First boson laser could save power Stanford University University of Michigan rightOriginal StudyPosted by Bjorn Carey-Stanford on May 24 2013STANFORD (US)  � Scientists have demonstrated a revolutionary electrically driven polariton laser that could significantly improve the efficiency of lasers. The physics powering lasers has remained relatively unchanged through 50 years of use. The new system however makes use of the unique physical properties of bosons subatomic particles that scientists have attempted to incorporate into lasers for decades. �We ve solidified our physical understanding and now it s time we think about how to put these lasers into practice � says physicist Na Young Kim a member of the Stanford University team which was led by Yoshihisa Yamamoto professor of electrical engineering and of applied physics.  �This is an exciting era to imagine how this new physics can lead to novel engineering. �Electrically driven polariton lasers Kim says would operate using one-hundredth of the power of conventional lasers and could one day be used in many places from consumer goods to quantum computers. The findings are published in Nature.Einstein s predictionAll lasers are based on Einstein s principle of stimulated emission. Charged particles such as electrons exist in discontinuous energy levels like rungs on a ladder. An electron provided with enough energy can become excited and  �jump � up to a higher energy level. Excited electrons can spontaneously fall down to an available lower energy level shooting off the difference in energy as a bit of light called a photon.The amount of time that passes before an excited electron drops down and releases a photon is usually random. However Einstein predicted that if an electron in an upper energy level was exposed to a photon with proper energy the electron would instantly fall down and release a second photon identical to the first one.A laser keeps this process going by continually providing energy for electrons to move into higher energy levels. As more and more electrons are stimulated to release photons the additional photons stimulate more and more electrons. Some of the photons are allowed to escape from the device to serve a purpose such as reading data off a CD or etching a circuit board.The process however is inefficient. There is a hard limit to the number of electrons that can inhabit a given energy level at any given time and conventional lasers waste energy unnecessarily exciting electrons to higher energy levels even when the lower levels are too full to accept the excited electrons when they fall.Exciting excitonsKim s polariton laser however pairs electrons with so-called  �holes � to form another type of particle an exciton. A hole is a gap where an electron could exist in a structure and is treated by physicists as a real separate particle.These excitons are bosons and an unlimited number of them can inhabit any given energy level. Using bosons in lasers has been a scientific goal for decades but Yamamoto s team is the first to successfully build an electrically driven laser using bosons. (The result was recently reproduced and confirmed by scientists at the University of Michigan who published their work in the journal Physical Review Letters.)This change drastically reduces the amount of power required to run the laser. The current iteration of the polariton laser requires two to five times less energy than a comparable conventional laser but could require 100 times less energy in the future. �The outcome would look similar to that of the traditional photon lasers but the physical mechanisms inside are very different � Kim says.The laser consists of an electron reservoir and a hole reservoir. When a current is applied electrons and holes come together to form excitons in excited energy levels. When a photon hits an exciton it forms a polariton and emits an identical photon.The entire process is like a solar cell in reverse Kim says. �In a solar cell you use light to form excitons and separate them into an electron and a hole electrically � she says.  �We bring together an electron and a hole electrically to emit light. �One benefit of the electrically driven polariton laser is it only needs to be attached to a power supply to emit photons allowing it to be easily integrated with existing semiconductor chips in the future.Still too coolThe current polariton laser can run only at a chilly 4 degrees Kelvin (minus 452 degrees Fahrenheit) and requires constant cooling by liquid helium to prevent the excitons inside the gallium arsenide semiconductors from being pulled apart by thermal energy.The team hopes switching to a material that requires more energy to break apart excitons will allow them to build polariton lasers that work at room temperature an important step toward widespread use. �We re hoping we can replace conventional semiconductor lasers with these polariton lasers in the future � Kim says.  �There are a lot of hurdles in the way but we aim to bring novel devices built on sound physical understanding for cost-effectiveness and efficient power consumption. �Stanford researchers are already using the polariton laser to develop quantum computers and quantum simulators. Kim believes similar lasers will be available to those outside the scientific community within the next five to 10 years.Researchers conducted the work in collaboration with the National Institute of Informatics in Tokyo Japan and a team from the University of W � �rzburg in Germany led by physicist Alfred Forchel.The National Science Foundation the DARPA QUEST program the Japan Society for the Promotion of Science and the State of Bavaria supported the research.Source: Stanford UniversityYou are free to share this article under the Creative Commons Attribution-NoDerivs 3.0 Unported license.