From Rehovoth Instruments to Elop

English
Prof. Joe Jaffe
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
In the 1960s, Prof. Joe Jaffe, a founder of optics research at Weizmann, opened a company to manufacture scientific instruments. Called Rehovoth Instruments Ltd., it was housed in a shop that Jaffe rented next to the Institute.
 

Application

 
Rehovoth Instruments eventually evolved into Elop, Electro-Optics Industries Ltd. in Kiryat Weizmann, today the leading company in Israel and one of the most prominent in the world in the field of electro-optics. It has a wide-ranging production program; many of the products are based on the findings and inventions of Institute researchers.
 
Prof. Joe Jaffe
Space & Physics
English
  • Joe Jaffe
  • Optical physics

Innovative Imaging System for the Detection of Breast Cancer

English
Prof. Emeritus Ephraim Frei
 
Prof. Emeritus Ephraim Frei, a founder of electronics research at the Weizmann Institute in the 1950s, spent several decades studying the effects of magnetic fields on living tissues.
 

Application

 
An innovative breast imaging system, T-Scan, developed on the basis of Frei's research, is manufactured and distributed by TransScan Medical. In 1999 the FDA approved T-Scan for the detection of breast cancer, citing it as a “significant medical device breakthrough.” Research is under way to apply T-Scan to the detection of skin cancer.
 
Prof. Emeritus Ephraim Frei
Space & Physics
English
  • Breast cancer
  • Ephraim Frei
  • Physics

How Can We Get to Know a Single Photon, Atom or Molecule?

English

 

 

Structure of GroEL, a barrel-shaped molecular machine found in bacterial cells that helps proteins fold; from the lab of Profs. Gilad Haran and Amnon Horowitz
 

 

 

 

Particles or molecules, like people, appear differently when seen as individuals rather than as part of a group. Identical protein molecules, for instance, can have idiosyncratic pathways of folding. Only by looking at them one at a time can one begin to tease out the most basic behavior of these molecules. Ensemble studies may yield averages – speed of motion, for example – that hide significant facts; some molecules may actually have two different means of locomotion, neither of them at the average speed.

Single molecules can also perform functions that larger bits of matter can’t. For example, signals emitted by individual molecules can help map nanoparticle surfaces and report on their interactions with light, opening up new possibilities for applications in nanotechnology. And the role of solitary molecules in electronics is likely to grow as the size of components continues to shrink. To understand how these will function in future devices, scientists are studying how electrons move through molecules and how changes in a molecule’s structure can alter the way it conducts electricity.

In the Faculty of Chemistry, Prof. Gilad Haran uses a wide variety of optical techniques to uncover the dynamics of different molecules, both biological and non-biological. With an optical microscope fitted with lasers and detectors capable of recording single photons, as well as fast cameras, he can observe a molecule’s progress down to the nanosecond and nanometer. Dr. Oren Tal captures single molecules in a tiny break in a sort of spring-loaded wire. By precisely manipulating the distance between the edges of the break, Tal is able to stretch and tilt molecules, changing their conductivity. The basic principles he is uncovering may one day help in designing a new generation of electronic devices.
 
(l-r) Prof. Gilad Haran and Dr. Oren Tal
 
 

 

Prof. Gilad Haran is Director of the Solo Dwek and Maurizio Dwek Research School of Chemical Science; his research is supported by the Carolito Stiftung.

Dr. Oren Tal is the incumbent of the Alvin and Gertrude Levine Career Development Chair.

 
 
Structure of GroEL, a barrel-shaped molecular machine found in bacterial cells that helps proteins fold; from the lab of Profs. Gilad Haran and Amnon Horowitz
Chemistry
English
  • Chemical Physics
  • Electronic devices
  • Gilad Haran
  • Oren Tal

Does God Play Dice?

English

Diagram of a hyperbolic surface with infinite genus, from the research of Prof. Omri Sarig

 
 
 
 
God does not play dice with the Universe,” was Einstein’s famous retort to the uncertainty principle – nowadays one of the basic tenets of modern physics. Certain aspects of material existence do seem truly random; they lack order and can never be completely predicted. Scientists in the Faculty of Mathematics and Computer Science investigate various aspects of randomness and use their findings to develop sophisticated research tools and information security protocols.
 
Randomness has always been seen as an impartial, unpredictable method of decision making. But is there such a thing as true randomness? According to Prof. Oded Goldreich, the question shouldn’t be whether a phenomenon is truly random, but whether it appears to us to be random, and whether we are capable of generating phenomena that appear random even though they are not. Such pseudo-random systems are used to preserve privacy and protect digital information, as well as providing research tools for scientists in many fields.
 
Prof. Omri Sarig researches chaotic systems. Due to their inherent instability, even simple laws (e.g., the laws of motion or Newton’s laws) can produce unexpected behavior. The evolution of such systems over time cannot be predicted, even though they act according to deterministic laws, and thus their behavior appears to be arbitrary and unpredictable.
 
Prof. Gideon Schechtman uses randomness to prove the existence of simple, multidimensional structures that are hidden as substructures within larger, complex formations. The basic example of such an application of randomness was discovered by Prof. Aryeh Dvoretzky, seventh president of the Weizmann Institute, some fifty years ago.
 
Profs. Omri Sarig, Gideon Schechtman and Oded Goldreich
 

 

 

Prof. Oded Goldreich’s research is supported by Walmart. Prof. Goldreich is the incumbent of the Meyer W. Weisgal Professorial Chair.

Prof. Omri Sarig’s research is supported by the Carolito Stiftung. Prof. Sarig is the incumbent of the Theodore R. Racoosin Chair.

Prof. Gideon Schechtman is the incumbent of the William Petschek Chair of Mathematics.

 
 
Diagram of a hyperbolic surface with infinite genus, from the research of Prof. Omri Sarig
Space & Physics
English
  • Annual Report 2010
  • Gideon Schechtman
  • Oded Goldreich
  • Omri Sarig

An Explosive Pair

English

 

Not all explosions are created equal: It’s as true for film effects as it is for the stars. Yet, until now, scientists had only observed two basic kinds of exploding stars, known as supernovae. Now, scientists at the Weizmann Institute of Science, in collaboration with others around the world, have identified a third type of supernova. Their findings appeared this week in Nature.

 

The first two types of supernova are either hot, young giants that go out in a violent display as they collapse under their own weight, or old, dense white dwarves that blow up in a thermonuclear explosion. The new supernova appeared in telescope images in early January, 2005 and scientists, seeing that it had recently begun the process of exploding, started collecting and combining data from different telescope sites around the world, measuring both the amount of material thrown off in the explosion and its chemical makeup. But Dr. Avishay Gal-Yam, Hagai Perets, (now at the Harvard-Smithsonian Center for Astrophysics), Iair Arcavi and Michael Kiewe of the Weizmann Institute’s Faculty of Physics, together with Paolo Mazzali of the Max-Planck Institute for Astrophysics, Germany, and the Scuola Normale Superiore, Pisa, and INAF/Padova Observatory in Italy, Prof. David Arnett from the University of Arizona, and researchers from across the USA, Canada, Chile and the UK, soon found that the new supernova did not fit either of the known patterns.

 

On the one hand, the amount of material hurled out from the supernova was too small for it to have come from an exploding giant. In addition, its location, distant from the busy hubs where new stars form, implied it was an older star that had had time to wander off from its birthplace. On the other hand, its chemical makeup didn’t match that commonly seen in the second type. ‘It was clear,’ says the paper’s lead author Perets, ‘that we were seeing a new type of supernova.’ The scientists turned to computer simulations to see what kind of process could have produced such a result.

 

The common type of exploding white dwarf (a type Ia supernova) is mainly made up of carbon and oxygen, and the chemical composition of the ejected material reflects this. The newly-discovered supernova had unusually high levels of the elements calcium and titanium; these are the products of a nuclear reaction involving helium, rather than carbon and oxygen. ‘We’ve never before seen a spectrum like this one,’ says Mazzali. ‘It was clear that the unique chemical composition of this explosion held an important key to understanding it.’ Where did the helium come from? The simulations suggest that a pair of white dwarves are involved; one of them stealing helium from the other. When the thief star’s helium load rises past a certain point, the explosion occurs. ‘The donor star is probably completely destroyed in the process, but we’re not quite sure about the fate of the thief star,’ says Gal-Yam.

 

The scientists believe that several other previously observed supernovae may fit this pattern. In fact, these relatively dim explosions might not be all that rare; if so, their occurrence could explain some puzzling phenomena in the universe. For example, almost all the elements heavier than hydrogen and helium have been created in, and dispersed by supernovae; the new type could help explain the prevalence of calcium in both the universe and in our bodies. It might also account for observed concentrations of particles called positrons in the center of our galaxy. Positrons are identical to electrons, but with an opposite charge, and some have hypothesized that the decay of yet unseen ‘dark matter’ particles may be responsible for their presence. But one of the products of the new supernova is a radioactive form of titanium that, as it decays, emits positrons. ‘Dark matter may or may not exist,’ says Gal-Yam, ‘but these positrons are perhaps just as easily accounted for by the third type of supernova.’


Dr. Avishay Gal-Yam’s research is supported by the Nella and Leon Benoziyo Center for Astrophysics; the Yeda-Sela Center for Basic Research; the Peter and Patricia Gruber Awards; the Legacy Heritage Fund Program of the Israel Science Foundation; the Minerva Foundation with funding from the Federal German Ministry for Education and Research; and Miel de Botton Aynsley, UK.


The Weizmann Institute of Science in Rehovot, Israel, is one of the world's top-ranking multidisciplinary research institutions. Noted for its wide-ranging exploration of the natural and exact sciences, the Institute is home to 2,600 scientists, students, technicians and supporting staff. Institute research efforts include the search for new ways of fighting disease and hunger, examining leading questions in mathematics and computer science, probing the physics of matter and the universe, creating novel materials and developing new strategies for protecting the environment.

 

Weizmann Institute news releases are posted on the World Wide Web at http://wis-wander.weizmann.ac.il/, and are also available at http://www.eurekalert.org/.

Space & Physics
English
  • Astrophysics
  • Avishay Gal-Yam
  • Computer simulation
  • Positron
  • Supernova

In the Eye of the Vortex

English

Prof. Eli Zeldov probes superconductor physics

Visitors to the lab of Prof. Eli Zeldov in the Weizmann Institute’s Condensed Matter Physics Department are often treated to the sight of a magnet floating in midair. The trick? Beneath the magnet, a superconductor – a chunk of copper oxide-laced ceramic, cooled to -196°C (-321°F) repels its magnetic field. This feat convinces most visitors that superconductors – materials able to conduct electricity with zero resistance – are super cool.

 
But it’s not nifty party tricks that make superconductivity such a buzz word these days. The complex interaction between superconducting materials and magnetic fields drives not only the levitation of Zeldov’s modest magnet but also entire trains. From super-fast trains that glide nearly frictionlessly over magnetic tracks at over 600 kilometers per hour to electronic filters associated with cell phone towers to MRI machines, superconductor applications are surprisingly diverse. “Although a lot is known about superconducting materials, there are still many gaps in our understanding as to why and how these substances superconduct in the first place,” says Zeldov.
 
What scientists do know about superconductors is that magnetic fields can entirely erase the superconductive properties of a material. Superconducting materials, however, often “defend” themselves by repelling external magnetic fields they are exposed to – a phenomenon known as the Meissner effect.
 
Yet magnetic fields are able to partially penetrate certain types of superconductors; the penetrating magnetic field breaks up into small “islands,” which take the form of tubular whirlpools called vortices. When this happens, superconductivity is maintained outside the vortices, even as it’s destroyed within them. Such vortices pose a problem: They move around through the material in the presence of an electric current and this movement results in resistance. Vortices can thus render a superconductor little better than conventional copper wiring. To impede vortex movement, scientists have devised methods for pinning them to carefully planned defects within the superconducting material, allowing the current to flow more efficiently.
 
Since the majority of superconductor applications involve magnetic fields, an in-depth understanding of vortex physics has far-reaching practical implications. A team of scientists at Stanford University, including Weizmann alumnus Dr. Ophir Auslaender, who took a leading role in the research, and Zeldov developed an innovative tool that has allowed scientists to get closer to vortices than ever before. In a paper published in Nature Physics, they provided an updated analysis of the microscopic defects at the root of vortex pinning, as well as of vortex structure and dynamics.
 
The novel method employs a magnetic force microscope; the scientists use its miniscule magnetized tip not only to measure the physical properties of individual vortices, but also to manually move the vortices around in the superconducting material. Thus, the Stanford and Weizmann scientists demonstrated how manipulating a single vortex can be used to probe both the interactions of vortices and the structure of pinning defects within the material. Understanding vortex interactions on such a small scale is invaluable for building the “big picture” of superconductor behavior needed for the effective application of superconductor technology.
 
The microscope study yielded some surprising results regarding one of the most studied superconducting materials to date – yttrium barium copper oxide (YBCO). This material is among the so-called “high-temperature” superconductors, which lose their resistance at temperatures that, while still inhumanly low, are much higher than the near-absolute-zero temperatures needed for most superconductors. This makes them useful candidates for many applications. Probing single vortices showed that the internal structure of YBCO is much more varied than previously thought, and there were new revelations about vortex dynamics, as well. For instance, by wiggling a vortex while dragging it, the team found that it can be pulled much farther than usual – by an order of magnitude. This finding may help to explain vortex behavior in the presence of alternating currents.
 
This method has an advantage over most local probing techniques, which only give information about the immediate surface of the superconductor as opposed to what lies beneath. The results of this research have given scientists quite a bit of material for further investigation and modeling is underway to help interpret them. Yet despite the advantages of the technology, this method of measurement is intrusive, as the magnetic tip interacts with vortices in the sample. Zeldov’s team at Weizmann is currently developing a new non-intrusive method for measuring individual vortices – one that will hopefully “levitate” an understanding of superconductivity to a higher plane.

Prof. Eli Zeldov is the incumbent of the David and Inez Myers Professorial Chair.
 
Prof. Eli Zeldov. Pinning down superconductivity
Space & Physics
English
  • Condensed Matter Physics
  • Eli Zeldov
  • Magnetic field
  • Superconductor

Shorter and Faster

English
 
Dr. Nirit Dudovich and Dror Shafir. Ultra-fast lasers freeze molecular action

 

 

 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
Like top athletes, leading scientists continually test the limits of human ability. While an athlete trains to break the 100-meter sprint record, for instance, a scientist might be found attempting to break the record for catching sight of the fastest movements known, such as those of the electrons moving inside molecules and atoms. For years scientists had referred to these movements as instantaneous. Are they truly instantaneous? Or has the available scientific equipment simply not been advanced enough to detect electrons in the act of getting from one place to another? By pushing the bounds of laser optic technology, physicists today are beginning to reveal electron movements taking place within unimaginably short timeframes.
 
Ultrafast pulses of laser light replace camera shutters when filming the very fastest activities; for instance, chemical reactions in which molecules break apart into smaller molecules. Like the fast-shutter cameras used to capture still shots of a basketball player in mid-dunk, the flashes of laser light serve to “freeze” molecular actions at various stages.
 
The faster the natural process, the shorter and faster the laser pulses must be to capture it on film. For a number of years, the fastest lasers available produced flashes down to the length of a femto-second – a millionth of a billionth of a second. This is rapid enough to observe many molecular processes. But, the movements of the electrons in a molecule are faster still and the technology was not up to capturing them.
 
“The limits on the capabilities of lasers stem from a basic, physical restriction,” says Dr. Nirit Dudovich, who joined the Weizmann Institute’s Physics of Complex Systems Department two years ago. “The single period of a light wave determines the lower limit for the duration of a laser pulse. A femtosecond pulse is the shortest that one can get from wavelengths in the visible range.”
 
Unwilling to stop pushing the physical boundaries, scientists have found a way to overcome this. An experiment with this method begins with powerful laser pulses lasting just a few femtoseconds aimed at a molecule, “tearing” out one of its electrons – a quantum phenomenon called tunneling. The electron, freed from its orbit around the molecule, takes a short “trip.” This escape is shortlived, and the electron soon returns to its home molecule. As the electron slips back into place, a photon (light particle) is emitted. The entire process evolves during less than one optical cycle of visible light; the duration of the emitted light is around an attosecond (a billionth of a billionth of a second).
 
This ability to capture the movements of electrons circling atoms or molecules in “freeze frames” has ushered in a new field of research. But Dudovich has taken that research a step further: “Why use lasers to trace other molecules, I thought, when so much could be learned about the process through the interaction of light with the molecules on which the laser itself is based?” In other words, she’s turned the camera back on itself to image the basic process in which photons are emitted and electrons change position.
 
Dudovich and her research team have been exploring ways to control the direction of the tunneling electrons so as to get them to reenter the molecule or atom from different angles. Like medical imaging that builds a three-dimensional picture from a series of “slices,” such an approach could give researchers an unprecedented view of molecules and molecular processes. In a paper that recently appeared in Nature Physics, the researchers demonstrated that by changing the polarization of the beam used to tear the electron from the atom, one can reroute the electron’s path and direct the angle of its reentry.
 
With this method, Dudovich and her team succeeded in characterizing the distribution of electrons in an atom. “In the future,” she says, “our goal is to measure the time, as well, and to integrate time with location. In other words, we’ll be able to produce a sort of movie that records electrons moving through various processes and chemical reactions as they take place.”
 
Dr. Nirit Dudovich’s research is supported by the Chais Family Fellows Program for New Scientists; the Lord Sieff of Brimpton Memorial Fund; the IPA Prize for a Promising New Scientist funded by Dana and John R. Burgess and Stacey and Gregg Steinberg; the estate of Jeanne K. Goldstein; the estate of Esther Ragosin; the estate of Julius and Hanna Rosen; the Charles and Julia Wolf Philanthropic Fund; and the Wolfson Family Charitable Trust.
 
Dr. Nirit Dudovich and Dror Shafir. Ultra-fast lasers freeze molecular action
Space & Physics
English
  • Laser
  • Nirit Dudovich
  • Physics of Complex Systems

A Super Surprise

English
 

Prof. Dan Shahar and Maoz Ovadia. Superconductor's twin

 

 

 

 

 

 

 

 

 

 

 

 

Tension between opposites is one of the pillars of human culture – from the evil counterparts of the good and all-powerful God in Western religions to Through the Looking Glass, in which Alice enters a world that is the exact opposite of the one in which we live.

The natural world is filled with opposing pairs: molecular “twins” that are identical in composition but oriented in diametrically opposite directions, like left and right hands, or elementary anti-matter particles that equal their matter counterparts in everything except their opposite charge. Still, Prof. Dan Shahar of the Condensed Matter Physics Department was surprised to discover a duality phenomenon that no one had observed before.
 
Shahar studies superconductivity, which takes place when a conductor – a metal or a ceramic material – is cooled to an extremely low temperature, such that its resistance drops to zero. When a material loses all its resistance, it allows electrical current to flow forever without charging it any “commission.”
 
Superconductivity occurs only at certain temperatures and when the material is somewhat orderly. One intriguing phenomenon takes place when a conductor becomes a superconductor – a relatively more orderly state – and later loses its superconducting ability, for example, due to heating. In this case, the material doesn’t return to its conductor state; rather, it becomes an insulator! This phenomenon is observed only when the disorder in the original conductor exceeds a certain level.
 
Shahar and his team decided to deprive a material of its superconducting ability in a different way: by activating a strong magnetic field. They created a superconductor from a material that was relatively disordered – though not disordered enough to cause the superconductor to turn into an insulator by heating – and placed it into a strong magnetic field. Next, they tested the current flowing through the material while gradually altering the strength of the magnetic field and the temperature. Much to their surprise, they discovered that at the point the material ceased being a superconductor, it became neither a regular conductor nor a regular insulator. Instead, the material entirely lost its ability to conduct any electrical current whatsoever. Shahar’s team, for the first time ever, was observing a superinsulator – the exact opposite of a superconductor.
 
The scientists still don’t understand superinsulation, which in the meantime has been discovered in a number of materials and observed in research institutions in other countries. This phenomenon might be connected to the fact that strong magnetic fields create a sort of a “magnetic whirlpool.” Theoretical physicists have proposed treating these whirlpools as particles, which in certain conditions respond to the current by generating great tension that results in superinsulation.
 
Whatever the explanation, much remains to be discovered in this area of research. Superinsulation today takes place at temperatures of 40 thousandths of a degree above absolute zero. If scientists one day succeed in creating superinsulators at room temperature, such materials could solve the problem of overheating in electronic components, making it possible to build transistors that don’t lose current and vastly increasing the durability of batteries.
 
 
(l-r) Prof. Dan Shahar and Maoz Ovadia. An exact opposite
Space & Physics
English
  • Condensed Matter Physics
  • Dan Shahar
  • Electric current
  • Superconductor

Deep Meanings

English
Lacalle and Moses. Effective communication
 
 
 
From dashing off an e-mail to writing War and Peace, communicating thoughts and meanings involves translating a complex idea or set of ideas into a one-dimensional string of words that another person can read in sequence and then recreate the meaning in his or her mind. Communication is at once one of the most basic and  the most mysterious of our daily activities: Everyone does it; few are really good at it.

Is there a basic, underlying structure to the effective communication of complex ideas? A team of scientists that included physicists and language researchers at the Weizmann Institute of Science and elsewhere investigated this question by applying scientific methods to some of our culture’s most successful models for the skillful transfer of ideas: classic writings that, by common agreement, get their messages across well. In research published in the Proceedings of the National Academy of Sciences (PNAS), the scientists created mathematical tools that allowed them to trace the development of ideas throughout a book. The international team included Prof. Elisha Moses and postdoctoral fellow Dr. Enrique Alvarez Lacalle of the Weizmann Institute’s Physics of Complex Systems Department as well as Prof. Jean-Pierre Eckmann, a frequent visitor from the University of Geneva, and research student Beate Dorow from the University of Stuttgart.

Because strings of words are one-dimensional, they literally lack depth. Yet our minds and memories are able to recreate complex ideas from this string. Moses and his team hypothesized that this process may rely on hierarchical structures “encoded” in the narrative. (An obvious hierarchical structure in a text is chapter-paragraph-sentence.) The implication is that our minds decipher not only the individual words, but the encoded structure, enabling us to comprehend abstract concepts.

The scientists applied their mathematical tools to a number of books known for their ability to convey ideas. They included the writings of Albert Einstein, Mark Twain’s Tom Sawyer, Metamorphosis by Franz Kafka and other classics of different styles and periods, to see if it was possible to identify common structures. They defined “windows of attention” of around 200 words (about a paragraph), and within these windows, they identified pairs of words that frequently occurred near each other (after eliminating “meaningless” words such as pronouns). From the resulting word lists and the frequency with which the single words appeared in the text, the scientists’ mathematical analysis was used to construct a sort of network of “concept vectors” – linked words that convey the principal ideas of the text.

Mathematically, these concept vectors can go in many directions. When we read a text, we’re taking a tour along the paths that make up the resulting network. The multidimensional concept vectors seem to span a whole “web” of ideas. The scientists’ findings suggest that this network is based on a tree-like hierarchy, and that such a hierarchy may be a basic underpinning of all language. The reader or listener can reconstruct the hierarchical structure of a text and so enter the multidimensional space of ideas. Thus, from a flat page and a one-dimensional string of words, we are able to grasp the full complexity of “the author’s meaning.”

Moses: “Philosophers from Wittgenstein to Chomsky have taught us that language plays a central evolutionary role in shaping the human brain, and that revealing the structure of language is an essential step to comprehending brain structure. Our contribution to research in this basic field is in using mathematical tools to connect concepts or ideas with the words used to express them. The structure serves to transmit concepts and reconstruct them in the mind of the reader. A deep question that remains open is whether the correlations we uncovered are related to making a text aesthetic as well as comprehensible.” 
 
 
Prof. Elisha Moses’s research is supported by the Clore Center for Biological Physics; the Center for Experimental Physics; and the Rosa and Emilio Segre Research Award. 
 

The Physics of Finger Tapping

 

The volunteer sits with earphones on his head and an electrode taped to his finger, tapping to a beat. Suddenly, his forefinger swings out of rhythm. The researcher standing behind him, postdoctoral fellow Dr. Nestor Handzy, has aimed a painless, external magnetic pulse at one part of his brain, which causes the finger to twitch involuntarily. For that split second, explains Handzy, the finger’s actions were controlled by two opposing instructions. This sort of competition, says Prof. Moses, lends itself to treatment with concepts from physics.

Moses and Handzy have teamed up with Dr. Avi Peled of the Technion and Shaar Menashe Mental Health Center, a psychiatrist who believes that physics can help find better treatments for schizophrenia. In Peled’s words: “The brain is an extremely complex, non-linear network of neurons, and schizophrenia is probably a disorder of connectivity.” Moses: “As physicists, we framed the question and set up the experiment using a complex systems approach.”

With the simple finger-tapping test, the team has already found that schizophrenics’ brains show an atypical response pattern. What’s more, they’ve seen evidence that magnetic pulses might be able to straighten out skewed lines of communication between brain areas in schizophrenia patients. The scientists’ dream is to eventually create a “brain pacemaker” to “reset” these faulty communication signals.
(l-r) Dr. Enrique Alvarez Lacalle and Prof. Elisha Moses.
Space & Physics
English
  • Elisha Moses
  • Physics of Complex Systems

Laser Quest

English
Eckhouse, Friesem, Davidson and Shimshi. Well-focused beam
 
 
 
You can't have your cake and eat it too. Or maybe sometimes you can, at least according to scientists at the Weizmann Institute of Science who set out on a quest to devise lasers that are both high-powered and razor-sharp - properties that are generally mutually exclusive.
   
Usually, powerful lasers have low beam quality, while high beam quality is attainable only in weak lasers. As opposed to light waves from a light bulb, which are emitted in all different wavelengths and directions, laser beam light waves are emitted in a single wavelength and direction. The more closely matched the waves, the higher the beam quality. A high-quality beam can be focused to a point like that of a sharp dagger, while a low-quality beam spreads out more like a blunt butter knife.

But what would happen if several weak lasers were combined? Would they turn into one strong, sharp laser? And the big question: Would the high quality of the separate weak beams be maintained once combined, or would some quality be lost in the process? A team headed by Profs. Asher Friesem and Nir Davidson of the Physics of Complex Systems Department, including Ph.D. students Amiel Ishaaya, Vardit Eckhouse and Liran Shimshi, sought answers to just these questions when they created a laser joining 16 individual weak beams into one powerful beam. In a paper published in Optics Letters, they showed their combination laser sustained a beam quality as high as that of the original weak beams.

To combine beams, the properties of all the light waves have to be coherent (identical in every way). Then the light waves must be superimposed in such a way that the peaks and troughs line up exactly with one another. But this is not so simple in practice: These conditions are very difficult to achieve, and the minutest disturbance can knock the waves out of their superimposed state.

The team - with a bit of "magic" - has managed to design a laser that largely overcomes such problems. In their device, 16 beams of light are produced and, like darts, they all travel straight toward a special optical element located within the laser cavity. This element is positioned such that beams that aren't coherent or properly aligned won't pass through; but if they are exactly the same and superimposed to boot, the element efficiently combines their individual powers. "And here comes the magic," says Davidson. "As if the laser beams have personalities and can make choices, they automatically choose to conform to one another. They seem to know their alternative is to be cast out, and they are able to rapidlyandcontinuouslyself-conform even under unstable conditions." The end result: an uncompromisingly stable, powerful and sharply focused combined beam.

Although this is not the first time laser beams have been joined, the team has taken laser combining to new heights. Other techniques face restrictions in beam numbers, but with this new innovation, the possibilities are unlimited, at least in theory. The design of this laser is also more stable and robust - crucial traits when translated to practical purposes. Their research, therefore, has significant implications in a wide range of commercial fields, from laser radars, optical communications, space exploration and material processing to laser treatments and surgery. Their next steps, already in progress, are to refine their design to eliminate practical constraints to combining even more beams, and to apply it to additional types of laser systems.

Prof. Nir Davidson's research is supported by the Fritz Haber Center for Physical Chemistry; the Levine Institute of Applied Science; the Rosa and Emilio Segre Fund; and the Cymerman-Jakubskind Prize. Prof. Davidson is the incumbent of the Peter and Carola Kleeman Professorial Chair of Optical Sciences.
      
    
 
(l-r) Vardit Eckhouse, Prof. Asher Friesem, Prof. Nir Davidson and Liran Shimshi
Space & Physics
English
  • Asher Friesem
  • Laser
  • Nir Davidson
  • Physics of Complex Systems

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