Synopsis: A Polariton Beam Amplifier

A scheme based on a planar waveguide can amplify a beam of polaritons without distorting it.
Synopsis figure
D. Niemietz et al., Phys. Rev. B (2016)

Polaritons are hybrid particles resulting from the coupling of photons to excitations of a material like phonons or excitons (electron-hole pairs). They could be used to carry signals in high-speed logic devices, but polaritons decay rapidly as they travel, making their amplification a key requirement for applications. However, demonstrated amplifiers often perturb or distort the polariton beam. Now, Marc Aßmann at the Technical University of Dortmund, Germany, and co-workers have realized a polariton amplifier that avoids this problem by trapping the polariton beam as it gets amplified.

Polaritons are typically created by hitting a solid with ultrashort laser pulses, they then propagate laterally away from the excitation region. Propagating polaritons can be amplified by a second laser, which creates excitons that, under certain conditions, provide a gain medium for polaritons. However, in previous schemes, the excitons also repelled the polariton beam, causing it to scatter or split into multiple unwanted beams.

Aßmann’s group engineered a planar waveguide made of quantum-well layers in which polaritons can be efficiently generated. By illuminating the device with two concentric semicircular laser spots, the researchers were able to generate a U-shaped “chicane” of polaritons, which flowed between the laser spots. At the output of the chicane the polaritons were channeled into a thicker section of the waveguide that acted as a polariton trap and amplifier. Thanks to the trapping effect, the beam was amplified sevenfold without being scattered.

This research is published in Physical Review B.

–Matteo Rini

Matteo Rini is the Deputy Editor of Physics.


Features

More Features »

Announcements

More Announcements »

Subject Areas

OpticsCondensed Matter Physics

Previous Synopsis

Fluid Dynamics

Droplet Hats

Read More »

Next Synopsis

Acoustics

Bang a Gong

Read More »

Related Articles

Synopsis: Reflectivity of Ultrathin Mirror Switches with Voltage
Semiconductor Physics

Synopsis: Reflectivity of Ultrathin Mirror Switches with Voltage

Researchers designed an atomically thin mirror with electronically switchable reflectivity that could be useful in optoelectronic circuits.   Read More »

Viewpoint: Spin Gyroscope is Ready to Look for New Physics
Optics

Viewpoint: Spin Gyroscope is Ready to Look for New Physics

An enhanced version of a magnetometer based on atomic spins could be used to search for theoretically predicted exotic fields with ultrahigh sensitivity. Read More »

Synopsis: An Atlas for 2D Metals
Materials Science

Synopsis: An Atlas for 2D Metals

A new “atlas” lists the predicted properties of two-dimensional materials that could be formed from many metallic elements in the periodic table. Read More »

More Articles