Research On Optical Absorption And Electromagnetic Control Characteristics Of Novel Metamaterial Structures

The manipulation of light absorption and propagation characteristics at the nanoscale has always been a hot topic in the field of optics.In recent years,with the continuous development of nanofabrication and characterization technologies,optical absorbers have shown great application potential in electromagnetic stealth,photoelectric detection,biosensors and photovoltaic power generation.At present,the research based on metamaterial absorbers has made significant progress,but still faces the following problems:In order to further reduce the size of the device,the interaction between light and matter is inevitably weakened,resulting in the deterioration of its light absorption effect,which is particularly prominent in the light absorption of the two-dimensional material film.Therefore,how to effectively enhance the light absorption of two-dimensional material film is one of the issues worth exploring;In order to further improve the absorption performance of the devices,broadband absorption has become another goal pursued by scientific researchers,but its absorption bandwidth requirements are different in different application fields.Therefore,how to achieve broadband spectral selective absorption is one of the problems to be solved urgently.This thesis focuses on the above issues,through theoretical analyses and numerical simulations,in-depth exploration of the light absorption behavior and electromagnetic response characteristics of different types of metamaterial absorbers.The main research contents and innovative achievements are as follows:(1)Combining with the critical coupling theory in waveguide resonances,a narrowband perfect absorber is designed to enhance the light absorption of the molybdenum disulfide thin film.The resonance effect in the model is used to limit the light field near the thin film,so that the light absorption rate in the visible light band can reach 98.3%,which is more than 12 times that of vacuum suspension.By adjusting the model parameters,light absorption at specific wavelengths can be selectively enhanced.And the model structure is simple and has strong versatility.Based on above,the structure is further optimized,a lossless dielectric Bragg mirror with fewer layers is used to replace the metal in the model,and the light absorption behavior of the graphene film at the communication wavelength is explored.The results showed that the absorption rate of single-layer graphene can reach more than 99%,which is about 43 times that of its suspension.And by changing the polarization state of incident light,multi-spectral absorption enhancement response can be achieved.The above scheme provides an effective way to study the interaction between light and two-dimensional material thin film.(2)Combining with the coupling theory of surface plasmon modes,a spectrally selective solar absorber composed of a dual-period vertical stacking metal/dielectric multilayer structure is designed.The model has a light absorption rate of more than 90% in the wavelength range of 300-1726 nm,while the emissivity in the mid-infrared band is less than 20%.When it is applied to a 600 K photothermal conversion system,its conversion efficiency can reach 95.5%.Based on above,the absorption bandwidth is further broadened,a solar absorber composed of metal nanowire array and planar dielectric/metal/dielectric multilayer stacking structure is proposed.This model can achieve a high light absorption rate(>90%)in the wavelength range of 300-1909 nm,and has a relatively low emissivity when the wavelengths exceed 2500 nm.Moreover,the model can be further simplified,and the high light absorption effect can still be maintained.The above scheme opens up a new idea for the development and application of large-area,low-cost,and high-efficiency solar absorbers.(3)Combining with the optical topology conversion theory in hyperbolic metamaterials,an angle selector based on metal nanowire array structure is designed.By appropriately cutting the topological shape of the isofrequency surface of the model,an ultra-narrow angle transparent window(<2°,the transmittance is as high as 98% at normal incidence)can be obtained,which can be applied to the imaging field to realize the reconstruction of detailed information of sub-wavelength objects in a longer distance(<12?).Based on the above theory,a broadband absorber based on a dielectric/dielectric/metal multilayer alternating stack structure is proposed.The model has a light absorption rate of more than 90% in the wavelength range of 300-2215 nm,and when it exceeds the abovementioned wavelength range,the light absorption rate drops rapidly due to the conversion of the model topology.And by changing the model parameters,the absorption bandwidth can be adjusted flexibly.This novel electromagnetic control method and excellent light absorption performance provide an advantageous solution for the design and application of the next generation of high-performance broadband absorbers.