Plasma exciter is an electromagnetic mode formed by the interaction of light and metal free electrons. It can break through the limit of optical diffraction and realize large-scale integration of nano-photon chip devices.
However, the optical loss caused by Joule heat is especially serious in the visible wavelength band, which seriously reduces the performance of Nano-photon devices.
Therefore, except for the few applications such as SERS and SPR, which have been commercialized in biomedicine, gas detection and environmental and food pollutant trace detection, most of them are still far from commercialization.
On October 18, the latest research results of Li Guangyuan, an associate researcher of the Shenzhen Institute of Advanced Technology, Chinese Academy of Sciences (hereinafter referred to as "Shenzhen Institute of Advanced Technology"), were published as a post-cover article.The team found that the loss could be reduced by an order of magnitude by using the conversion of two surface lattice resonance modes (SLRs). The quality factor for evaluating the loss was increased by an order of magnitude (i.e., more than the previous record (330).
This study is expected to improve the performance of up/down conversion fluorescence enhancement, nano-laser, white LED, high performance biochemical sensing, nonlinear optical frequency conversion, etc.
Refresh existing quality factor records
Previously, researchers had optimized the preparation process of precious metals such as gold and silver to reduce their absorption and scattering losses.In recent years, although scientists have explored materials such as alkali metals (such as sodium metal), transparent conductive oxides (ITO, AZO), and dielectric materials (such as silicon, silicon nitride, titanium dioxide) to overcome the loss of precious metals.
Therefore, it is a very challenging problem to study new structural physics to effectively inhibit the loss of plasma excited element nanophotonic devices under the given conditions.
Many new physical mechanisms have been explored to suppress the absorption and scattering losses of noble metal nanophoton structures.SLR, which is composed of local plasma excitation element resonance and in-plane diffraction optical coherent coupling, has the advantages of narrow linewidth, high quality factor and large electric field.
SLR can be divided into out-of-plane SLR and in-plane SLR.Out-of-plane SLR has higher quality factors than in-plane SLR.
In 2011, scientists measured a quality factor of up to 150 and broke the record, but it has been difficult to improve, because scientists believe that metal nanoparticles that support the SLR must be more than 90 nanometers.
In this study, the research team used gold and silver in precious metals and their conventional nanomachining technology to investigate the effect of parameters on SLR quality factors.
The experimental results show that when the height of the gold column is reduced from 100 nm to 50 nm, or the incidence angle is increased from 15° to 35°, the quality factor of the SLR is increased by one order of magnitude.
In addition, the researchers extended the array to nano-silver arrays. Experimental results show that by halving the height of nano-silver columns from 100 nanometers to 50 nanometers, the simulated quality factor can be increased by an order of magnitude.
"For example, a 50nm high nano-silver column array is produced by conventional processing, and the quality factor simulation value of the off-planar SLR can be up to 1500, and the experimental measurement value is up to 790, 2.4 times the existing world record." Li Guangyuan, author of the paper, said.
Promote the development and commercialization of plasma excitation devices
"The plasma excitation element is an important way to realize the nanization of photoelectric chip. It has been studied for 25 years since 1998. However, the loss of plasma excitation element is difficult to solve." Li Kuang-yuan analyzed.
Li Guangyuan's team has been engaged in the research of isoelectric element grating, nano laser and nonlinear optical devices for many years to explore the new mechanism of SLR loss inhibition.
Previously, the research team proposed ultra-high quality factor SLR based on non-uniform dielectric environment, metal-dielectric-metal grating and quadrupole, and ultra-high quality factor quasi-continuous domain bound states based on SLR interference cancellation.
Based on the previous research, the team solved a series of key problems from "simulation calculation" to "experimental measurement", and finally "theoretical prediction" of ultra-high quality factors.
"Our research has shown that using conventional precious metal materials and their micro-nano processing technology can greatly inhibit the loss of iso-excited elements and obtain super high quality factors by breaking the existing mindset and structural design."" said Lee Kwang-