Scientists Create Smallest Semiconductor Laser That Works In Visible Range At Room Temperature

An international team of researchers announced the development of the world’s most compact semiconductor laser that works in the visible range at room temperature. According to the authors of the research, the laser is a nanoparticle of only 310 nanometers in size (which is 3,000 times less than a millimeter) that can produce green coherent light at room temperature. The research article was published in ACS Nano.

This year, the international community of optical physicists celebrates the anniversary of a milestone event: 60 years ago, in the middle of May, American physicist Theodor Maiman demonstrated the operation of the first optical quantum generator - a laser. This gave way to a new era in which lasers have become an essential part of our lives.

Sixty years later, an international team of scientists, most of whom are from ITMO University, published a research where they demonstrated experimentally the world’s most compact semiconductor laser that works in the visible range at room temperature. This means that the coherent green light that it produces can be easily registered and even seen by a naked eye using a standard optical microscope.

It’s worth mentioning that the scientists succeeded in conquering the green part of the visible band which was considered problematic for nanolasers.

Material selection
The green gap problem hindered the creation of small green lasers based on metal-dielectric technology which has been successfully used in the creation of subwavelength lasers that work in the infrared (IR) band.

In order to solve these problems, a team of physicists and chemists from ITMO University and their foreign colleagues from the Australian National University, the Chalmers University of Technology and the University of Texas at Dallas decided to avoid the metal-dielectric designs and develop the fully dielectric concept, so they turned their attention to halide perovskite, which has prospective light-emitting properties due to high quantum efficiency of luminescence in the visible band. What’s more, the physical properties of perovskite allowed the researchers to come up with the laser’s original design.

Two in one
A traditional laser consists of two key elements – an active medium that allows it to generate coherent stimulated emission and an optical resonator that helps confine electromagnetic energy inside for a long time. Perovskite can provide both of these properties: a nanoparticle of a certain shape can act as both the active medium and the efficient resonator.

Despite the fact that perovskite has a cubic crystalline lattice and under the right conditions, its particles take on the shape that’s close to that of a cube on their own, producing a nanoparticle of a specific size, form and quality is not easy. You need special conditions.

But even this method produces particles of different sizes. After the synthesis, it was necessary to use complex theoretical modeling to identify the crystals that were good for the experiment. In the end, it turned out that those were particles of 310 nanometers in size.

How it works
But the crystal by itself is not a laser yet. In order to emit coherent light, one has to excite it or, as they say, “pump” it with energy until a stimulated emission occurs.

The uniqueness of the developed nanolaser is not limited to its small size. The novel design of nanoparticles allows for efficient confinement of the stimulated emission energy to provide a high enough amplification of electromagnetic fields for laser generation.

Prospects
Another important thing is that there is no need to apply external pressure or very low temperature for the nanoparticle to work as a laser. All the effects described in the research were produced at a regular atmospheric pressure and room temperature. This makes the technology attractive for specialists who focus on the creation of optical chips, sensors and other devices that use light to transfer and process information, including chips for optical computers.

The benefit of lasers that work in the visible range is that with all other properties being equal, they are smaller than red and infrared sources with the same properties. Thing is, the volume of the small lasers generally has a cubic dependence on the emission’s wavelength, and as the wavelength of green light is three times less than that of infrared light, the limit of miniaturization is a lot greater for green lasers. This is essential for the production of ultracompact components for future optical computer systems.

The article has been published in ACS Nano, one of the leading journals in the associated research field. It’s worth mentioning that it is indexed by Nature Index, a prestigious ranking that shows the level of research institutions with regard to not just the number of high-level articles, but also the contribution to them by authors from universities and institutes. According to this ranking, ITMO University is among Russia’s top three universities in physics, and also holds leading positions in several other categories.