基于双稳态光致相变特性的太赫兹超结构动态调制机理研究

The development of terahertz (THz) science has been hindered by the lack of THz dynamic controlling devices with high speed and efficiency. This program proposed a study on the design, preparation and laser-induced ultrafast bistable phase transition mechanism of a new phase transition oxides, named λ-Ti3O5, and then a combination of this phase transition characteristics with metamaterials for optically controlled THz dynamic devices with high speed and efficiency. .Based on our precious work, we will focus on preparation of the controlled high quality λ-Ti3O5 film, relation between the nanometer size effect , quantum size effect and λ-Ti3O5 phase transition characteristic, such as phase transition speed, depth, threshold value and THz transmission properties. With the time-resolved terahertz spectroscopy，the carrier evolution rule of the laser-induced bistable semimetal-semiconductor phase transition during the phase transition in λ-Ti3O5 film will be investigated. Then the λ-Ti3O5 film will be incorporated into the designed THz metamaterials. Particularly, the ultrafast semimetal-semiconductor phase transition accompanied with drastic changes in the electromagnetic parameters will be evaluated ，and their function on the dynamic THz controlling properties of the combined λ-Ti3O5 /Metamaterials will be investigated. Our researches aim at developing a metamaterial dynamic THz modulator combined with λ-Ti3O5 film, which possess a modulation depth over 80% and a modulation speed of 100 Mb/s.

太赫兹波（THz）的高速、高效动态调制一直是亟待解决的问题。本项目旨在将光激发下具有超快类金属-半导体双稳态相变特性的新型相变氧化物λ-Ti3O5与人工电磁谐振结构结合，实现光控THz的高速、高效动态调制。我们将在所掌握的λ-Ti3O5薄膜制备技术基础上，制备高质量的、组织结构可控的光致超快双稳态相变λ-Ti3O5薄膜；采用泵浦-探测THz光谱技术，研究其纳米尺寸效应、量子尺寸效应对光致相变速度、相变幅度、激发阈值、THz波传输特性等的影响规律。通过研究光激发下λ-Ti3O5相变过程中的光致超快相变动力学过程，揭示金属态自由电子（自由载流子）与半导体态束缚载流子之间的演化规律和物理机制。设计制备出嵌套λ-Ti3O5的THz人工电磁谐振结构器件，进行λ-Ti3O5/Metamaterials的光激励THz动态调制研究，得到调制幅度大于80%，调制速度高于100Mb/s的THz动态功能器件。

太赫兹波（THz）的高效动态调制是太赫兹器件亟待解决的问题。本项目利用光激发下具有光致相变特性的相变氧化物进行光控THz的高效动态调制研究。我们分别采用先制备粉体再粘接成膜以及采用溶胶-凝胶法和磁控溅射法直接制备成膜的方法，在蓝宝石/石英基底上进行了λ-Ti3O5薄膜的制备研究，掌握了制备λ-Ti3O5薄膜的关键工艺条件。使用THz-TDS技术研究了λ-Ti3O5随温度变化的THz透射特性，并通过泵浦-探测THz光谱技术研究了λ-Ti3O5的光致相变特性，发现λ-Ti3O5的相变过程在ps量级内，并分析研究其超快光致相变过程的载流子动力学过程及其物理机制。由于目前方法所制备的λ-Ti3O5薄膜不能满足电磁结构微结构加工的要求。我们选用同样具有光致相变特性的二氧化钒薄膜进行了Metamaterial THz调制器件设计。研究了基于光致相变的太赫兹透射式相位调控超表面结构的等效模型和THz波动态调制机理。通过将耦合谐振人工微结构阵列与二氧化钒相变材料有机结合在一起，实现了光激励和电激励下130°以上的动态相位调控。基于光致相变复合超表面的太赫兹焦点可调太赫兹平面透镜，在光照诱导下两个焦点之间的焦距差达到3倍，实现了焦距在2.5- 7.5 mm范围内的远焦和近焦切换。基于光控相变的多维度太赫兹调控技术的研究，实现了对太赫兹波的多维度调控以及双功能解耦。