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Can silver nanoparticles be the key to a more compact laser

first_img Explore further Citation: Can silver nanoparticles be the key to a more compact laser? (2008, June 9) retrieved 18 August 2019 from https://phys.org/news/2008-06-silver-nanoparticles-key-compact-laser.html Holographic imaging of electromagnetic fields using electron-light quantum interference “In random media, multiple scattering and interference reduce the diffusion of light, and in case of extremely strong scattering, photon localization, or Anderson localization of light, is predicted like electrons in glasses,” Katsuhisa Tanaka, a scientist in Kyoto University, tells PhysOrg.com. He and his colleagues are interested in using so-called disordered material to create lasers that could increase our understanding of physics – as well as make the laser creation process simpler. This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only. Tanaka points out that silver nanoparticles make a difference: “First, localized optical modes near silver nanoparticle surface provide high optical gain for lasing. Second, scattering properties can be flexibly controlled by the size and shape of nanoparticles, and significantly contribute to light transport in random systems compared to that in dielectric nanoparticles.”In terms of application, Tanaka sees possibilities for fundamental physics knowledge, as well as practical uses for this set-up. “Since the phenomena of random laser are reported for systems having very different scattering strength from nearly transparent to highly-scattering media, it is possible that the laser mechanism — or dominating laser mode — is different depending on the scattering strength. Thus the primal importance is to clarify the mechanism, which is beneficial to the progress of the physics.”As far as practical applications, he says that there is a strong possibility of a compact laser. Plus, Tanaka continues, “Since this type of lasers does not require rigorous alignment of reflectors to form cavity in contrast to the conventional Fabry-Perot type ones, the making process is much simpler.”The team at Kyoto continues to work on this project. Tanaka and his coworkers say that more needs to be known with regard to how the distribution of the silver nanoparticles within the polymer affects the laser. Additionally, they feel that this work could lead to advances in lasers that are based on organic semiconductors. Copyright 2007 PhysOrg.com. All rights reserved. This material may not be published, broadcast, rewritten or redistributed in whole or part without the express written permission of PhysOrg.com. With Xiangeng Meng, Koji Fujita (also doing work at PRESTO in Saitama, Japan), Yanhua Zong and Shunsuke Murai at Kyoto University, Tanaka has been working on using transparent films embedded with nanoparticles of silver to study the feedback coherence from certain random lasers. Their work can be seen in Applied Physics Letters: “Random lasers with coherent feedback from highly transparent polymer films embedded with silver nanoparticles.”“Random lasers are laser sources that arise from multiple scattering events in random systems so that the strength of light scattering is of large importance in determining the feedback type of laser oscillation, Tanaka explains. “We are interested in such lasers because their fabrication process is technically simple while high gain is involved. At present, researchers are focusing on random lasers based on dielectrics with high refractive index, while little attention has been paid to metal nanostructures-based amplifying random media.” He continues: “Actually, metal nanostructures are rather potential materials in laser devices. The use of surface plasmon resonance of metal nanostructures is extremely attractive because they bring about surface enhanced Raman scattering, enhancement of spontaneous emission, and amplified spontaneous emission, and so on. What we have consisdered for a long time is whether laser actions with high gain could be achieved by combining metal nanostructures and laser working medium.”Indeed, this led Tanaka and his peers to wonder if surface plasmon resonance can help random lasing. The answer, in their minds, is yes: “We found that the presence of silver nanoparticles results in the coherent output even though the scattering strength of the system is very weak. We believe that surface plasmon plays an important role in the laser operation.”In order to make the demonstration work, the Kyoto team embedded silver nanoparticles on highly transparent polymer films. The process was made possible through the in situ method, in which heat is used to create the hybrid material, combining polymer with metal in a way that is useful in terms of lasing. “We have calculated the transport mean free path of our sample and found that it is far larger than the sample size. The light propagates in such systems nearly freely without resistance,” Tanaks says. “Then, the issue that puzzles us is this: What on earth induces laser oscillation?”last_img read more

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Mini Gradiometer Could Map Other Planets Gravity Fields

first_img Recently, Jaap Flokstra and colleagues from the University of Twente in Enschede, the Netherlands, have designed a miniature gravity gradiometer that can map a planet’s gravity field. The device is a much smaller version of a gravity gradiometer called GOCE (Gravity field and steady-state Ocean Circulation Explorer), which is a European Space Agency satellite that is currently orbiting and measuring Earth’s gravity field. While GOCE has a mass of several hundred kilograms, the new mini gradiometer weighs just one kilogram. As the scientists explain, the mini gravity gradiometer is made of a single wafer of silicon. The design consists of two masses, each hanging on a spring a few centimeters part (compared with half a meter in GOCE). Whichever mass is slightly closer to a planet’s surface will feel a stronger pull on its spring compared to the other mass, allowing researchers to determine the gravity gradient. In the new design, the position of the masses is measured to within 1 picometer by a device whose capacitance changes as the masses move up and down. Flokstra and his colleagues hope that the new lightweight design would be more practical and cheaper to send into outer space for investigating the gravity fields of other planets in our solar system. For instance, such a device could search for the subterranean ocean suspected to exist near the South Pole of Saturn’s moon Enceladus. The researchers calculate that the device could have a high sensitivity, with the ability to sense changes in a planet’s gravity field due to geological features of about 200 kilometers across or more. The researchers plan to build and demonstrate the device to use on Earth in the next few months.via: New Scientist© 2009 PhysOrg.com This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only. Citation: Mini Gradiometer Could Map Other Planets’ Gravity Fields (2009, August 10) retrieved 18 August 2019 from https://phys.org/news/2009-08-mini-gradiometer-planets-gravity-fields.html (PhysOrg.com) — Although it may seem like gravity is the same everywhere on the Earth, it actually varies a small amount from place to place. Factors such as mountains, ocean trenches, and interior density variations can all cause gravity differences. By measuring the gravity field of Earth or another planet, scientists can gain insight into that planet’s otherwise hidden geological features. GOCE’s ‘heart’ starts beating Explore further A mini gravity gradiometer could search for the subterranean ocean suspected to exist near the South Pole of Saturn’s moon Enceladus. Image credit: NASA.last_img read more

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IFLs created from piconjugated polymers improve performance and stability of optoelectronic devices

first_img This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only. Stabilization of the doping profile by counter-ion immobilization in self-compensated doped polymer organic semiconductors. Credit: (c) Nature (2016). DOI: 10.1038/nature20133 To make optoelectronic devices a layering technique is used—a thin film conductor is caused to be in contact with a semiconductor allowing an electric charge to move between them—to facilitate the transfer an IFL is placed between them. But as Facchetti notes, conventional IFLs are considered to be inefficient—improvements would allow greater efficiency in solar cells, for example. In this new effort, the researchers suggest a particular type of polymer, part of a group called π-conjugated polymers—a type of stable polymer with high doping content that has a self-compensation mechanism that involves covalently bonded counter ions that serve to block the migration of dopants—they offer not only improved efficiency but stronger performance and more stability. But, as Facchetti also notes, most such polymers in their native state are not able to transfer large numbers of charged particles—to overcome that problem the researchers used a chemical doping process that caused the charge carriers to become denser which in turn caused the polymer to become much more conductive.To test their ideas, the researchers modified several devices (solar cells, LEDs, photodiodes, etc.), replacing conventional IFLs with ones they had created and then tested their performance. The team reports that the expected improvements in efficiency were realized, which they note, suggests such polymers have the potential to improve the efficiency of a wide variety of optoelectronic devices. More work will need to be done though before that can be proven—first it remains to be seen if such polymers can be scaled up and then it must be shown that they can stand up to the rigors of real-world demands. © 2016 Phys.org New polymer able to store energy at higher temperatures Citation: IFLs created from pi-conjugated polymers improve performance and stability of optoelectronic devices (2016, November 24) retrieved 18 August 2019 from https://phys.org/news/2016-11-ifls-pi-conjugated-polymers-stability-optoelectronic.htmlcenter_img More information: Cindy G. Tang et al. Doped polymer semiconductors with ultrahigh and ultralow work functions for ohmic contacts, Nature (2016). DOI: 10.1038/nature20133AbstractTo make high-performance semiconductor devices, a good ohmic contact between the electrode and the semiconductor layer is required to inject the maximum current density across the contact. Achieving ohmic contacts requires electrodes with high and low work functions to inject holes and electrons respectively, where the work function is the minimum energy required to remove an electron from the Fermi level of the electrode to the vacuum level. However, it is challenging to produce electrically conducting films with sufficiently high or low work functions, especially for solution-processed semiconductor devices. Hole-doped polymer organic semiconductors are available in a limited work-function range, but hole-doped materials with ultrahigh work functions and, especially, electron-doped materials with low to ultralow work functions are not yet available. The key challenges are stabilizing the thin films against de-doping and suppressing dopant migration. Here we report a general strategy to overcome these limitations and achieve solution-processed doped films over a wide range of work functions (3.0–5.8 electronvolts), by charge-doping of conjugated polyelectrolytes and then internal ion-exchange to give self-compensated heavily doped polymers. Mobile carriers on the polymer backbone in these materials are compensated by covalently bonded counter-ions. Although our self-compensated doped polymers superficially resemble self-doped polymers, they are generated by separate charge-carrier doping and compensation steps, which enables the use of strong dopants to access extreme work functions. We demonstrate solution-processed ohmic contacts for high-performance organic light-emitting diodes, solar cells, photodiodes and transistors, including ohmic injection of both carrier types into polyfluorene—the benchmark wide-bandgap blue-light-emitting polymer organic semiconductor. We also show that metal electrodes can be transformed into highly efficient hole- and electron-injection contacts via the self-assembly of these doped polyelectrolytes. This consequently allows ambipolar field-effect transistors to be transformed into high-performance p- and n-channel transistors. Our strategy provides a method for producing ohmic contacts not only for organic semiconductors, but potentially for other advanced semiconductors as well, including perovskites, quantum dots, nanotubes and two-dimensional materials. (Phys.org)—A team of researchers from Singapore and the U.K. has found that using a particular type of polymer allowed for creating interfacial layers (IFLs) in optoelectronic devices with improved performance and stability. In their paper published in the journal Nature, the team describes their technique and their results when they made actual devices using the polymer. Antonio Facchetti with Northwestern University offers a News & Views piece on the work done by the team in the same journal issue and outlines some of the benefits of self-compensated polymers as well as some of the hurdles that will need to be overcome before they can be used in commercial products. Explore further Journal information: Naturelast_img read more

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Mysterious faint object detected in the vicinity of a quadruply lensed quasar

first_img More information: Evidence for a Dusty Dark Dwarf Galaxy in the Quadruple Lens MG0414+0534, arXiv:1701.05283 [astro-ph.GA] arxiv.org/abs/1701.05283AbstractWe report the 4σ detection of a faint object with a flux of ~ 0.3 mJy, in the vicinity of the quadruply lensed QSO MG0414+0534 using the Atacama Large Millimeter/submillimeter array (ALMA) Band 7. The object is most probably a dusty dark dwarf galaxy, which has not been detected in either the optical, near-infrared (NIR) or radio (cm) bands. An anomaly in the flux ratio of the lensed images observed in Band 7 and the mid-infrared (MIR) band and the reddening of the QSO light color can be simultaneously explained if we consider the object as a lensing substructure with an ellipticity ~ 0.7 at a redshift of 0.5≲z≲1. Using the best-fit lens models with three lenses, we find that the dark matter plus baryon mass associated with the object is ∼109M⊙, the dust mass is ∼107M⊙ and the linear size is ≳5kpc. Thus our findings suggest that the object is a dusty dark dwarf galaxy. A substantial portion of faint submillimeter galaxies (SMGs) in the universe may be attributed to such dark objects. ALMA 0.88 mm (Band 7) dust continuum images of MG 0414+0534. A faint spot inside a red circle (left) is the “object Y”. Credit: Inoue et al., 2017. Dozens of new ultra-diffuse galaxies discovered in Abell 2744 MG 0414+0534 is a quadruply lensed, radio-loud quasar that showcases a strong sign of anomaly in the flux ratio and reddening in the optical and near-infrared band. This anomaly baffles scientists as its origin is not fully understood yet.In order to reveal more insights into this mysterious anomaly, a team of researchers led by Kaiki Taro Inoue of Kindai University in Japan conducted continuum observations of MG 0414+0534 with ALMA. The observational campaign, which was carried out in June and August 2015, resulted in the discovery of a faint object with a flux of about 0.3 mJy in the vicinity of the quasar. For the purpose of the research, this newly found object was designated “object Y.”According to the paper, “object Y” has an ellipticity of about 0.7 at a redshift between 0.5 and 1.0 and its linear size is at least 16,300 light years. The scientists estimate that the dark matter plus baryon mass associated with the object is about one billion solar masses, while its dust mass is approximately 10 million times greater than that of the sun.The images obtained by ALMA allowed the researchers to draw conclusions that the newly detected object is most likely a dusty dark dwarf galaxy, previously undetected in either optical, near-infrared or radio bands.”Our findings suggest that the object is a dusty dark dwarf galaxy,” the paper reads.However, the astronomers also explore the possibility that “object Y” could be an UDG. With stellar masses typical of dwarf galaxies, UDGs are extremely-low-density galaxies. The largest UDGs have sizes comparable to the Milky Way but contain only about one percent as many stars as our home galaxy. Notably, the phenomenon of UDGs still puzzles scientists as they try explain why these faint but large galaxies are not ripped apart by the tidal fields of their host clusters.The researchers explain that if “object Y” is a UDG, then its stellar components may have been expanded due to outflow caused by starburst or active galactic nucleus (AGN) activity. Therefore, the surface brightness in the optical and near-infrared band can be extremely small despite being gas-rich, which makes this object difficult to spot.The team concluded that more detailed analysis of the newly found object could provide important information about the origin of past starburst activity. They also noted that if “object Y” is residing in the intervening line of sight, many faint submillimeter galaxies may be classified in the future as gas-rich dusty dark dwarf galaxies.”A substantial portion of faint submillimeter galaxies (SMGs) in the universe may be attributed to such dark objects,” the researchers wrote in the paper. Citation: Mysterious faint object detected in the vicinity of a quadruply lensed quasar (2017, January 25) retrieved 18 August 2019 from https://phys.org/news/2017-01-mysterious-faint-vicinity-quadruply-lensed.html (Phys.org)—Astronomers have spotted a mysterious faint object in the vicinity of a quadruply lensed quasar designated MG 0414+0534. The object, which was discovered using the Atacama Large Millimeter/submillimeter Array (ALMA), appears to be a dusty, dark dwarf galaxy or an ultra-diffuse galaxy (UDG). The findings were presented January 19 in a paper published on arXiv.org. © 2017 Phys.org Explore further This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only.last_img read more

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Memory marks and markers

first_img‘Marks are made by markers, but the marks also define the markers. This show is all about memory and history. Memories are like marks which have been created by a particular time and at the same time, eroded by time too. So “time” is the marker here, a personal/private time and Time as an eternal flow. Marks are then the signs of/for my intrinsic unconscious self and these could be read also as conscious choices from my socio-private experiences, mediated by time,’ says artist Samindranath Majumdar, talking about his work. Also Read – ‘Playing Jojo was emotionally exhausting’Paintings of this Kolkata-based artist will be on exhibition at the Gallerie Ganesha in a show called Marks And Markers. Samindranath Majumdar’s paintings look back to his own experiences, using abstraction and multiple layers of paint to redefine space and memory.His works tread the fine line between completely abstract and representative forms, calling into question the role that narrative threads play in experiencing art. For Majumdar, memory unfolds in a series of unstable visuals. Born in a Kolkata suburb, he grew up among greenery which was slowly being replaced by the growing space of a crowded metropolis. Observing the imposing and, sometime, crumbling buildings on a daily basis left its mark on his memory, to surface many years later in his canvases.last_img read more