Research On Third-Order Nonlinearities Of Nanofunctional Materials And Their Application In Fast Optical Holography

Holographic display has become a research focus in the field of display by recording and reconstructing object wavefront information.Conventional computational holography tech-niques preprocess original images to meet practical application needs for better hologram qual-ity,with image scaling being an important step.With the development of imaging and display technology,small-sized imaging displays have attracted attention and extensive research from researchers due to their ability to provide more realistic and clearer effects,such as augmented reality（AR）and virtual reality（VR）devices.However,when images are scaled down to smaller sizes,distortion inevitably occurs due to loss of information.In addition,linear optical effects are usually considered in the reconstruction of far-field holographic images.Nonlinear holog-raphy research has also become an effective way to address the need for important applications such as holographic multiplexing and multidimensional optical data storage where there are fewer information channels or low data throughput.The main research works are as follows:（1）A fast optical holographic method based on nanofunctional films is proposed to address the low fidelity issue of small-sized images in computation-generated holographic prepro-cessing.Firstly,a superpixel scaling algorithm is proposed by combining the superpixel algo-rithm with the weight kernel.To investigate the performance of the proposed superpixel scaling algorithm,it is compared with classical image scaling algorithms in terms of structural similar-ity and peak signal-to-noise ratio performance indicators.The results show that whether in gray-scale amplitude holography or color amplitude holography,the superpixel scaling algorithm has a significant advantage.Then,by using femtosecond laser direct writing technology and the computation-generated holographic method,holograms with different scaling ratios and pre-served key information are successfully implemented on GO nanofilm.Finally,holographic reproductions of holographic images with different orders are realized by the holographic re-production optical setup.The experimental results indicate that both the computation and pro-cessing speed of holograms have improved by three orders of magnitude compared to the orig-inal hologram size.This lays the foundation for the development of diffractive layers in diffrac-tive neural networks.（2）The third-order nonlinearity of thin films of two nanofunctional materials was investi-gated to probe the experimental observation of the large nonlinear optical response of GO films under two different photoreduction mechanisms.The nonlinear optical response of the reduced graphene oxide was characterized by the Z-scan method using a femtosecond laser beam with a wavelength of 800 nm after UV light-induced photochemical reduction and continuous-wave laser-induced photothermal reduction.A huge two-photon absorption（TPA）coefficient of～10⁵cm/GW was observed for reduced graphene oxide under two photoreduction mechanisms（pho-tochemical and photothermal）.A huge enhancement effect of TPA was observed in graphene-based materials,and the TPA coefficient was an order of magnitude higher than the highest value previously reported.（3）The huge saturable absorption（SA）of WO₃ films prepared based on the seedless layer hydrothermal method was experimentally detected,and the coefficient can be as high as-2.59×10⁵ cm GW^-1.This SA coefficient is one to two orders of magnitude higher than the previously reported highest value.The intensity-dependent nonlinear absorption performance was also ob-served.The nonlinear absorption coefficient continuously increased with the increase of laser power intensity.By comparing the third-order nonlinearity of the original WO₃ film and the film used for 30 days after aging,it was found that the maximum nonlinear absorption coeffi-cient of the film used for 30 days was only less than three times lower than that of the original film,which still remained several orders of magnitude higher than that of most two-dimensional materials.This demonstrated its good air stability and durability.Furthermore,during the entire process of UV-induced photochromism and bleaching,the enormous third-order nonlinear ab-sorption and nonlinear refraction of WO₃ were observed using an 800 nm femtosecond laser beam as the probing light through the Z-scan method,and the effective nonlinear absorption and nonlinear refraction coefficients were found to be in the order of 10⁴cm GW^-1 and 1cm²GW^-1,respectively.By changing the concentration ratio of oxalic acid and ammonium meta-tungstate in the hydrothermal method to prepare WO₃ films,different optical bandgaps were displayed,showing completely different optical nonlinearities.To date,research on the nonlin-ear refraction of WO₃ films has been rarely reported,and the optical properties of WO₃ dynamic modulation are persistent.（4）To address the issues of limited holographic channels and low optical information throughput,a nonlinear hologram is simulated and designed based on the enormous nonlinear absorption coefficient measured in the study.The further implementation of hologram multi-plexing in multiple dimensions is achieved.Optical information encryption and decryption can be achieved through encoding.Specifically,encryption can be implemented in linear holog-raphy.Decryption can be achieved by introducing third-order nonlinear holography technology（after the irradiation of femtosecond laser）,with a corresponding increase in transmittance byΔT,enabling the decoding of optical information.This technique has remarkable application value and research significance in areas such as information storage,optical imaging,infor-mation encryption,and neural networks.