Literatura académica sobre el tema "Ultrafast characterisation"
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Artículos de revistas sobre el tema "Ultrafast characterisation"
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Chernysheva, Maria, Aleksey Rozhin, Yuri Fedotov, Chengbo Mou, Raz Arif, Sergey M. Kobtsev, Evgeny M. Dianov y Sergei K. Turitsyn. "Carbon nanotubes for ultrafast fibre lasers". Nanophotonics 6, n.º 1 (6 de enero de 2017): 1–30. http://dx.doi.org/10.1515/nanoph-2015-0156.
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AbstractCarbon nanotubes (CNTs) possess both remarkable optical properties and high potential for integration in various photonic devices. We overview, here, recent progress in CNT applications in fibre optics putting particular emphasis on fibre lasers. We discuss fabrication and characterisation of different CNTs, development of CNT-based saturable absorbers (CNT-SA), their integration and operation in fibre laser cavities putting emphasis on state-of-the-art fibre lasers, mode locked using CNT-SA. We discuss new design concepts of high-performance ultrafast operation fibre lasers covering ytterbium (Yb), bismuth (Bi), erbium (Er), thulium (Tm) and holmium (Ho)-doped fibre lasers.
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Nagatsuma, T., K. Iwatsuki, M. Shinagawa, A. Kozen, M. Yaita, K. Suzuki y K. Kato. "Electro-optic characterisation of ultrafast photodetectors using adiabatically compressed soliton pulses". Electronics Letters 30, n.º 10 (12 de mayo de 1994): 814–16. http://dx.doi.org/10.1049/el:19940433.
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Hu, Xinyu, Rui Pan, Mingyong Cai, Weijian Liu, Xiao Luo, Changhao Chen, Guochen Jiang y Minlin Zhong. "Ultrafast laser micro-nano structured superhydrophobic teflon surfaces for enhanced SERS detection via evaporation concentration". Advanced Optical Technologies 9, n.º 1-2 (25 de febrero de 2020): 89–100. http://dx.doi.org/10.1515/aot-2019-0072.
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AbstractEvaporation concentration of target analytes dissolved in a water droplet based on superhydrophobic surfaces could be able to break the limits for sensitive trace substance detection techniques (e.g. SERS) and it is promising in the fields such as food safety, eco-pollution, and bioscience. In the present study, polytetrafluoroethylene (PTFE) surfaces were processed by femtosecond laser and the corresponding processing parameter combinations were optimised to obtain surfaces with excellent superhydrophobicity. The optimal parameter combination is: laser power: 6.4 W; scanning spacing: 40 μm; scanning number: 1; and scanning path: 90 degree. For trapping and localising droplets, a tiny square area in the middle of the surface remained unprocessed for each sample. The evaporation and concentration processes of droplets on the optimised surfaces were performed and analyzed, respectively. It is shown that the droplets with targeted solute can successfully collect all solute into the designed trapping areas during evaporation process on our laser fabricated superhydrophobic surface, resulting in detection domains with high solute concentration for SERS characterisation. It is shown that the detected peak intensity of rhodamine 6G with a concentration of 10−6m in SERS characterisation can be obviously enhanced by one or two orders of magnitude on the laser fabricated surfaces compared with that of the unprocessed blank samples.
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Tan, T. Y. T. y G. S. H. Yeo. "Advances in Imaging in Prenatal Diagnosis and Fetal Therapy". Annals of the Academy of Medicine, Singapore 32, n.º 3 (15 de mayo de 2003): 289–93. http://dx.doi.org/10.47102/annals-acadmedsg.v32n3p289.
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Technological advances in ultrasound have contributed to improvements in prenatal diagnosis. Transvaginal scanning and harmonic imaging have allowed better resolution and improved structural characterisation. Doppler techniques have further been improved, which allow accurate flow studies of vessels in the placenta and fetus. These have contributed much to the management of intrauterine growth restriction, fetal anaemia and twin-twin transfusion syndrome (TTTS). Three-dimensional sonography and magnetic resonance imaging ultrafast sequences are useful adjuncts to conventional 2-dimensional sonography, increasing the confidence and diagnostic accuracy of prenatal diagnosis. Fetal therapy has seen major advances in recent years as well, secondary to improvements in endoscopic instruments and surgical techniques. Selective Nd:YAG laser photocoagulation of communicating vessels and cord occlusion have been used to treat complications of monochorionic twins like TTTS and twin-reversed arterial perfusion sequence.
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Donis-González, Irwin R., Daniel E. Guyer, Anthony Pease y Frank Barthel. "Internal characterisation of fresh agricultural products using traditional and ultrafast electron beam X-ray computed tomography imaging". Biosystems Engineering 117 (enero de 2014): 104–13. http://dx.doi.org/10.1016/j.biosystemseng.2013.07.002.
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Bhudolia, Somen K., Goram Gohel, Jayaram Kantipudi, Kah Fai Leong y Robert J. Barsotti. "Ultrasonic Welding of Novel Carbon/Elium® Thermoplastic Composites with Flat and Integrated Energy Directors: Lap Shear Characterisation and Fractographic Investigation". Materials 13, n.º 7 (1 de abril de 2020): 1634. http://dx.doi.org/10.3390/ma13071634.
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The current research work presents a first attempt to investigate the welding attributes of Elium® thermoplastic resin and the fusion bonding using ultrafast ultrasonic welding technique. The integrated energy director (ED) polymer-matrix composites (PMCs) panel manufacturing was carried out using the Resin Transfer Moulding (RTM) technique and the scheme is deduced to manufacture a bubble-free panel. Integrated ED configurations and flat specimens with Elium® film of different thickness at the interface were investigated for ultrasonic welding optimization. Optimised weld time for integrated ED and flat Elium® panels with film (0.5 mm thick) configuration was found to be 1 s and 5.5 s, respectively. The ED integrated configuration showed the best welding results with a lap shear strength of 18.68 MPa. The morphological assessment has shown significant plastic deformation of Elium® resin and the shear cusps formation, which enhances the welding strength. This research has the potential to open up an excellent and automated way of joining Elium® composite parts in automotive, wind turbines, sports, and many other industrial applications.
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Lau, Y. M., F. Möller, U. Hampel y M. Schubert. "Ultrafast X-ray tomographic imaging of multiphase flow in bubble columns – Part 2: Characterisation of bubbles in the dense regime". International Journal of Multiphase Flow 104 (julio de 2018): 272–85. http://dx.doi.org/10.1016/j.ijmultiphaseflow.2018.02.009.
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Juodkazis, Saulius, Arturas Vailionis, Eugene G. Gamaly, Ludovic Rapp, Vygantas Mizeikis y Andrei V. Rode. "Femtosecond laser-induced confined microexplosion: tool for creation high-pressure phases". MRS Advances 1, n.º 17 (30 de diciembre de 2015): 1149–55. http://dx.doi.org/10.1557/adv.2015.41.
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ABSTRACTNew material phases formed under non-equilibrium conditions at pressures above 100 GPa and temperatures exceeding 104K, the conditions of the warm dense matter (WDM), have become accessible using micro-explosions triggered by ultra-short sub-1 ps pulses tightly focused into micro-volume with cross sections comparable with the wavelength of light. Laser-induced micro-explosions convert a material in a focal volume into a non-equilibrium disordered plasma state confined inside the bulk of pristine crystal. Ultra-high quenching rates overcome kinetic barriers to the formation of new metastable high pressure phases, which are preserved in the surrounding pristine crystal for following recovery and exploitation. Direct laser writing was used to pattern large areas by closely packed arrays of the microexplosion modified sites for structural characterisation of the minute volumes of nano-materials with transmission electron microscopy, diffraction and synchrotron X-ray diffraction. The method of ultrafast-laser induced confined microexplosion is demonstrated for modification and creation of new phases in case of bcc-Al inside sapphire, valence change of Fe-ions in olivine, formation of new tetragonal bt8 and st12 phases of silicon, Ge and O separation in GeO2 glass and molecular oxygen formation inside voids at the site of microexplosion inside glasses.
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Costa, P. M. F. J. "Imaging the stimuli response of nanostructured materials inside a transmission electron microscope: from today’s sub-second recording to ultrafast phenomena". Microscopy and Microanalysis 19, S4 (agosto de 2013): 93–94. http://dx.doi.org/10.1017/s1431927613001086.
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Over the last decade, with the advent of aberration correctors and energy-filters, transmission electron microscopes (TEMs) have seen phenomenal developments both in regards to spatial and spectral resolutions. Today, the TEM is a characterisation tool pervasive to nanoscaled sciences and technologies. Imaging and identifying single atoms, including low Z elements such as B or C, is within reach of a skilful operator with access to this new generation of microscopes.Parallel to these advances, sample holders have also been evolving. Instead of just fixing and orienting the sample for observation, these ancillary components of TEMs have gradually been morphing into full-fledged instruments. Increasingly sophisticated devices enable a multitude of experiments performed inside the column of the TEM which includes the manipulation and exposure of discrete nanostructures to a variety of stimuli (heat, pressure, electrical current…). An example is the real-time observation of solid-vapour phase transitions in filled carbon nanotubes acting as interconnects and experiencing the dynamical effects of Joule heating. Together with resolution improvements, these added capabilities represent a paradigmatic shift in how we perceive and work with TEMs. No longer is the electron microscopist limited to simply analyse specimens in “post-mortem” state but (s)he can now take hold of a full set of physical and chemical experiments that encompass a much broader range of scientific interests.Despite all progress, there is a crucial part of the TEM capabilities that is still awaiting a similar leap in resolution: the time-domain. In result of the past dominance of “post-mortem” analysis, a temporal resolution enhancement has been overlooked by most instrument manufacturers and researchers. However, with the growing interest on in situ methodologies, the ability to perform time-resolved experiments has suddenly become a fundamental necessity. Classically, registering tools such as photographic films, charge-coupled devices or video-rated cameras have been adequate to acquire data on events that take place on timescales ranging from seconds to hours. Such temporal resolution is not sufficient for an immensity of life- and materials science-related processes. To illustrate this, Figure 1 shows the before and after states of a ZnS-filled carbon nanotube that was subjected to a pulse of electrical current. Although it is possible to observe clearly the end result, one can only speculate on how the confined semiconductor was released, transported and delivered to the receiving substrate. Considering that the pulse lasted for 250 ms, a temporal resolution of at least 50 ms (or 20 frames per second) for the registering device would be necessary to build a reasonable impression of the mechanism behind this delivery-procedure.PMFJC acknowledges the support from the Fundação para a Ciência e Tecnologia (Ciencia2007 Fellowship and project grant PTDC/EME-PME/112073/2009) and Alexander von Humboldt Foundation (Advanced Researcher Fellowship).
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Peralta, L., E. Mourier, C. Richard, P. Chavette-Palmer, M. Muller, M. Tanter y G. Rus. "117 IN VIVO EVALUATION OF THE CERVICAL STIFFNESS EVOLUTION DURING INDUCED LABOR IN EWES USING ELASTOGRAPHY". Reproduction, Fertility and Development 27, n.º 1 (2015): 150. http://dx.doi.org/10.1071/rdv27n1ab117.
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Despite numerous advances and intensive research in perinatal medicine, spontaneous preterm birth (PTB) is the leading global cause of neonatal mortality and morbidity. On the other hand, labour has to be induced in ~23% of pregnancies worldwide. Both issues may be related to the distensibility of the cervical tissue. Quantitative and objective monitoring of the cervix ripening may provide a complementary method to identify cases at risk of PTB and assess the likelihood of successful induction of labour. Currently, however, no reliable clinical tools for such a quantitative and objective evaluation exist. Elastography aims at imaging tissue stiffness. All elastography techniques rely on the same basics: an external force is applied to the tissue and the resulting movements are then followed. Supersonic shear imaging (SSI) is a dynamic method that uses the propagation of mechanical waves to excite the tissue. Its speed is tracked then by ultrafast imaging, allowing characterisation of stiffness [Bercoff et al. 2004 IEEE Trans. Ultrason. Ferroelect. Freq. Contr. 51, 396–409]. Understanding the mechanisms that take place in normal pregnancy will allow a better comprehension of the cervical remodelling and lead to better methods of diagnosis of PTB and successful induction of labour. In this work, we propose a preliminary assessment of the evolution of stiffness during the cervical maturation process in the sheep. The main goal was to study the feasibility of elastography using SSI to quantify cervical stiffness during the maturation process and to assess the potential of this technique for diagnosis of preterm labour and for labour induction success. Cervical stiffness was quantified, by 2 different operators, in 9 pregnant ewes in vivo by using SSI. The cervical ripening was induced by a dexamethasone injection in 5 animals, and 4 animals constituted the control group. The stiffness of the second ring of the cervix was quantified over a circular region of interest of 5 mm of diameter during vaginal ultrasound examination. Images were acquired every 4 h during 24 h to monitor the cervical maturation induced by the dexamethasone injection. Cervical stiffness was found to decrease significantly throughout the cervical ripening (from 9.5 ± 0.9 kPa to 5.0 ± 0.8 kPa; P = 2.7e–5). The intraobserver and interobserver repeatability of measurements were assessed using Bland-Altman analysis with 95% CI. The principal findings of the study were that elastography measurements using SSI technique were highly reproducible in all cases. Second, stiffness of the uterine cervix decreases throughout the maturation process induced by the dexamethasone injection. Finally, it was possible to quantify the decrease of stiffness through the cervical maturation process. Elastography may be a valuable method to quantify objectively and noninvasively the cervical stiffness in vivo, and ultimately could be a useful tool for the diagnosis of PTB and the assessment of labour induction success.
Tesis sobre el tema "Ultrafast characterisation"
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Baynes, Nicholas de Brissac. "Ultrafast characterisation of gallium arsenide devices and nanostructures". Thesis, University of Cambridge, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.388822.
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Turnbull, Andrew. "Design and characterisation of ultrafast semiconductor disk lasers". Thesis, University of Southampton, 2015. https://eprints.soton.ac.uk/381283/.
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In this thesis I present my work on improving the design of semiconductor gain and saturable absorber structures towards the goal of a Watt-level, sub-200 fs mode-locked vertical-external cavity surface-emitting laser (ML-VECSEL). The performance of MLVECSELs has increased significantly in recent years with sub-500 fs pulse durations demonstrated at Watt-level average output powers. However, ML-VECSELs with sub-200 fs pulse durations have only been reported with milliwatt average output powers. Absence of detailed knowledge of the dynamic response of both gain and saturable absorber structures makes it di�fficult to develop new designs for improved laser performance. It is, therefore, critical to fully characterise the macroscopic parameters of the semiconductor laser structures used in ML-VECSELs. Here, I present the characterisation of ultrafast surface recombination semiconductor saturable absorbers, with a design that has given the shortest pulse durations from a ML-VECSEL to date. I demonstrate a ML-VECSEL utilising a cavity design based on the extracted absorber parameters that would be suitable for high average mode-locked output powers using surface-recombination absorbers. An understanding of fundamental mode-locking mechanisms present in ML-VECSELs is vital for optimising structures as pulse durations approach 100 fs. The evolution of the spectral components present from lasing onset and during pulse formation in a ML-VECSEL is measured; identifying three distinct regimes in the spectral evolution. I interpret the measured transients to extract a value for pulse-shortening per cavity round-trip, allowing a qualitative description of pulse formation in ML-VECSELs to be developed. I present construction and characterisation of a ML-VECSEL containing new "shortmicrocavity" gain structures that have demonstrated FWHM pulse durations of 193 fs with 1 KW peak output powers; a benchmark result for peak output power from a ML-VECSEL with sub-200 fs pulse duration.
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Huang, Leilei. "Fabrication and characterisation of ultrafast direct laser written waveguides". Thesis, University of Oxford, 2015. https://ora.ox.ac.uk/objects/uuid:7e40e1ee-fcc3-4797-953d-8be5c7af1334.
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A novel ultrafast direct laser writing (DLW) system using adaptive optics is proposed and demonstrated. This system has the potential to generate high-quality three-dimensional (3D) optical waveguides and components. The experimental setup and procedures for the DLW process are studied, after which various optical waveguides are fabricated in different transparent materials. The resulting waveguides are characterised by the measurement of the near-field laser coupling profiles in combination with optical microscopy techniques. Quantum random number generation (QRNG) and the potential application of the DLW technique in quantum information is also discussed. To completely understand the fabrication procedures for the DLW system, the experimental equipment and effects of different fabrication parameters are studied and analysed. With the use of a liquid-crystal spatial light modulator (SLM) in the DLW system, dynamic control of phase modulation can be provided to correct aberrations adaptively. An SLM can also make the cross-sectional profile of the written waveguides more circular and facilitate the fabrication of more complex 3D structures. Experiments reveal that the shape of the focal spot can be improved dramatically with adaptive optics, resulting in higher-quality optical waveguides. The refractive-index information of the written waveguides and their optical properties are measured using the propagation-mode near-field method (PMNFM). Simulation results and experimental measurements of a commercial single-mode fiber and a waveguide sample are demonstrated and compared. Quantitative phase measurement is also applied via the transport of intensity equation (TIE) to monitor the refractive-index change during fabrication. The propagation losses of the waveguides are measured and discussed. Different optical waveguides are fabricated using DLW in fused silica, potassium dihydrogen phosphate (KDP), and lithium niobate (LiNbO3) crystals. Different materials have different characteristics and properties, requiring different fabrication parameters and resulting in waveguides exhibiting different properties. Waveguides at various depths are demonstrated both with and without effects of adaptive optics. Experimental results indicate great improvements in the quality of the written waveguides after aberration correction. With an understanding of the optical properties of the straight waveguides using the characterisation methods, modelling and fabrication of bend waveguides and y-splitters are presented and studied. A high-speed QRNG system is also demonstrated in this thesis, with potential implementation using the DLW technique for a more compact and stable system. Finally, the possibility of the DLW fabrication of complex 3D optical components and their applications are discussed for future work.
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Kassier, Gunther Horst. "Ultrafast electron diffraction : source development, diffractometer design and pulse characterisation". Thesis, Stellenbosch : University of Stellenbosch, 2010. http://hdl.handle.net/10019.1/5359.
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Thesis (PhD (Physics))--University of Stellenbosch, 2010.ENGLISH ABSTRACT: Ultrafast Electron Diffraction (UED) is a rapidly maturing field which allows investigation of the evolution of atomic arrangement in solids on timescales comparable to the vibrational period of their constituent atoms (~10-13 s). The technique is an amalgamation of conventional high energy electron diffraction methods and pump-probe spectroscopy with femtosecond (1 fs = 10-15 s) laser pulses. Ultrafast pulsed electron sources generally suffer from limitations on the attainable electron number per pulse (brightness) due to Coulomb repulsion among the electrons. In this dissertation, the design and construction of a compact UED source capable of delivering sub-300 fs electron pulses suitable for diffraction experiments and containing about 5000 electrons per shot is described. The setup has been characterised by measurement of the transverse beam size and angular spread, and through recording and analyzing an electron diffraction pattern from a titanium foil. Measurement of the temporal duration of fs electron pulses is not trivial, and a specialised compact streak camera operating in accumulation mode has been developed as part of this study. A sub-200 fs temporal resolution has been achieved, and the dependence of temporal duration on electron number per pulse was investigated for the current UED source. The observed trends correlate well with detailed electron bunch simulations. In order to investigate ultrafast processes on samples that cannot be probed repeatedly, it becomes necessary to significantly increase the brightness of current state of the art compact sources such as the one constructed in the present study. UED sources employing electron pulse compression techniques offer this possibility. Traditional pulse compression schemes based on RF cavities, while simple in principle, pose significant technical challenges in their realisation. The current thesis describes two novel UED pulse compression methods developed by the author: achromatic reflectron compression and pulsed cavity compression. Both concepts are expected to be easier to realise than conventional RF compression. Detailed simulations predict that such sources can attain a brightness improvement of more than one order of magnitude over compact sources that do not employ compression techniques. In addition, such sources show much promise for the attainment of pulse durations in the sub-100 fs range.
AFRIKAANSE OPSOMMING: Ultra vinnige elektron diffraksie is ‘n meettegniek wat tans in die proses is om vinnige ontwikkeling te ondergaan. Die tegniek het ten doel om strukturele omsettingsprosesse op ‘n lengteskaal van atoombindings en ‘n tydskaal van die vibrasie periode van atome in materie, ongeveer 10-13 s, te ondersoek. Dit word bewerkstellig deur die spasieresolusievermoë van gewone hoë energie elektron diffraksie met die tydresolusievermoë van femtosekonde (1 fs = 10-15 s) laserspektroskopie te kombineer. Die aantal elektrone per puls (intensiteit) van ultravinnige gepulsde elektronbronne word beperk deur die Coulomb afstootingskragte tussen die elektrone. Hierdie dissertasie beskryf die ontwerp en konstruksie van ‘n kompakte ultravinnige elektron bron. Die elektronpulse wat geproduseer word bevat tot 5000 elektrone per puls met ‘n tyd durasie van minder as 300 fs, en is geskik vir diffraksie eksperimente. Die aparaat is gekarakteriseer deur die volgende metings: elektronpulsdiameter, straaldivergensie, en ‘n titaan foelie se statiese diffraksie patroon. Dit is nie triviaal om die durasie van femtosekonde elektronpulse te meet nie, en n spesiale kompakte akkumulerende “streak camera” is vir die doeleindes van hierdie projek onwikkel. Die tydresolusie van hierdie “streak camera” is beter as 200 fs, en die afhanklikheid van die pulsdurasie wat deur die ultravinnige elektron bron geproduseer word as n funksie van die elektrongetal per puls is met behulp van hierdie toestel bepaal. Die resultate klop redelik goed met gedetaileerde simulasies van die elektron puls dinamika. Die karakterisasie van monsters wat nie herhaaldelik gemeet kan word nie vereis verkieslik ‘n nog hoër pulsintensiteit as wat met huidige bronne bereik kan word. ‘N verdere doelstelling is dus om ultravinnige elektron bronne te ontwikkel wat pulse met meer elektrone per puls kan genereer. Dit kan bewerkstellig word deur bronne wat van elektron puls kompressie tegnieke gebruik maak. Die tradisionele manier waarop dít gedoen word is deur middel van n kontinu gedrewe radio frekwensie holte. Hierdie metode gaan egter gepaard met aanmerklik hoë tegniese uitdagings. Om hierdie rede het die outeur twee alternatiewe puls kompressie konsepte ontwikkel: akromatiese reflektron kompressie and gepulsde holte kompressie. Albei konsepte sal waarskeinlik makliker wees om te realiseer as die tradisionele radio frekwensie kompressie, en is deur middel van gedetaileerde simulasies geverifiseer. Hierdie simulasies voorspel dat die intensiteit van genoemde bronne met ten minste n grooteorde meer kan wees as wat tans met kompakte ultravinnige elektron bronne moontlik is. Verder blyk dit dat sulke bronne n pulsdurasie van minder as 100 fs kan bereik.
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Mang, Matthias M. "Interferometric spatio-temporal characterisation of ultrashort light pulses". Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:163c5374-1466-4c4d-a0f5-c4e66b27e2ac.
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The main topic of this thesis is the development of novel diagnostics for the characterisation of infrared femtosecond and extreme-ultraviolet (XUV) attosecond pulses. High-resolution interferometric methods are applied to high harmonic radiation, both to measure the properties of the XUV light and to relate this information to the physics of the fundamental generation process. To do so, a complete high harmonic beamline has been built and optimised to enable the observation of strong signatures of the macroscopic response of the medium. The distinct spatial characteristics of long and short trajectories are studied, as well as the interference between them. An interferometric measurement allows the extraction of the atomic dipole phase, which gives direct access to the sub-cycle electron dynamics. A major focus of this thesis is on the development of a novel method which simultaneously characterises two independent electric fields as a function of any degree of freedom in which it is possible to shear one of the beams. Since each field alternately takes the role of the reference to retrieve the other field, this technique is referred to as mutual interferometric characterisation of electric-fields (MICE). One of the key features of MICE is that no sheared but otherwise identical replica of the test pulse needs to be generated, which is a typical requirement of self-referencing techniques. Furthermore, no a priori information is needed for the reconstruction. The strength and the wide applicability of MICE are demonstrated using two fundamentally different examples. First, the temporal pulse profiles of two infrared femtosecond pulses are simultaneously reconstructed in a single laser shot. In the second demonstration, the MICE approach is used to simultaneously reconstruct the wavefronts of two high harmonic beams. Having this new technique at hand, the phase properties of the different quantum trajectories are compared. All pulse characterisation techniques implicitly assume full coherence of the beam. This, however, is often not the case in practice, in particular when dealing with complex XUV light sources. Here the standard characterisation techniques fail to provide an accurate description of the electric field. Instead, the electric field must be seen as a statistical mixture of different contributions to the overall field. Here an interferometric experiment is first proposed and then performed involving multiple lateral shears to measure the two-point correlation function of high harmonic radiation. This directly provides information about the existence and the magnitude of partial coherence of high harmonics.
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Macpherson, James. "Characterisation and Optimization of Ultrashort Laser Pulses". Thesis, University of Waterloo, 2003. http://hdl.handle.net/10012/1237.
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The ultrafast optical regime is defined, as it applies to laser pulses, along with a brief introduction to pulse generation and characterisation technologies. A more extensive description of our particular amplified pulse generation and SPIDER characterisation systems follows. Data verifying the correct operation of the characterisation system is presented and interpreted. Our laser system is then characterised in two different configurations. In each case, the data describing the system is presented and analyzed. Conclusions are made regarding the performance of both the characterisation and laser systems, along with suggested improvements for each.
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Wriglesworth, Alisdair. "Investigation into C-H activation and characterisation of excited states using ultrafast TRIR spectroscopy". Thesis, University of Nottingham, 2014. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.718861.
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Abajyan, Pavel. "Génération et contrôle de peignes de fréquences optiques dans les lasers à cascade d'interbande (ICL)". Electronic Thesis or Diss., Sorbonne université, 2024. http://www.theses.fr/2024SORUS024.
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Les peignes de fréquence optique (OFC) sont des sources de lumière cohérente qui émettent un large spectre de modes discrets parfaitement espacés, chacun avec une fréquence absolue mesurable avec la précision d'une horloge atomique.Les OFC dans l'infrarouge moyen (MIR 3-12 μm) sont récemment devenus d'un grand intérêt pour la spectroscopie moléculaire par la présence de forte absorption des modes de vibration et de rotation moléculaires dans la région des "empreintes digitales" spectroscopiques. Néanmoins, le fonctionnement de l'OFC dans la région cruciale de l'infrarouge moyen (MWIR 3-6 μm) reste nettement sous-développé par rapport aux autres parties du MIR.Dans ce travail, nous présentons une étude expérimentale approfondie d'une nouvelle génération de laser à cascade interbande (ICL) et de leur potentiel pour les OFC dans MWIR. La thèse apporte la preuve du régime OFC à la fois par spectroscopie des battements (BN) à haute fréquence, et par la nouvelle technique de reconstruction temporelle de la dynamique ultrarapide de ces lasers, celle-ci permettant de "visualiser" le contrôle du type de fonctionnement de l'OFC dans les ICL. En particulier, a été effectuer la caractérisation opto-électrique d'un ensemble d'ICL avec une gamme de géométries, dans le but d'étudier les ICL à faible dispersion de retard de groupe (GDD) à des longueurs d'onde plus longues que celles étudiées auparavant: un ICL fonctionnant à 3.8 μm avec une architecture en 2-sections, des ICL fonctionnant à 4.1 μm, et une autre génération d'ICL fonctionnant à une longueur d'onde de 4.2 μm conçue avec un gain spectral large. La formation du régime OFC et le GDD sont liées et importantes pour comprendre les mécanismes fondamentaux de la formation de l'OFC. Les ICL ont été étudiés à l'aide de la spectroscopie BN optique et électrique. Les verrouillages de mode passif (PML) (ou fonctionnement libre) et actif (AML) ont été démontrés. Pour les ICL à 2-sections, où l'ICL est divisé en une partie longue et une partie courte pour une seule cavité, l'effet exact de la petite section sur le BN a été explicité: permets de (a) contrôler très finement le GDD intracavité, (b) introduire des pertes et montrant que l'on converge vers un comportement PML. Ce travail étend l'étude au cas des ICL fonctionnant à des longueurs d'onde plus longues dans une cavité à section unique et où le GDD est censé être inférieur.Pour un ICL à 4.1 μm, il est montré qu'un BN optique puissant peut être verrouillé par injection radiofréquence (RF) à la fréquence d'un aller-retour de l'ICL, premières étapes de AML. Ce verrouillage par injection a été réalisé à l'aide d'une architecture laser à 1-section avec une très faible GDD montrant ainsi que l'adaptation du guide d'onde ICL au fonctionnement RF n'est pas une exigence fondamentale.Dans sa dernière partie, la thèse montre la mise en œuvre de la technique "Shifted Wave Interference Fourier Transform Spectroscopy" (SWIFTS), utilisée selon deux configurations différentes, pour reconstruire le profil d'intensité temporel du laser à des échelles de temps ultrarapides. Cela démontre la nature des OFC générés dans ces ICL. L'ICL fonctionne en régime de modulation de fréquence (FM) lorsqu'il est en fonctionnement libre et transite vers un régime de modulation d'amplitude (AM) lorsqu'il est en régime AML en par injection RF. L'étude montre également que les ICL peuvent générer des impulsions courtes de ∼6.7 ps en fonctionnement libre, malgré leur caractère FM, et met en évidence le contrôle de la largeur d'impulsion et de l'intensité maximale via l'injection RF. Cela permet de compresser d'un facteur de 2.3 les impulsions libres pour obtenir des impulsions inférieures à 3 ps.Ces travaux constituent une étape importante dans la réalisation et le contrôle des OFC dans la région MWIR. Les perspectives sont d'élargir la bande passante spectrale des ICL et de générer des impulsions ultracourtes de haute puissance dans le MWIR et au-delàOptical frequency combs (OFCs) are coherent light sources that emit a broad spectrum of discrete, perfectly spaced modes, each with an absolute frequency measurable with the precision of an atomic clock.OFCs in the mid-infrared (MIR 3-12 μm) have recently become of great interest to molecular spectroscopy by the presence of strong absorption of molecular vibration and rotation modes in the spectroscopic "fingerprint" region. Nevertheless, the operation of the OFC in the crucial mid-infrared region (MWIR 3-6 μm) remains significantly underdeveloped compared to other parts of the MIR.In this work, we present an in-depth experimental study of a new generation of interband cascade laser (ICL) and their potential for OFCs in MWIR. The thesis provides proof of the OFC regime both by high-frequency beatnote spectroscopy (BN), and by the new technique of temporal reconstruction of the ultrafast dynamics of these lasers, this making it possible to "visualize" the control of the type of operation of the OFC in ICL. In particular, was carried out the optoelectrical characterization of a set of ICLs with a range of geometries, with the aim of studying low group delay dispersion (GDD) ICLs at longer wavelengths than those previously studied: an ICL operating at 3.8 μm with a 2-section architecture, ICLs operating at 4.1 μm, and another generation of ICL operating at a wavelength of 4.2 μm designed with a wide spectral gain. OFC regime formation and GDD are linked and important for understanding the fundamental mechanisms of OFC formation. ICLs were studied using optical and electrical BN spectroscopy. Passive mode locking (PML) (or free running) and active mode locking (AML) were demonstrated. For 2-section ICLs, where the ICL is divided into a long part and a short part for a single cavity, the exact effect of the small section on the BN has been explained: allows to (a) control very finely the intracavity GDD, (b) introducing losses and showing that we converge towards PML behavior.This work then feeds into the case of ICLs operating at longer wavelengths in a single section cavity and where the GDD is expected to be less. In the particular case of the ICLs operating at 4.1 μm, we demonstrate a strong optical BN, which can be injection locked by radio frequency (RF) injection at the round trip frequency of the ICL, showing the first-steps of active modelocking. This injection locking was achieved using a simple single-section laser architecture with very low waveguide dispersion, and showing that adapting the ICL waveguide for RF operation is not a fundamental requirement. In the final part of the thesis, we show the implementation of the "Shifted Wave Interference Fourier Transform Spectroscopy" (SWIFTS) technique, used in two different configurations, to reconstruct the laser's temporal intensity profile at ultrafast timescales. This permits to demonstrate the nature of OFC generated in these ICLs. Indeed, we show that the ICL operates in the frequency modulation (FM) regime when free-running and transits towards an amplitude modulation (AM) regime when actively modelocked. Interestingly, we also show that ICLs can generate short pulses of ~6.7 ps in free-running operation, despite FM operation, and highlight the control of the pulse width and peak intensity via RF injection. This permits to compress the free-running pulses by a factor of 2.3 to obtain sub-3 ps pulses.This work constitutes an important step in the creation and control of OFCs in the MWIR region. The prospects are to broaden the spectral bandwidth of ICLs and generate high-power ultrashort pulses in the MWIR and beyond
Capítulos de libros sobre el tema "Ultrafast characterisation"
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Martinsson, Peter, Jari A. I. Oksanen, Marcus Hilgendorft, Eva Åkesson, Paavo Hynninen y Villy Sundström. "Characterisation of Chlorophyll a and Chlorophyll b Monomers in Various Solvent Environments with Ultrafast Spectroscopy". En Photosynthesis: Mechanisms and Effects, 457–60. Dordrecht: Springer Netherlands, 1998. http://dx.doi.org/10.1007/978-94-011-3953-3_109.
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Amy, Dominique. "Breast Elastography". En Elastography - Applications in Clinical Medicine [Working Title]. IntechOpen, 2022. http://dx.doi.org/10.5772/intechopen.102445.
Texto completoResumen
Breast elastography has become a key complementary technique. A modality in the framework of breast pathology, complementary of B-mode imaging and colour doppler analysis. Breast ultrasound has provided morphological grayscale images and functional flow analysis of the soft breast tissues. Elastography now brings new physio-pathological information through the assessment of tissue elasticity. There are two different modalities: Real Time Elastography (RTE) and Shear Waves (SWE) ultrafast Imaging. Both techniques require a minimum adhesion to the skill rules for acquisition and interpretation so as to limit the operator dependant dimension and diagnostic errors. Elastography thus becomes perfectly reproducible with good accuracy in the different scores of the RTE or SWE classification. The aim of elastography in cancer screening is to achieve reliable lesion characterisation and better therapy monitoring/management.
Actas de conferencias sobre el tema "Ultrafast characterisation"
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Bona, Nicola, Dario Santonico, Saida Machicote y Alessandra Battigelli. "Ultrafast Core Analysis for Tight Gas Reservoirs". En SPE Reservoir Characterisation and Simulation Conference and Exhibition. Society of Petroleum Engineers, 2019. http://dx.doi.org/10.2118/196648-ms.
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Reid, D. T., P. Loza-AIvarez, C. T. A. Brown, T. Beddard y W. Sibbett. "Complete characterisation of mid-infrared femtosecond pulses using XFROG". En International Conference on Ultrafast Phenomena. Washington, D.C.: OSA, 2000. http://dx.doi.org/10.1364/up.2000.mf28.
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Ogawa, K., J. Allam, J. J. Baumberg, N. de B. Baynes, J. R. A. Cleaver, T. Mishima y I. Ohbu. "Ultrafast characterisation of parasitics in in-plane-gate field-effect transistors". En Ultrafast Electronics and Optoelectronics. Washington, D.C.: OSA, 1995. http://dx.doi.org/10.1364/ueo.1995.utue10.
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Beaulieu, Y., R. Normandin, P. van der Meer, F. Chatenoud, A. Delage y B. K. Garside. "Picosecond Optical Time Domain Reflectometer for Optoelectronic IC Device Characterisation". En International Conference on Ultrafast Phenomena. Washington, D.C.: Optica Publishing Group, 1994. http://dx.doi.org/10.1364/up.1994.md.26.
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Several years ago Stegeman and Normandin predicted, and subsequently demonstrated [1], the nonlinear mixing of oppositely propagating guided waves. The resultant second harmonic field was coupled to radiation modes and propagated in a direction perpendicular to the waveguide surface, in the case of equal fundamental frequencies. Its application to picosecond signal processing [2], the creation of all optical transient digitizers [3] and spectrometers [4] demonstrated the potential usefulness of this approach. Finally, the nonlinear cross section for uniform GaAs optical waveguides was calculated and published [5], and recently this GaAs prediction was verified [6] by Vakhsoori et al. In their geometry, the oppositely propagating beam was supplied by the reflection from the exit surface. Their use of picosecond pulses also demonstrated the potential for optical correlation in a geometry similar to references 2 and 3. However, the use of simple GaAs films results in low conversion efficiencies, due to difficult input coupling and absorption and phase cancellation effects at the harmonic wavelength.
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Thakur, Siddharatha, Behrooz Semnani, Safieddin Safavi-Naeini y Amir Hamed Majedi. "Experimental Characterisation of the Ultrafast Kerr Nonlinearity in Graphene". En Nonlinear Optics. Washington, D.C.: OSA, 2019. http://dx.doi.org/10.1364/nlo.2019.ntu4a.28.
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Tan, Howe-Siang, Elmar Schreiber y Warren S. Warren. "The generation, amplification and characterisation of shaped ultrafast laser pulses, tunable in the visible wavelengths". En International Conference on Ultrafast Phenomena. Washington, D.C.: OSA, 2000. http://dx.doi.org/10.1364/up.2000.mf41.
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Dichtl, Paul, Sylvain D. Gennaro, Yi Li, Stefan A. Maier y Rupert F. Oulton. "Exploiting the Nonlinear Optical Response of Gold Nanoantennas for ultrafast pulse characterisation". En Frontiers in Optics. Washington, D.C.: OSA, 2019. http://dx.doi.org/10.1364/fio.2019.jtu3a.47.
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Gennaro, Sylvain D., Yi Li, Stefan A. Maier y Rupert F. Oulton. "Double blind ultrafast pulse characterisation by mixed frequency generation in gold antennas (Conference Presentation)". En Active Photonic Platforms X, editado por Ganapathi S. Subramania y Stavroula Foteinopoulou. SPIE, 2018. http://dx.doi.org/10.1117/12.2320736.
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Oulton, Rupert F., Sylvain D. Gennaro, Yi Li y Stefan A. Maier. "Double-blind ultrafast pulse characterisation by mixed frequency generation in gold antennas (Conference Presentation)". En High Contrast Metastructures VIII, editado por Connie J. Chang-Hasnain, Weimin Zhou y Andrei Faraon. SPIE, 2019. http://dx.doi.org/10.1117/12.2511463.
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Ams, Martin, Michael J. Withford, Judith M. Dawes y James A. Piper. "Characterisation of waveguides written in bulk materials with femtosecond laser pulses". En PICALO 2004: 1st Pacific International Conference on Laser Materials Processing, Micro, Nano and Ultrafast Fabrication. Laser Institute of America, 2004. http://dx.doi.org/10.2351/1.5056144.
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