The Smallest Semiconductor Laser Is Born

July 29, 2020

Recently, an international team of researchers led by researchers from ITMO University (Russia)announced that it has developed the world's most compact semiconductor laser in the visible light range at room temperature. According to the author of the research team, this laser is a nanoparticle with a size of only 310 nanometers (about 1/3000 of a millimeter), which can generate green coherent light at room temperature and can even be seen with the naked eye using a standard optical microscope.


It is worth mentioning that scientists have successfully overcome the green part of the visible light band. The main researcher of this article, Sergey Makarov, a professor at the School of Physics and Engineering of ITMO University, said: “In modern light-emitting semiconductors, In the field, there is a ‘green gap’ problem. The green gap means that the quantum efficiency of conventional semiconductor materials used in light-emitting diodes drops sharply in the green part of the spectrum. This problem complicates the development of room temperature nanolasers made of conventional semiconductor materials. "


The ITMO University research team chose perovskite halide as the material for its nano laser. Traditional lasers are composed of two key elements-an active medium that allows coherent excitation and emission and an optical resonator that helps confine electromagnetic energy inside for a long time. Perovskite can provide these two characteristics: a certain shape of nanometer Particles can act as both active media and high-efficiency resonators. As a result, the scientists succeeded in producing 310-nanometer-sized cube-shaped particles that, when excited by femtosecond laser pulses, can generate laser radiation at room temperature.


Said Ekaterina Tiguntseva, a junior researcher at ITMO University and one of the co-authors of the paper. "We use femtosecond laser pulses to pump nanolasers. We irradiate isolated nanoparticles until the laser generation threshold of a specific pump intensity is reached. We have proven that this nanolaser can operate within at least one million excitation cycles. "The uniqueness of the nanolaser developed by the research team is not limited to its small size. The newly designed nanoparticles can also effectively limit the stimulated emission energy and provide sufficiently high electromagnetic field amplification for laser generation.


Kirill Koshelev, a junior researcher at ITMO University and one of the co-authors of the article, explained: “The idea is that laser generation is a threshold process. That is, you use laser pulses to excite nanoparticles at a specific ‘threshold’ intensity of an external light source. The particles start to produce laser emission. If you can’t limit the light to a good enough range, there will be no laser emission. In previous experiments with other materials and systems, but with similar ideas, it shows that you can use fourth-order Or fifth-order Mie resonance, which means that at the frequency generated by the laser, the light wavelength in the material matches the resonator volume four to five times the resonance. We have proved that our particles support third-order Mie resonance, which is the previous Never done. In other words, when the size of the resonator is equal to three wavelengths of light inside the material, we can produce coherent stimulated emission."


Another important thing is that the nanoparticles can be used as a laser without applying external pressure or very low temperatures. All the effects described in the study were produced at normal atmospheric pressure and room temperature. This makes this technology attractive to experts who specialize in manufacturing optical chips, sensors, and other devices that use light to transmit and process information, including chips for optical computers.


The advantage of lasers working in the visible light range is that they are smaller than red and infrared light sources with the same characteristics when all other characteristics are the same. In fact, the volume of a small laser usually has a cubic relationship with the emitted wavelength, and since the wavelength of green light is three times smaller than that of infrared light, the limit of miniaturization is much greater for green lasers. This is essential for the production of ultra-compact components for future optical computer systems.