Αρχικά μελετήσαμε την μη-γραμμική οπτική και τα βασικά μη-γραμμικά φαινόμενα, όπως για παράδειγμα τον οπτικό περιορισμό, τη γένεση δεύτερης αρμονικής, τη γένεση τρίτης αρμονικής, την αυτοεστίαση, το οπτικό φαινόμενο kerr και το συνεχές φαινόμενο kerr. Eπιπλέον περιγράψαμε την τεχνική z-scan και εκτιμήσαμε τις μη-γραμμικές οπτικές ιδιότητες του C60 και C120. / First of all, research the nonlinear optics and basic nonlinear phenomena, for example, optical limiting, second harmonic generation, third harmonic generation, self-focusing, optical kerr effect and DC kerr effect. In addition description technique z-scan and estimate the nonlinear optical properties C60 and C120

Optical regeneration has the potential to significantly increase the reach of long-haul transmission systems. In this thesis, wavelength-preserving polarization-insensitive all-optical 3R regeneration is investigated and demonstrated for 10 and 40 Gb/s signals. The all-optical regenerator utilizes a self-pulsating laser for clock recovery, cross-phase modulation (XPM) based spectral broadening in a highly nonlinear fiber (HNLF) and offset filtering for retiming, and self-phase modulation based spectral broadening in a HNLF and offset filtering for reshaping. Raman amplification is used to increase the XPM-based spectral broadening and thus allow a design that meets the tradeoffs involved in simultaneously achieving good retiming and reshaping performance. The regenerator is shown to reduce amplitude noise and timing jitter while not causing a BER penalty. To fully validate the regeneration scheme, the cascadability is demonstrated using a recirculating loop. For a 10 Gb/s signal, with a regenerator spacing of 240 km, a return-to-zero, on-off-keyed (RZ-OOK) signal was transmitted over 18,000 km (75 loops) with a power penalty of 1.6 dB at a BER of 1E-9 compared to the back-to-back case. For a 40 Gb/s signal, with a regenerator spacing of 80 km, a RZ-OOK signal was transmitted over 8,000 km (100 loops) with a power penalty of 1.2 dB. In addition, all-optical 3R regeneration is demonstrated using a multimode quantum-dot Fabry Petot laser with ultra-low timing jitter. / Thesis (Ph.D, Electrical & Computer Engineering) -- Queen's University, 2009-10-19 14:11:53.826

Thesis (Ph. D.)--University of Texas at El Paso, 2009. / Title from title screen. Vita. CD-ROM. Includes bibliographical references. Also available online.

Terahertz (THz) spectroscopy is an emerging technology with promising applications in imaging, homeland security, and material detection and quantification. Frequencies in the THz region can be generated by optical rectification of ultrafast near-infrared laser pulses in the presence of a nonlinear optical (NLO) materials such as organic crystals. Non-centrosymmetric organic THz generating crystals such as DAST, HMQ-TMS, and OH1 have received special attention due to the strong generated fields on the order of MV/cm. The cation of these organic salts is designed by connecting electron-donating with electron-accepting groups via a highly planar aromatic system. To improve the performance of organic crystals for THz generation, the molecular hyperpolarizability (β) can be optimized by introducing modifications in the architecture of these push-pull chromophores. However, the large dipole moments associated with molecules that have a large β promote the formation of NLO inactive centrosymmetric molecular alignments in the crystal state. This dissertation provides important insights into the design of new push-pull chromophores that feature a) higher β values compared with state-of-the-art organic crystals, and b) non-centrosymmetric molecular packing in the crystalline state. The first strategy presented on this dissertation relates to the introduction of a triple bond instead of a double bond in the cation of DAST to improve the β parameter. The newly designed 4DEP core was combined with different anions to promote non-centrosymmetric molecular packing with almost ideal arrangements for THz generation. However, large single crystals were difficult to obtain and high THz generation was not achieved. The second strategy presented in this dissertation raises the value of β by extending the π-conjugation length in different cations with dimethylamino and methoxy electron-donating groups. A new molecular cation, 6MNEP, was found to have large β value combined with ideal non-centrosymmetric molecular packing. Combining these two factors, a ~ 75% higher performance for THz generation is expected for 6MNEP compared with DAST. Currently, we are testing different crystallization techniques to grow large single crystals of 6MNEP. In addition to the strategies developed to increase the β parameter value, we also introduce a new molecular modification to induce non-centrosymmetric packing in organic salt THz generating crystals. This is achieved by substituting a methyl by an ethyl group in the quaternary nitrogen of hydrogen-bonded crystals. We showed the applicability of this method for changing molecular packing in the crystal state from centrosymmetric to non-centrosymmetric in two different molecular cations. We also demonstrated the generation of strong THz fields in the novel NLO crystal EHPSI-4NBS.

Indiana University-Purdue University Indianapolis (IUPUI) / Background: Stimulated Raman spectroscopy (SRS) is a nondestructive tool for biochemical characterization of tissues. The aims were: 1) To evaluate the ability of SRS and Spontaneous Raman spectroscopy (SpRS) to differentiate among sound, demineralized and remineralized bovine enamel by phosphate and carbonate ratio (P/C-Ratio); and 2) To determine the correlation between the outcomes of transverse microradiography (TMR: Integrated mineral loss (ΔZ) and lesion depth) and P/C-Ratio. Material and Methods: Thirty, 5×5×2-mm ground and polished bovine enamel blocks were prepared. The surface was divided into 3 equal areas. Each area was chemically demineralized (demin) by Carbopol demineralized solution for 0 (Sound-Demin), 24 (24h-Demin), and 48h (48h-Demin), respectively. Then, specimens were sectioned for TMR analysis, and the remaining one part of each specimen was remineralized (remin) for 15days using a pH-cycling model (Sound-Remin, 24hD-Remin=24h-Demin and remineralization, 48hD-Remin = 48h-Demin and remineralization). Demin and remin groups were scanned to obtain P/C-Ratio by SpRS and SRS. SRS was further scanned from 0 (surface) up to 100 µm into the dentine at 10-µm intervals. Remineralized specimens were sectioned for TMR analysis. Wilcoxon signed-rank tests were used to compare between TMR and SpRS/SRS. Spearman correlation coefficients were used to correlate among TMR, SpRS, and SRS. A 5-percent significance level was used for each test. Results: As demin time increased, both ΔZ and lesion depth were increased. After remineralization, both values were decreased. There were significant differences between demine and remin groups and between demin times. For SpRS, Sound-Demin had significantly larger P/C-Ratio than 24h-Demin and 48h-Demin (p ≤ 0.001). The 24h-Demin had significantly larger values than 48h-Demin (p = 0.048). Sound-Remin had larger P/C-Ratio than 24hD-Remin (p = 0.316) and 48hD-Remin (p = 0.015). 24hD-Remin was larger than 48hD-Remin (p = 0.269). 24hD-Remin had significantly larger P/C-Ratio than 24h-Demin (p ≤ 0.001). 48hD-Remin had significantly larger P/C-Ratio than 48h-Demin (p ≤ 0.001). For SRS, at surface (0 µm), for demin group, Sound-Demin had significantly larger P/C-Ratio than 24h-Demin (p = 0.020) and 48h-Demin (p = 0.032). 24h-Demin had larger value than 48h-Demin; but no significant difference (p = 0.117). Among remin groups, Sound-Remin was not statistical significance different for 24hD-Remin (p = 0.172) and 48hD-Remin (p = 0.134). However, 24hD-Remin was smaller; but not statistical significance different from 48hD-Remin (p = 0.688). At deeper levels (10 µm to 100µm), it was found that 1) After demineralization, Sound-Demin had significantly larger P/C-Ratio than 24h-Demin and 48h-Demin at 0 µm to 20 µm, and 80 µm to 100µm; Sound-Demin had significantly larger P/C-Ratio than 48h-Demin; and no statistical significance differences were found among Sound-Demin and 24h-Demin, 24h-Demin and 48h-Demin. 2) After remineralization, no statistical significance differences were found among Sound-Remin, 24hD-Remin, and 48hD-Remin. 3) Sound-Demin had significantly larger P/C-Ratio than Sound-Remin at 0 µm ,10 µm, 20 µm; and no statistical significance differences were found at levels deeper than 30 µm. 4) No statistical significance differences were found between 24h-Demin and 24hD-Remin from 0 µm to 70µm; and 24hD-Remin had significantly larger P/C-Ratio than 24h-Demin from 80 µm to 100 µm. 5) No statistical significance differences were found between 48h-Demin and 48hD-Remin. For correlation, moderate correlation was found between SpRS demineralized/remineralized groups and ΔZ, and between SpRS demineralized groups and lesion depth. Conclusion: SpRS and SRS have the potential to quantify demineralization through calculation of the phosphate and carbonate ratio. In addition, SpRS can detect the change of remineralization. A nondestructive caries detection approach using SpRS and SRS would be beneficial in clinical practice.

京都大学 / 0048 / 新制・課程博士 / 博士(エネルギー科学) / 甲第19201号 / エネ博第321号 / 新制||エネ||65(附属図書館) / 32193 / 京都大学大学院エネルギー科学研究科エネルギー応用科学専攻 / (主査)准教授 中嶋 隆, 教授 大垣 英明, 教授 作花 哲夫 / 学位規則第4条第1項該当 / Doctor of Energy Science / Kyoto University / DGAM

No description available.

Main objectives of the present dissertation can be divided in two parts. The first part deals with setting up a spectroscopic technique for reliable and accurate measurements of the two-photon absorption (2PA) cross section spectra. In the second part, this firmly established experimental technique together with conventional spectroscopic characterization, quantum-chemical computations and theoretical modelling calculations was combined and therefore used as a tool to gain information for the so-called structure-property relationship through several molecular compounds. / Die Hauptziele der vorliegenden Dissertation lassen sich in zwei Teile gliedern. Der erste Teil befasst sich mit dem Aufbau einer spektroskopischen Technik zur zuverlässigen und genauen Messung der Zwei-Photonen-Absorptionsquerschnittsspektren (2PA). Im zweiten Teil wurde diese fest etablierte experimentelle Technik zusammen mit konventioneller spektroskopischer Charakterisierung, quantenchemischen Berechnungen und theoretischen Modellrechnungen kombiniert und damit als Werkzeug genutzt, um über mehrere molekulare Verbindungen Informationen für die sogenannte Struktur-Eigenschafts-Beziehung zu gewinnen.

Optical trapping of metallic nanoparticles investigates phenomena at the interface of plasmonics and optical micromanipulation. This thesis combines ideas from the optical properties of metals, originating in solid-state physics, with the force mechanisms resulting from optical trapping. I explore the influence of enhanced light-matter interaction due to the plasmon resonances of gold particles on their trapping properties. I present theories for trapping mechanisms of gold metallic particles and then verify these theories through experiments. Optical trapping of metallic nanoparticles is considered challenging, especially in air, as they are highly absorbing and reflecting at optical wavelengths. Yet the optical levitation of these particles provides an excellent tool to investigate their plasmonic properties away from any interface and offers opportunities to explore interaction processes between light and particles. The optical and thermal forces acting on the particle depend on their microscopic optical and thermal properties. These parameters vary drastically around the plasmon resonance, thus not only changing the magnitude but also the direction and entire nature of the acting forces. So far, optical trapping of metallic particles has focused on wavelengths far from the particle's resonance in the infrared, and on liquids rather than air. In this thesis, I concentrate on optical trapping of gold micro and nanoparticles, expanding the knowledge of metallic nanoparticle trapping available to date. In Mie regime, I present both the theory and experiment of a trapping scheme based on dynamic potential manipulation that is capable of trapping gold microparticles in air for more than one hour. In the dipole regime, I present a theory based on nonlinear optical trapping which opens new insights in the field of levitated optomechanics. For the first time, I show that two-photon absorption is the reason for the longitudinal stability of gold nanoparticles. This theory correctly addresses the effect of four-wave mixing and two-photon absorption on the behavior of the trapping system.

NLO materials have been researched for nearly five decades from the point of view of understanding the basic mechanisms and also in the pursuit of new materials possessing improved properties. Materials satisfying a set of physico-chemical properties such as wide transmission range, good mechanical hardness, high po-larizablity, noncentric crystal structure, good chemical stability, etc are the ones which are sought after. Several organic and inorganic molecules have been synthe-sized with the hope of finding materials that possess the desired NLO properties. Most of the organic materials are known to possess high figure of merit. However, their poor mechanical strength and needle like growth habit are hindrances to practical applications. Inorganic NLO materials have better mechanical properties but many of them possess small deff and laser induced damage threshold. Semi-organic NLO materials are intended to have the merits of both organic and inorganic counterparts. In this investigation, three important NLO crystals, viz cesium hydrogen L-malate monohydrate (CsLM, CsH[C4H4O5]H2O), cesium lithium borate(CLBO,CsLiB6O10)and near stoichiometric lithium niobate codoped with Nd and Zn (Nd:Zn:LiNbO3)are chosen for detailed study. The thesis is organized into 6 chapters. First chapter contains the theoretical background of the physical and chemical phenomena including a review of nonlin-ear optics, second harmonic generation, multiphoton absorption & refraction con-cepts, single crystal growth, principles of ferroelectricity and the scope of the work involved. For better connectivity, a brief review of the earlier work carried out on the chosen materials is given in the beginning of each chapter. The second chapter discusses the methodology of work and experimental details used in the present study. The third chapter deals with studies on CsLM, the new organometallic NLO crystal. Its structure, electro-optical properties and dielectric properties in FIR region are reported very recently. This material is also reported to show a phase transition at 50 0C though not much is understood about its nature. Further details of crystal growth conditions, nonlinear optical properties and laser damage thresholds are little known on this newly discovered NLO material. In this chapter detailed crystal growth studies and investigations of physical properties are presented. During growth, CsLM crystals manifest in platy and prismatic morphologies depending on level of super saturation invoked. The maximum dimensions of the grown crystal are 20 x15 x35 mm3. It has very good transmission in the range, 250-1300 nm and dislocation density of ≈104/cm2 . The dc conductivity measurements place this crystal between an ionic conductor and a dielectric. Dielectric properties show considerable frequency dispersion and axial anisotropy with є′ being the highest along the polar b axis. Maker fringes experiment reveals that CsLM possesses good second harmonic generation efficiency, an order of magnitude higher than KDP. It also has high laser damage threshold for fundamental and second harmonic wavelengths of Nd:YAG pulsed laser. TGA/DTA experiments are performed on the crystals grown below and above the reported transition temperature(labelled as CsLM and Anhydrous-CsLM respectively). The present investigations on Anhydrous-CsLM show that it crystallizes in a structure different from that of CsLM and the nature of the reported ′phase transition ′is driven by sluggish hydration and dehydration processes. Recently UV transparent nonlinear optical materials were evaluated for the fab-rication of all solid state UVlasers and CLBO is one such NLO material. It crystal-lizes in non-centrosymmetric tetragonal space group, I42d. It is highly transparent in the wide range of wavelengths from 180 to 2500 nm and has good deff. It pos-sesses very good angular and spectral bandwidth tolerances compared to its contemporaries such as lithium triborate(LBO) and beta barium borate(β-BBO). There is, however, a problem associated with this material that it cracks when exposed to atmosphere due to its hygroscopic nature. This chapter details the fabrication of the required instrumentation to grow single crystals of this material and the study of possible solutions to avoid cracking problem besides its new nonlinear properties. Since the melts of borate materials are known to be highly viscous, the crystal growth apparatus should have the options for tuning the parameters like seed and crucible rotation rates, temperature isotherms, slow pulling rate, etc. Keeping the above in mind, a high temperature top seeded solution growth unit was designed and fabricated inhouse. Highly transparent single crystals of CLBO were grown using the above unit which were characterized for the defects/dislocations using X-ray topography. The average dislocation density estimated is ≈103/cm2. The nonlinear optical absorption(NLA) and refraction(NLR) properties are studied. Z-scan experiments reveal that five photon absorption(5PA )is responsible for nonlinear absorption when the wavelength and pulse width are 800 nm and 110 fs respectively. For 532 nm and 6 ns pulses, dielectric breakdown occurs before NLA could occur due to high pulse influence. CLBO is found to show negative nonlinear refraction under high intensities. Hygroscopicity of CLBO is attributed to the entry of water through the channels that are present along a and b axes, which in turn, cause cracking. Doping, is expected to modify the size of the channels. Since certain dopants are found to improve the stability of CLBO, substitution of Cs site with Zn and Gd is carried out to reduce the size of channels. As there was no significant improvement with doping experiments, an alternate approach is attempted by coating with SiO2 thin films on the optical elements to prevent the water molecules from entering lattice through the channels. The results and discussion of the above studies are presented in the chapter 4. Lithium niobate is the most widely used single crystal for fabricating optical modulators, waveguides, SAW devices and optical parametric oscillators. Although single crystals of this ferroelectric material were grown way back in 1965 by Ball-man and Fedulov independently, most of the work till the beginning of 90’s was concentrated on crystals with congruent composition(CLN) because there were no suitable methods available for growing homogeneous single crystals of stoichiomet-ric lithium niobate(SLN). Recently, Double Crucible Czochralski method with au-tomatic powder feeding technique and top seeded solution growth technique with Li2O and K2O fluxes are shown to produce SLN crystals. In this work, top seeded solution growth technique with58.6 mol% Li2O composition(self flux) is adopted to grow SLN crystals and the details of the growth and investigations are presented in chapter 5. Initially, crystal growth of SLN, and Zn & Nd codoped SLN are de-scribed. The maximum dimesions of the SLN crystals are 20 mm diameter and 35 mm length. CLN crystals(30mm diameter and 70 mm length) are also grown for comparison. The growth rate for SLN crystals is approximately 25 times lower than that for CLN. The maximum amount of Zn added to the melt is 2.5 mol%. For Nd codoping, four concentrations (0.2, 0.5, 0.9, 1.5 mol%) have been chosen with Zn concentration in the melt fixed at 2.5 mol%. Addition of Zn is to enhance the pho-torefractive damage threshold and Nd to use SLN as laser host. Structural studies on the grown crystals using powder X-ray diffraction show no additional phases. The domain structure analysis by chemical etching studies reveal that it is sensitive to doping and temperature gradient above the melt surface. The grown crystals possess good transmission in the UV-Vis-NIR region. Apparent increase in the dielectric constant found in doped crystals is attributed to space charge effect. In Nd:Zn codoped SLN, the parameters corresponding to lasing (Judd-Ofelt parameters, radiative transition probabilities, branching ratios) have been evaluated and found to be better than those obtained for codoped CLN. Surface laser damage and photorefractive damage thresholds are enhanced by 2 and 4 orders of magnitude respectively for the crystals grown with 2.5 mol% Zn in the melt. Nonlinear absorption and refraction studies using femtosecond Z-scan experiments reveal a correlation between the nonstoichiometric defects and nonlinear absorption & refraction coefficients. Polarization switching studies carried out on pure and Zn doped samples indicate an enhancement in switching rate at elevated temperatures. In the sixth and final chapter, a comprehensive summary of the present work and the scope for further investigations related to this work are given.