowing that "state of the art" also meant "no idea of long term effects"). 20 years later another eye surgeon commented "oh God, that looks like someone drove through there with a tank". That was while he was prepping me for Lasik. Looks like I didn't get the message the first time, but then, going from 20 and a mile to 20/30 in 5 min was pretty eyeopening.

Don't forget that lasers allow surgeons to operate where they can't get a scalpel, such as the retina of the eye. Without lasers, people with detached retinas would go permanently blind. With lasers, it's just a minor surgical procedure.

Dave

P.S. I have a nice photograph of a "really sweet" laser retina surgery result.

Lasers are frequently used to treat diabetic eye disease, prevent or treat retinal tears. What exists now is very different than what used to exist - the power, size, duration, and placement is much more precise. If it helps any, it is so precise that you can use the same equipment on mouse eyes. There are also many more kinds of lasers used with eye surgery now, including so-called "cold" ones. There are even some applications now that you could not do, or not as well without a laser. And yes, the LASIK ads are annoying.

That is a might freaky picture accompanying the article.

Is that really how they do laser eye surgery? I wouldn't think the human head is a great precision pointing instrument, and it's a long lever arm from that dude's head to whatever he's zapping.

What the heck is going on there? (Other than giving me nightmares.)

LASIK Surgery has become quite common and the percentage of failures is minute when compared to past. Most of the people prefer LASIK surgery becoz they can avoid lens and glasses when used.LASIK surgery has gained popularity and suggested by many optometrist. I use contact lens and planning to go for surgery as i have constant sight since last year.
http://americanlasiksurgeons.com/

Amazing Laser Application 9: Fusion!

drorzel — Mon, 19 Apr 2010 09:05:29 +0000

Amazing Laser Application 9: Fusion!

What's the application? The goal of laser ignition fusion experiments is to heat and compress a target to the point where the nuclei of the atoms making up the sample fuse together to form a new, heavier nucleus, releasing energy in the process. Nuclear fusion is, of course, what powers stars, and creating fusion in the laboratory has been the holy grail (well, a holy grail, at any rate) of nuclear physics research for the last sixty-plus years.

What problem(s) is it the solution to? 1) "Can we create fusion reactions in a laboratory setting on Earth?" 2) "How can we get more helium without mining it from the Moon?"

How does it work? The basic idea is appealingly simple: Get a whopping hug laser, focus it down onto a target, and BLAM! instant star:

In practice, it's much more difficult than the idea makes it sound-- you can very easily blast a target into plasma, but getting that plasma hot and dense enough to let fusion occur requires incredible care in arranging the beams so that the target is uniformly illuminated, and collapses in a symmetric manner.

But stripped down to its essence, that's really all there is to gigantic experiments like the National Ignition Facility (WARNING: auto-playing video with sound): You just build the biggest laser you can, focus it down to a point, and blast away.

Why are lasers essential? You could theoretically do this with any really bright light source, but the current record is about 0.7MJ of energy in the pulse hitting the target, which would be awfully tough to arrange without a laser. Having the light pulse in laser form makes it vastly easier to direct and focus it appropriately.

Why is it cool? Dude, they're, like, bringing the sun down to Earth!

Controllable fusion reactions in a lab setting would be a huge boon to nuclear research. And, of course, if scientists can figure out a way to generate power from nuclear fusion, they could ~~be gunned down by assassins hired by the Eeeeevil oil companies~~ provide clean energy for the entire world.

Why isn't it cool enough? They've made a lot of progress recently, but have not actually achieved fusion yet, though they hope to reach the required pulse energies this year, maybe. Commercial fusion power generation is twenty years off, and expected to remin that way for the next twenty-odd years.

drorzel Mon, 04/19/2010 - 05:05

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The nuclear and high-energy physics experiments never fail to come up with the coolest looking hardware. Seriously, everyone needs to check out the galleries on that NIF site. The target apparatus looks exactly like the sort of thing that should be powering a starship. I thought at first that the image you put up was some fanciful artist's conception, maybe pulled off of some decades-old pulpy scifi magazine. But no, it's just an earlier experiment in the field.

Same goes for all of the big particle accelerators... the LHC certainly looks more badass than any doomsday device dreamed up by hollywood.

...wait, so shouldn't this be on the list of best POSSIBLE laser applications?

Along with mind control, scalable quantum computing and world domination...err, forget the last one.

Awesome photo. This is the kind of stuff that Obama's Sect'y of Energy, Stephen Chu is into. And if I'm not mistaken, there's no question that this will will create fusion. As with the ITER Tokomak, and a number of other research approaches now being funded by DoD, and DoE, and showing promise towards reaching break-even, fusion isn't the trick so much these days. The trick is getting more energy out of the system than it takes to "burn" the hydrogen. As for 20 years in the future, not unlikely but once fusion excedes break even the game will be changed when it comes to energy, and just what these next 20 years will look like could be very very interesting.

Well, Tokamak fusion has already more-or-less reached break-even, the problem is that commercial generation requires 20:1 or so. The Joint European Torus reached 0.7 back in 1997 for a few seconds, the JT-60 has exceeded that since then. ITER should reach ~10:1 for ~1000 secs, and provide the information necessary to build DEMO: 15% larger, 30% greater plasma density, capable of (hopefully...) 25:1, and generating power.

Amazing Laser Application 8: Holography!

drorzel — Fri, 16 Apr 2010 09:30:23 +0000

Amazing Laser Application 8: Holography!

What's the application? Holograms are images of objects that appear three-dimensional-- if you move your head as you look at a hologram, you will see the usual parallax effects, unlike a normal photograph, which is fixed. So, if your hologram includes one object that is partly behind another object, you can see around the obstruction by moving a bit to the side, just as you would if the original objects were in front of you.

What problem(s) is it the solution to? 1) "How can we jazz up flat images and make them look more lifelike?" 2) "How can we make credit cards harder to copy?"

How does it work? The key to holography is the interference of light. The simplest sort of hologram to make is a transmission hologram, which works very nicely to illustrate the key ideas, as in this image from HyperPhysics:

To make a transmission hologram, you split the beam from your laser, and use half of it to illuminate your object, while the other half falls directly on the film. The two different beams will interfere with each other, and what you record on the film will be the interference pattern, rather than a normal image of the scene. If you look directly at the film, you will just see a pattern of stripes and whorls that doesn't look like much of anything.

If, rather than looking directly at the developed film, you shine a laser onto the film from the same angle as the beam that directly illuminated it in the original set-up, though, the light from the laser will diffract off the interference pattern, and what you end up with on the far side of the film will be identical to the light from the other beam, the one that was illuminating the object. Which means that somebody on that side of the film looking back through it will see an image of the object that was originally present, as if it were still there, and illuminated by the laser being used to project the image.

This diffracted light has all of the characteristics of the original light, including the phases and everything. Which means that it recreates the full pattern of the original light in the cone of the beam, including the parallax effects and all that. So you get a complete three-dimensional image.

With a slightly different arrangement of components, you can make a reflection hologram, and you can convert one of those into a rainbow hologram that doesn't require coherent light to make it work. Which leads to all those shiny rainbow hologram stickers and holograms on credit cards and currency.

Why are lasers essential? In order to get a clean interference pattern, you need a coherent source of light. That is, the waves that are directly illuminating the film need to have basically the same phase as the waves that are bouncing off the object-- in the absence of the object, the question of whether the peaks line up to give you constructive interference should only depend on the lengths of the two different paths they followed to the film.

In an incoherent source like a lamp, the phase of the light fluctuates rapidly and randomly. That means that the interference pattern you get changes from one nanosecond to the next, and unless you're absurdly careful about setting things up, you'll just get a big smear on the film. A laser has vastly better coherence properties, and will give you a steady pattern, provided your paths are reasonably similar in length.

You could make a hologram using heavily filtered light from a lamp, and extraordinary care, but you really don't want to do it that way. A laser turns it into something that can be done as a lab for non-science majors.

Why is it cool? Dude, it's a three-dimensional image!

Also, because it is an interference phenomenon, the pattern at any given point on the film depends on light from all parts of the illuminated object. Which means that any piece of the image contains the whole picture. This makes holography a very robust image-storing method, and also provides the hook for a really good William Gibson story.

(The "every part contains the whole" aspect is also what inspired yesterday's optics quiz. It's not exactly the same, but the end effect is somewhat similar, and for a similar reason-- just as the light that makes up an image from a lens passes through all parts of the lens, the light that produces the interference pattern at the hologram film comes from all parts of the illuminated object.)

You don't have to take my word for it, though. Holograms are sufficiently cool that Dennis Gabor won the 1971 Nobel Prize in Physics for inventing the technique.

Why isn't it cool enough? It's still a bit of a hassle to make holograms, and their use is somewhat limited. It hasn't yet led to the three-dimensional home viewing systems that I was promised by science fiction stories when I was a kid. No matter what cheesy effects CNN may use.

drorzel Fri, 04/16/2010 - 05:30

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recreates the full pattern of the original light in the cone of the beam

Yeah, that's pretty damn cool.

Despite your detailed and well written description, I am going to go on believing that holograms are simply magic because it's easier >_>

Click here Chad for a most interesting recent use (interpretation?) of Holography, maybe, according to arXiv.

I would also ask, in your best understanding, when will we see "Holography Sets" like R2D2 gives us of Princess Leia saying "Help us Obi-Wan Kenobi, you're our only hope..." in the first Star Wars film?

I believe that the security holograms you see on credit cards and such are actually transmission holograms, but with a reflective backing allowing them to be viewed in reflection. Actual reflection holograms usually appear black where there is no image, as opposed to the silver background seen on credit card holograms.

Speaking of holograms, did you ever see the method for making "scratch holograms"? They are drawn by hand, no laser.

http://amasci.com/amateur/hand1.html

Of course, it is debatable whether they are really holograms, but they do generate a recognizable 3-D image. I've drawn them myself on pieces of scrap plexiglass, it does work.

I just covered holography in my non-majors course on light today. I used the geometrical model developed by T.H. Jeong. See his article: "Geometric model for holography," American Journal of Physics, Volume 43, Issue 8 (1975), pp. 714-717. I adapted his figures to describe reflection holograms because most of my students did that as an extra credit activity in the previous week. We used a simple kit from Integraf (Jeong's company). Everyone had a lot of fun!

Holograms may be intended to improve credit card security, but in fact they're easy to clone. This is from Wired in 2007: http://www.wired.com/science/discoveries/multimedia/2007/02/72664

Thank you for getting this mostly right! Holography is used to describe many things that are not holographic and its frustrating to those of us who understand the true potential of this REAL 3D technology.

i want to make a simple hologram for science fair.so if you can guide me how to do it,i shall be very thankful to you..

For those of you who ever desired to create their own holograms. The ultimate "how to" guide is available.
Imagine projecting images on the ceiling of your room, impressing your friends.
Check out my link! You definitely will not regret it!

really amazing