1,000 times less energy needed for alternative polariton laser

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An alternative to the laser, the Light Amplification by Stimulated Scattering of Polaritons (LASSP) has been achieved by the US University of Michigan, and it needs 1,000 times less energy to operate.

Using polaritons, particles that are part light, and part matter, to create a coherent beam of light, researchers predict that LASSP can be used in any application where a laser is today, such as optical communications and surgery. The LASSP can only operate at cryogenic temperatures now, but its developers expect to be able to get it to work at room temperature.

The researchers generated polaritons by electrically exciting samples of the semiconductor gallium arsenide in a microcavity. The polaritons quickly decayed by transferring their energy to photons, which, due to properties of the original polaritons, escaped the cavity as a single-coloured beam of light.

Pallab Bhattacharya is the Charles M. Vest distinguished university professor of electrical engineering and computer science, and the James R. Mellor professor of engineering, who led the LASSP team. Bhattacharya  said: ‘We report the first electrically injected polariton laser. Since the proposal of such a device in 1996, researchers around the world have been trying to demonstrate it. It is no longer a scientific curiosity. It's a real device.’

Bhattacharya expects the LASSP to be used in computers as microchips move to using light for communication on the chip and from chip to chip. ‘Our success is based on two novel features', he added. ‘First, we deployed additional electron-polariton scattering to enhance the relaxation of polaritons to form the coherent ground state. Second, we applied a magnetic field so that more carriers can be injected with the bias current without losing the required conditions for polariton lasing.’

Battacharya's team's work was reported in a paper in the journal Physical Review Letters.