Imperfections and irregularities are unavoidable in nanoscience due to the limited level of control of nanofabrication processes. Disorder is potentially detrimental to nanosystems but if well-contained, disorder could lead to novel physical concepts and applications. By introducing a slight degree of disorder in nanolasers, the laser no longer emits in one specific direction but in all directions.
Development of nanoscale lasers (smaller than the thickness of a human hair) is a very active field of research. In a normal laser, each photon (light particle) is cloned many times in a medium that is located inside a cavity (e.g. a pair of mirrors between which the photon moves back and forth, producing other photons with the same characteristics). To achieve laser emission, an electrical current is usually injected through the medium or it is illuminated with high-energy light. The minimum energy needed for a laser to emit is called the lasing threshold.
A different kind of laser is the polariton laser. This works on the principle not of cloning photons but making non-identical photons identical in much the same way as water vapor molecules, moving in all directions with different velocities, are condensed into a single drop. Condensation of photons gives rise to the intense and directional emission characteristic of a laser. An important advantage of polariton lasers is that they have a much lower lasing threshold, which makes them excellent candidates for many applications.
A major problem with polariton lasers has been that they need to operate at very low temperatures (like vapor condensation that takes place only when the temperature is lowered) but by using organic materials, it is possible to obtain polariton laser emission even at ambient temperature. Researchers have developed a new type of low-energy nanoscale laser that shines in all directions. The key to its omnidirectional light emission is the introduction of irregularities in the materials.
The new polariton laser consists of a regular pattern of silver nanostripes covered with colored PMMA-polymer whose dye comprises organic emitting molecules; however, the silver stripes deliberately have some degree of imperfection and disorder. The emission from this non-perfect nanolaser is omnidirectional and mainly is determined by the properties of the organic molecules. This result is not expected in the framework of condensation, as omnidirectional emission requires emissions from independent organic molecules instead of the collective emission that is typical for condensation. The demonstration of omnidirectional emission defines new boundaries for the development of nanoscale lasers at ambient temperatures.
The laser is a good candidate for microscopy lighting, which currently uses LEDs; LiDAR is another potential application. Current LiDAR uses one or more lasers and a set of fast-moving mirrors in order to cover large areas to image distant objects. An omnidirectional laser does not require the moving mirrors, thereby significantly reducing the complexity.
For more information, contact Barry Van Der Meer at