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Physicists demonstrate acceleration of electrons by laser in vacuum

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Each row of two frames represents one snapshot-pair of laser on (on the right side) and laser off (on the left side) with unchanged configuration. One can see a clear increase from these pictures, proof that the laser accelerates the 20 mega electron volts electron beam in vacuum. Pictures of the beam momentum spread after the spectrometer taken with the laser off (left column) and the laser on (right column). The length of the beam image reveals the energy spread of the beam. The experiment recorded 30 shots. Twenty shots were high intensity and showed effects of the laser on/laser off difference. Four shot examples are shown here. Pictures are taken from spectrometer on Beam Line #1 at BNL-ATF.

Each row of two frames represents one snapshot-pair of laser on (on the right side) and laser off (on the left side) with unchanged configuration. One can see a clear increase from these pictures, proof that the laser accelerates the 20 mega electron volts electron beam in vacuum. Pictures of the beam momentum spread after the spectrometer taken with the laser off (left column) and the laser on (right column). The length of the beam image reveals the energy spread of the beam. The experiment recorded 30 shots. Twenty shots were high intensity and showed effects of the laser on/laser off difference. Four shot examples are shown here. Pictures are taken from spectrometer on Beam Line #1 at BNL-ATF.

Accelerating a free electron with a laser has been a longtime goal of solid-state physicists. David Cline, a distinguished professor in the UCLA Department of Physics and Astronomy, and Xiaoping Ding, an assistant researcher at UCLA, have conducted research at Brookhaven National Laboratory in New York and have established that an electron beam can be accelerated by a laser in free space….

Read more at: http://phys.org

Written by physicsgg

February 28, 2013 at 10:02 am

Posted in PHYSICS, TECHNOLOGY

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Characterize the Behavior of Individual Electrons

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A schematic of a new design for a laser that emits ultrashort pulses of light

An international collaboration of researchers is working on a new method of understanding what happens during chemical reactions. The approach is extremely complex, as it involves tracking the behavior of individual electrons as this happens.

Doing so is a monumentally difficult task, considering that the elementary particle completes a full orbit around an atomic nucleus in just 151 attoseconds. An attosecond is a billionth of a billionth of a second, equal to the time it takes light to travel the length of three hydrogen atoms.

What researchers are trying to accomplish is create laser devices capable of releasing light pulses lasting only one attosecond, or a quintillionth of a second. What this will enable is a clearer understanding of how chemical reactions occur.
These interactions could be understood down to the molecular and atomic levels, which has been in a goal in chemistry research for decades. Once these behaviors are learned, then researchers could begin developing ways of applying the knowledge to engineering, pharmaceutical research and so on.

Eight members of the international team are based at the Massachusetts Institute of Technology‘s (MIT) Research Laboratory of Electronics (RLE). They are at the forefront of producing the new lasers.

“If you can generate a pulse that has a shorter duration [than 151 attoseconds], then you can investigate dynamics that happen on that time scale,” explains MIT Department of Electrical Engineering and Computer Science adjunct professor Franz Kaertner, the leader of the investigation.

“That connects back to this work from [MIT electrical engineering professor Harold] Edgerton, where he was able to make optical flash photography in the microsecond range and nanosecond range,” he adds.

In order to measure electron dynamics, the team is using a technique called time-resolved spectroscopy. This method requires significant light pulse intensity in order to function, something which previous attosecond lasers could not provide.

At this point, the theoretical framework is in place, and the team has already began constructing the new laser. MIT investigators explain that the machine will be able to produce the required pulses by combining light of various wavelengths.

Whether or not the group will succeed in its endeavor is still uncertain, but scientists are confident in the few avenues of research they have at their disposal. They say that, in a few years, we may be able to finally crack the mystery surrounding atomic interactions during chemical interactions.
http://news.softpedia.com

Written by physicsgg

August 16, 2011 at 2:56 pm

Posted in ATOMIC PHYSICS, Chemistry

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Measuring Fundamental Constants with Methanol

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Diagram of the methanol molecule

Key to the astronomical modeling process by which scientists attempt to understand our universe, is a comprehensive knowledge of the values making up these models. These are generally measured to exceptionally high confidence levels in laboratories. Astronomers then assume these constants are just that – constant. This generally seems to be a good assumption since models often produce mostly accurate pictures of our universe. But just to be sure, astronomers like to make sure these constants haven’t varied across space or time. Making sure, however, is a difficult challenge. Fortunately, a recent paper has suggested that we may be able to explore the fundamental masses of protons and electrons (or at least their ratio) by looking at the relatively common molecule of methanol.
The new report is based on the complex spectra of the methanol molecule. In simple atoms, photons are generated from transitions between atomic orbitals since they have no other way to store and translate energy. But with molecules, the chemical bonds between the component atoms can store the energy in vibrational modes in much the same way masses connected to springs can vibrate. Additionally, molecules lack radial symmetry and can store energy by rotation. For this reason, the spectra of cool stars show far more absorption lines than hot ones since the cooler temperatures allow molecules to begin forming.
Many of these spectral features are present in the microwave portion of the spectra and some are extremely dependent on quantum mechanical effects which in turn depend on precise masses of the proton and electron. If those masses were to change, the position of some spectral lines would change as well. By comparing these variations to their expected positions, astronomers can gain valuable insights to how these fundamental values may change.
The primary difficulty is that, in the grand scheme of things, methanol (CH3OH) is rare since our universe is 98% hydrogen and helium. The last 2% is composed of every other element (with oxygen and carbon being the next most common). Thus, methanol is comprised of three of the four most common elements, but they have to find each other, to form the molecule in question. On top of that, they must also exist in the right temperature range; too hot and the molecule is broken apart; too cold and there’s not enough energy to cause emission for us to detect it. Due to the rarity of molecules with these conditions, you might expect that finding enough of it, especially across the galaxy or universe, would be challenging.
Fortunately, methanol is one of the few molecules which are prone to creating astronomical masers. Masers are the microwave equivalent of lasers in which a small input of light can cause a cascading effect in which it induces the molecules it strikes to also emit light at specific frequencies. This can greatly enhance the brightness of a cloud containing methanol, increasing the distance to which it could be readily detected.
By studying methanol masers within the Milky Way using this technique, the authors found that, if the ratio of the mass of an electron to that of a proton does change, it does so by less than three parts in one hundred million. Similar studies have also been conducted using ammonia as the tracer molecule (which can also form masers) and have come to similar conclusions.
http://www.universetoday.com/86574/measuring-fundamental-constants-with-methanol/

Written by physicsgg

June 14, 2011 at 8:45 am

Posted in Chemistry, COSMOLOGY

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Electrons are fantastically round, say British scientists

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Most precise measurements of the roundness of the electron to date provide a window ‘on the high-energy soul of the cosmos’

Part of the laser system used by scientists at Imperial College to measure the shape of the electron. Photograph: Joe Smallman/Imperial College


After three months of experiments in a basement laboratory in London, scientists can confirm – with more confidence than ever – that the electron is very, very round.
In the most exquisite measurements yet, researchers declared the particle to be a perfect sphere to within one billionth of a billionth of a billionth of a centimetre. Were the electron scaled up to the size of the solar system, any deviation from its roundness would be smaller than the width of a human hair, the team said.
Abstruse as the experiment might seem, the work has profound implications for scientists wrestling with the mysteries of the cosmos. Even the slightest elongation of the electron can reveal what unknown particles might exist in nature, and even explain why matter won out over antimatter in the universe we observe.
The findings, published in the journal Nature, already rule out some kinds of particles that theories suggested could pop into existence at the Large Hadron Collider at Cern, the European particle physics laboratory near Geneva.
“It’s been hard work. We’ve been working on this for a long time and we’ve had a lot of ups and downs,” said Jony Hudson, a physicist at Imperial College London. “We have measured the shape really precisely. The deviations we were looking for are much smaller than the size of the electron. It is very, very round.”
The concept of shape might seem obscure when it comes to a subatomic particle, but the rules are the same as for everyday objects. Pick up a pen, for example, and you feel its shape because electrons in the pen push back against the electrons in your hand.
And so it is with the electron itself. The particle is negatively charged, and the more evenly distributed the charge is around the centre of the particle, the more spherical it appears to be.
Scientists pursue ever more accurate measurements of the electron’s roundness because any sign of it being mishapen could herald a major discovery. One leading idea known as supersymmetry, which says that every kind of particle we know has a heavy twin, requires the electron to have a slightly distorted shape.
“What’s interesting is that the electron is so round it is becoming difficult for theories like supersymmetry to explain it,” said Hudson, whose finding already rules out the existence of some supersymmetric particles.
Evidence that the electron is mishapen on a minuscule scale might also explain why the universe we see is made of matter instead of antimatter. At the birth of the cosmos, both were made in equal measure, but some subtle difference between the two caused antimatter to disappear. If the electron is elongated, it will behave differently to its antimatter counterpart, the positron. For example, each would wobble differently in an electric field.
“There must be a difference in the behaviour of matter and antimatter that we’ve not observed, and amazingly, the shape of the electron might just be enough to explain how the matter-antimatter imbalance built up over billions of years,” Hudson said.
His team studied the roundness of electrons by measuring how much, or how little, the particles wobbled in an electric field. The rounder the electron, the less wobble it will display. In the experiment, electrons were anchored to a molecule called ytterbium fluoride and examined with a laser beam. Each measurement took only one thousandth of a second.
Running their experiment non-stop for more than three months, Hudson’s team took 25 million measurements of electrons and averaged them out. They found no sign of the electron wobbling in the field, meaning it is more spherical than any previous experiment had shown. “To the best of our knowledge, with the experimental precision we have, the electron appears to be round,” Hudson said.
In an accompanying article, Aaron Leanhardt at the University of Michigan, Ann Arbor, said the work provided a window “on the high-energy soul of the cosmos”.
“This work has important ramifications for the types of particles that can be discovered at high-energy accelerators, and may eventually help to explain the composition of the observable universe,” Leanhardt wrote.
With improvements to their equipment, Hudson’s team hopes to make even more precise measurements of the electron in the coming years. “If we could make it 10 times better we could pretty conclusively rule in or out supersymmetry, and that would be a huge result for us,” he said.
http://www.guardian.co.uk/science/2011/may/25/electrons-round-cosmos

Written by physicsgg

May 25, 2011 at 11:09 pm

Posted in High Energy Physics

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