A research team from Russia, Belarus and China has developed microscopic lasers on sapphire substrates capable of emitting ultraviolet light at room temperature.
These devices are characterized by extremely small sizes of about two micrometers, which is comparable to the size of a bacterium.
The press service of the Higher School of Economics in Moscow reported that these lasers can be used in sensors, optical chips, and communication devices.
Edward Moiseev, senior researcher at the International Laboratory for Quantum Optoelectronics at the Graduate School of Economics, explained: "Sapphire is widely used in industries and can be handled in ways familiar to microelectronics, namely layering, pattern forming, and etching of device elements, which opens the way for the creation of integrated photonic chips for spectroscopy, biosensors, and communication systems in the ultraviolet range."
The research team has been working for many years to develop ultra-small lasers that can be integrated into integrated circuits and miniaturized devices comparable in size to red blood cells . Achieving this is a highly complex process because miniaturizing the laser leads to a rapid increase in problems with light trapping within the resonator, a structure where light is reflected and amplified many times over.
Scientists recently discovered that this problem can be solved using a so-called " whispering gallery" effect, along with a special insulating layer made of a mixture of aluminum nitride and gallium aluminum nitride . The composition of this layer gradually changes as the material thickens. This intermediate layer compensates for the mechanical stresses between the substrate and the gallium-indium nitride layers, and also reduces radiation leakage, allowing the laser to operate stably even at small scales.
Subsequent experiments with these structures showed that the use of ruby-based substrates allows them to be used to create compact lasers operating in the deep ultraviolet range. Their performance rivals that of other top compact laser models, but the diameter of the emitting element itself is only two micrometers, a size comparable to that of bacteria.
The origin of the name "Whispering Gallery":
The name is derived from a famous phenomenon in the dome of St. Paul's Cathedral in London. If someone whispers towards the wall of the dome on one side, another person standing on the other side of the dome (tens of meters away) can hear the whisper very clearly.
This happens because the sound waves are repeatedly reflected off the curved walls of the dome and slide along the surface without losing their energy, as if they were "walking" on the wall.
How does the "whispering gallery" work in physics (light and lasers)?
When used in light or lasers, the concept relies on total internal reflection . When a beam of light enters a very small, circular object (such as a sphere or glass disc), the light is reflected off the internal walls at very large angles, causing it to swirl around the perimeter and become trapped in a very small circular orbit.
In the context of micro lasers, the "Whispering Gallery" represents the magic solution to the problem of miniaturization, and its idea lies in the following:
In a regular laser, you need mirrors facing each other to confine the light.
In a miniature laser (disc-shaped or spherical), the curved surface itself acts as a "circular mirror". The light reflected internally travels in this circular orbit (the whispering gallery effect) and remains trapped long enough to be amplified and become a laser, without the need for a large area or external mirrors.
This is why scientists were able to create a laser that is only 2 micrometers in size (smaller than a red blood cell) while maintaining its efficiency.
