Anti-Laser - The "Coherent Perfect Absorber" Is Born

In an anti-laser, or coherent perfect absorber, the outgoing laser beams are replaced by incoming ones, and light flows into a light-absorbing material instead of out of a light-amplifying one. Image Credit: Science/AAAS

Anti-Laser - The "Coherent Perfect Absorber" Is Born

Everyone is familiar with laser light emitting devices such as pointers used in presentations and lectures, lightshows performed at events, openings, and concerts, even with the red-light that hits a barcode on the front of one's morning newspaper and pastry purchase at the corner 7-11 ... but this was not the case 51 years ago.

Now there is a new tool that has been developed through the the use of focused wavelength of light but unlike with the laser, where the focused wavelength is passed through a material that amplifies the light, the anti-laser utilities the opposite concept of passing a focused wavelength of light through material that absorbs the light. The process has been given the name "Coherent Perfect Absorber" giving a new, future meaning to the an-acronym "CPA".

In the anti-laser, incoming light waves are trapped in a cavity where they bounce back and forth until they are eventually absorbed. Their energy is dissipated as heat. Image Credit: Yidong Chong/Yale University

When the laser was first conceptualized and developed into a working device, no one knew that it would eventually lead to replacing records and needles when one listens to music or film projectors when one watches a home movie transferred from a computer to a laser/DVD disc. The same could be said at the dawn of the anti-laser CPA process, No one knows what this new tool will bring to the tool-box, and what new applications can be developed, to solve the many problems we encounter that make our lives easier and more efficient.

Coherent light is incident on an absorbing material in a resonator formed by two parallel reflective surfaces or mirrors. The interplay of absorption and interference leads to perfect absorption of the incoming radiation and its conversion into other forms of energy1. The schematic of a laser would be entirely analogous, with only the arrows for light and energy reversed: energy pumped in would result in coherent light out. Image Credit: Nature Volume: 467, Pages: 37–39 Date published: (02 September 2010)


Dr. Wenjie Wan, a Phd from Princeton University, is a post-doctoral associate in applied physics at Yale. In photo, Wan works with the optical set up for an anti-laser experiment in the applied physics lab at Yale which involves prisms, mirrors and silicon. An anti-laser (or, in technical terms, "coherent perfect absorber") works in the reverse of a conventional laser. Instead of emitting a beam of light, it absorbs it. Two laser beams with the exact same frequencies are emitted into a silicon wafer. The silicon aligns the light waves so that they become interlocked and oscillate until they are absorbed and transformed into heat. The concept is in it's infancy and may be adapted to new computer technology down the road. Image Credit: STEPHEN DUNN, Hartford Courant (2011)

This excerpted and edited from the Hartford Courant -

The Anti-Laser Is Here
Yale researchers butild device that absorbs light
By William Weir - Hartford Courant - Feb. 17, 2011

A. Douglas Stone, a physicist, and his team describe the anti-laser in Friday's issue of Science.
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The possibility of an anti-laser had been suggested by other scientists, but only in passing, Stone said. And other physicists have stumbled upon the basic premise while working on other projects, he said, but they did not follow through.

"Nobody took it serious, until us," Stone said. "It was literally a footnote."
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Any dark material can absorb light — a car's black interior on a summer day, for instance — but to absorb near 100 percent of the light of a laser beam requires a bit more precision. The difference in the anti-laser is that instead of using an amplifying material, it uses one that absorbs it — or a "loss medium." After his research team did the math, Stone said, they decided that silicon was the best choice.

The anti-laser is set up to split a single laser beam into two and direct the two beams to head toward each other, meeting at the paper-thin silicon wafer. The light's waves are precisely tuned to interlock with each other and become trapped. They then dissipate into heat.

Perhaps the most novel part of the device is that it allows the operator to tune the light's wavelengths and determine how much of the laser light is absorbed. That allows the device to work as an on-off switch for light.

Stone first proposed the idea last year, in a paper published in the journal Physical Review Letters. But it's one thing to write about it and do the math, and it's another to actually create it. That's where Stone's collaborators came in, a team of applied physicists headed by Hui Cao and Wenjie Wan. The divide between theoretical physics and applied physics is a stark one. As of Wednesday, Stone hadn't yet seen the finished device, built in another building on campus
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Wan said it took about a year to build the device. Pointing at the mirrors, prism, beam splitter and the silicon wafer that make up the device's basic components, he said the design is fairly simple. But achieving the necessary level of precision was a challenge. Even now, they're fine-tuning it.
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Now that the anti-laser has been built, what exactly do you do with it? Its best potential use, so far, appears to be in optical switches, used in the next generation of computers, which operate on light as well as electrons. Cao also has suggested that it could be useful in radiology, capturing images of human tissue normally too deep to see.

But as with much of science, the practical applications will be for others to figure out.
Reference Here>>

Digital Imaging Camera Conversion: Records To MP3

Peter Alyea, a digital conservation specialist at the Library of Congress, scans a record from the 1930s. Image Credit: Nell Boyce/NPR

Digital Imaging Camera Conversion: Records To MP3

Digital imaging technology is an amazing tool. It provides biometric information to help keep us safe, it reads symbologies so that we can get information delivered to us through a camera and sofware (up to 20 seconds of low-res video on our cellphone screens - a 4 meg file), and now this type of technology can take a picture of a round phonograph record and deliver a sound reproduction via a MP3 file converted from reading the grooves of the record.

What more versitility does one want from a technology?

Excerpts from National Public Radio -

You Can Play the Record, but Don't Touch
by Nell Boyce - Morning Edition, July 16, 2007

At the Library of Congress, in a small, white room with bright red carpet, physicist Carl Haber sits down to play a record from 1930. It's a recording of Gilbert and Sullivan's "Iolanthe." But here's the strange thing: This record is broken.

"It looks like somebody just got hungry and took a bite out of it," says Haber. He has positioned the record on a turntable and fitted the broken piece back into place, like it's a jigsaw puzzle. "If we spun this thing fast, the piece would come flying off, you know, and maybe hit somebody," he says.

But this turntable doesn't spin like a normal record player. And there's no needle hovering over the record. Instead, there's a camera linked to a computer. It snaps detailed images of the groove cut into the disc, and uses the images to reconstruct the sound without ever touching the record.

Haber got the idea for this setup a few years ago, when he was driving to work and listening to NPR. He heard a report on how historic audio recordings can be so fragile that they risk being damaged if someone plays them by dragging a needle over their surfaces. It made Haber wonder if he could get the sound off old recordings without touching their delicate surfaces. He worked with a colleague, Vitaliy Fadeyev, and they managed to reconstruct sound on a 1950 recording of "Goodnight, Irene" performed by the Weavers.

This was just a proof of principle. They have now developed their hands-off technique to the point that it's being tested at the Library of Congress to see whether it's good enough to someday scan the library's vast archive of sound recordings.

One thing they've learned: A broken record is no problem. Haber clicks a mouse and the camera takes pictures of the groove on "Iolanthe."

"And by taking these pictures, it essentially just unwinds the record into a big long stripe," Haber explains.

A scanned photo image of the grooves in the record from "Hemlock Blues" by David Lee Johnson from the early 1950s. IRENE skips right over the scratched parts (as seen above) of normally unplayable records. Image Credit: physicist Carl Haber

The picture appears on Haber's computer screen. It looks like a black and white photo of a tire tread.

"Here's the break," he says, pointing to a line. "You can see, there's a little piece of dust, little scratch marks on it." The computer ignores all these flaws as it translates the images into sound.
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IRENE was installed at the Library of Congress late last year. The library has millions of old audio recordings, and many are in poor condition or use obsolete formats. Peter Alyea, a digital conservation specialist at the library, says that to play old records, you often need trained technicians who can do things like choose the proper needle out of dozens of options. But if IRENE lives up to its potential, Alyea says, anyone could make a digital copy of an old record.
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Alyea says it's like a photocopy machine for sound. "It brings the possibility of automation much closer to reality for these kinds of materials."

And given that he has thousands and thousands of records that he would like to digitize and make widely available, the prospect of automation is hugely attractive.
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Exactly how good is IRENE at making digital copies?
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One test involves a disc etched with simple tones to see how well IRENE can read some old-fashioned discs coated with lacquer. The library has thousands of these one-of-a-kind records. The format is obsolete.

But luckily, Haber says, audio engineer George Horn still makes them at Fantasy Studios in California. Horn cut some discs with well-defined tones. Haber says, IRENE can reproduce the tones amazingly well.

"The machine is not adding its own color. It's not adding anything of its own nature," he says.

Haber says IRENE does take some things away. He plays one record from 1953, a Les Paul and Mary Ford recording of the song "Johnny Is the Boy for Me." This record has a bad skip in it that's very apparent on a regular record player. But IRENE skips over the skip like it's not there.
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IRENE, an audio-recording system, can scan old and damaged records and wax cylinders ... and make digital recordings from them. Image Credit: physicist Carl Haber

IRENE isn't perfect. It removes pops and clicks, but it sometimes has a hissing noise in the background. Still, the Library of Congress finds all this encouraging enough that it has started testing the system on hundreds of discs, what Alyea describes as a kind of simulation of what a mass digitization project would be like.

When taking flat photographs, it can create a three-dimensional image of the groove on a record, or on an old wax cylinder. Haber been working with the University of California's Phoebe Hearst Museum of Anthropology, to reconstruct sound from field recordings, like one wax cylinder made around 1911 that features a Native American called Ishi.

Haber says it's amazing to hear these voices from the past. "There's this whole human and cultural component to what we're looking at," says Haber, whose main job is studying subatomic particles at Lawrence Berkeley National Laboratory in California. "That makes it wonderful."
Read All (audio examples of IRENE conversion compared at story source)>>

Try doing this with laser technology!