The Control Of Infrared Thermal Radiation Based On Metasurfaces And Its Appllications

The thermal radiations from natural objects are typically incoherent,i.e.,broadband,un-polarized,and nearly isotropic,and the only way to control their emitted power is by changing their temperatures.However,recent advancements in metasurfaces,which consist of engineered nanostructures,have challenged the conventional view of thermal radiation.The properties of thermal radiation including wavelength,polarization,and angle are controlled by structures at wavelength or subwavelength scale.Such artificial engineering has broad applications in infrared camouflage,energy harvesting and thermal information processing,etc.Nevertheless,the metasurface-assisted thermal radiation control still has limitations.For instance,the development of mid-infrared-compatible multi-band camouflage is impeded by incompatible structural requirements of different camouflage effects and thermal challenge.Another example is,direct thermal radiation of circularly polarized light,which is demanded in fields such as quantum computation,is rarely reported.Moreover,research on broad-band angular control of thermal radiation is still lacking.Therefore,this dissertation focuses on the metasuface-assisted thermal radiation control,including the spectral control,polarization control and spatial(angular)control,and the corresponding application scenarios are demonstrated.For the spectral control,the static and dynamic engineering of infrared radiations are demonstrated,respectively.In the static case,the challenging compatibility for camouflages to visible,mid-infrared,and laser radar wavelengths is achieved via a tri-layered film or a wavelength-scale grating.The fabricated structures exhibit dual-band mid-infrared camouflage with low emission,radar camouflage to CO2 laser with high absorption at 10.6 ?m,visual camouflage with structural colors,and thermal management with high emission towards 5-8 ?m band.The temperature of the sample is 15? lower than conventional infrared camouflage materials.In the dynamic case,phase-changing material Ge2Sb2Te5(GST)is incorporated into the metal-insulator-metal structures and thus optical properties of the metasurface can be thermally engineered.Multiple images depending on temperature are displayed on the same metasurface,i.e.,a temperature-division thermal imaging device is demonstrated.The specific images can only be thermally displayed at corresponding temperatures,hence the metasurface can also be functionalized as an infrared information thermal encryption device.For the polarization control,a non-chiral metasurface is proposed instead of a conventional chiral structure.The circularly polarized light is emitted due to the chiral distribution of electromagnetic field supported by the anti-symmetric metal-insulator-metal structure.A refractory and circular-polarization-sensitive absorber working in the 3-5 ?m band is proposed,and a micro-scale circularly polarized light emitter working in the 8-14 ?m band is fabricated for the experimental demonstration.Left-handed circular radiation and right-handed circular radiation are dominant at different temperatures,respectively.The device can also be applied as a reflective linear-to-circular polarizer,and nearly perfect left-handed circularly polarized light or right-handed circularly polarized light is experimentally obtained.For the angular control,a gradient grating is proposed.To overcome the spatial incoherence of thermal radiation,surface plasmon is utilized to mediate the coupling coefficient of free-space radiation and the localized magnetic resonances.The light-matter interaction strengths of the two opposite radiated angles are different owing to the geometric asymmetry.Thus,the broad-band(8-14?m)single-sided radiation is realized.The thermal radiation power within the angle range[0,90°](positive side)is twice larger than that within the angle range[90,180°](negative side).It is experimentally demonstrated that the radiation temperature of the positive side is 7.1? larger than that of the negative side.Though the systematic study on the thermal radiation control via metasurface,this dissertation shows that the metasurface-engineered thermal radiation has a vast prospect in settling practical problems,which promotes the progress of science and technology.