New Laser Can Recycle Lost Energy

KAIST scientists have fabricated a new laser system generating highly interactive quantum particles at room temperature. The team published their findings recently, noting that the breakthrough could lead to single microcavity laser systems requiring lower threshold energy as energy loss increases.The system created by the researchers shines a light through a single hexagon-shaped microcavity that has been treated with a loss-modulated silicon nitride substrate. The system can generate a polariton laser at room temperature, which is significant because that type of generation typically requires cryogenic temperatures. Researchers also discovered that while energy is typically lost during laser operation, the new system reduced the amount of energy needed as energy loss increased.

Exploiting their discovery could lead to the development of high-energy, low threshold lasers usable for future quantum optical devices. The team applied a concept in quantum physics known as parity-time reversal symmetry. That allows energy loss to be used as gain can be used to reduce laser threshold energy for classical optical devices and sensors. It can also be used to control the direction of light.

The key to the breakthrough is design and materials. The hexagonal microcavity divides light into different modes, with one that passes through the upward-facing triangle of the hexagon and the other that passes through the downward-facing triangle. Both modes for the light particles have the same energy but don't interact.

The light particles interact with other particles called excitons provided by the hexagonal microcavity, made of semiconductors. The interaction creates new quantum particles called polaritons that interact with each other to generate the polariton laser. Scientists found that by controlling the degree of loss between the microcavity and the semiconductor substrate, threshold energy becomes smaller as energy loss increases.