Strong Nonlinear Optical Response in the Visible Spectral Range with Epsilon-Near-Zero Organic Thin Films
Strong Nonlinear Optical Response in the Visible Spectral Range with Epsilon-Near-Zero Organic Thin Films
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DOI：
10.1002/adom.201701400
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发表时间：
2018-07-18
影响因子：
9
通讯作者：
D'Aleo, Anthony
中科院分区：
文献类型：
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作者：
Lee, Yeon Ui;Garoni, Eleonora;D'Aleo, Anthony
在超材料如导电氧化物和掺杂的无机半导体薄膜中观察到增强的克尔非线性，在红外区域显示ε近零（ENZ）响应。然而，为了在可见光中实现ENZ，必须专门设计具有更复杂纳米结构的人造超材料。这里，使用钠[5，6-二氯-2-[[5，6-二氯-1-乙基-3-（4-磺丁基）-苯并咪唑-2-亚基]-丙烯基]-1-乙基-3-（4-磺丁基）-苯并咪唑鎓氢氧化物]和[2，4-双[8-羟基-1，1，7，7-四甲基久洛尼啶-9-基]方酸]有机薄膜，证明了450和620 nm之间的ENZ响应。在ENZ光谱区，非线性折射率和非线性吸收系数都提高了两个数量级以上。这些光学效应在可见光谱范围内来自于激子跃迁偶极耦合产生的分子聚集体的强色散介电常数。这些发现为下一代高性能可溶液加工的有机非线性光学材料开辟了道路，这些材料具有可通过分子工程调节的ENZ特性。
Enhanced Kerr nonlinearities are observed in metamaterials such as conducting oxides and doped inorganic semiconductor thin films showing epsilon-near-zero (ENZ) response in the infrared region. However, to achieve ENZ in the visible, artificial metamaterials with more complex nanostructures have to be specifically designed. Here, using sodium [5,6-dichloro-2-[[5,6-dichloro-1-ethyl-3-(4-sulphobutyl)-benzimidazol-2-ylidene]-propenyl]-1-ethyl-3-(4-sulphobutyl)-benzimidazolium hydroxide] and [2,4-bis[8-hydroxy-1,1,7,7-tetramethyljulolidin-9-yl]squaraine] organic thin films, ENZ responses between 450 and 620 nm are demonstrated. Both nonlinear refractive index and nonlinear absorption coefficient are enhanced by more than two orders of magnitude in the ENZ spectral region. These optical effects in the visible spectral range come from the strongly dispersive permittivity of molecular aggregates resulting from the coupling of excitonic transition dipoles. These findings open the path toward a next generation of high-performance solution-processable organic nonlinear optical materials with ENZ properties that can be tuned by molecular engineering.