3 research outputs found
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Surface terahertz phenomena
With the massive advantages of THz radiation and the current technical difficulties in mind, I have chosen to undertake research into terahertz surface phenomena, which is the focal point of my thesis. Ultrathin surface terahertz emitters have many advantages as they have an extremely thin active region, typically hundreds of atomic layers. In this framework, III-V semiconductors, such as InAs and InSb, have record-breaking conversion efficiencies per unit thickness. In addition, the phase mismatch, which commonly limits the generation of terahertz from optical crystal, is negligible and so there is an opportunity for enhancing the emitted bandwidth. My thesis is born as the core of many research interests of my research lab (Emergent Photonics), which enabled the appropriate availability of resources that made my results possible. It also created several spin-out research lines. All the work presented is my work (with the exception of the background research). Parts of chapters have been published in journals and publications which see me as the first author. The structure of this thesis is as follows. First I discuss optical pump rectification emission, and the saturation of InAs terahertz emissions. Then I introduce my work on terahertz enhancement emission through graphene. Finally, I present my work on an exotic terahertz emission mechanism, namely the all-optical surface optical rectification and I place my concluding remarks
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Dataset for Paper: High-energy terahertz surface optical rectification
Data for a research paper published in Nano Energy April 2018 The data provided is the data used to compile each of the 10 figures in
the research paper. The .txt files
contain the variables for the measured raw data contained in the related .mat
file.The format of the raw data is .mat - MATLAB binary -v7, which is
compatible and portable to GNU Octave version >4.0 (tested). You will need access to the Matlab
environment or GNU Octave environment to view these files.AbstractThe 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.</div
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Dataset for: Terahertz Emission Mediated for Ultrafast Time-Varying Metasurfaces
Data for paper 'Terahertz Emission Mediated for Ultrafast Time-Varying Metasurfaces', appearing in Physical Review Research (2021).Systems with ultrafast time-varying dielectric properties represent an emerging novel physical framework. We demonstrate here the first observation of sub-cycle dynamics interacting directly with an electromagnetic source comprised of morphologically constrained photoexcited carriers in a surface nanostructure. A transition to a metallic metasurface state occurs on time scales faster than the Terahertz-field period, inducing large nonlinear ultrafast phase shifts in the Terahertz emission and exposing a novel and previously unexplored physical setting</div