China Instrument Network Instrument Research and Development Recently, Ma Renmin, a researcher and co-worker of the School of Physics of Peking University, has demonstrated through theoretical analysis and systematic experiments that plasmon lasers can be smaller, faster, and lower in frequency than conventional lasers. Threshold and power consumption; and revealed that there are essential differences between plasmonic nano lasers and traditional lasers, and their radiation fields can all be surface plasmon forms formed by free electron oscillations in metals. Relevant work was reported by Nature Communications and Science and Progress magazine under the headings "Unusual scaling laws for plasmonic nanolasers beyond the diffraction limit" and "Imaging the dark emission of spasers."
The development of lasers has deepened people's understanding of the interaction between light and matter, and greatly promoted the development of modern science and technology. Since the invention of the laser, its miniaturization has been one of the core research directions in the laser field. Its purpose is to obtain lasers with smaller volume, higher modulation speed and lower power consumption. For example, the application of a laser on an optical interconnect on a chip directly requires the laser to have a characteristic dimension close to that of the electronic device, and its power consumption is less than that of a mature electrical interconnect, and should be about 10 femtojoules per bit. The power consumption of the laser has a positive correlation with its scale, and the power consumption of a 10-feet cosine per-bit level directly requires the laser mode volume to be less than about 0.02 wavelength cubes.
Fig.1 Schematic diagram of basic principle of traditional laser (left) and nano laser (right)
The miniaturization of lasers in the past 40 years has achieved tremendous success. Microspotters such as VCSELs, microdisk lasers, photonic crystal lasers, and nanowire lasers have been developed. However, in these conventional optical lasers, the gain medium amplifies the photons by stimulated radiation, so the size of the laser is limited by the diffraction limit of the optics. The smallest dimension in each dimension is greater than half the wavelength, making it difficult to achieve miniaturization (Figure 1 left). .
Plasmon nano-laser is a new laser with a three-dimensional physical dimension that can be much smaller than the outgoing wavelength at the same time (Figure 1 right). This kind of nano laser is different from the traditional optical laser. It is the surface plasmon formed by amplifying the free electron oscillation in the metal instead of the photon, so that the light field limitation of the characteristic dimension of the deep subwavelength of the order of 10 nm can be realized. However, the spatial localization of the electromagnetic field brought about by the plasmon effect in nano lasers must be accompanied by metal absorption loss. Therefore, there has been controversy over whether nano lasers have the performance advantage over traditional lasers.
Ma Renmin and his collaborators have optimized the gain materials, metal materials, and resonators in the same system to reduce the nanolaser lasing threshold to 10 kilowatts per square centimeter, which is two orders of magnitude lower than the lowest reported nano laser threshold. For the first time, the nano laser threshold is reduced to the laser threshold level of commercially available lasers. They further systematically studied more than 100 sets of plasmonatic nano-lasers and more than 100 sets of control samples without metal confinement. Experiments have given the Scaling Laws of the key properties of plasmon lasers. Compared to conventional lasers, nano lasers can simultaneously have smaller physical dimensions, faster modulation speeds, lower thresholds and power consumption (Figure 2). This work was published in Nature Communications (8,1889, 2017).
Fig. 2 plasmonic nano lasers can be smaller (a) than conventional optical lasers, consume less power (b), and are faster (c)
In another work published this year in “Science and Progress†(3, e1601962, 2017), researchers and collaborators Ma Renmin used leakage radiation microscopic imaging technology to plasmon the surface of a nano laser by means of momentum matching. The elemental dark radiation is coupled to the far field, realizing the direct imaging of real space, momentum space and spectrum space, as shown in FIG. 3 . The results show that there are essential differences between nano lasers and conventional lasers, and their radiation fields can all be surface plasmon forms formed by free electron oscillations in metals. This work reveals for the first time that the radiant energy of the nano-laser can be coupled to the surface plasmon in one hundred percent of the propagation mode, which lays the foundation for further manipulation and application of the nano-laser.
Fig. 3 Imaging images of real space (a), momentum space (b) and frequency space (c) of nano-laser
Doctoral student Wang Sheng and postdoctoral fellow Wang Xingyuan of Peking University are the first authors of the "Nature·Communication" paper; Doctoral student Chen Huazhou of Peking University, Hu Jiaxuan and PhD student Wang Sheng of the 2011 undergraduate students are the first authors of the "Science and Progress" dissertation; major collaborators Including Prof. Dai Lun of Peking University and Prof. Rupert Oulton of British Imperial College; Ma Renmin is a correspondence author of two papers. These two tasks have been supported by the "Years of Thousand People" project, the National Natural Science Foundation of China, the Ministry of Science and Technology, the State Key Laboratory of Artificial Microstructure and Mesoscopic Physics, and the Collaborative Innovation Center for Quantum and Substance Science.
(Original title: “Nature·Communications†and “Science·Progress†report on the research progress of Nano-Semiconductors and Optoelectronics Physics Team Ma Renmin and Dai Lun in the field of nano-laser)
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