Nano funnel used to generate extreme ultraviolet light pulses

ScienceDaily (Oct. 17, 2011) — If you want to avoid spilling when you are pouring liquids in the kitchen you may appreciate a funnel. Funnels are not only useful tools in the kitchen. Light can also be efficiently concentrated with funnels. In this case, the funnels have to be about 10.000-times smaller.

An international team of scientists from the Korea Advanced Institute of Science and Technology (KAIST) in Daejeon (South Korea), the Max Planck Institute of Quantum Optics (MPQ) in Garching (Germany), and the Georgia State University (GSU) in Atlanta (USA) has now managed to concentrate the energy of infrared light pulses with a nano funnel and use the concentrated energy to generate extreme ultraviolet light flashes. These flashes, which repeated 75 million times per second, lasted only a few femtoseconds. The new technology can help in the future to measure the movement of electrons with the highest spatial and temporal resolution.

Light is convertible. The wavelengths composing the light can change through interactions with matter, where both the type of material and shape of the material are important for the frequency conversion. An international team of scientists from the Korea Advanced Institute of Science and Technology (KAIST), the Max Planck Institute of Quantum Optics (MPQ), and the Georgia State University (GSU) has now modified light waves with a nano funnel made out of silver. The scientists converted femtosecond laser pulses in the infrared spectral range to femtosecond light flashes in the extreme ultraviolet (EUV). Ultrashort, pulsed EUV light is used in laser physics to explore the inside of atoms and molecules. A femtosecond lasts only a millionth of a billionth of a second.

Light in the infrared (IR) can be converted to the EUV by a process known as high-harmonic generation, whereby the atoms are exposed to a strong electric field from the IR laser pulses. These fields have to be as strong as the fields holding the atom together. With these fields electrons can be extracted from the atoms and accelerated with full force back onto the atoms. Upon impact highly energetic radiation in the EUV is generated.

To reach the necessary strong electric fields for the production of EUV light, the team of scientists has now combined this scheme with a nano funnel in order to concentrate the electric field of the light. With their new technology, they were able to create a powerful EUV light source with wavelengths down to 20 nanometers. The light source exhibits a so far unreached high repetition rate: the few femtoseconds lasting EUV light flashes are repeated 75 million times per second.

The core of the experiment was a small, only a few micrometers long, slightly elliptical funnel made out of silver and filled with xenon gas. The tip of the funnel was only ca. 100 nanometers wide. The infrared light pulses were sent into the funnel entrance where they travel through towards the small exit. The electromagnetic forces of the light result in density fluctuations of the electrons on the inside of the funnel. Here, a small patch of the metal surface was positively charged, the next one negative and so on, resulting in new electromagnetic fields on the inside of the funnel, which are called surface plasmon polaritons. The surface plasmon polaritons travel towards the tip of the funnel, where the conical shape of the funnel results in a concentration of their fields. “The field on the inside of the funnel can become a few hundred times stronger than the field of the incident infrared light. This enhanced field results in the generation of EUV light in the Xe gas.”, explains Prof. Mark Stockman from GSU.

The nano funnel has yet another function. Its small opening at the exit acts as “doorman” for light wavelengths. Not every opening is passable for light. If the opening is smaller than half of a wavelength, the other side remains dark. The 100 nanometer large opening of the funnel did not allow the infrared light at 800 nm to pass. The generated EUV pulses with wavelengths down to 20 nanometers passed, however, without problems. “The funnel acts as an efficient wavelength filter: at the small opening only EUV light comes out.”, explains Prof. Seung-Woo Kim from KAIST, where the experiments were conducted.

“Due to their short wavelength and potentially short pulse duration reaching into the attosecond domain, extreme ultraviolet light pulses are an important tool for the exploration of electron dynamics in atoms, molecules and solids”, explains Seung-Woo Kim. Electrons are extremely fast, moving on attosecond timescales (an attosecond is a billionth of a billionth of a second). In order to capture a moving electron, light flashes are needed, which are shorter than the timescale of the motion. Attosecond light flashes have become a familiar tool in the exploration of electron motion. With the conventional techniques, they can only be repeated a few thousand times per second. This can change with the nano funnel. “We assume that the few femtosecond light flashes consist of trains of attosecond pulses”, argues Matthias Kling, group leader at MPQ. “With such pulse trains, we should be able to conduct experiments with attosecond time resolution at very high repetition rate.”

The repetition rate is important for e.g. the application of EUV pulses in electron spectroscopy on surfaces. Electrons repel each other by Coulomb forces. Therefore, it may be necessary to restrict the experimental conditions such that only a single electron is generated per laser shot. With low repetition rates, long data acquisition times would be required in order to achieve sufficient experimental resolution. “In order to conduct experiments with high spatial and temporal resolution within a sufficiently short time, a high repetition rate EUV source is needed”, explains Kling. The novel combination of laser technology and nanotechnology can help in the future to record movies of ultrafast electron motion on surfaces with so far unreached temporal and spatial resolution in the attosecond-nanometer domain.

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Journal Reference:

In-Yong Park, Seungchul Kim, Joonhee Choi, Dong-Hyub Lee, Young-Jin Kim, Matthias F. Kling, Mark I. Stockman, Seung-Woo Kim. Plasmonic generation of ultrashort extreme-ultraviolet light pulses. Nature Photonics, 2011; DOI: 10.1038/NPHOTON.2011.258

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Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

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Nano funnel used to generate extreme ultraviolet light pulses

ScienceDaily (Oct. 17, 2011) — If you want to avoid spilling when you are pouring liquids in the kitchen you may appreciate a funnel. Funnels are not only useful tools in the kitchen. Light can also be efficiently concentrated with funnels. In this case, the funnels have to be about 10.000-times smaller.

An international team of scientists from the Korea Advanced Institute of Science and Technology (KAIST) in Daejeon (South Korea), the Max Planck Institute of Quantum Optics (MPQ) in Garching (Germany), and the Georgia State University (GSU) in Atlanta (USA) has now managed to concentrate the energy of infrared light pulses with a nano funnel and use the concentrated energy to generate extreme ultraviolet light flashes. These flashes, which repeated 75 million times per second, lasted only a few femtoseconds. The new technology can help in the future to measure the movement of electrons with the highest spatial and temporal resolution.

Light is convertible. The wavelengths composing the light can change through interactions with matter, where both the type of material and shape of the material are important for the frequency conversion. An international team of scientists from the Korea Advanced Institute of Science and Technology (KAIST), the Max Planck Institute of Quantum Optics (MPQ), and the Georgia State University (GSU) has now modified light waves with a nano funnel made out of silver. The scientists converted femtosecond laser pulses in the infrared spectral range to femtosecond light flashes in the extreme ultraviolet (EUV). Ultrashort, pulsed EUV light is used in laser physics to explore the inside of atoms and molecules. A femtosecond lasts only a millionth of a billionth of a second.

Light in the infrared (IR) can be converted to the EUV by a process known as high-harmonic generation, whereby the atoms are exposed to a strong electric field from the IR laser pulses. These fields have to be as strong as the fields holding the atom together. With these fields electrons can be extracted from the atoms and accelerated with full force back onto the atoms. Upon impact highly energetic radiation in the EUV is generated.

To reach the necessary strong electric fields for the production of EUV light, the team of scientists has now combined this scheme with a nano funnel in order to concentrate the electric field of the light. With their new technology, they were able to create a powerful EUV light source with wavelengths down to 20 nanometers. The light source exhibits a so far unreached high repetition rate: the few femtoseconds lasting EUV light flashes are repeated 75 million times per second.

The core of the experiment was a small, only a few micrometers long, slightly elliptical funnel made out of silver and filled with xenon gas. The tip of the funnel was only ca. 100 nanometers wide. The infrared light pulses were sent into the funnel entrance where they travel through towards the small exit. The electromagnetic forces of the light result in density fluctuations of the electrons on the inside of the funnel. Here, a small patch of the metal surface was positively charged, the next one negative and so on, resulting in new electromagnetic fields on the inside of the funnel, which are called surface plasmon polaritons. The surface plasmon polaritons travel towards the tip of the funnel, where the conical shape of the funnel results in a concentration of their fields. “The field on the inside of the funnel can become a few hundred times stronger than the field of the incident infrared light. This enhanced field results in the generation of EUV light in the Xe gas.”, explains Prof. Mark Stockman from GSU.

The nano funnel has yet another function. Its small opening at the exit acts as “doorman” for light wavelengths. Not every opening is passable for light. If the opening is smaller than half of a wavelength, the other side remains dark. The 100 nanometer large opening of the funnel did not allow the infrared light at 800 nm to pass. The generated EUV pulses with wavelengths down to 20 nanometers passed, however, without problems. “The funnel acts as an efficient wavelength filter: at the small opening only EUV light comes out.”, explains Prof. Seung-Woo Kim from KAIST, where the experiments were conducted.

“Due to their short wavelength and potentially short pulse duration reaching into the attosecond domain, extreme ultraviolet light pulses are an important tool for the exploration of electron dynamics in atoms, molecules and solids”, explains Seung-Woo Kim. Electrons are extremely fast, moving on attosecond timescales (an attosecond is a billionth of a billionth of a second). In order to capture a moving electron, light flashes are needed, which are shorter than the timescale of the motion. Attosecond light flashes have become a familiar tool in the exploration of electron motion. With the conventional techniques, they can only be repeated a few thousand times per second. This can change with the nano funnel. “We assume that the few femtosecond light flashes consist of trains of attosecond pulses”, argues Matthias Kling, group leader at MPQ. “With such pulse trains, we should be able to conduct experiments with attosecond time resolution at very high repetition rate.”

The repetition rate is important for e.g. the application of EUV pulses in electron spectroscopy on surfaces. Electrons repel each other by Coulomb forces. Therefore, it may be necessary to restrict the experimental conditions such that only a single electron is generated per laser shot. With low repetition rates, long data acquisition times would be required in order to achieve sufficient experimental resolution. “In order to conduct experiments with high spatial and temporal resolution within a sufficiently short time, a high repetition rate EUV source is needed”, explains Kling. The novel combination of laser technology and nanotechnology can help in the future to record movies of ultrafast electron motion on surfaces with so far unreached temporal and spatial resolution in the attosecond-nanometer domain.

Recommend this story on Facebook, Twitter,
and Google +1:

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Story Source:

The above story is reprinted from materials provided by Max Planck Institute of Quantum Optics.

Note: ScienceDaily reserves the right to edit materials for content and length. For further information, please contact the source cited above.

Journal Reference:

In-Yong Park, Seungchul Kim, Joonhee Choi, Dong-Hyub Lee, Young-Jin Kim, Matthias F. Kling, Mark I. Stockman, Seung-Woo Kim. Plasmonic generation of ultrashort extreme-ultraviolet light pulses. Nature Photonics, 2011; DOI: 10.1038/NPHOTON.2011.258

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

View the original article here

Why biggest stellar explosions often happen in tiniest galaxies: Ultraviolet probe sheds light on mystery

ScienceDaily (Apr. 21, 2011) — Astronomers using NASA's Galaxy Evolution Explorer may be closer to knowing why some of the most massive stellar explosions ever observed occur in the tiniest of galaxies.

"It's like finding a sumo wrestler in a little 'Smart Car,'" said Don Neill, a member of NASA's Galaxy Evolution Explorer team at the California Institute of Technology in Pasadena, and lead author of a new study published in the Astrophysical Journal.

"The most powerful explosions of massive stars are happening in extremely low-mass galaxies. New data are revealing that the stars that start out massive in these little galaxies stay massive until they explode, while in larger galaxies they are whittled away as they age, and are less massive when they explode," said Neill.

Over the past few years, astronomers using data from the Palomar Transient Factory, a sky survey based at the ground-based Palomar Observatory near San Diego, have discovered a surprising number of exceptionally bright stellar explosions in so-called dwarf galaxies up to 1,000 times smaller than our Milky Way galaxy. Stellar explosions, called supernovae, occur when massive stars -- some up to 100 times the mass of our sun -- end their lives.

The Palomar observations may explain a mystery first pointed out by Neil deGrasse Tyson and John Scalo when they were at the University of Austin Texas (Tyson is now the director of the Hayden Planetarium in New York, N.Y.). They noted that supernovae were occurring where there seemed to be no galaxies at all, and they even proposed that dwarf galaxies were the culprits, as the Palomar data now indicate.

Now, astronomers are using ultraviolet data from the Galaxy Evolution Explorer to further examine the dwarf galaxies. Newly formed stars tend to radiate copious amounts of ultraviolet light, so the Galaxy Evolution Explorer, which has scanned much of the sky in ultraviolet light, is the ideal tool for measuring the rate of star birth in galaxies.

The results show that the little galaxies are low in mass, as suspected, and have low rates of star formation. In other words, the petite galaxies are not producing that many huge stars.

"Even in these little galaxies where the explosions are happening, the big guys are rare," said co-author Michael Rich of UCLA, who is a member of the mission team.

In addition, the new study helps explain why massive stars in little galaxies undergo even more powerful explosions than stars of a similar heft in larger galaxies like our Milky Way. The reason is that low-mass galaxies tend to have fewer heavy atoms, such as carbon and oxygen, than their larger counterparts. These small galaxies are younger, and thus their stars have had less time to enrich the environment with heavy atoms.

According to Neill and his collaborators, the lack of heavy atoms in the atmosphere around a massive star causes it to shed less material as it ages. In essence, the massive stars in little galaxies are fatter in their old age than the massive stars in larger galaxies. And the fatter the star, the bigger the blast that will occur when it finally goes supernova. This, according to the astronomers, may explain why super supernovae are occurring in the not-so-super galaxies.

"These stars are like heavyweight champions, breaking all the records," said Neill.

Added Rich, "These dwarf galaxies are especially interesting to astronomers, because they are quite similar to the kinds of galaxies that may have been present in our young universe, shortly after the Big Bang. The Galaxy Evolution Explorer has given us a powerful tool for learning what galaxies were like when the universe was just a child."

Caltech leads the Galaxy Evolution Explorer mission and is responsible for science operations and data analysis. NASA's Jet Propulsion Laboratory in Pasadena manages the mission and built the science instrument. Caltech manages JPL for NASA. The mission was developed under NASA's Explorers Program managed by the Goddard Space Flight Center, Greenbelt, Md. Researchers sponsored by Yonsei University in South Korea and the Centre National d'Etudes Spatiales (CNES) in France collaborated on this mission.

Graphics and additional information about the Galaxy Evolution Explorer are online at http://www.nasa.gov/galex/ and http://www.galex.caltech.edu .

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by NASA/Jet Propulsion Laboratory.

Journal Reference:

James D. Neill, Mark Sullivan, Avishay Gal-Yam, Robert Quimby, Eran Ofek, Ted K. Wyder, D. Andrew Howell, Peter Nugent, Mark Seibert, D. Christopher Martin, Roderik Overzier, Tom A. Barlow, Karl Foster, Peter G. Friedman, Patrick Morrissey, Susan G. Neff, David Schiminovich, Luciana Bianchi, José Donas, Timothy M. Heckman, Young-Wook Lee, Barry F. Madore, Bruno Milliard, R. Michael Rich, Alex S. Szalay. The Extreme Hosts of Extreme Supernovae. The Astrophysical Journal, 2011; 727 (1): 15 DOI: 10.1088/0004-637X/727/1/15

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View the original article here