Dissertations / Theses on the topic 'Nonlinear optical property'

This dissertation reports on the investigation of the relationships between molecular structure and two-photon absorption (2PA) properties for a series of polymethine and squaraine molecules. Current and emerging applications exploiting the quadratic dependence upon laser intensity, such as two-photon fluorescence imaging, three-dimensional microfabrication, optical data storage and optical limiting, have motivated researchers to find novel materials exhibiting strong 2PA. Organic materials are promising candidates because their linear and nonlinear optical properties can be optimized for applications by changing their structures through molecular engineering. Polymethine and squaraine dyes are particularly interesting because they are fluorescent and showing large 2PA. We used three independent nonlinear spectroscopic techniques (Z-scan, two-photon fluorescence and white-light continuum pump-probe spectroscopy) to obtain the 2PA spectra revealing 2PA bands, and we confirm the experimental data by comparing the results from the different methods mentioned. By systematically altering the structure of polyemthines and squaraines, we studied the effects of molecular symmetry, strength of donor terminal groups, conjugation length of the chromophore chain, polarity of solvents, and the effects of placing bridge molecules inside the chromophore chain on the 2PA properties. We also compared polymethine, squaraine, croconium and tetraon dyes with the same terminal groups to study the effects of the different additions inserted within the chromophore chain on their optical properties. Near IR absorbing squaraine dyes were experimentally observed to show extremely large 2PA cross sections ([approximately equal to] 30000GM). A simplified three-level model was used to fit the measured 2PA spectra and detailed quantum chemical calculations revealed the reasons for the squaraine to exhibit strong 2PA. In addition, two-photon excitation fluorescence anisotropy spectra were measured through multiple 2PA transitions. A theoretical model based on four-levels with two intermediate states was derived and used for analysis of the experimental data.
Ph.D.
Other
Optics and Photonics
Optics

This dissertation reports on the investigation of two-photon absorption (2PA) in a series of fluorenyl molecules. Several current and emerging technologies exploit this optical nonlinearity including two-photon fluorescence imaging, three-dimensional microfabrication, site-specific photodynamic cancer therapy and biological caging studies. The two key features of this nonlinearity which make it an ideal candidate for the above applications are its quadratic dependence on the incident irradiance and the improved penetration into absorbing media that it affords. As a consequence of the burgeoning field which exploits 2PA, it is a goal to find materials that exhibit strong two-photon absorbing capabilities. Organic materials are promising candidates for 2PA applications because their material properties can be tailored through molecular engineering thereby facilitating optimization of their nonlinear optical properties. Fluorene derivatives are particularly interesting since they possess high photochemical stability for organic molecules and are generally strongly fluorescent. By systematically altering the structural properties in a series of fluorenyl molecules, we have determined how these changes affect their two-photon absorbing capabilities. This was accomplished through characterization of both the strength and location of their 2PA spectra. In order to ensure the validity of these results, three separate nonlinear characterization techniques were employed: two-photon fluorescence spectroscopy, white-light continuum pump-probe spectroscopy, and the Z-scan technique. In addition, full linear spectroscopic characterization was performed on these molecules along with supplementary quantum chemical calculations to obtain certain molecular properties that might impact the nonlinearity. Different designs in chemical architecture allowed investigation of the effects of symmetry, solvism, donor-acceptor strengths, conjugation length, and multi-branched geometries on the two-photon absorbing properties of these molecules. In addition, the means to enhance 2PA via intermediate state resonances was investigated. To provide plausible explanations for the experimentally observed trends, a conceptually simple three level model was employed. The subsequent correlations found between chemical structure and the linear and nonlinear optical properties of these molecules provided definitive conclusions on how to properly optimize their two-photon absorbing capabilities. The resulting large nonlinearities found in these molecules have already shown promise in a variety of the aforementioned applications.
Ph.D.
Optics and Photonics
Optics and Photonics;
Optics

Au cours des dernières années, les matériaux optiques non linéaires ont attiré beaucoup d'attention en raison de leur application dans les télécommunications optiques. Les vitro-céramiques pour l’optique non-linéaire, ayant une microstructure alignée, présentent des propriétés physiques anisotropes. Il est donc intéressant de maîtriser la cristallisation dans ce genre de verre. Nous avons étudié ici la distribution, la taille et l'orientation sous un champ supplémentaire, en particulier par l’irradiation femtoseconde, de verres silicatés. Ce travail est important pour la conception et la production de nouveaux matériaux optiques non linéaires multi- fonction. Dans cette thèse, le champ thermique a été utilisé pour produire des cristaux dans un verre SrO-TiO₂-SiO₂. L’analyse a été menée à l’aide de la méthode des franges de Maker et de de diffraction des rayons X pour étudier la cristallisation et les propriétés optiques non-linéaires. Il a montré que les cristaux non linéaires Sr₂TiSi₂O₈ peut être obtenue dans la couche de surface par traitement thermique. L'axe polaire de cristaux orientés est perpendiculaire à la surface du verre. En augmentant la température ou en prolongeant la durée de traitement thermique, l’apparition d’une intensité non-nulle de génération de second harmonique (GSH) en incidence perpendiculaire indique la présence de cristaux orientés de manière aléatoire dans le volume du verre. Etant donné la cristallisation, spatialement difficile à contrôler par traitement thermique, l’irradiation laser femtoseconde pour contrôler la cristallisation dans le verre sont proposée en raison de son contrôle précis du dépôt d'énergie dans le temps et dans l'espace. Il ouvre des possibilités fantastiques pour la fabrication de matériaux multifonctionnels par maîtrisant la cristallization des cristaux non linéaires dans le verre. Nous avons précipité des cristaux orientés de LiNbO₃ et de Sr₂TiSi₂O₈ en volume par irradiation laser femtoseconde à haute cadence (typ. 300 kHz). Dans le verre Li₂O-Nb₂O₅-SiO₂, les micro-/nano-cristaux en variant l'énergie d'impulsion et la direction de polarisation ont obtenu. En particulier, lors de l'application à basse énergie et de la polarisation parallèle à la direction d'inscription du laser, la cristallization orientée en nanomètre a été démontrée par EBSD (Electron diffraction rétro-diffusée). Le mesure microscopique de SH a prouvé l’orientation préférentielle de cristallisation parallèlement à la direction de déplacement du faisceau laser. Afin de comprendre l'orientation exacte des cristaux par rapport à la direction d'écriture, une série de mesurer les signaux cohérent de SH ont été réalisés dans des paires de lignes de laser avec des orientations de déplacement opposées. EDS (spectromètre à dispersion d'énergie) et la micro-sonde nucléaire ont été utilisées pour réaliser l'analyse chimique dans les lignes de laser. Nous discutons aussi le mécanisme de cristallisation orientée en mode statique et en mode dynamique en illustrant la distribution des gradients différents. Pour le système SrO-TiO₂-SiO₂, l'irradiation du laser a été appliquée dans les verres stoechiométrique et non-stoechiométrique. Dans le premier cas, non seulement la taille et la distribution peuvent être contrôlées en variant les paramètres du laser, mais aussi la phase peuvent être choisis dans l'échantillon. La mesure de SH a montré que l'axe polaire de cristaux est toujours dans le sens de l'écriture. Pour le verre non-stoechiométrique, des purs cristaux de Sr₂TiSi₂O₈ ont été obtenus seulement. En utilisant EBSD, l'écriture asymétrique ont été étudiés en variant l’orientation de la polarisation et de l'écriture. On a montré ainsi que le mécanisme d'orientation est probablement dû à l'action combinée du front « tilté » de l’impulsion et à l’orientation du plan de polarisation qui conduit à une photosensibilité anisotrope. En conséquence, cela induit une distribution asymétrique des gradients thermiques et chimiques
In the past few years, nonlinear optical materials have attracted much attention due to their application in optical telecommunications. Nonlinear optical glass-related materials have been widely studied according to their advantages. Glass ceramics having an aligned microstructure would exhibit an anisotropy of physical properties. This dissertation mainly contributes to the control of micro/nano-crystallization in silicate glass in crystalline phase, distribution, size and orientation under additional field, particularly by femtosecond irradiation, to master the nonlinear optical properties of glass further. This work is significant for the design and production of novel nonlinear optical material with multi-function in future. In this thesis, thermal field was used to induce crystals in SrO-TiO₂-SiO₂ glass. The crystallization behavior of glasses in different heat-treated condition and their second-order nonlinear optical properties have been analyzed by Maker fringes method and X-ray diffraction measurement, respectively. It showed that the oriented crystallization of nonlinear Sr₂TiSi₂O₈ crystals can be obtained in the surface layer by heat treatment. The polar axis of oriented crystals was perpendicular to the sample surface. Moreover, by applying higher temperature or prolonging the time duration of heat treatment, the maximum intensity of second harmonic generation shifting toward 0º is likely due to the presence of randomly distributed crystals in glass and surface crystallization turns to be volume at this moment. However, since it is hard to control crystallization by heat treatment and time-consuming, femtosecond laser irradiation was proposed to realize the control of crystallization in glass owing to the accessible control of energy deposition in time and in space. It opens fantastic opportunities to manufacture novel multifunctional materials by manipulating the crystallization of nonlinear crystals embedded in glasses. Therefore, we achieved to precipitate preferential oriented LiNbO₃ and Sr₂TiSi₂O₈ crystals in glass with femtosecond laser irradiation at high repetition rate (typ. 300 kHz). In Li₂O-Nb₂O₅-SiO₂ glass, we obtained micro-/nano-crystals in glass sample by varying pulse energy and polarization direction. Specifically, when applying low pulse energy and polarization parallel to laser writing direction, the oriented nano-crystallization has been obtained as shown by EBSD (Electron back-scattered diffraction). Second harmonic (SH) microscopy measurement illustrated preferred orientation of crystallization in laser lines. In order to understand the exact orientation of crystals with respect to the writing direction, a series of coherent SH measurement has been achieved in pairs of laser lines written in opposite orientation. EDS (Energy Dispersive Spectrometer) and nuclear micro-probe has been used to realize the chemical analysis in laser lines. The mechanism of oriented crystallization was discussed both in static mode and in dynamic mode through illustrating the distribution of different gradients. In SrO-TiO₂-SiO₂ system， laser irradiation was applied both in stoichiometric and non-stoichiometric glasses. In the former case, not only the size and distribution can be controlled by varying laser parameters, but also the crystalline phase can be chosen in samples. SH microscopy measurement was used to characterize the nonlinear properties of glass and it implied that the polar axis of crystals is always along the writing direction. In non-stoichiometric glass, only pure Sr₂TiSi₂O₈ crystals were obtained. The asymmetric writing involving oriented crystallization has been studied by varying polarization and writing orientation. The orientational dependent is likely due to the combined action of oblique pulse front tilt affected by the polarization orientation plane leading to different anisotropic photosensitivity and its aftereffects to induce asymmetric distribution of thermal and chemical gradients

碩士
國立中正大學
物理系
90
In this study, the nonlinear absorption and refraction of metallophthalocyanines (C32H16N8-M) /NMP solutions belonging to the D4h and C4v group and carbon nanoparticles/toluene solutions belonging to the icosahedral and D5h group are investigated using Z-scan technique with a frequency doubled Q-switch and mode locked Nd:YAG laser. Our Z-scan results reveal that almost all the samples show reverse saturable absorption. Moreover, the symmetry species of the molecular states of metallophthalocyanines are determined via their corresponding HOMO-LUMO electronic configuration. Through the group theory calculation, we succeed in explaining the reverse saturable absorption of metallophthalocyanines using the modified five-energy-band model.

The aims of this work were to highlight changing trend in the nonlinear optical (NLO) behaviour of ruthenium alkynyl complexes on structure modification. Chapter 1 discusses the theoretical background of NLO properties. This is followed by a brief review on the research that has been conducted in the field of organometallic NLO materials. Chapter 2 is concerned with the synthesis of a series of ruthenium bis-alkynyl complexes varying in ligand composition by chain lengthening and/or changing the arylalkynyl para-substituted functional groups, together with their cyclic voltammetric data and linear optical data. Chapter 3 discusses the strategies for synthesizing wedges with ABC composition and their use in the syntheses of dendrimers with C{u2083}_{h -symmetry. A series of alkynylruthenium dendrimers with different peripheral groups was made. The electrochemical properties of these dendrimers were assessed, and the linear optical and cubic nonlinear optical properties were studied. Chapter 4 examines the effect of the number of ruthenium centers on dendrimer NLO behaviour. Mono-ruthenium, bi-ruthenium and tri-ruthenium dendrons were synthesized and their linear optical properties studied. Chapter 5 focuses on the electronic communication between ruthenium centers in multi-ruthenium alkynyl complexes. A series of linear and branched ruthenium alkynyl complexes was made. Electrochemical and linear optical properties were examined.}

碩士
國立中央大學
化學學系
101
This research focues on the design, synthesis and characterization of several series of molecules containing indenoquinoxaline group. Their linear optical properties were studied by one-photon absorption, one-photon fluorescence, fluorescence quantum yield and life time. The experimental results from one-photon fluorescence has shown that model molecules with indenoquinoxaline units incorporated possess large Stokes shifts on their fluorescence emission which is mainly due to intramolecular charge-transfer (ICT). The two-photon absorption (2PA) properties were measured by two-photon induced fluorescence techniques with a mode-locked Ti: sapphire pulsed laser in the range of 680 nm-1000 nm. The compound 9 exhibits 31700 GM on 730 nm. This result indicates that increasing the branch number and inserting indenoquinoxaline units into a D-π-A structure framework could be an effective approach to achieve a strong molecular 2PA and also, such structural motif could be a useful approach for the molecular design for quick-responsive optical-suppressing-related applications.

碩士
國立中央大學
化學學系
101
The purpose of this study is the systematic design and synthesis of several series containing the Quinoxaline groups model molecules. We want to explore the molecular changes in the structure of two-photon absorption properties of influence by increase in molecular π-electron conjugated bridge and increase the number of molecular branches. After a series of linear and nonlinear optical measurement and discussion can be summarized as the following results. The first is to increase the molecular center of the π-electron conjugation bridge length, can contribute to enhance the degree of charge transfer in the electronics and increase the two-photon excitation cross section value. The second is increasing the number of molecular branches can Promote dramatically of two-photon excitation performance. The third is Quinoxaline this type of structure have much longer fluorescence lifetime, this behavior is likely to cause the excited state re-absorption, it can be applied to optical power limiting marerials.

碩士
國立中山大學
光電工程學系研究所
106
2D layer structures have been attracted plenty of attention due to their remarkable properties and application potential. To realize 2-D material nonlinear optical applications, including wavelength generation, ultrafast optical processing, and saturable absorber for ultrafast laser, the information of optical nonlinearity property for given material is very important. In this thesis, using home-made Z-scan measurement with tunable peak intensity ranging from 103 to 108 W/cm2, Ge/SiC super-lattice layers structure and Bi2Te3 were studied. In the first part, using HVPE growth, Ge/Si super-lattice layer structures were fabricated. The thickness of Ge or SiC was 10nm and the name of Ge/SiC pair and total thickness are 10 and 200nm, respectively. The clear power dependent Z-scan measurement was observed. The increasing saturation intensity from to and almost fixed two photon absorption coefficient of as increasing excitation peak intensity from 15.8 to 132 were analyzed. The n2 of around 4.12 was accordingly estimated. In the second part, ultra-low peak intensity (103 to 105 W/cm2) z-scan measurement was proposed and buildup for understanding the discontinuity of conventional nonlinear transmission with low and high pulse energy. The two photon absorption behavior was observed and is with tremendous large coefficient of for excitation power of 100W. This can be therefore used to interpret and resolve the discontinuity. The clear self-defocusing phenomena was investigated as well.

碩士
國立中央大學
化學研究所
100
In this thesis we have synthesized two series of chromophore with extended π-conjugation and another series are also been studied and discussed. We use UV/Visible absorption spectrometer and fluorescence spectrometer to study linear optical properties; use Nd:Yag Laser and Ti:Sapphire to probe nonlinear optical properties. In first series we use nitrogen atoms as π- bridge to extend conjugation to see whether if it’s a good π- bridge. In second series, four electron donor branches are fixed, only one electron acceptor branch is modified, thus we can inspect whether if it will does many differences on chromophores. The third series, with different number or orientation electron donors on carbon-carbon double bond, we can further study and realize molecular design in order to enhance 2PA.

碩士
國立中央大學
化學研究所
100
Several series of multi-branched chromophores containing tetra-substituted ethylene and quinoxalinoid hetercyclic structures have been synthesized and characterized for their linear and nonlinear optical properties. The experimental results show that adding electron donor to the structure or extending the??-conjugation length will make a red-shift in the best absorption wavelength and also enhance the molecular two-photon absorptivities. We also found that inserting quinoxalinoid hetercyclic structures to our model chromophores especially indenoquinoxaline structure may exhibit strong two-photon activities and also cause conspicuous solvent effects in solution phase. It will have higher fluorescence quantum yield in nonpolar solvent like toluene, but longer fluorescence life time in polar solvent like THF. Because these model chromophores possessed excellent effective optical power limiting behaviors with strong two-photon absorption, so they could be efficacious optical limiters especially when against longer laser pulses.