High-energy terahertz surface optical rectification
High-energy terahertz surface optical rectification
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DOI：
10.1016/j.nanoen.2018.01.027
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发表时间：
2018-04
期刊：
影响因子：
17.6
通讯作者：
L. Peters;J. Tunesi;A. Pasquazi;M. Peccianti
中科院分区：
文献类型：
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作者：
L. Peters;J. Tunesi;A. Pasquazi;M. Peccianti
对表面太赫兹发射器的兴趣在于其极薄的有源区，通常为数百个原子层，以及灵活的表面可扩展性。可实现的发射的最终极限由与太赫兹频率转换同时发生的几种不同机制的饱和度决定。虽然有一个非常多产的辩论的贡献，每个过程中，表面光整流已被强调为在高激发的主导过程，但在转换的有效限制在很大程度上是unknow.The目前的最新技术水平表明，在场诱导的光整流的最大限度的排放可能存在，它是由光生载流子诱导的介质的表面场的中和。这将是最重要的障碍，在高能量THz emitters.We的实验揭示了新的物理见解，在高激发能介导的超快表面光学整流过程中的THz转换的应用。主要发现是太赫兹发射与泵浦能量的预期完全饱和实际上并没有发生。在高能量下，表面场区域朝向表面收缩。我们认为，这种机制削弱了主要的饱和过程，重新建立一个清晰可见的二次发射太赫兹能量和激发之间的依赖关系。这与能够在高通量下获得密集发电有关。
The interest in surface terahertz emitters lies in their extremely thin active region, typically hundreds of atomic layers, and the agile surface scalability. The ultimate limit in the achievable emission is determined by the saturation of the several different mechanisms concurring to the THz frequency conversion. Although there is a very prolific debate about the contribution of each process, surface optical rectification has been highlighted as the dominant process at high excitation, but the effective limits in the conversion are largely unknown.The current state of the art suggests that in field-induced optical rectification a maximum limit of the emission may exist and it is ruled by the photocarrier induced neutralisation of the medium's surface field. This would represent the most important impediment to the application of surface optical rectification in high-energy THz emitters.We experimentally unveil novel physical insights in the THz conversion at high excitation energies mediated by the ultrafast surface optical rectification process. The main finding is that the expected total saturation of the Terahertz emission vs pump energy does not actually occur. At high energy, the surface field region contracts towards the surface. We argue that this mechanism weakens the main saturation process, re-establishing a clearly observable quadratic dependence between the emitted THz energy and the excitation. This is relevant in enabling access to intense generation at high fluences.