Ultrafast nonlinear optics of bulk and two-dimensional materials for infrared applications

This thesis presents the results of an experimental study into the nonlinear optical properties of novel nonlinear materials at infrared regions of the electromagnetic spectrum for the realisation of nonlinear optical devices in the near- and mid-infrared. Because of its exceptional nonlinear optical properties and its promise of implementation in a range of mid-infrared applications graphene had a prominent place in this research. Extensive investigations in the nonlinear optical properties of single and multilayer chemical vapour deposition (CVD) graphene are presented. This study revealed that graphene presents a nonlinear phase shift due to a negative, irradiance-dependent nonlinear refraction. The high peak powers available enabled the study of both saturable absorption (SA) and two-photon absorption (2PA), identifying the irradiance limits at which the contribution of two-photon absorption exceeded that of saturable absorption. Moreover, the nonlinear optical properties of graphene-polyvinyl alcohol (G-PVA) composite films were studied. The results indicate the thermal damage of the host polymer due to graphene heating and temperature transfer. Studies in the third order nonlinear optical properties of chalcogenide glasses with the perspective of integration with graphene for the development of mid-infrared devices and applications are also performed. Of all the glasses investigated, gallium lanthanum sulphide (GLS) was found to have the most interesting nonlinear optical properties. Its optical Kerr nonlinearity was found to be approximately 35 times higher than silica and the upper limit of its two-photon absorption coefficient was the lowest of all the chalcogenide glasses analysed, implying that GLS would be an excellent candidate for ultrafast all-optical switching. Subsequently GLS was chosen as the host material for optical waveguide and device fabrication via ultrafast laser inscription (ULI). Near- and mid-infrared waveguides were successfully fabricated; fundamental features such as, refractive index profiles and material dispersion were investigated. The Zero Dispersion Wavelength (ZDW) of GLS was experimentally measured for the first time; the ZDW was determined to be between 3.66-3.71 μm for the waveguides and about 3.61 μm for the bulk. Single mode directional couplers at 1550 nm were also developed and their ultrafast all-optical switching properties were investigated, leading to the assessment of the nonlinear refractive index n2 of the ULI modified area. Furthermore, waveguides in Er3+ doped GLS were successfully fabricated and the infrared transitions at 1550 and 2750 nm were detected opening the potential for GLS waveguide lasers

100 kW peak power external cavity diamond Raman laser at 2.52 μm

We report an external cavity diamond Raman laser operating at 2.52 μm, pumped by a 1.89 μm Tm:LiYF4 (YLF) laser. The maximum pulse energy at 2.52 μm is 1.67 mJ for 4.4 mJ of pump, yielding a conversion efficiency of 38 %. The best slope efficiency is ~60% and the Raman pulse duration is between 11 and 15 ns for ~33 ns pump pulse duration. The peak power at 2.52 μm is >100 kW. This demonstration of a Thulium laser pumped diamond Raman laser paves the way for accessing the industrially important wavelength region of ~2.5 μm

Mobile citizenship, states of exception and (non)border regimes in the pandemic and post-Covid19 Cyprus

This study examined the impact of the emergency measures on community relations, fundamental rights, and mobility rights during the Covid19 pandemic in de facto divided Cyprus. It explored states of exception, as well as solidarity aiming to counter those restrictions. Internal and external borders were mobilised to separate ‘us’ from ‘them’, shaped by the pandemic policies and media discourses via a hygiene emergency with suspension of rights, hitting severely the most vulnerable, often migrants and asylum-seekers. The hostile and securitised climate was generated by the political elites and the media and was built on the ‘Cypriot states of exception’ and colonial laws by extending old and generating new bordering processes. An illiberal policy frame towards migrants and asylum-seekers was manifested in form of a state exception of immobility, which affects the relations between the two communities, the division of Cyprus, peace-keeping and peace-making. Contra this hostile environment and given the welfare state crisis, acts for citizenship have generated praxis-based solidarity. Via digital networking, we observed processes of reorganisation of activism. This is prefiguring a potential for reassembling socialities, paving ways for social imaginaries of a mobile citizenship transcending old and new divisions of Cyprus and the world

Second Stokes oscillation and Raman gain-guiding in micro-lensed monolithic diamond Raman lasers

Second Stokes generation at 620nm in 2mm long micro-lensed monolithic diamond Raman lasers is reported with 63% conversion efficiency. The Raman intracavity mode radius was found to be half that expected from the ABCD calculations of the resonator mode. Raman gain-guiding mechanism is suggested as an explanation

Energy scaling, second Stokes oscillation and Raman gain-guiding in monolithic diamond Raman lasers

Energy scaling of the 1st Stokes oscillation is compared in micro-lensed and plane-plane monolithic diamond Raman lasers under 532 nm pumping. A maximum Raman pulse energy of 92 µJ at 573 nm was achieved with the micro-lensed device, while in a plane-plane configuration the maximum Raman pulse energy was 3.1 mJ. 2nd Stokes generation at 620 nm in 2 and 1 mm long micro-lensed monolithic diamond Raman lasers is also reported. The best conversion efficiency from the pump at 532 nm, namely 63 %, was observed in a 2 mm long crystal at the pump pulse intensity of 4.5 GW/cm2. By measuring the output Raman laser beam caustic it was found that the 2nd Stokes intracavity beam radius at the output coupler of the micro-lensed device is at least two times smaller than that expected from the ABCD matrix calculations of the resonator mode. A Raman gain-guiding mechanism is suggested to explain this difference

Metaverse and circular economy

The revolutionary concepts of the Metaverse and circular economy are poised to reshape the future of society, academia and all business sectors. The Metaverse as a digital realm promises to transform peoples' way of life, while circular economy offers a sustainable and regenerative approach to economic growth. Together, these concepts can be combined to unlock new opportunities, drive innovation and address pressing challenges facing humanity. Within this new era of technological and environmental transformation, understanding the capabilities and potential of the Metaverse intertwined with the circular economy is crucial for individuals and nations alike

Towards specification of a software architecture for cross-sectoral big data applications

The proliferation of Big Data applications puts pressure on improving and optimizing the handling of diverse datasets across different domains. Among several challenges, major difficulties arise in data-sensitive domains like banking, telecommunications, etc., where strict regulations make very difficult to upload and experiment with real data on external cloud resources. In addition, most Big Data research and development efforts aim to address the needs of IT experts, while Big Data analytics tools remain unavailable to non-expert users to a large extent. In this paper, we report on the work-in-progress carried out in the context of the H2020 project I-BiDaaS (Industrial-Driven Big Data as a Self-service Solution) which aims to address the above challenges. The project will design and develop a novel architecture stack that can be easily configured and adjusted to address cross-sectoral needs, helping to resolve data privacy barriers in sensitive domains, and at the same time being usable by non-experts. This paper discusses and motivates the need for Big Data as a self-service, reviews the relevant literature, and identifies gaps with respect to the challenges described above. We then present the I-BiDaaS paradigm for Big Data as a self-service, position it in the context of existing references, and report on initial work towards the conceptual specification of the I-BiDaaS software architecture.This work is supported by the IBiDaaS project, funded by the European Commission under Grant Agreement No. 780787.Peer ReviewedPostprint (author's final draft

9 W average power, 150 kHz repetition rate diamond Raman laser at 1519 nm, pumped by a Yb fibre amplifier

Commercially available pulsed fibre lasers at ~1.5 μm have many uses in imaging, defense, communications and light radar (LIDAR) [1]. For 3D scanning LIDAR, higher signal-to-noise ratio requires lasers with high average power and high pulse repetition rate (ideally several MHz) for faster scanning rate, whereas to improve distance resolution requires pulse durations <10 ns [2,3]. One limitation of the pulsed fibre lasers at ~1.5 μm is scaling to high average powers [4]. Raman frequency conversion of high average power fibre master oscillator power amplifier (MOPA) systems at ~1 μm is a potential alternative. The large Raman shift and Raman gain of diamond allows two-stage Raman conversion to ~1.5 μm for ~1 μm pumping [5]. Excellent thermal properties make diamond suitable for high average powers [6]. Much work has been done on conversion of 1.064 μm lasers to 1.485 μm using diamond [7]; however, the “eye-safety” requirements for LIDAR typically call for wavelengths above 1.5 μm, due to the order of magnitude higher Maximum Permissible Exposure limit [8]. Developing such a diamond Raman laser (DRL) was the major motivation for this research

The mediterranean dietary pattern and breast cancer risk in Greek-Cypriot women: a case-control study

Background: Diet has long been suspected to impact on breast cancer risk. In this study we evaluated whether the degree of adherence to a Mediterranean diet pattern modifies breast cancer risk amongst Greek-Cypriot women. Methods: Subjects included 935 cases and 817 controls, all participating in the MASTOS case-control study in Cyprus. The study was approved by the Cyprus National Bioethics Committee. Information on dietary intakes was collected using an interviewer administered 32-item Food Frequency Questionnaire. Information on demographic, anthropometric, lifestyle, and other confounding factors was also collected. Adherence to the Mediterranean Diet pattern was assessed using two a-priory defined diet scores. In addition, dietary patterns specific to our population were derived using Principal Component Analysis (PCA). Logistic regression models were used to assess the association between the dietary patters and breast cancer risk. Results: There was no association with breast cancer risk for either score, however, higher consumptions of vegetables, fish and olive oil, were independently associated with decreased risk. In addition, the PCA derived component which included vegetables, fruit, fish and legumes was shown to significantly reduce risk of breast cancer (ORs across quartiles of increasing levels of consumption: 0.89 95%CI: 0.65-1.22, 0.64 95%CI: 0.47-0.88, 0.67 95%CI: 0.49-0.92, P trend < 0.0001), even after adjustment for relevant confounders. Conclusions: Our results suggest that adherence to a diet pattern rich in vegetables, fish, legumes and olive oil may favorably influence the risk of breast cancer. This study is the first investigation of dietary effects on breast cancer risk in Cyprus, a country whose population has traditionally adhered to the Mediterranean diet