Scientists Develop Effective Microlasers as Small as a Speck of Dust

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Researchers at HSE University–St Petersburg have discovered a way to create effective microlasers with diameters as small as 5 to 8 micrometres. They operate at room temperature, require no cooling, and can be integrated into microchips. The scientists relied on the whispering gallery effect to trap light and used buffer layers to reduce energy leakage and stress. This approach holds promise for integrating lasers into microchips, sensors, and quantum technologies. The study has been published in Technical Physics Letters.

The devices around us are becoming increasingly compact without sacrificing functionality. Smartphones now handle tasks that once required a computer, and small cameras can capture images with quality approaching that of professional equipment. Miniaturisation has also extended to lasers—sources of directed light that are embedded in optical chips, sensors, medical devices, and communication systems. 

However, shrinking a laser while preserving its optical properties, efficiency, and reliability remains a significant challenge. Developing a laser measuring 5–8 micrometres—approximately the diameter of a red blood cell—requires complex calculations, and its fabrication demands high precision. The main challenge lies in the design of the laser itself. Unlike conventional light sources, lasers amplify radiation within a resonator—a structure where light is repeatedly reflected and amplified. The more compact the laser, the harder it is to trap the light inside so that it undergoes continuous reflection and amplification without losing energy, which is essential for stable operation.

Another challenge is the presence of defects in the material. Lasers rely on crystals that can amplify light, but microscopic defects often form during their growth, reducing the efficiency of light generation. To minimise these irregularities, scientists carefully select synthesis conditions and simulate the properties of crystals under various scenarios in advance. However, solving one problem often gives rise to others, turning laser development into a continual search for balance.

HSE scientists have developed microlasers with diameters as small as 5 to 8 micrometres that operate at room temperature. The researchers used a crystal structure composed of indium, gallium, nitrogen, and aluminium compounds grown on a silicon substrate. To trap light in a tiny space, the scientists relied on the whispering gallery effect. 

Eduard Moiseev

'This phenomenon is well-known in acoustics: in some churches and cathedrals, you can whisper words against one wall, and the sound will be clearly heard on the opposite wall—even though, under normal conditions, the sound would not travel that far. A similar effect enables light to be repeatedly reflected inside the disk-shaped microlaser, minimising energy loss,' explains Eduard Moiseev, Senior Research Fellow at the International Laboratory of Quantum Optoelectronics, HSE University–St Petersburg.

However, even under these conditions, light waves can partially escape into the substrate and be lost. To prevent this, the researchers added a stepped buffer layer, which compensates for mechanical stresses between the silicon and nitride layers and reduces radiation leakage, enabling the laser to operate stably even at such small sizes.

The photoluminescence spectrum of the microlaser. A narrow, intense line in the spectrum corresponds to laser radiation, which results from multiple reflections of light inside the microresonator due to the whispering gallery effect and the optical amplification of the quantum-confined active region. The inset on the right presents a numerical simulation demonstrating that the light remains confined within the structure and does not escape into the substrate. Above is a photo of three photoluminescent microlasers.

© E. Moissev et al

Natalia Kryzhanovskaya

'Our microlasers operate stably at room temperature without the need for cooling systems, making them convenient for real-world applications. In the future, such devices will enable the creation of more compact and energy-efficient optoelectronic technologies,' explains Natalia Kryzhanovskaya, Head of the International Laboratory of Quantum Optoelectronics at HSE University–St Petersburg.

The paper has been prepared as part of a project implemented within the framework of the International Academic Cooperation competition at HSE University.