Translation. Region: Russian Federal
Source: State University Higher School of Economics – State University Higher School of Economics –
Researchers HSE University in Saint Petersburg have found a way to create efficient microlasers with a diameter of only 5–8 micrometers. They operate at room temperature, do not require cooling, and can be built into microchips. The scientists used the whispering gallery effect to confine light and buffer layers to reduce energy leakage and stress. The approach is promising for integrating lasers into chips, sensors, and quantum technologies. Study published in “Letters to the Journal of Technical Physics”.
The devices around us are becoming more compact without losing functionality. Smartphones solve problems that previously required a computer, and small cameras shoot almost like professional ones. Miniaturization has also affected lasers — sources of directed light radiation that are built into optical chips, sensors, medical devices, and communication systems.
But it is not easy to reduce the size of a laser while maintaining its optical properties, efficiency and reliability. Developing a laser 5–8 micrometers in size (roughly the diameter of a red blood cell) requires complex calculations, and its production requires high precision. The main difficulty lies in the design of the laser itself. Unlike conventional light sources, lasers amplify radiation inside a resonator – a structure where light is repeatedly reflected and amplified. And the more compact the laser, the more difficult it is to contain the light inside it so that it is repeatedly reflected, amplified and does not lose energy – this is what is important for its stable operation.
Another difficulty is defects in the material. Lasers use crystals that can amplify light. But when they are grown, microscopic defects often arise that reduce the efficiency of light generation. To minimize such disturbances, scientists carefully select the synthesis conditions and model the properties of the crystals in advance in different modes. At the same time, solving one problem often causes others to appear, and laser development becomes a constant search for balance.
Scientists from the National Research University Higher School of Economics have created microlasers with a diameter of only 5–8 micrometers that operate at room temperature. They used a crystalline structure of indium, gallium, nitrogen, and aluminum compounds grown on a silicon substrate. To confine the light in a tiny space, the scientists used the whispering gallery effect.
“This phenomenon is well known in acoustics: in some churches and cathedrals, you can whisper words near one wall, and the sound will be clearly heard near the opposite wall, despite the fact that under normal conditions the sound would not travel such a distance. A similar effect allows light to be reflected multiple times inside a disk microlaser, thereby minimizing losses,” explains the senior researcher. International Laboratory of Quantum Optoelectronics HSE University in St. Petersburg Eduard Moiseev.
However, even under such conditions, light waves can partially escape into the substrate and be lost. To avoid this, the researchers added a stepped buffer layer. It compensates for mechanical stress between the silicon and nitride layers and reduces radiation leakage, allowing the laser to operate stably even at small sizes.
“Our microlasers operate stably at room temperature, without cooling systems, which makes them convenient for real use. In the future, such devices will allow the creation of more compact and energy-efficient optoelectronic devices,” explains Natalia Kryzhanovskaya, head of the International Laboratory of Quantum Optoelectronics at the National Research University Higher School of Economics in St. Petersburg.
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