Nanotechnology Now





Heifer International

Wikipedia Affiliate Button


DHgate

Home > Press > Princeton researchers discover new type of laser

Quantum cascade lasers are small and efficient sources of mid-infrared laser beams, which are leading to new devices for medical diagnostics and environmental sensing.

Credit: Frank Wojciechowski
Quantum cascade lasers are small and efficient sources of mid-infrared laser beams, which are leading to new devices for medical diagnostics and environmental sensing.

Credit: Frank Wojciechowski

Abstract:
A Princeton-led team of researchers has discovered an entirely new mechanism for making common electronic materials emit laser beams. The finding could lead to lasers that operate more efficiently and at higher temperatures than existing devices, and find applications in environmental monitoring and medical diagnostics.

Princeton researchers discover new type of laser

Princeton, NJ | Posted on December 22nd, 2008

"This discovery provides a new insight into the physics of lasers," said Claire Gmachl, who led the study. Gmachl, an electrical engineer, is the director of the Mid-Infrared Technologies for Health and the Environment (MIRTHE) center. The phenomenon was discovered in a type of device called quantum cascade laser, in which an electric current flowing through a specially designed material produces a laser beam. Gmachl's group discovered that a quantum cascade laser they had built generated a second beam with very unusual properties, including the need for less electrical power than the conventional beam. "If we can turn off the conventional beam, we will end up with a better laser, which makes more efficient use of electrical power," said Gmachl.

The team that conducted the study includes Gmachl's graduate student Kale Franz, who built the laser that revealed the new phenomenon, and Stefan Menzel, a graduate student from the University of Sheffield, UK, who unearthed the unique properties of the phenomenon during an internship at Princeton University last summer. The study was published online in Nature Photonics on Dec. 14.

The light emitted by a laser differs fundamentally from light produced by common sources such as the sun, fire, or electric lamps. According to the field of physics called quantum electrodynamics, light is made up of particles called photons. Common sources of light emit photons that are in a random order, like crowds milling about a busy marketplace. In contrast, photons in a laser are "in sync" with each other, like a music band marching in formation. This property, called coherence, allows laser light to shine in an intense, narrow beam of a single, very pure color.

One way to produce a laser beam is to pass an electric current through a semiconductor such as gallium arsenide. The electric current pumps energy into the material, forcing a large number of its electrons to a higher energy level than normal. Under certain conditions, these electrons drop to a lower level of energy, and emit the extra energy in the form of synchronized photons of light. This is the mechanism underlying lasers used in CD writers, laser pointers and other common electronic devices.

The laser used in the Princeton study is a special type called a quantum cascade laser. Built at Princeton University's nanofabrication facility, the device is about one-tenth as thick as a human hair and 3 millimeters long. Despite its tiny size, it is made of hundreds of layers of different semiconductor materials. Each layer is only a few atoms thick. In this device, electrons "cascade" down through the layers as they lose energy and give off synchronized photons.

In an earlier study published in Applied Physics Letters in June 2007, Franz, Gmachl and others had reported that a quantum cascade laser they had built unexpectedly emitted a second laser beam of slightly smaller wavelength than the main one. Further studies by Menzel and others revealed that the second beam could not be explained by any existing theory of quantum cascade lasers. Unlike a conventional semiconductor laser, the second beam grew stronger as the temperature increased, up to a point. Further, it seemed to compete with the "normal" laser, growing weaker as the latter strengthened when more electric current was supplied. "It's a new mechanism of light emission from semiconductor lasers," said Franz.

To explain this mechanism, the researchers invoked a quantum property of electrons called momentum. In the conventional view of quantum cascade lasers, only electrons of nearly zero momentum participate in "lasing" (producing laser light). Further, a substantial number of electrons has to attain the same level of energy and momentum - be in a so-called "quasi-equilibrium" condition -- before they can participate in laser action. In contrast, studies by Gmachl's group showed that the second laser beam originated from electrons of lower energy, but higher momentum that were not in equilibrium. "It showed, contrary to what was believed, that electrons are useful for laser emission even when they are in highly non-equilibrium states," said Franz.

The new laser phenomenon has some interesting features. For instance, in a conventional laser relying on low momentum electrons, electrons often reabsorb the emitted photons, and this reduces overall efficiency. In the new type of laser, however, this absorption is reduced by 90%, said Franz. This could potentially allow the device to run at lower currents, and also makes it less vulnerable to temperature changes. "It should let us dramatically improve laser performance," he said.

The device used in the study does not fully attain this level of performance, because the conventional, low-efficiency laser mechanism dominates. To take full advantage of the new discovery, therefore, the conventional mechanism would need to be turned off. The researchers have started to work on methods to achieve this outcome, said Franz.

Unlike other lasers, quantum cascade lasers operate in the mid- and far-infrared range, and can be used to detect even minute traces of water vapor, ammonia, nitrogen oxides, and other gases that absorb infrared light. As a result, these devices are finding applications in air quality monitoring, medical diagnostics, homeland security, and other areas that require extremely sensitive detection of different chemicals. The new discovery should help make these devices smaller, more efficient, and more sensitive, said Gmachl.

The research was partly sponsored by the MIRTHE center, which is funded by the National Science Foundation and directed by Gmachl. MIRTHE is a multi-institutional research collaboration for developing compact sensors to detect trace amounts of gases in the atmosphere and in human breath. Partial support was also provided by the European Union's Marie Curie Research Training Network and its Physics of Intersubband Semiconductor Emitters (POISE) program, which sponsored Stefan Menzel's visit to Princeton University. Kale Franz was supported by the NSF Graduate Fellowship Program.

####

For more information, please click here

Contacts:
Steven Schultz

609-258-3617

Copyright © Princeton University, Engineering School

If you have a comment, please Contact us.

Issuers of news releases, not 7th Wave, Inc. or Nanotechnology Now, are solely responsible for the accuracy of the content.

Bookmark:
Delicious Digg Newsvine Google Yahoo Reddit Magnoliacom Furl Facebook

Related News Press

News and information

Researchers develop new way to manufacture nanofibers May 21st, 2015

Nanotherapy effective in mice with multiple myeloma May 21st, 2015

Turn that defect upside down: Twin boundaries in lithium-ion batteries May 21st, 2015

INSIDDE: Uncovering the real history of art using a graphene scanner May 21st, 2015

Govt.-Legislation/Regulation/Funding/Policy

Nanotherapy effective in mice with multiple myeloma May 21st, 2015

Turn that defect upside down: Twin boundaries in lithium-ion batteries May 21st, 2015

INSIDDE: Uncovering the real history of art using a graphene scanner May 21st, 2015

SUNY Poly CNSE and NIOSH Launch Federal Nano Health and Safety Consortium: May 20th, 2015

Sensors

Record high sensitive Graphene Hall sensors May 21st, 2015

Graphene enables tunable microwave antenna May 15th, 2015

Janusz Bryzek Joins MEMS Industry Group to Lead New TSensors Division - New Division will Focus on Accelerating Development of Emerging Ultra-high Volume Sensors Supporting Abundance, mHealth and IoT May 14th, 2015

Nano-policing pollution May 13th, 2015

Discoveries

Simulations predict flat liquid May 21st, 2015

Researchers develop new way to manufacture nanofibers May 21st, 2015

Nanotherapy effective in mice with multiple myeloma May 21st, 2015

Turn that defect upside down: Twin boundaries in lithium-ion batteries May 21st, 2015

Announcements

Researchers develop new way to manufacture nanofibers May 21st, 2015

Nanotherapy effective in mice with multiple myeloma May 21st, 2015

Turn that defect upside down: Twin boundaries in lithium-ion batteries May 21st, 2015

INSIDDE: Uncovering the real history of art using a graphene scanner May 21st, 2015

Homeland Security

UCLA nanoscientists are first to model atomic structures of three bacterial nanomachines: Cryo electron microscope enables scientists to explore the frontiers of targeted antibiotics April 21st, 2015

Optics, nanotechnology combined to create low-cost sensor for gases April 3rd, 2015

The Universitat Politècnica de València is coordinating a European project to develop a device for the quick and early diagnosis of cancer March 7th, 2015

Detecting chemical weapons with a color-changing film January 28th, 2015

Environment

Directa Plus in Barcelona to present the innovative project GEnIuS for oil spills clean-up activities: The company has created a graphene-based product for the remediation of water contaminated by oil and hydrocarbons May 21st, 2015

Nano-policing pollution May 13th, 2015

Chemists strike nano-gold: 4 new atomic structures for gold nanoparticle clusters: Research builds upon work by Nobel Prize-winning team from Stanford University April 28th, 2015

Nanoparticles Used to Improve Mechanical, Thermal Properties of Cellulose Fibers April 23rd, 2015

Photonics/Optics/Lasers

Samtec, Global Provider of Interconnect Systems, Joins IRT Nanoelec Silicon Photonics Program May 21st, 2015

Taking control of light emission: Researchers find a way of tuning light waves by pairing 2 exotic 2-D materials May 20th, 2015

Computing at the speed of light: Utah engineers take big step toward much faster computers May 18th, 2015

Wearables may get boost from boron-infused graphene: Rice U. researchers flex muscle of laser-written microsupercapacitors May 18th, 2015

NanoNews-Digest
The latest news from around the world, FREE




  Premium Products
NanoNews-Custom
Only the news you want to read!
 Learn More
NanoTech-Transfer
University Technology Transfer & Patents
 Learn More
NanoStrategies
Full-service, expert consulting
 Learn More










ASP
Nanotechnology Now Featured Books




NNN

The Hunger Project