Nano-laser has achieved a major breakthrough!

Lasers are widely used in household appliances, medicine, industry, telecommunications and other fields. A few years ago, scientists introduced Nano Russell. Their design is similar to conventional semiconductor lasers based on heterostructures that have been commonly used for decades. The difference is that the cavity of the nano-lacquer is very small, which is determined by the wavelength of the light emitted by the root. Since they mainly produce visible light and infrared light, they are about one millionth of a meter in size. Nanomaterials have unique properties that are significantly different from macroscopic lasers. However, it is almost impossible to determine at what current the output radiation of the nanolaser becomes coherent. In addition, in practical applications, it is important to distinguish between two states of the nanolaser: true laser action with high current coherent output and low The LED-like state of the current incoherent output. Researchers from the Moscow Institute of Physics and Technology have developed a method to determine under what circumstances a nanolaser is a true laser.

In the near future, nano-silicon will be integrated into integrated optical circuits, which is necessary for a new generation of high-speed interconnects based on photonic waveguides, which will increase the performance of cpu and gpu by several orders of magnitude. Similarly, the advent of fiber-optic Internet has increased the speed of connectivity while also increasing energy efficiency. So far, this is not the only possible application of Nano Rather. Researchers are already developing chemical and biosensors that are only a millionth of a meter wide, while mechanical stress sensors are only a fraction of a billion meters. Nanoglycans are also expected to be used to control biological neuronal activity, including humans. To make a radiation source a qualified laser, it needs to meet many requirements, the most important of which is that it must emit coherent radiation. A significant characteristic closely related to coherence is the presence of so-called laser thresholds. When the pump current is below this threshold, the output radiation is primarily spontaneous and its characteristics are no different from those of conventional light-emitting diodes (LEDs).

Nanolaser test, picture: tsarcyanide/MIPT but once the threshold current is reached, the radiation becomes coherent. At this point, the conventional macroscopic laser emission spectrum is reduced, and its output power is peak. The latter feature provides a simple way to determine the laser threshold—by studying the output power as a function of pump current (Figure 1A). Many nanomolecular sieves behave like conventional macromolecular sieves and exhibit threshold currents. However, for some devices, since it has no special characteristics, it is just a straight line on the log-log scale (red line in Figure 1B), so the laser threshold cannot be determined by analyzing the output power versus pump current curve. This nanoglycan is referred to as "no threshold." This raises the question: At what current does their radiation become coherent, or like a laser? The most obvious way to answer this question is to measure coherence. However, unlike emission spectra and output power, coherence is difficult to measure in nanolasers because it requires equipment capable of recording intensity fluctuations in parts per trillionth of a second (the time scale in which the nanolaser internal process occurs).

 

The relationship between the output power of conventional macro lasers (a) and typical nanolasers (B) and pump current at a given temperature. Photo: A.A. Vyshnevyy and D.Yu. Fedyanin, DOI: 10.1364/OE.26.033473 Andrey Vyshnevyy and Dmitry Fedyanin of the Moscow Institute of Physics and Technology have found a way to bypass the technically challenging direct coherent measurements. They developed a method to quantify the coherence of nanolaser radiation using the main laser parameters. Researchers claim that their technology can determine the threshold current of any nanolaser (Figure 1B). They found that even a "thresholdless" nanolaser actually has a unique threshold current that separates the LED from the laser. The emitted radiation is incoherent below the threshold current and is coherent above the threshold current. Surprisingly, the threshold current of a nanolaser has nothing to do with the narrowing of the output characteristics or the emission spectrum, which are characteristic of the laser threshold in macroscopic lasers. Figure 1B clearly shows that even if a significant kinking is seen in the output characteristics, a transition to the laser state occurs at higher currents. This is what laser scientists cannot expect from nanolasers.

The relationship between the threshold current of the nanolaser and the device temperature, the blue and green curves closely approximate the exact value shown by the red line. Image: Andrey A. Vyshnevyy and Dmitry Yu. Fedyanin, DOI: 10.1364/OE.26.033473 Calculations show that in most papers on nanolasers, the laser system is not implemented. Although the researchers measured the laser above the kink on the output characteristics, the nanolaser emission was inconsistent because the actual laser threshold was on the order of magnitude above the kink value. In general, due to the self-heating of nanolasers, it is impossible to achieve a consistent output. It is therefore important to distinguish the virtual laser threshold from the actual laser threshold. Despite the difficulty of coherence measurement and calculation, Vishnevsky and Fedianin proposed a simple formula that can be applied to any nanolaser. Using this formula and output characteristics, nanolaser engineers can now quickly measure the threshold currents they create structures (see Figure 2). The results reported by Vyshnevyy and Fedyanin allow us to predict in advance how the radiation of the nanolaser (regardless of its design) becomes consistent. This will enable engineers to deterministically develop nanolasers with predetermined characteristics and guaranteed coherence.