| Metasurfaces,made of sub-wavelength two-dimensional artificial periodic micro/nano-structures that have the flexible strategy of structure design and unique electromagnetic response,can realize the functionalities of traditional optical devices meanwhile exhibit many novel optical effects,which meets the requirement for miniaturized and integrated devices in modern optical systems.However,there are still many limitations for metasurfaces towards the practical applications,for example,the operating wavelengths are usually located at the visible and near-infrared spectrum;the high-coherence sources such as lasers are needed mandatorily for most metasurfaces;the metasurfaces with complex-amplitude modulation have not been exploited comprehensively.To extend the territory of its applications further,this thesis is focused on the modulation of amplitude,phase,complex-amplitude and coherence of light by designing and fabricating various micro-/nano-structured metasurfaces in areas,such as focusing of vaccum ultraviolet light,optical camouflage,and white-light holography.The innovative achievements in this thesis are shown below:1.To solve the problem of large focal spot and spherical aberration of vacuum ultraviolet(VUV)source in angular-resolved photo-electron emission spesctropy(ARPES),a flat diffraction lens with amplitude modulation is demonstrated with a small focal spot of 0.76 μm and a long focal length of 4.5 cm at the operating wavelength of 177 nm.Compared with other previously reported results,flat lens exhibits an enhancement factor of 3 in spatial resolution of ARPES.This flat lens enables high-resolution scanning imaging of periodic gratings and 2D graphene flakes meanwhile can be used for off-axis fluorescence spectral excitation,which provides technical support for the development of low-cost and high-performance ARPES.2.Inspired by biological masquerade,the concept of optical masquerade is proposed by using perturbative metasurfaces made of three-dimensional nanostructures with complex-amplitude modulation.By matching optical properties of the metasurface and the camouflaged object,their combined pattern is observed as a completely new and unrelated object,thus realizing optical masquerade with the property of "detection without being recognized"at the opreating bandwidth of 160 nm in the visible spectrum.Furthermore,a dielectric metasurface hologram with geometric phase is proposed to encode an amplitude-type camouflaged object into a phase object with random profile,thus realizing another type of optical masquerade.This optical masquerade,with large angle of view,unlimited camouflaged objects,and material adaptability,offers a new method for the design of optical camouflage..3.Based on Young’s double-slit interference experiment,the enhancement effect of dielectric metasurface on optical coherence is studied systematically.Interference fringes with different slit-distance are measured under a monochromatic LED light source and a broadband laser light source,respectively.By fitting the visibility function,it is proved that the metasurface can reduce the size of the light source to enhance its spatial coherence,meanwhile compress the spectral width of the light source to enhance its temporal coherence,which provides the straightforward proof for the coherencemodulation of metasurfaces.Based on the coherence enhancement effect of metasurfaces,a color hologram with the non-coherent white-light illumiation is demonstrated with the suppressed speckles in reconstructed images,offering the scientific origins for developing incoherent-light metasurfaces. |
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