Forum for Science, Industry and Business

Many bodies make 1 coherent burst of light

In a flash, the world changed for Tim Noe – and for physicists who study what they call many-body problems.

The Rice University graduate student was the first to see, in the summer of 2010, proof of a theory that solid-state materials are capable of producing an effect known as superfluorescence.

That can only happen when "many bodies" – in this case, electron-hole pairs created in a semiconductor – decide to cooperate.

Noe, a student of Rice physicist Junichiro Kono, and their research team used high-intensity laser pulses, a strong magnetic field and very cold temperatures to create the conditions for superfluorescence in a stack of 15 undoped quantum wells. The wells were made of indium, gallium and arsenic and separated by barriers of gallium-arsenide (GaAs). The researchers' results were reported this week in the journal Nature Physics.

Noe spent weeks at the only facility with the right combination of gear to carry out such an experiment, the National High Magnetic Field Laboratory at Florida State University. There, he placed the device in an ultracold (as low as 5 kelvins) chamber, pumped up the magnetic field (which effectively makes the "many body" particles – the electron-hole pairs – more sensitive and controllable) and fired a strong laser pulse at the array.

"When you shine light on a semiconductor with a photon energy larger than the band gap, you can create electrons in the conduction band and holes in the valence band. They become conducting," said Kono, a Rice professor of electrical and computer engineering and in physics and astronomy. "The electrons and holes recombine – which means they disappear – and emit light. One electron-hole pair disappears and one photon comes out. This process is called photoluminescence."

The Rice experiment acted just that way, but pumping strong laser light into the layers created a cascade among the quantum wells. "What Tim discovered is that in these extreme conditions, with an intense pulse of light on the order of 100 femtoseconds (quadrillionths of a second), you create many, many electron-hole pairs. Then you wait for hundreds of picoseconds (mere trillionths of a second) and a very strong pulse comes out," Kono said.

In the quantum world, that's a long gap. Noe attributes that "interminable" wait of trillionths of a second to the process going on inside the quantum wells. There, the 8-nanometer-thick layers soaked up energy from the laser as it bored in and created what the researchers called a magneto-plasma, a state consisting of a large number of electron-hole pairs. These initially incoherent pairs suddenly line up with each other.

"We're pumping (light) to where absorption's only occurring in the GaAs layers," Noe said. "Then these electrons and holes fall into the well, and the light hits another GaAs layer and another well, and so on. The stack just increases the amount of light that's absorbed." The electrons and holes undergo many scattering processes that leave them in the wells with no coherence, he said. But as a result of the exchange of photons from spontaneous emission, a large, macroscopic coherence develops.

Like a capacitor in an electrical circuit, the wells become saturated and, as the researchers wrote, "decay abruptly" and release the stored charge as a giant pulse of coherent radiation.

"What's unique about this is the delay time between when we create the population of electron-hole pairs and when the burst happens. Macroscopic coherence builds up spontaneously during this delay," Noe said.

Kono said the basic phenomenon of superfluorescence has been seen for years in molecular and atomic gases but wasn't sought in a solid-state material until recently. The researchers now feel such superfluorescence can be fine-tuned. "Eventually we want to observe the same phenomenon at room temperature, and at much lower magnetic fields, maybe even without a magnetic field," he said.

Even better, Kono said, it may be possible to create superfluorescent pulses with any desired wavelength in solid-state materials, powered by electrical rather than light energy.

The researchers said they expect the paper to draw serious interest from their peers in a variety of disciplines, including condensed matter physics; quantum optics; atomic, molecular and optical physics; semiconductor optoelectronics; quantum information science; and materials science and engineering.

There's much work to be done, Kono said. "There are several puzzles that we don't understand," he said. "One thing is a spectral shift over time: The wavelength of the burst is actually changing as a function of time when it comes out. It's very weird, and that has never been seen."

Noe also observed superfluorescent emission with several distinct peaks in the time domain, another mystery to be investigated.

The paper's co-authors include Rice postdoctoral researcher Ji-Hee Kim; former graduate student Jinho Lee and Professor David Reitze of the University of Florida, Gainesville; researchers Yongrui Wang and Aleksander Wojcik and Professor Alexey Belyanin of Texas A&M University; and Stephen McGill, an assistant scholar and scientist at the National High Magnetic Field Laboratory at Florida State University, Tallahassee.

Support for the research came from the National Science Foundation, with support for work at the National High Magnetic Field Laboratory from the state of Florida.

Read the abstract at http://www.nature.com/nphys/journal/vaop/ncurrent/abs/nphys2207.html

Images for download:

media.rice.edu/images/media/NewsRels/0127_KONO.JPG

Rice University researchers have confirmed a long-held theory that solid-state materials are capable of producing an effect known as superfluorescence. From left: Rice physicist Junichiro Kono, postdoctoral researcher Ji-Hee Kim and graduate student Tim Noe. (Credit: Jeff Fitlow/Rice University)

media.rice.edu/images/media/NewsRels/0130_figfs.jpg

Pumping laser pulses into a stack of quantum wells created an effect physicists had long sought but not seen until now: superfluorescence in a solid-state material. The Rice University lab of physicist Junichiro Kono reported the results in Nature Physics. (Credit: Tim Noe/Rice University)

Located on a 300-acre forested campus in Houston, Rice University is consistently ranked among the nation's top 20 universities by U.S. News & World Report. Rice has highly respected schools of Architecture, Business, Continuing Studies, Engineering, Humanities, Music, Natural Sciences and Social Sciences and is known for its "unconventional wisdom." With 3,708 undergraduates and 2,374 graduate students, Rice's undergraduate student-to-faculty ratio is less than 6-to-1. Its residential college system builds close-knit communities and lifelong friendships, just one reason why Rice has been ranked No. 1 for best quality of life multiple times by the Princeton Review and No. 4 for "best value" among private universities by Kiplinger's Personal Finance. To read "What they're saying about Rice," go to http://www.rice.edu/nationalmedia/Rice.pdf

David Ruth | EurekAlert!
Further information:
http://www.rice.edu

Im Focus: Temperature-controlled fiber-optic light source with liquid core

In a recent publication in the renowned journal Optica, scientists of Leibniz-Institute of Photonic Technology (Leibniz IPHT) in Jena showed that they can accurately control the optical properties of liquid-core fiber lasers and therefore their spectral band width by temperature and pressure tuning.

Already last year, the researchers provided experimental proof of a new dynamic of hybrid solitons– temporally and spectrally stationary light waves resulting...

Im Focus: Overdosing on Calcium

Nano crystals impact stem cell fate during bone formation

Scientists from the University of Freiburg and the University of Basel identified a master regulator for bone regeneration. Prasad Shastri, Professor of...

Im Focus: AchemAsia 2019 will take place in Shanghai

Moving into its fourth decade, AchemAsia is setting out for new horizons: The International Expo and Innovation Forum for Sustainable Chemical Production will take place from 21-23 May 2019 in Shanghai, China. With an updated event profile, the eleventh edition focusses on topics that are especially relevant for the Chinese process industry, putting a strong emphasis on sustainability and innovation.

Founded in 1989 as a spin-off of ACHEMA to cater to the needs of China’s then developing industry, AchemAsia has since grown into a platform where the latest...

Im Focus: First real-time test of Li-Fi utilization for the industrial Internet of Things

The BMBF-funded OWICELLS project was successfully completed with a final presentation at the BMW plant in Munich. The presentation demonstrated a Li-Fi communication with a mobile robot, while the robot carried out usual production processes (welding, moving and testing parts) in a 5x5m² production cell. The robust, optical wireless transmission is based on spatial diversity; in other words, data is sent and received simultaneously by several LEDs and several photodiodes. The system can transmit data at more than 100 Mbit/s and five milliseconds latency.

Modern production technologies in the automobile industry must become more flexible in order to fulfil individual customer requirements.

Im Focus: Sharp images with flexible fibers

An international team of scientists has discovered a new way to transfer image information through multimodal fibers with almost no distortion - even if the fiber is bent. The results of the study, to which scientist from the Leibniz-Institute of Photonic Technology Jena (Leibniz IPHT) contributed, were published on 6thJune in the highly-cited journal Physical Review Letters.

Endoscopes allow doctors to see into a patient’s body like through a keyhole. Typically, the images are transmitted via a bundle of several hundreds of optical...