| The infrared band is of great importance in the electromagnetic spectrum.The study of the infrared absorption/radiation characteristics of objects has important significance for energy utilization,stealth technology,molecular detection and many other fields.The infrared absorption/radiation characteristics of the object can be adjusted by selecting specific optical materials and designing reasonable micro-nano structures.Materials with adjustable optical parameters were introduced into the photonic structure to achieve tunable devices.In the past ten years,researchers have adjusted the infrared absorption/radiation characteristics of objects by introducing photonic structures such as gratings and metal-insulator-metal structures,and realized tunable infrared absorption/radiation by introducing materials such as graphene,liquid crystal,vanadium dioxide and Ge2Sb2Te5(GST).In this paper,the phase-change material GST is combined with the Fabry-Perot resonant cavity to explore the changing laws of optical parameter in the thermal and laser-induced phase transition of GST,and realize the adjustable infrared radiation/absorption devices of specific wavelength bands.Switching between different states can be achieved by heating,applying voltage and laser induction.In order to explore the changing laws of GST optical parameters during the phase transition,two methods of heating and laser induction were used,and the influence of different external stimuli parameters on the phase transition of GST was explored.As the temperature rises,firstly the refractive index and extinction coefficient of GST increase at the same time,then the refractive index no longer changes and the extinction coefficient continues to increase.During the laser-induced GST phase transition,the absorption of the 405nm laser by the sample mainly occurs in the nanometer range of the surface layer,and the remaining part of the phase transition depends on heat conduction heating.In order to realize the reversible phase transition of GST,the GST-ZnS-Au-Substrate film structure containing 30nm ultra-thin GST film is adopted,and the thickness of each layer is optimized to maximize the difference in reflectance of visible light when the GST is in different states.The crystallization and amorphization of GST are realized by applying continuous laser and nanosecond double-pulse laser,respectively,and this reversible phase transition is repeatable.This kind of film structure has an absorption/radiation peak near 8?m due to the interference reduction effect of the film.By changing the crystallization ratio of GST,the effective emissivity of the sample at 7-9?m can be adjusted from 0.07 to 0.77.An infrared camera working at 7-9?m waveband was used to observe the sample at an actual temperature of 80? and the result showed that the radiation temperature can be reversibly switched from below 10? to above 60?.The GST-Au structure containing 530nm thick GST with the first-order anti-reflection mode located in the range of 8-14?m is used,and the laser direct writing system is used to change the state of part of the GST in the sample to form one-dimensional gratings and two-dimensional metasurfaces,in which the optical parameters are periodically arranged.By optimizing the structural parameters,the first-order anti-reflection mode of the film is coupled with the electromagnetic resonance in the structure so that a broad-spectrum absorption/radiation device with an effective absorptivity/emissivity of above 0.8 at 8-14?m waveband is realized.Additionally,the device has a low absorptivity/emissivity about 0.22 at 5-8 ?m.Besides,stepwise change of the effective absorptivity/emissivity from 0.13 to 0.81 was achieved through writing different patterns on the sample surface.The all-optical reversible switching of the state of the ultra-thin GST achieved in our work has important application value for tunable photonic devices,the structure with high absorptivity/emissivity at 8-14?m and low absorptivity/emissivity at 5-8?m can be used in radiative cooling applications and the device whose absorptivity/emissivity can be switched stepwise is applicable in infrared camouflage. |
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