Quantum dots selftune their color for ultraefficient nano lasers

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. The laser, one of the most valuable scientific instruments, is getting smaller and more efficient. Scientists have designed a miniature laser, whose nanoscale dimensions and low optical losses will be instrumental in future developments of integrated photonic circuits. Compared with a regular flashlight, a laser emits a very intense and strongly collimated beam of monochromatic light. These properties arise from an interaction between the gain medium and an optical cavity. In order for a laser to generate its tiny colored spot, the active gain medium, which amplifies the beam, must provide photons that are all emitted at the same wavelength in a process called “stimulated emission.” While generating sufficient stimulated emission usually requires a great deal of gain material, scientists have discovered a method to create a nano laser with only a few tiny objects called “quantum dots.” Physicists from UC Santa Barbara and the University of Pavia in Italy have designed a new nano-device that works with only two to four quantum dots. The design, which provides ultra-efficient lasing performance, is published in a recent Physical Review Letters. “While conventional quantum dot lasers require many layers with thousands of dots, this new design takes advantage of a quantum dot property that effectively self-tunes the dots’ photon emission wavelength into resonance with the cavity,” explained co-author Stefan Strauf to PhysOrg.com. When the gain medium resonates with the cavity, a laser can be created.” Individual quantum dots have very sharp transition energy, and a large number of dots will display a broad emission bandwidth due to their natural size variations. While this broad emission makes them an ideal gain material for large volume lasers, device miniaturization presents a challenge since the sharp transitions of a few quantum dots no longer resonate with the laser cavity.The team of scientists found a way out of this dilemma by embedding the dots in a photonic crystal nano cavity, which enables light to be confined in a very small volume. A photonic crystal can be made by drilling many holes within a thin membrane of a semiconductor material such as GaAs (see figure). This particular design provides a finely tuned distribution of the electromagnetic field inside the nanocavity, which optimizes the overlap of the embedded quantum dots with the field profile and increases the quality of the cavity. ‘Connecting the dots’ for quantum networks Fig. A. In this design of the ultra-efficient photonic crystal nano laser, a top-view electron microscope image shows the drilled hole pattern in a GaAs membrane. The three missing holes in a row at the center define the nano cavity, which confines the light. To finely tune the electromagnetic field, a waveguide (w) has been inserted and neighboring holes have been resized and shifted. Photo Credit: Stefan Strauf. Explore furthercenter_img “This optimization process is a lot like the skillful fine-tuning of a violin producing resonance tones, but for light instead of sound,” said Strauf. This design drastically inhibits the emission of the dots at their natural sharp energies and forces them to interact with electronic carriers in their immediate surroundings. Because this interaction provides additional energy, the dots can self-tune their emission color into resonance with the cavity. Since this is a very pronounced interaction, the nano lasers display a hundredfold improvement of their lasing threshold values compared with any other semiconductor laser. In addition to the record low lasing threshold produced with a couple of quantum dots, the scientists found a much higher optical efficiency than exhibited in high density quantum dot devices. Measuring the optical efficiency with the spontaneous emission coupling factor (which has a theoretical limit of 1.0), the team found that the new method exhibited a value of 0.85, while multi-layer quantum dot lasers have a factor ranging from 0.1-0.2. “The record low lasing thresholds combined with the high efficiencies make these nano lasers useful for future applications in integrated photonic circuits on a chip and for bio sensing of individual molecules,” said Strauf. “Such nano lasers may now be formed with only a few or even a single quantum dot.”Citation: Strauf, S. et al. Self-Tuned Quantum Dot Gain in Photonic Crystal Lasers. Physical Review Letters 96, 127404 (2006).By Lisa Zyga, Copyright 2006 PhysOrg.com Fig. B and C. (B) This image shows a close-up of the resulting field profile around the tuned nano cavity region, where the yellow-white color is the highest field strength. (C) This atomic-force microscope image shows a typical layer of the low-density quantum dot gain material that is embedded underneath the surface of the membrane. The bright spots are individual InAs quantum dots, about 20 nm in size. The dashed blue circles indicate that there are on average only a few dots spatially positioned within the field profile of the nano cavity. Photo Credit: Stefan Strauf. Citation: Quantum dots self-tune their color for ultra-efficient nano lasers (2006, April 14) retrieved 18 August 2019 from https://phys.org/news/2006-04-quantum-dots-self-tune-ultra-efficient-nano.htmllast_img read more

Researchers show increased risk of predators can evoke adaptive response in birds

first_imgA juvenile Eurasian Sparrowhawk in Betuwe, Netherlands. Image credit: Wikipedia. © 2010 PhysOrg.com 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. More information: Predation risk affects offspring growth via maternal effects, Michael Coslovsky, Heinz Richner, Functional Ecology, Article first published online: 1 March 2011. DOI: 10.1111/j.1365-2435.2011.01834.xvia Nature. To get these results, Coslovsy and Richner went out into Bremgartenwald forest, near Bern and chose a group of great tits to use as a study group. They then exposed part of the group of mothers (during ovulation) to stuffed sparrow hawks and audio recordings of their calls; the control group was exposed to song thrushes. Two days after the nestlings hatched, they (both groups) were captured, tagged and carted off to another part of the forest to be raised by adoptive parents. As they grew, they were all monitored and it was then the researchers discovered that the offspring of stressed mothers were in fact smaller, as expected, but they also grew their wings at an unusually brisk pace, and grew them longer (1.8 millimeters on average) than other birds from the control group.Prior to this research, it’s been assumed that smaller growth in bird offspring is generally a negative effect brought about by a buildup of the stress hormone corticosterone. Now, with the news that smaller offspring also produce wings at an earlier age, and grow them longer, it might be argued that all three changes are nature’s way of helping the nestlings survive in a more hostile than normal environment; less weight, combined with longer wings at an earlier age, would seem to increase the nestling’s ability to fly away at a younger age, and to do so more speedily to ward off attacks.Of course, the results shown by Coslovsy and Richner are just one study, and have only been done on one species of bird; many more field trials will have to be made before any definitive conclusions can be drawn. Scientists shake Darwin’s foundation — chickens inherited parents’ stress symptoms (PhysOrg.com) — Evolutionary ecologists Michael Coslovsky and Heinz Richner of the University of Bern in Switzerland, have published a study in Functional Ecology where they show that when a female bird is exposed to more stress from predators, such as hawks, when ovulating, they tend to produce offspring that are smaller, which isn’t a surprise as stressed offspring in many species wind up smaller than average; the surprise is that the smaller offspring also grew their wings both faster and longer than what would be considered normal for their species. Citation: Researchers show increased risk of predators can evoke adaptive response in birds (2011, March 28) retrieved 18 August 2019 from https://phys.org/news/2011-03-predators-evoke-response-birds.htmllast_img read more

from hungary with love

first_imgThe Hungarian Information and Cultural Centre, presents international artworks exhibition Cocos Nuciferas by MD Deleep from France-Switzerland and Spirit and Matter – Three Artists – Three Generation by Ilona Lovas, Anna Makovecz and Villo Turcsány from Hungary, organised by Anna Bagyó , curated by Katalin Keserü. The two exhibitions will be inaugurated by Szilvezster Bus, Ambassador of Hungary, in the presence of François Richier, Ambassador of France. Also Read – ‘Playing Jojo was emotionally exhausting’The artworks by MD Deleep are an attempt to translate and share spiritual and ethnic emotions, sensations through these intermediaries. Thus, it is important that there exists barely any distance between the viewer and the work. With such participation, there is enough scope for the individuals to enter the specific work-scope and create new relationships between creation, creator and spectator. The artist’s aim is to work in interaction with the public, resulting in a timeless piece, which everyone can interpret in his/ her own way. An exhibition-cum-performance, curated by art historian, writer and curator Katalin Keserü, organised by art consultant Anna Bagyó, with the participation of three Hungarian woman artists: Ilona Lovas, Anna Makovecz and Villo Turcsány. The three artists, representing three different generations, coexist well with each other. Their works examine the metamorphosis of matter, body and spirit. These evergreen topics of art are translated into the language of contemporary mediums and will be presented as installations, photos and videos.When: January 27 – February 28 Where: HICC Garden and Exhibition Hall.last_img read more

S Machendranathan is new AERA chairman

first_imgS Machendranathan took over as chairperson of Airports Economic Regulatory Authority of India on Monday.   Machendranathan who hails from Tirunelveli District, Tamil Nadu had a distinguished  academic career. After completing MBA from Cochin University, he joined the Indian Police Service (IPS) in 1977 and thereafter the Indian Administrative Service (IAS) in 1979. An IAS officer of the Tamil Nadu cadre, S Machendranathan held several important positions in the Government of Tamil Nadu and in the Government of India.   Also Read – I-T issues 17-point checklist to trace unaccounted DeMO cashIn the Government of Tamil Nadu, he worked as Collector of Thanjavur District; Commissioner/ Secretary to the Government of Tamil Nadu in the Departments of Transport, Food, Cooperation and Consumer Protection; Chairman of Tamil Nadu Electricity Board.  And in the Government of India, he worked as Chairman of Tuticorin Port Trust; Additional Secretary & Financial Advisor in the Ministry of Steel as well as in the Ministry of Civil Aviation and finally as Secretary (Coordination) in Cabinet Secretariat, before superannuating from the Government Service in March, 2014.  He has also served as Government Director in several Public Sector companies such as Air India, Airports Authority of India, Steel Authority of India Limited, Rashtriya Ispat Nigam Limited, Kudremukh Iron Ore Company Limited and Metallurgical & Engineering Consultants (India) Limited.last_img read more

Traditional homes are more sustainable

first_imgAlthough people around the world want the kind of houses seen in Europe and North America, rather than those they grew up with, traditional homes can be more sustainable, says an Indian-origin engineer.Industrial building materials are often scarce and expensive and alternative, locally sourced, sustainable materials are often a better choice, said Khanjan Mehta, assistant professor of engineering design at the Pennsylvania State University.“People want to build a good house, everyone wants to have a good house. But what makes a good house? Is it wood, steel, concrete or bamboo? It all depends on the context,” Mehta said.Individuals can use locally available but scarce materials to build their individual homes, but that strategy will not build all the houses in a city or village because it cannot be scaled up to meet the demand.“People see western stuff as better, more modern and therefore they think it is good,” said Mehta.“Traditional homes can be just as cool, and maybe more sustainable,” he said.Mehta shared his thoughts at the annual meeting of the American Association for the Advancement of Science in Washington DC on Friday.last_img read more