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Intense laser propagation in sapphireTate, Jennifer Lynn 19 May 2004 (has links)
No description available.
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Novel coherent supercontinuum light sources based on all-normal dispersion fibersHeidt, Alexander Matthias 12 1900 (has links)
Thesis (PhD)--Stellenbosch University, 2011. / ENGLISH ABSTRACT: The concept of broadband coherent supercontinuum (SC) generation in all-normal dispersion
(ANDi) fibers in the near-infrared, visible and ultraviolet (UV) spectral regions
is introduced and investigated in detail. In numerical studies, explicit design criteria are
established for ANDi photonic crystal fiber (PCF) designs that allow the generation of
flat and smooth ultrabroad spectral profiles without significant fine structure and with
excellent stability and coherence properties. The key benefit of SC generation in ANDi
fibers is the conservation of a single ultrashort pulse in the time domain with smooth and
recompressible phase distribution. In the numerical investigation of the SC generation
dynamics self-phase modulation and optical wave breaking are identified as the dominant
nonlinear effects responsible for the nonlinear spectral broadening. It is further demonstrated
that coherence properties, spectral bandwidth and temporal compressibility are
independent of input pulse duration for constant peak power. The numerical predictions
are in excellent agreement with experimental results obtained in two realizations of ANDi
PCF optimized for the near-infrared and visible spectral region. In these experiments,
the broadest SC spectrum generated in the normal dispersion regime of an optical fiber
to date is achieved. The exceptional temporal properties of the generated SC pulses are
verified experimentally and their applicability for the time-resolved study of molecular
dynamics in ultrafast transient absorption spectroscopy is demonstrated. In an additional
nonlinear pulse compression experiment, the SC pulses obtained in a short piece of
ANDi PCF could be temporally recompressed to sub-two cycle durations by linear chirp
compensation. Numerical simulations show that even shorter pulse durations with excellent
quality can be achieved by full phase compensation. The concept is further extended
into the UV spectral regime by considering tapered optical fibers with submicron waist
diameter. It is shown that coherent SC spectra with considerable spectral power densities
in the usually hard to reach wavelength region below 300 nm can be generated using
these freestanding photonic nanowires. Although technological difficulties currently prevent
the fabrication of adequate nanofibers, the concept could be experimentally verified
by coherent visible octave-spanning SC generation in tapered suspended core fibers with
ANDi profile. The work contained in this thesis therefore makes important contributions
to the availability and applicability of fiber-based broadband coherent SC sources with
numerous high-impact applications in fundamental science and modern technology. / AFRIKAANSE OPSOMMING: Die konsep van breëband koherente superkontinuum (SK) in alles-normaal dispersiewe
(ANDi) vesels in die naby-infrarooi, sigbare en ultraviolet (UV) spektrale gebiede word
voorgestel en in detail ondersoek. In numeriese studies word eksplisiete ontwerpskriteria
vasgestel vir ANDi fotoniese kristal vesel (FKV) ontwerpe wat dit moontlik maak om plat
en gladde ultra-breë spektrale profiele te genereer sonder noemenswaardige fynstruktuur
en met uitstekende stabiliteit en koherensie eienskappe. Die sleutel voordeel van SK
genering in ANDi vesels is die behoud van ’n enkele ultrakort puls in tyd met ’n gladde
en saamdrukbare fase distribusie. In die numeriese ondersoek van die SK generering is die
dinamika van fase selfmodulering geïdentifiseer as die dominante nie-lineêre effek wat verantwoordelik
is vir die nie-lineêre spektrale verbreding. Daar word voorts aangetoon dat
die koherensie eienskappe, spektrale bandwydte en saamdrukbaarheid in tyd onafhanklik
is van die inset pulsduur vir konstante drywing. Die numeriese voorspellings stem uitstekend
ooreen met die eksperimentele resultate wat verkry is met twee ANDi FKVÕs
wat optimeer is vir die naby-infrarooi en sigbare spektrale gebied. In hierdie eksperimente
is die breedste SK spektrum gegenereer wat tot hede in die normaal dispersiewe regime
met ’n optiese vesel behaal is. Die besondere eienskappe van die genereerde SK pulse is
eksperimenteel bevestig en die toepasbaarheid vir tyd opgelosde studie van molekulêre
dinamika is gedemonstreer. In ’n addisionele nie-lineêre puls kompressie eksperiment is
SK pulse verkry in ’n kort stuk ANDi FKV wat in tyd saamgedruk kon word tot sub-twee
siklus tydsduur deur liniêre tjirp kompensering. Numeriese simulasies toon aan dat selfs
korter pulse met uitstekende kwaliteit behaalbaar is met volledige fase kompensasie. Die
konsep is verder uitgebrei na die UV spektrale gebied deur ’n koniese vesel te beskou met
sub-mikron diameter. Daar is aangetoon dat koherente SK spektra met noemenswaardige
spektrale drywing in die golflengte gebied onder 300 nm, wat gewoonlik as moeilik toeganklik
beskou word, bereik kan word deur hierdie vrystaande fotoniese nano-vesels aan
te wend. Alhoewel tegnologiese probleme die vervaardiging van voldoende nano-vesels
verhinder, kon die konsep eksperimenteel bewys word deur koherente sigbare oktaafspannende
SK te genereer in koniese gesuspendeerde kern vesels met ’n ANDi profiel
aan te wend. Die werk wat in die tesis vervat is, maak dus belangrike bydraes tot die
beskikbaarheid en toepasbaarheid van vesel gebaseerde breëband koherente SK bronne
met verskeie hoë impak toepassings in fundamentele wetenskap en moderne tegnologie.
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Hole control in photonic crystal fibresChen, Yong January 2014 (has links)
Photonic crystal fibres (PCFs) are special fibres with air holes which run along the whole fibre length. These holes not only determine the fibres' unique properties, but also provide a new degree of freedom for fibre modications. In this thesis, we focus on hole control in PCFs from two perspectives: during their fabrication and after they have been made. We found for the first time that the direct information of viscosity was not necessary for description of the fibre drawing process. This conclusion matched our experimental results without recourse to any adjustable fitting parameters. By post-processing of PCFs, which modifies the cladding and core structure and shape, we have achieved a series of novel devices for both linear and nonlinear applications. We have demonstrated fibre devices with cores resembling Young's double slits that have good performance in terms of compatibility and intensity enhancement for a specific application in fibre optic spectrometers. The bulk of this thesis reports on higher-order modes and their nonlinear applications. We achieved all-fibre, low loss and broadband mode converters in highly nonlinear PCFs (HNPCFs) which converted the fundamental mode (LP01) to a higher-order mode (LP02), which can then be converted back if necessary. This higher-order mode has been used for supercontinuum (SC) generation and four wave mixing (FWM) at wavelengths unobtainable for the fundamental mode. This is achieved by utilising the profound dispersion properties of the higher-order mode. We also demonstrated another kind of mode conversion: from the fundamental mode to a Bessel-like beam or its Fourier transform version, an annular beam. Three different methods were implemented experimentally to achieve this non-diffractive, self-healing beam.
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Raman Signal Enhancement and CARS MicroscopyNaji, Majid January 2014 (has links)
Raman biosensors are appealing for many biomedical applications, due to their accuracy and speed. In addition, Raman microscopy is a non-labeled imaging technique that offers chemical contrast based on Raman vibrational frequencies. However, the weak Raman signal represents a significant obstacle to using Raman in biological applications. The objective of my PhD research, presented in this thesis, is to enhance the Raman signal, thereby enabling it to be used in a wide variety of biomedical applications.
More specifically, the research focuses on two different Raman signal enhancement techniques. The first is to improve the Raman signal using hollow-core photonic crystal fibers; this enhanced the Raman signal of ethanol 40 times. The second approach is by generating a coherent anti-Stokes Raman scattering (CARS) signal.
We demonstrated CARS microscopy of myelin (lipid-rich) structures using a single femtosecond Ti:sapphire laser, and a photonic crystal fiber (PCF) with two closely lying zero dispersion wavelengths (ZDWs). Generating low noise supercontinuum (Stokes beam) out of two closely lying ZDW PCFs, enabled us to perform fast data acquisition (84 μs per pixel) CARS imaging using a homebuilt microscope. However, the application of this fiber is often limited to CARS imaging of molecular species with vibrations at wavenumbers ≥ 2000 cm−1 Raman shift. In addition, as it is not a polarization maintaining fiber, it cannot be used for polarization CARS microscopy. A polarization-maintaining PCF with two far-lying zero dispersion wavelengths offers important advantages for polarization CARS microscopy, and for CARS imaging in the fingerprint region. This PCF, though commercially available, has had limited use for CARS microscopy in the C-H bond region. The main problem is that the supercontinuum from this fiber is typically noisier than that from a standard PCF with two closely-lying zero dispersion wavelengths. To overcome this, we determined the optimum operating conditions for generating a low-noise supercontinuum out of a PCF with two far-lying zero dispersion wavelengths, in terms of the input parameters of the excitation pulse. We measured the relative intensity noise (RIN) of the Stokes and the corresponding CARS signal, as a function of the input laser parameters in this fiber. We demonstrated that the results of CARS imaging using this alternate fiber are comparable to those achieved using the standard fiber for input laser pulse conditions of low average power, narrow pulse width with a slightly positive chirp, and polarization direction parallel to the slow axis of the selected fiber.
Finally, we demonstrated a novel fiber-delivered, portable, multimodal CARS exoscope, for minimally invasive in-vivo imaging of tissues. The device was based on a micro-electromechanical system-scanning mirror and miniaturized optics, and light delivery by photonic crystal fibre. A single Ti:sapphire femtosecond laser approach is used to produce CARS and two photon excitation fluorescent and second harmonic generation images of different samples using the new setup. The high resolution and distortion-free images achieved with various samples, particularly in the reverse direction (epi), successfully demonstrate proof of concept, and paves the way to minimally or non-invasive in vivo imaging. Moreover, combining this novel endoscope with a portable femtosecond fiber laser will accelerate delivering multimodal nonlinear imaging endoscopy/microscopy to clinical bed-side applications.
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ULTRA HIGH RESOLUTION AND CONTRAST SENSITIVE OPTICAL COHERENCE TOMOGRAPHYWang, Hui 03 April 2008 (has links)
No description available.
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Intense, Ultrashort Pulse, Vector Wave Propagation in Optical FibersAlmanee, Mohammad S. 24 May 2017 (has links)
No description available.
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Progress Towards Attosecond Science with a Turn-Key Industrial-Grade Ytterbium LaserTruong, Thi Tran Chau 01 January 2023 (has links) (PDF)
Advancements in laser technology over the last decades have allowed compression of laser light pulses to few-femtosecond durations. To obtain even shorter pulses, a new mechanism was required. The discovery of high-order harmonic generation, a non-perturbative nonlinear optical process, allowed the conversion of ultrafast laser pulses into a coherent extreme ultraviolet light (XUV) source of attosecond pulses. The attosecond XUV light source, which corresponds to the natural time and energy scales of electron motion in matter, has provided a tool to capture the fastest dynamics in atoms, molecules, and solids and opened the field of attosecond science. However, the generation of isolated attosecond pulses has traditionally required state-of-the-art, few-cycle Ti:Sapphire laser systems and advanced facilities, which limit its applications in other science fields. Recently, ytterbium-doped solid state and fiber lasers have become attractive tools for ultrafast science and industrial applications, due largely to their prospects for scaling to high peak- and average power and their turn-key operation. However, applying these sources as driving lasers for attosecond pulse generation is challenging due to their long pulse durations.
In this dissertation, I discuss progress towards attosecond time-resolved experiments using a turn-key Yb:KGW laser amplifier. First, we overcome the unfavorable long laser pulse duration by generating broadband, coherent supercontinuum spectra via nonlinear propagation in a molecular gas-filled hollow-core fiber. The pulses are compressed to sub-two-cycle durations using a two-channel field synthesizer, and methods to mitigate thermal effects at high average powers are explored. The laser pulses are characterized using a new single-shot waveform measurement technique based on multiphoton excitation in a solid medium, and we demonstrate its applicability to studies of attosecond field reshaping during nonlinear propagation. Finally, a source of isolated iv attosecond pulses based on a two-stage hollow-core fiber compressor with carrier-envelope phase stabilization and temporal gating is proposed.
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Intense, Ultrafast Light-Solid Interactions in the Near-InfraredTripepi, Michael Vincent 30 August 2022 (has links)
No description available.
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Dispositivos baseados no preenchimento de fibras de cristal fotônico por líquidos e materiais nanoestruturados / Devices based on the filling of photonic crystal fibers by liquids and nanostructured materialsSantos, Alexandre Bozolan dos 17 April 2012 (has links)
Esta tese descreve a demonstração experimental de dispositivos baseados em fibras de cristal fotônico (PCFs), que aproveitam a flexibilidade estrutural oferecida pela matriz de capilares que compõe a seção reta da fibra, de forma a preencher estes capilares com líquidos e materiais nanoestruturados. Para o caso de materiais nanoestruturados, uma vez preenchida a fibra, os materiais nela inseridos interagem eficientemente com a luz guiada. Essa arquitetura diferenciada em relação às fibras ópticas convencionais abre novas perspectivas no desenvolvimento de aplicações como óptica não-linear e sensoriamento. PCFs de núcleo líquido, por outro lado, impõe dificuldades para a implementação de dispositivos práticos, devido às altas taxas de evaporação dos líquidos inseridos. Por esta razão, foi desenvolvida uma nova técnica para vedar seletivamente ambas as faces externas do núcleo líquido de uma PCF, utilizando um polímero curável. Estes tampões poliméricos evitam a evaporação, causando um impacto mínimo no guiamento da luz, tornando o dispositivo usável por semanas. Esta nova técnica de vedação foi empregada em um experimento para a geração de supercontínuo em uma PCF com núcleo de água destilada, proporcionando uma estabilidade de pelo menos 1 hora. Combinando líquidos e materiais nanoestruturados, foi também foi desenvolvido um sensor de temperatura baseado no preenchimento do núcleo de uma PCF por uma amostra coloidal de nanopartículas semicondutoras de CdSe/ZnS, dispersas em óleo mineral. O espectro de luminescência destes pontos quânticos coloidais é fortemente dependente da temperatura e os resultados obtidos mostraram que a grande interação entre a luz e o colóide, aliada a geometria da fibra, proporcionando uma sensibilidade ~5,5 vezes maior que a apresentada por uma rede de Bragg escrita em uma fibra óptica padrão, com boa relação sinal-ruído. / This thesis describes the experimental demonstration of devices based on photonic crystal fibers (PCFs). PCFs are optical fibers whose core is surrounded by a regular matrix of holes, which runs longitudinally across its length. This singular configuration allows the insertion of liquids and nanostructured material into the fiber. Nanostructured materials embedded inside the fiber efficiently interact with the guided light, opening up possibilities of novel applications regarding the fields of non-linear optics, as well as optical sensing. On the other hand, liquid-core PCFs suffer from some disadvantages concerning practical device applications, on account of the high evaporation of the inserted liquids. In order to address this issue, we developed a novel technique to selectively seal the external faces of a liquid-core PCF, by using a polymer plug. These polymer plugs avoid evaporation while causing a minimum impact on the light guiding characteristics of the PCF. This novel sealing technique was employed in a supercontinuum generation experiment, by using a PCF whose core was water-filled. A temporal stability of at least one-hour on the resulting spectrum was achieved. Combining the above techniques, we also developed a temperature sensor based on the core-filling of a PCF by a colloidal ensemble of CdSe/ZnS semiconductor nanoparticles dispersed in mineral oil. Those colloidal quantum-dots display a luminescence spectrum which is strongly dependent on temperature and the experimental results indicated that the greater interaction between the guided light and the colloidal sample, provided by the fiber geometry, allowed a sensitivity which is approximately 5.5 times than possible with a conventional Bragg grating, while keeping a satisfactory signal-to-noise ratio.
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Hollow core fibre-based gas discharge laser systems and deuterium loading of photonic crystal fibresBateman, Samuel January 2015 (has links)
Research towards the development of a gas-discharge fibre laser using noble gases, with target emission wavelengths in the mid-IR. Additional and separate work on gas treatment methods for managing the formation of photo-induced defects in silica glass.
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