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This dissertation is focused on the interaction between femtosecond laser and patterned two-dimensional gold nanostructures. The sample was prepared by two different lithographic techniques, the nanosphere lithography and the electron beam lithography. Characterization was carried out with scanning electron microscopy, transmission electron microscopy, atomic force microscopy, and UV-vis absorption spectroscopy. Femtosecond transient absorption spectroscopy was used to answer a number of fundamental questions regarding the laser-nanostructure interaction. Under a low density irradiation of a femtosecond laser, we examined the effect of the lattice crystallinity on the electron-phonon relaxation in monolayer periodic array nanoparticles prepared with nanosphere lithography. We found that the electron-phonon relaxation rate was faster in polycrystalline nanoparticles and decreases greatly in single crystalline nanospheres, which is explained by the presence of high density grain boundaries. The ultrafast laser-induced coherent phonon oscillations in patterned gold nanoparticles are also fully characterized. We studied the effect of size, shape, thickness, monitoring wavelength, and materials of the prismatic array nanoparticles on the period of their coherent phonon oscillations. In a gold nanodisk pair system, we found that the fractional change in the vibration frequency increases exponentially with decreasing the ratio of the interparticle separation to the particle diameter, which is explained by the coupling of the induced electric field in one nanodisk by the strong surface plasmon field of its pair partner. Based on the coherent phonon oscillation of gold caps on a polystyrene sphere monolayer array, a new all-optical gigahertz modulation technique is developed. Under a high density irradiation of a femtosecond laser, the melting and ablation processes can be induced in gold nanoparticles. We studied femtosecond laser induced shape and localized surface plasmon resonance band changes of gold prismatic array nanoparticles. We also observed that the femtosecond laser irradiation of the nanoprisms at the surface plasmon resonance absorption maximum can cause them to detach from the substrate and 'fly away'. Atomic force microscopy and scanning electron microscopy measurements revealed that the displaced nanoparticles are thinner and smaller than the undisplaced ones, which supports an atomic ablation mechanism.

i Abstract: This doctoral thesis is dedicated to the study of magnetization dynamics in ferromagnetic semiconductor (Ga,Mn)As using magneto-optical (MO) spectroscopy methods. The character of the magnetization dynamics after the impact of the laser pulse was investigated under different experimental conditions in an extensive set of optimized (Ga,Mn)As samples with Mn doping ranging from 1.5% to 14%. The thorough analysis of the measured MO signal enabled us to develop a new method that can be used to determine the laser pulse-induced real-space magnetization trajectory without any numerical modelling. Moreover, the investigation of the measured MO signals allowed us to determine the basic micromagnetic properties of (Ga,Mn)As, such as the magnetic anisotropy, the Gilbert damping or the spin stiffness. In addition to this, we found out that the light-induced magnetization precession can be caused by three distinct mechanisms - the sample heating due to the energy transfer from the laser pulses, the angular momentum transfer from the circularly polarized photons, and the influence of the non-equilibrium hole polarization induced by the relativistic spin-orbit interaction. The first of these mechanisms is rather well known but the two remaining ones, which are the optical analogues of the spin-transfer torque...

Submitted by Irene Nascimento (irene.kessia@ufpe.br) on 2017-04-25T19:25:57Z No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) ACGW_Dissertação.pdf: 2393143 bytes, checksum: 1dc4bede5ad081bffd11e546c86a753a (MD5) / Made available in DSpace on 2017-04-25T19:25:58Z (GMT). No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) ACGW_Dissertação.pdf: 2393143 bytes, checksum: 1dc4bede5ad081bffd11e546c86a753a (MD5) Previous issue date: 2016-07-26 / CNPQ / Apresentamos um estudo da interação de um laser de femtosegundos de Ti:safira, com alta taxa de repetição, com vapor atômico de Rubídio. Trabalhamos no regime de acumulação coerente, em que o tempo de relaxação dos átomos do meio é maior que o tempo entre os pulsos. Para sondar a excitação produzida pelo laser pulsado sobre os vários grupos de velocidades atômicos usamos um laser contínuo de diodo. Estudamos a transmissão do laser de diodo em função de sua frequência, na presença e na ausência do laser pulsado, quando ambos os lasers estão sintonizados na transição 5S1=2 !5P3=2. Os resultados experimentais mostram que a transmissão do laser de diodo aumenta ou diminui dependendo do modo do pente de frequências que está interagindo com o grupo de átomos. Descrevemos os resultados experimentais trabalhando no domínio da frequência e modelando o meio atômico por um conjunto de dois sistemas de três níveis tipo L e um sistema de dois níveis, todos independentes entre si, interagindo com os modos do pente de frequência. Assim, a modelagem teórica considera os vários níveis hiperfinos e discrimina a interação com a transição cíclica do efeito de bombeio ótico, apresentado um resultado em concordância com os dados experimentais obtidos. O experimento foi realizado sem travar a taxa de repetição nem a frequência de off-set do laser de femtosegundos. / We present a study of the interaction of a high repetition rate femtosecond Ti:sapphire laser with a vapor atomic rubidium. We work on coherent accumulation regime, in which the atomic relaxation time is greater than the time interval between pulses. The action of the ultrashortpulsed laser over different atomic velocity groups is probed by a diode laser. We studied the transmission of the diode laser as a function of frequency, with and without the presence of the ultrashort-pulsed laser, when both lasers are tuned to 5S1=2!5P3=2 transition. The experimental results show that the diode laser transmission increases or decreases depending on the mode of the frequency comb that interacts with different velocity groups. The experimental results are described in the frequency domain and the atomic system is modeled by a set of two threelevel L systems and a system of two-level all independent and interacting with the frequency comb modes. The theoretical treatment considers the hyperfine transitions and distinguishes the interaction between the cyclic transitions from optical pumping effect, showing results in good agreement with the experimental data. The experiment is performed without lock repetition rate or the off-set frequency of the femtosecond Ti:sapphire laser.

This thesis describes the development of several spectroscopic methods based on impulsive vibrational spectroscopy as well as of the technique itself. The first chapter describes the ultrafast time domain Raman spectrometer including the development of two noncollinear optical parametric amplifiers for sub-10 fs pulse generation with 343 or 515 nm pumping. In the first spectroscopic study we demonstrate, for the first time, that impulsive vibrational spectroscopy can be used for recording transient Raman spectra of molecules in excited electronic states. We obtain spectra of beta-carotene with comparable, or better, quality than established frequency domain based nonlinear Raman techniques. The following two chapters address the questions on the fate of vibrational coherences when generated on a reactive potential energy surface. We photoexcite bacteriorhodopsin and observe anharmonic coupling mediated vibrational coherence transfer to initially silent vibrational modes. Additionally, we are able to correlate the vibrational coherence activation with the efficiency of the isomerisation reaction in bR. Upon generation of vibrational coherence in the second excited electronic state of beta-carotene, by excitation from the ground electronic state, we are able to follow the wavepacket motion out of the Franck-Condon region. We observe vibrationally coherent internal conversion, through a conical intersection, into the first excited electronic state and are hence able to demonstrate that electronic surface crossings can occur in a vibrationally coherent fashion. Additionally, we find strong evidence for vibronic coupling mediated back and forth crossing between the two electronic states. As a combination of this work we develop a IVS based technique that allows for the direct recording of background and baseline free Raman spectra in the time domain. Several proof of principle experiments highlight the capabilities of this technique for time resolved Raman spectroscopy. In the final chapter we present work on weak-field coherent control. Here, we address the question of whether a photochemical reaction can be controlled by the phase term of an electric excitation field, in the one photon excitation limit. We study the systems rhodamine 101, bacteriorhodopsin, rhodopsin and isorhodopsin and, contrary to previous reports, find no evidence for one photon control.

This Thesis describes the synthesis, structural, photochemical and photophysical studies of modified retinal protonated Schiff bases in solution. Ultrafast laser spectroscopy, NMR and circular dichroism studies were employed to investigate speed, yield and selectivity of photoisomerisation in these chromophores. <b>Chapter 1</b> introduces relevant biological, photophysical and photochemical aspects of retinal protonated Schiff base photoisomerisation. It includes an overview of synthetic approaches to modified retinal synthesis pertinent to this this work. <b>Chapter 2</b> discuses the investigation of the hypothesis that twisting of the chromophore’s isomerising double bond is responsible for ultrafast photoisomerisation in the protein environment. In these studies it was discovered that addition of a methyl group to the retinal backbone in solution results in protein-like photophysics. <b>Chapter 3</b> presents photopysical and photochemical studies of modified all-trans retinal protonated Schiff bases that culminate in a qualitative model for the influence of electronic factors on photochemical and photophysical behaviour of these chromophores in solution. <b>Chapter 4</b> describes structural and photophysical investigations of 11-cis retinal protonated Schiff bases. NMR studies indicate conformational flexibility of the chromophores. The first synthetic solution-based chromophore to reach rhodopsins’s speed of photoisomerisation is described. <b>Chapter 5</b> presents an attempt to gain conformational information on retinal protonated Schiff bases using circular dichroism spectroscopy. Transfer of stereochemical information from the covalently attached stereogenic centre to the retinal backbone is demonstrated.

The topic of this Master’s thesis is combination of laser spectroscopic methods. LIBS and Raman spectroscopy were chosen for the combination. This combination is applied to plastic identification and separation as a mean to automate sorting of plastic waste. Data handling was done via different methods of computer learning algorithms scripted in R language. Plastic sorting accuracy over 90 % was reached thanks to the combination of chosen methods. This work also addresses some issues implied by combination of two different methods.

Ce travail est consacré à l’étude des effets de chiralité dans des dipeptides cycliques construits sur un cycle dikétopiperazine (DKP) et comportant deux résidus de chiralités identiques ou opposées, LL et LD. Les mêmes systèmes sont étudiés dans différents environnements par spectroscopie optique couplée à des calculs de chimie quantique. Les molécules neutres sont isolées et refroidies en jet supersonique et caractérisées par spectroscopie laser UV et IR sélective en conformère. La structure des systèmes protonés, isolés dans un spectromètre de masse ICR, est déterminée par spectroscopie de dissociation induite par absorption de multiples photons IR. Enfin, le dichroïsme circulaire vibrationnel (VCD) est appliqué aux échantillons en phase solide. Les systèmes étudiés comportent un résidu aromatique tyrosine (cyclo Tyr-Pro) ou phénylalanine (cyclo Phe-Phe et Phe-His). Le diastéréomère LD est en général moins stable et plus flexible que LL, et ils ne diffèrent structurellement que par des interactions faibles de type NH…π ou CH…π. Le conformère le plus stable correspond en général à une structure où le chromophore aromatique est replié sur le cycle peptidique, l’autre partie étant étendue. Un effet très important de la chiralité est observé dans certains dimères protonés. Enfin, les expériences de VCD en phase condensée montrent que la phase cristalline de cyclo LPhe-DPhe formée par déshydratation du dipeptide linéaire en phase solide est chirale à cause de la synchronisation des chiralités transitoires des monomères. / This work focuses on the study of chirality effects on the structure of cyclic dipeptides built on a diketopiperazine (DKP) ring with residues of identical (LL) or opposite (LD) chirality. The same systems are studied in different environments by means of optical spectroscopy coupled to quantum chemical calculations. The neutral molecules are isolated and cooled down to a few K in a supersonic expansion and characterized by UV and conformer-specific IR laser spectroscopy. The structure of the protonated systems, isolated in an ICR mass spectrometer, is determined by infrared multiple photon dissociation spectroscopy. Last, vibrational circular dichroism (VCD) is applied to the solid-state samples.The studied systems possess an aromatic residue, either tyrosine (cyclo Tyr-Pro) or phenylalanine (cyclo Phe-Phe and Phe-His). The LD diastereomer is in most of the cases less stable and more flexible than LL. LL and LD differ from each other by weak interactions like NH…π or CH…π interactions. The most stable conformer usually corresponds to a structure with the aromatic chromophore folded over the DKP ring, the other part being extended. A dramatic effect of chirality is observed for some of the protonated dimers. Last, VCD experiments in the condensed phase show that the crystal phase of LPhe-DPhe formed by solid-state dehydration of the linear dipeptide is chiral due to synchronization of the transient chirality of the monomers.

L’objectif de cette thèse est l'étude par spectroscopie laser colinéaire à haute résolution de la structure nucléaire des isotopes d’étain riches en neutrons, vers de la fermeture de couche N=82 et au-delà. Les structures hyperfines et les déplacements isotopiques le long de ¹⁰⁸⁻¹³⁴Sn ont été mesurés en utilisant l’expérience COLLAPS à ISOLDE au CERN. Deux expériences indépendantes, utilisant des propriétés de transitions complémentaires l’une à 452 et l’autre à 286 nanomètres, ont étudiées les états 5p6s ¹P₁ et 5p6s ³P₁ dans l'atome neutre. L'état singlet fournit une sensibilité élevée au moment quadrupolaire tandis que le triplet facilite une grande séparation magnétique. A partir d'une analyse auto-cohérente des deux ensembles de données, les spins nucléaires, les moments électromagnétiques et les rayons de charge ont été extraits. Les propriétés des isomères à vie longue des noyaux ¹¹³Sn, ¹²³Sn, ¹²⁸Sn ainsi que l'état fondamental de ¹³³Sn et ¹³⁴Sn ont été évalués pour la première fois. Les moments quadrupolaires des états 11/2⁻, déterminés avec une plus grande précision que les études précédentes, suivent une tendance presque linéaire. Un coude à N=82 dans la courbe des rayons a été observé pour la première fois. Des calculs de champ moyen fournissent une description précise des rayons et relient en outre la tendance globale aux corrélations provenant des fluctuations des moments quadrupolaires. / The aim of this thesis is the study of nuclear structure properties of the neutron-rich Sn isotopes towards the N=82 shell closure and beyond by high-resolution collinear laser spectroscopy. The hyperfine structures and isotope shifts along ¹⁰⁸⁻¹³⁴Sn were measured using the COLLAPS instrumentation at ISOLDE, CERN. Two independent experiments using transitions with complementary properties, respectively at 452 and 286 nanometres studied the 5p6s ¹P₁ and the 5p6s ³P₁ states in the neutral atom. The singlet state provided high sensitivity to quadrupole moments while the triplet facilitated a large magnetic splitting. From a self-consistent analysis of the two data sets, nuclear spins, electromagnetic moments and charge radii have been extracted. The properties of the long-lived isomers in ¹¹³Sn, ¹²³Sn, ¹²⁸Sn and the ground state of ¹³³Sn and ¹³⁴Sn have been assessed for the first time. The quadrupole moments of the 11/2⁻ states, determined with much higher precision than in previous studies, have been found to follow a nearly linear trend. A "kink" in the radii trend at N=82 was observed for the first time. Beyond mean-field calculations provide an accurate description of the radii and further relate the overall trend to correlations stemming from the fluctuations of the quadrupole moments.

<p>The hydrogen bond is one of nature’s ubiquitous molecular interactions. Its role ranges from that of a static provider of structural integrity in proteins to that of a dynamic coordinate, along which excited state deactivation in sunscreen molecules is achieved. The work in this dissertation employs a supersonic expansion to collisionally cool peptide oligomers and a sunscreen chromophore to the zero-point vibrational level of their low lying conformational minima. These species are interrogated using high-resolution, conformer-specific ultraviolet and infrared laser spectroscopic techniques with the aim of elucidating their intrinsic conformational preferences, hydrogen bonding networks, and excited state deactivation mechanisms.</p><p>Synthetic foldamers are oligomers composed of non-natural building blocks, such as b- and g-amino acids. Incorporation of such residues into a peptide backbone results in secondary and tertiary structures that are distinct from those found in nature. Herein, the folding propensity of a series of mixed a/b and pure b-peptides is presented. In each case, both the left- and right-handed emergence of mixed-helical secondary structures, the 11/9- and the 12/10-helix, are observed. Next, the intrinsic conformational preferences of a series of increasingly complex asparagine-containing peptides are characterized. Asparagine, with its flexible carboxamide sidechain, is omnipresent within the prion forming domain of the misfolded proteins associated with several neurodegenerative diseases. Asparagine’s propensity for b-turn structures is discussed and compared with that of analogous peptide sequences found in nature.</p><p>Methyl anthranilate is a natural product that contains an identical electronic chromophore to the sunscreen agent, meradimate. The excited state deactivation mechanism of methyl anthranilate and its water complex is determined with extensive ultraviolet spectroscopic characterization, and is discussed within the broader context of its role as a sunscreen agent. Vibronic analysis coupled with computational results indicate extensive heavy-atom rearrangement leading to hydrogen atom dislocation, rather than full transfer, on the S₁ surface. This phenomenon is further characterized with infrared spectroscopy and theoretical modeling, in which the NH stretch is adiabatically separated from other internal coordinates. Extensive dilution of the dislocated NH stretch oscillator strength over many transitions and ~1,300 cm^-1 is predicted. These results may have implications for similar molecules, such as salicylic acid and its derivatives.</p>