”This is it—the paradigm shift,” archaeologist Chris Fisher told Ars. “Just like the advent of radiocarbon dating, LiDAR will have the same impact.”

LiDAR, or “light detection and ranging,” acts as a sort of radar with light, painting the target area with lasers and recording the time it takes to reflect back to the instruments.

An archaeologist specializing in Western Mexico, Fisher studies the way environments affect and change cultures. LiDAR has helped him repaint the picture of ancient Mexico, bringing the little-known Purepecha empire a lot more historical prominence.

(via Indiana Jones goes geek: Laser-mapping LiDAR revolutionizes archaeology) 

I don’t know about you, but when I think of lasers, I think of boxes on heavy, stabilized tables. Inside the boxes, the optical elements are mounted on stabilized mounts and everything is generally held as solidly in place as possible. The one thing that you generally don’t do is give a laser a good shaking. Unless it has already stopped working, in which case, have at it… preferably with a hammer.

Finding a paper that demonstrated a laser with better performance when it was being shaken compared to when it was held came as a bit of a shock.

The reason why the idea of shaking a laser is so shocking to me is that the lasers I am used to working with have optical elements that need to maintain a precise alignment with respect to one another. Temperature changes, vibrations, shaking, and “thumping the box to fix it” are all really bad ideas. But of course not all lasers are like this.

The laser in your laser pointer, CD, DVD, and Blu-Ray players are all monolithic devices. That is, they are made from a single piece of material, or materials, that are deposited on one another. You can obviously shake a laser pointer (much to the delight of cats), but this capability doesn’t scale. If you were to shake a laser pointer with acoustic waves that had a wavelength about the same size as the device (in the GHz range), then I would expect that things would probably go wrong rather quickly.

In most cases, at least. A group of researchers from Germany and Russia have now made a laser that works better when it is shaken. The reason why this occurs lies in the peculiar nature of the laser used by the researchers.

The laser that the researchers worked with was made from quantum dots (see side bar) embedded in a semiconductor material that had mirrors deposited on either side of it. This means that the distance between the two mirrors was extremely short. The researchers don’t state how big the distance was, but from the figures, I estimate that it wasn’t much longer than eight micrometers. For comparison, the wavelength emitted by the quantum dots was around 900nm.

(via A laser that works better shaken, not stirred)

Cloaking devices are one of the inventions of science fiction that have made a few tentative steps towards the real world in recent years. Now, researchers have moved the concept into the fourth dimension, creating a setup that hides a specific point in time from being perceived by observers. But if you want to make an event disappear, you have to act fast: right now, we can only hide a few picoseconds worth of time.

The cloaking devices we’ve made all work based on a similar principle: light that enters the device is bent in such a way that when it exits, its location and direction make it appear that the device itself, and anything within it, were not present. In other words, while within the device, light travels as if it were present. It’s just that, once it exits the other side, there’s no evidence that anything unusual has taken place. The same general idea governs the action of a temporal cloaking device.

The basic idea is that, when it’s not in operation, a light beam can pass through the cloaking device unhindered. When it’s switched on, a short temporal gap is opened up in the beam, then sealed back up on its way out of the hardware. One way to think of this is to view the light beam as a bit of old-fashioned magnetic tape. You can cut the tape so that a single instant of a recording can be physically separated. While separated, you can pass anything you want through the gap, but when you glue the tape back together, the recording is seamless. There’s only a before and after while the tape is cut and separated.

It’s easy to do that with tape, but a bit harder to do it with a beam of light. The key to the process is what’s being termed a split time lens, which is matched with a dispersive medium. When activated, the lens takes the light that comes before the point of cloaking and shifts it to bluer wavelengths, which travel faster through the dispersive medium than the base speed of the light in the same medium. At the cloak point, the lens switches, shifting the light beam to longer, redder wavelengths. These travel through the dispersive medium more slowly.

(via Optical setup helps researchers hide an event from time)

New nanostructured glass for imaging and recording

University of Southampton researchers have developed new nano-structured glass, turning it into new type of computer memory, which has applications in optical manipulation and will significantly reduce the cost of medical imaging.

In a paper entitled Radially polarized optical vortex converter created by femtosecond laser nanostructuring of glass published in Applied Physics Letters, a team led by Professor Peter Kazansky at the University’s Optoelectronics Research Centre, describe how they have used nano-structures to develop new monolithic glass space-variant polarisation converters. These millimetre-sized devices change the way light travels through glass, generating ‘whirlpools’ of light that can then be read in much the same way as data in optical fibres. This enables more precise laser material processing, optical manipulation of atom-sized objects, ultra-high resolution imaging and potentially, table-top particle accelerators. Information can be written, wiped and rewritten into the molecular structure of the glass using a laser.

(via University of Southampton)

Space-Time Cloak Possible, Could Make Events Disappear?

Material would adjust speed of light to hide actions, physicists say.

It’s no illusion: Science has found a way to make not just objects but entire events disappear, experts say.

According to new research by British physicists, it’s theoretically possible to create a material that can hide an entire bank heist from human eyes and surveillance cameras.

“The concepts are basically quite simple,” said Paul Kinsler, a physicist at Imperial College London, who created the idea with colleagues Martin McCall and Alberto Favaro.

Unlike invisibility cloaks—some of which have been made to work at very small scales—the event cloak would do more than bend light around an object.

(Also see “Acoustic ‘Invisibility’ Cloaks Possible, Study Says.”)

Instead this cloak would use special materials filled with metallic arrays designed to adjust the speed of light passing through.

In theory, the cloak would slow down light coming into the robbery scene while the safecracker is at work. When the robbery is complete, the process would be reversed, with the slowed light now racing to catch back up.

If the “before” and “after” visions are seamlessly stitched together, there should be no visible trace that anything untoward has happened. One second there’s a closed safe, and the next second the safe has been emptied.

(via National Geographic)

Laser is produced by a living cell

A single living cell has been coaxed into producing laser light, researchers report in Nature Photonics.

The technique starts by engineering a cell that can produce a light-emitting protein that was first obtained from glowing jellyfish.

Flooding the resulting cells with weak blue light causes them to emit directed, green laser light.

The work may have applications in improved microscope imaging and light-based therapies.

Laser light differs from normal light in that it is of a narrow band of colours, with the light waves all oscillating together in synchrony.

Most modern forms use carefully engineered solid materials to produce lasers in everything from supermarket scanners to DVD players to industrial robots.

(via BBC News)

Twisty light tells left-handed molecules from right

A super twisty beam of light has been created that can distinguish between left and right-handed molecules with unprecedented precision.

Molecules often come in mirror images that can have different properties, and researchers take advantage of this “chirality” to design new drugs. They sort left from right versions using circularly polarised light, whose electric field corkscrews through space in a left or right-handed direction. Unfortunately, the technique often fails when the light’s coils are bigger than the molecules themselves.

Now Yiqiao Tang and Adam Cohen of Harvard University have created “superchiral” light that twists very tightly in places.

(via New Scientist)

 ’We’ve all been taught that this doesn’t happen’

A dramatic and surprising magnetic effect of light discovered by University of Michigan researchers could lead to solar power without traditional semiconductor-based solar cells.

The researchers found a way to make an “optical battery,” said Stephen Rand, a professor in the departments of Electrical Engineering and Computer Science, Physics and Applied Physics.

In the process, they overturned a century-old tenet of physics.

“You could stare at the equations of motion all day and you will not see this possibility. We’ve all been taught that this doesn’t happen,” said Rand, an author of a paper on the work published in the Journal of Applied Physics. “It’s a very odd interaction. That’s why it’s been overlooked for more than 100 years.”

Light has electric and magnetic components. Until now, scientists thought the effects of the magnetic field were so weak that they could be ignored. Rand and his colleagues found that at the right intensity, when light is traveling through a material that does not conduct electricity, the light field can generate magnetic effects that are 100 million times stronger than previously expected. Under these circumstances, the magnetic effects develop strength equivalent to a strong electric effect.

“This could lead to a new kind of solar cell without semiconductors and without absorption to produce charge separation,” Rand said. “In solar cells, the light goes into a material, gets absorbed and creates heat. Here, we expect to have a very low heat load. Instead of the light being absorbed, energy is stored in the magnetic moment. Intense magnetization can be induced by intense light and then it is ultimately capable of providing a capacitive power source.”

What makes this possible is a previously undetected brand of “optical rectification,” says William Fisher, a doctoral student in applied physics. In traditional optical rectification, light’s electric field causes a charge separation, or a pulling apart of the positive and negative charges in a material. This sets up a voltage, similar to that in a battery. This electric effect had previously been detected only in crystalline materials that possessed a certain symmetry.

(via Michigan Today)

GRIN plasmonics: A practical path to superfast computing, invisibility carpet-cloaking devices

Berkeley Lab researchers have carried out the first experimental demonstration of GRIN plasmonics, a hybrid technology that opens the door to a wide range of exotic applications in optics, including superfast photonic computers, ultra-powerful optical microscopes and “invisibility” carpet-cloaking devices.

They said it could be done and now they’ve done it. What’s more, they did it with a GRIN. A team of researchers with the U.S. Department of Energy (DOE)’s Lawrence Berkeley National Laboratory (Berkeley Lab) and the University of California, Berkeley, have carried out the first experimental demonstration of GRIN – for gradient index – plasmonics, a hybrid technology that opens the door to a wide range of exotic optics, including superfast computers based on light rather than electronic signals, ultra-powerful optical microscopes able to resolve DNA molecules with visible light, and “invisibility” carpet-cloaking devices.

Working with composites featuring a dielectric (non-conducting) material on a metal substrate, and “grey-scale” electron beam lithography, a standard method in the computer chip industry for patterning 3-D surface topographies, the researchers have fabricated highly efficient plasmonic versions of Luneburg and Eaton lenses. A Luneburg lens focuses light from all directions equally well, and an Eaton lens bends light 90 degrees from all incoming directions.

“This past year, we used computer simulations to demonstrate that with only moderate modifications of an isotropic dielectric material in a dielectric-metal composite, it would be possible to achieve practical transformation optics results,” says Xiang Zhang, who led this research. “Our GRIN plasmonics technique provides a practical way for routing light at very small scales and producing efficient functional plasmonic devices.”

GRIN plasmonics combines methodologies from transformation optics and plasmonics, two rising new fields of science that could revolutionize what we are able to do with light. In transformation optics, the physical space through which light travels is warped to control the light’s trajectory, similar to the way in which outer space is warped by a massive object under Einstein’s relativity theory. In plasmonics, light is confined in dimensions smaller than the wavelength of photons in free space, making it possible to match the different length-scales associated with photonics and electronics in a single nanoscale device. 

World’s first microlaser emitting in 3-D

If this is true, this is huge.

Versatile electronic gadgets should employ a number of important criteria: small in size, quick in operation, inexpensive to fabricate, and deliver high precision output. A new microlaser, developed at the Jožef Stefan Institute in Ljubljana, Slovenia embodies all these qualities. It is small, tunable, cheap, and is essentially the world’s first practical three-dimensional laser

As described in Optics Express, an open-access journal published by the Optical Society (OSA), Slovenian scientists Matjaž Humar and Igor Muševič have developed a microdroplet 3-D laser system in which laser light shines forth in all directions from dye molecules lodged within spherical drops of helical molecules dispersed in a liquid solution.

This is the first practical 3-D laser ever produced,” says Muševič, who expects that the microdroplet lasers, which can be made by the millions in seconds, will be used in making arrays of coherent light emitters. These will be handy for a variety of imaging purposes, for example “internal-source holography.” Here a 3-D laser would be embedded inside the object which is to be imaged; light coming directly from the source interferes with the light scattered by the surroundings. A three-dimensional image of the object can then be reconstructed from the interference pattern.

(Source: opticsinfobase.org)

Image credit: Thomas Scheidl, et al. and Google Earth, ©2008 Google, Map Data ©Tele Atlas.

Physicists close two loopholes while violating local realism

Physicists performed a Bell experiment between the islands of La Palma and Tenerife at an altitude of 2,400 m. Starting with an entangled pair of photons, one photon was sent 6 km away to Alice, and the other photon was sent 144 km away to Bob. The physicists took several steps to simultaneously close the locality loophole and freedom-of-choice loophole. 

The physicists, who belong to the group of Rupert Ursin and Anton Zeilinger and were all at either the Austrian Academy of Sciences in Vienna or the University of Vienna when performing the experiments in 2008, have published their study on the new Bell test in the early edition of PNAS. As they explain in their study, local realism consists of both realism – the view that reality exists with definite properties even when not being observed – and locality – the view that an object can only be influenced by its immediate surroundings. If a Bell test shows that a measurement of one object can influence the state of a second, distant object, then local realism has been violated.

“The question of whether nature can be understood in terms of classical concepts and explained by local realism is one of the deepest in physics,” coauthor Johannes Kofler told PhysOrg.com. “Getting Bell tests as loophole-free as possible and confirming quantum mechanics is therefore an extremely important task. From a technological perspective, certain protocols of quantum cryptography (which is entering the market at the moment) are based on entanglement and violation of Bell’s inequality. This so-called ‘unconditional security’ must in practice take care of the loopholes in Bell tests.”

The physicists explained that, in experimental tests, there are three loopholes that allow observed violations of local realism to still be explained by local realistic theories. These three loopholes can involve locality (if there is not a large enough distance separating the two objects at the time of measurement), the freedom to choose any measurement settings (so measurement settings may be influenced by hidden variables, or vice versa), and fair sampling (a small fraction of observed objects may not accurately represent all objects due to detection inefficiencies).

Previous experiments have closed the first loophole, which was done by ensuring a large spatial separation between the two objects (in this case, two quantum mechanically entangled photons) so that measurements of the objects could not be influenced by each other. Special relativity then ensures that the objects cannot influence each other, since no physical signals can travel faster than the speed of light. In these experiments, classically unexplainable correlations were still observed between the objects, indicating a violation of local realism. (The fair sampling loophole was closed in another earlier experiment using ions, where large detection efficiencies can be reached.) 

In the current experiment, the physicists simultaneously ruled out both the locality loophole and the freedom-of-choice loophole. They performed a Bell test between the Canary Islands of La Palma and Tenerife, located 144 km apart. On La Palma, they generated pairs of entangled photons using a laser diode. Then they locally delayed one photon in a 6-km-long optical fiber (29.6-microsecond traveling time) and sent it to one measurement station (Alice), and sent the other photon 144 km away (479-microsecond traveling time) through open space to the other measurement station (Bob) on Tenerife.

The scientists took several steps to close both loopholes. For ruling out the possibility of local influence, they added a delay in the optical fiber to Alice to ensure that the measurement events there were space-like separated from those on Tenerife such that no physical signal could be interchanged. Also, the measurement settings were randomly determined by quantum random number generators.

To close the freedom-of-choice loophole, the scientists spatially separated the setting choice and the photon emission, which ensured that the setting choice and photon emission occurred at distant locations and nearly simultaneously (within 0.5 microseconds of each other). The scientists also added a delay to Bob’s random setting choice. These combined measures eliminated the possibility of the setting choice or photon emission events influencing each other. But again, despite these measures, the scientists still detected correlations between the separated photons that can only be explained by quantum mechanics, violating local realism.

More information: Thomas Scheidl, et al. “Violation of local realism with freedom of choice.” 19708-19713, PNAS, November 16, 2010, vol. 107, no. 46. DOI:10.1073/pnas.1002780107

A classical diagram of a krypton atom (background) shows its 36 electrons arranged in shells. Researchers have measured oscillations of quantum states (foreground) in the outer orbitals of an ionized krypton atom, oscillations that drive electron motion. Credit: courtesy Lawrence Berkeley National Laboratory

For the First Time Ever, Scientists Watch an Atom’s Electrons Moving in Real Time

August 4, 2010 by Paul Preuss

An international team of scientists led by groups from the Max Planck Institute of Quantum Optics (MPQ) in Garching, Germany, and from the U.S. Department of Energy’s Lawrence Berkeley National Laboratory and the University of California at Berkeley has used ultrashort flashes of laser light to directly observe the movement of an atom’s outer electrons for the first time.

Through a process called attosecond absorption spectroscopy, researchers were able to time the oscillations between simultaneously produced quantum states of valence electrons with great precision. These oscillations drive electron motion.

“With a simple system of krypton atoms, we demonstrated, for the first time, that we can measure transient absorption dynamics with attosecond pulses,” says Stephen Leone of Berkeley Lab’s Chemical Sciences Division, who is also a professor of chemistry and physics at UC Berkeley. “This revealed details of a type of electronic motion - coherent superposition - that can control properties in many systems.”

Leone says an example of the importance of coherent dynamics is its crucial role in photosynthesis, citing recent work by the Graham Fleming group at Berkeley. “The method developed by our team for exploring coherent dynamics has never before been available to researchers. It’s truly general and can be applied to attosecond electronic dynamics problems in the physics and chemistry of liquids, solids, biological systems, everything.”

The team’s demonstration of attosecond absorption spectroscopy began by first ionizing krypton atoms, removing one or more outer valence electrons with pulses of near-infrared laser light that were typically measured on timescales of a few femtoseconds (a femtosecond is 10^-15 second, a quadrillionth of a second). Then, with far shorter pulses of extreme ultraviolet light on the 100-attosecond timescale (an attosecond is 10^-18 second, a quintillionth of a second), they were able to precisely measure the effects on the valence electrons.

The results of the pioneering measurements performed at MPQ by the Leone and Krausz groups and their colleagues are reported in the August 5 issue of the journal Nature.

Parsing the fine points of valence electron motion

Valence electrons control how atoms bond with other atoms to form molecules or crystal structures, and how these bonds break and reform during chemical reactions. Changes in molecular structures occur on the scale of many femtoseconds and have often been observed with femtosecond spectroscopy, in which both Leone and Krausz are pioneers.

                     
Enlarge

In krypton’s single ionization state, quantum oscillations in the valence shell cycled in a little over six femtoseconds. Attosecond pulses probed the details (black dots), filling the gap in the outer orbital with an electron from an inner orbital, and sensing the changing degrees of coherence between the two quantum states thus formed (below). Credit: Courtesy Lawrence Berkeley National Laboratory

Zhi-Heng Loh of Leone’s group at Berkeley Lab and UC Berkeley worked with Eleftherios Goulielmakis of Krausz’s group to perform the experiments at MPQ. By firing a femtosecond pulse of infrared laser light through a chamber filled with krypton gas, atoms in the path of the beam were ionized by the loss of one to three valence electrons from their outermost shells.

The experimenters separately generated extreme-ultraviolet attosecond pulses (using the technique called “high harmonic generation”) and sent the beam of attosecond probe pulses through the krypton gas on the same path as the near-infrared pump pulses.

By varying the time delay between the pump pulse and the probe pulse, the researchers found that subsequent states of increasing ionization were being produced at regular intervals, which turned out to be approximately equal to the time for a half cycle of the pump pulse. (The pulse is only a few cycles long; the time from crest to crest is a full cycle, and from crest to trough is a half cycle.)

“The femtosecond pulse produces a strong electromagnetic field, and ionization takes place with every half cycle of the pulse,” Leone says. “Therefore little bursts of ions are coming out every half cycle.”

Although expected from theory, these isolated bursts were not resolved in the experiment. The attosecond pulses, however, could precisely measure the production of the ionization, because ionization - the removal of one or more electrons - leaves gaps or “holes,” unfilled orbitals that the ultrashort pulses can probe.

                      
Enlarge

Femtosecond-scale pulses were fired to ionize krypton atoms (wide beam). Separately created attosecond-scale pulses (narrow beam) were absorbed by the krypton atoms. Spectroscopy mapped the precise timing of the oscillation between quantum states thus created. Credit: Courtesy Lawrence Berkeley National Laboratory

The attosecond pulses do so by exciting electrons from lower energy orbitals to fill the gap in krypton’s outermost orbital - a direct result of the absorption of the transient attosecond pulses by the atoms. After the “long” femtosecond pump pulse liberates an electron from the outermost orbital (designated 4p), the short probe pulse boosts an electron from an inner orbital (designated 3d), leaving behind a hole in that orbital while sensing the dynamics of the outermost orbital.

In singly charged krypton ions, two electronic states are formed. A wave-packet of electronic motion is observed between these two states, indicating that the ionization process forms the two states in what’s known as quantum coherence.

Says Leone, “There is a continual ‘orbital flopping’ between the two states, which interfere with each other. A high degree of interference is called coherence.” Thus when the attosecond probe pulse clocks the outer valence orbitals, it is really clocking the high degree of coherence in the orbital motion caused by ionization.

Indispensable attosecond pulses

“When the bursts of ions are made quickly enough, with just a few cycles of the ionization pulse, we observe a high degree of coherence,” Leone says. “Theoretically, however, with longer ionization pulses the production of the ions gets out of phase with the period of the electron wave-packet motion, as our work showed.”

So after just a few cycles of the pump pulse, the coherence is washed out. Thus, says Leone, “Without very short, attosecond-scale probe pulses, we could not have measured the degree of coherence that resulted from ionization.”

The physical demonstration of attosecond transient absorption by the combined efforts of the Leone and Krausz groups and their colleagues will, in Leone’s words, “allow us to unravel processes within and among atoms, molecules, and crystals on the electronic timescale” - processes that previously could only be hinted at with studies on the comparatively languorous femtosecond timescale.

More information: “Real-time observation of valence electron motion,” by Eleftherios Goulielmakis, Zhi-Heng Loh, Adrian Wirth, Robin Santra, Nina Rohringer, Vladislav Yakovlev, Sergey Zherebtsov, Thomas Pfeifer, Abdallah Azzeer, Matthias Kling, Stephen Leone, and Ferenc Krausz, appears in the 5 August 2010 issue of the journal Nature.

Provided by Lawrence Berkeley National Laboratory (news : web)

[Source: Phys.org]

physicsphysics:

unknownskywalker:

Rainbow trapping in light pulses

Over the past decade, scientists have succeeded in slowing pulses of light down to zero speed by letting separate frequency components of the pulse conspire in such a way that a receptive medium through which the pulse is passing can host the information stored in the pulse but not actually absorb the pulse’s energy.

Trapping light means either stopping the light temporally or confining the light in space. Scientists have also been able to trap a light pulse in a tiny enclosure bounded by metamaterials; the light pulse retains its form but is kept from moving away.

Previously only light of a short frequency interval could be trapped in this way. Now a group of scientists at Nanjing University in China have shown how a rather wide spectrum of light — a rainbow of radiation — can be trapped in a single structure.

They propose to do this by sending the light rays into a self-similar-structured dielectric waveguide (SDW) — essentially a light pipe with a cladding of many layers.

Light of different colors propagates separately in different layers, each being tailored by color. They replace the conventional periodically-spaced, identical cladding layers with a non-periodic, self-similar pattern of successive layers made from two materials, A and B, with slightly different thicknesses and indices of refraction.

Self similarity, in this case, means that the pattern of layers successively outwards would be as follows: A, AB, ABBA, ABBABAAB, and so forth.

The effect might be applied for on-chip spectroscopy or on-chip ‘color-sorters.’ It might also be used for photon processing and information transport in optical communications and quantum computing.” Scientists expect that they can create trapped “rainbows” for light in many portions of the electromagnetic spectrum, including microwave, terahertz, infrared, and even visible.

Image: Different frequency components of a guided wave packet stop at correspondingly different thicknesses inside a tapered left-handed heterostructure (LHH). [+]

Source: PhysOrg.com, Nature

Holography without Lasers: Hand-drawn Holograms [SCIENCE HOBBYIST]

“Giant-fringe holography? nondiffractive holograms? single-fringe holograms? scratch holograms? sandpaper holograms? abrasion holograms? scratch-o-grams? holosketches? wire-brush holograms? car-hood holograms? phonograph holograms? incoherent holography? Aha: chatoyant holography!

I’ve stumbled across a technique for drawing holograms directly upon a plastic plate by hand. It sounds impossible, but I’ve been sitting on the living room sofa making holographic images of floating polyhedra, words, 3D star fields, opaque objects, etc. No laser, no isolation table, no darkroom, no expensive film plates. This takes nothing more than a compass and some scraps of plexiglas. Too cool, if I say so myself!”