Le cadre général de cette thèse est l'étude de nouvelles sources laser solides, pompées par diode, émettant un rayonnement continu monomode longitudinal dans le proche infrarouge (1000 nm) et dans le bleu-vert par doublement de fréquence, particulièrement à 501,7 nm. Ces sources laser visent des applications métrologiques telles que la spectroscopie de l'iode (127I2) à ultra-haute résolution et la mise en pratique du mètre, domaines dans lesquels les lasers à argon sont actuellement utilisés.<br />Le premier chapitre de ce travail présente le contexte de cette étude, à travers un état de l'art des sources laser autour de 500 nm, les solutions retenues et explorées, ainsi que des éléments théoriques pour la génération de seconde harmonique. Le principe commun des deux voies est de produire une émission laser monomode spectrale à 1000 nm qui est ensuite doublée en fréquence.<br />Le deuxième chapitre traite de la solution utilisant des cristaux dopés ytterbium émettant à 1000 nm, dont l'émission est doublée en fréquence intracavité dans un cristal non linéaire de KNbO3. Deux cristaux laser sont utilisés : le Yb:YSO et le Yb:KYW. Dans les deux cas, à 501,7 nm, nous démontrons des puissances en régime monofréquence comprises entre 35 et 60 mW pour une puissance de pompe de 4W à 980 nm.<br />Le troisième chapitre concerne la seconde voie étudiée utilisant un milieu amplificateur semiconducteur à puits quantiques de type VCSEL. La structure active, formée d'un miroir de Bragg et de puits quantiques, est montée en cavité étendue et pompée optiquement. L'émission autour de 1000 nm est doublée en fréquence pour produire 60 mW en régime monomode spectral à 500 nm, à partir d'une puissance de pompe de 6,5 W à 808 nm.

Cette étude a pour objectif de développer des matériaux luminescents avec un rendement quantique supérieur à 100% permettant d'améliorer l'efficacité des cellules photovoltaïques. Ces travaux sont basés sur des sulfures avec une faible énergie de phonon. Les verres Ga₂S₃-GeS₂-CsCl dopés par des terres-rares sont d'abord étudiés. Il a été démontré qu'un photon visible peut être divisé en deux photons infrarouges par les couples d'ions Er³⁺/Yb³⁺ou Pr³⁺/Yb³⁺ Cependant, le rendement quantique mesuré avec une sphère intégrante est beaucoup plus faible que 100%. Ceci est attribué aux impuretés qui conduisent au désexcitation non-radiative, et à l'absorption du transfert de charge d'Yb³⁺ qui se situe dans le visible dans le cas des sulfures. Grâce à l'électronégativité plus élevée de l'oxygène par rapport au soufre, la bande de transfert de charge d'Yb³⁺ est repoussée vers l'UV dans des oxysulfures de terres-rares. Les oxysulfures très purs ont été préparés avec la méthode de combustion complétée par une sulfuration. La multiplication de photon dans l'IR a été observée dans La₂O₂S dopé par Pr³⁺/Yb³⁺, Er³⁺/Yb³⁺ ou Tb³⁺/Yb³⁺. Un rendement quantique supérieur à 100% est pour la première fois directement mesuré dans La₂O₂S :Er³⁺,Yb³⁺. Une structure "core-shell" est conçue pour sensibiliser des ions Er³⁺ dans les oxysulfures par des ions Ce³⁺ dans le YAG. Par une précipitation homogène, on a réussi à déposer du Y₂O₂S sur des poudres fines de YAG : Ce³⁺. Bien que la structure désirée ne soit pas encore obtenue due à la diffusion d'Er³⁺ dans le YAG, cette piste de recherche est intéressante pour développer des convertisseurs spectrales avec une bande d'absorption large et intense.

In this work, we investigated the spectroscopic characteristics of Nd3+ and Yb3+ doped/co-doped materials for potential applications in photonic devices, particularly lasers emitting in the IR and visible (blue) and thermal sensing operating in the first and second biological windows. For such purposes, we used the fluorescence spectroscopy technique in steady state and time resolved. Initially we investigated the spectroscopic characteristics of the Yb3+ doped oxyfluoride glass, analyzing three important effects present in Yb3+ doped systems: Radiation Trapping (RT), Self-Quenching (SQ), and Cooperative Luminescence (CL). We show that the effects of RT and SQ affect substantially the line shape of Yb3+ emission spectrum, thereby inducing miscalculations of the emission cross section, overestimation of the laser level lifetime, as well as errors in non-radiative decay rates. On the other hand, we show that the strong presence of RT favors the CL effect between Yb3+ ions, which configures an advantageous feature for the generation of blue light via CL. In the thermal sensing context, we carried out a study on application of Nd3+ single doped materials for optical temperature sensors based on Fluorescence Intensity Ratio (FIR) using the 4F3/2, 4F5/2 and 4F7/2 Nd3+ energy levels, more precisely, Nd3+ doped Q-98 phosphate glass, where we showed that the investigated phosphate glass present good perspectives for applications in optical thermometer, being its thermal sensitivity and the maximum thermal range, strongly dependent on the considered energy levels. Following the studies on thermal sensing, we investigated the effects of structure core and core@shell of lanthanum fluoride nanocrystals (LaF3) doped/co-doped with Nd3+ and Yb3+ for temperature sensor based on energy transfer (ET). For this, LaF3 nanocrystals in structural configurations LaF3:Nd (only core), LaF3:Nd/Yb (only core), LaF3 :Nd@LaF3:Yb (Nd3+ in core and Yb3+ in shell), and LaF3:Yb@LaF3:Nd (Yb3+ in core and Nd3+ in shell) were synthesized. We evaluated the FIR of the emission from Yb3+ (2F5/2→2F7/2 at ~990 nm) and Nd3+ (4F3/2→4I13/2 at ~1060 nm) against the temperature and we concluded that their sensitivities are strongly dependent on the structural configurations, i.e., we get control the ET processes and their temperature dependence. In addition, we show that FIR, using 990 and 1330 nm emissions present thermal sensitivity at least one order of magnitude greater that the other FIR’s. / Conselho Nacional de Desenvolvimento Científico e Tecnológico / Neste trabalho investigamos as características espectroscópicas de materiais dopados/co-dopados com os íons terras-raras Nd3+ e Yb3+ para potenciais aplicações em dispositivos fotônicos, particularmente lasers emissores no infravermelho e visível (azul) e sensoriamento térmico operando na primeira e segunda janelas biológicas. Para tais propósitos, usamos a técnica de espectroscopia de fluorescência no estado estacionário e resolvida no tempo. Inicialmente investigamos as características espectroscópicas do vidro oxifluoreto dopado com Yb3+, analisando três importantes efeitos presentes em sistemas dopados com Yb3+: Radiation Trapping (RT), Self- Quenching (SQ) e Luminescência Cooperativa (LC). Mostramos que os efeitos de RT e SQ afetam de forma substancial a forma de linha do espectro de emissão do Yb3+, induzindo, assim, cálculos errôneos na seção de choque de emissão, superestimação do valor do tempo de vida do nível laser emissor, bem como erros nas taxas de decaimentos não-radiativos. Por outro lado, mostramos que a forte presença dos efeitos de RT observados favorece o processo de LC entre íons Yb3+, o que de certa forma constitui uma característica vantajosa para a geração de luz azul via processo de LC do Yb-Yb. Já no âmbito de sensoriamento térmico, realizamos um estudo sobre a aplicação de materiais mono-dopados com Nd3+ em sensores ópticos de temperatura baseados na Razão de Intensidade de Fluorescência (RIF) dos níveis de energia 4F3/2, 4F5/2 e 4F7/2 do Nd3+, mais precisamente, vidro fosfato Q-98 dopado com Nd3+, onde mostramos que o vidro fosfato investigado apresenta boas perspectivas para aplicações em termômetro óptico, sendo sua sensibilidade térmica, bem como o intervalo de temperatura de máxima sensibilidade, fortemente dependente dos níveis de energia considerados. Continuando os estudos sobre sensoriamento térmico, investigamos os efeitos da estrutura core e core@shell de nanocristais de fluoreto de lantânio (LaF3) dopados/co-dopados com Nd3+ e Yb3+ para sensor térmico por Transferência de Energia (TE). Para tanto, nanocristais de LaF3 nas configurações estruturais de LaF3: Nd (somente core), no LaF3: Nd/Yb (somente core), LaF3: Nd@LaF3: Yb (com Nd3+ no core e Yb3+ no shell) e LaF:Yb@LaF3:Nd (com Yb3+ no core e Nd3+ no shell) foram sintetizados. Nós avaliamos as RIF das emissões do Yb3+ (2F5/2 → 2F7/2 em ~990 nm) e do Nd3+ (4F3/2→4I13/2 em ~1060 nm) com a temperatura e concluímos que suas sensibilidades são fortemente dependentes das configurações estruturais, ou seja, conseguimos controlar os processos de TE e a dependência destes com a temperatura. Adicionalmente, mostramos que o sensor de RIF, usando as emissões em 990 nm e 1330 nm, apresenta uma sensibilidade térmica de pelo menos uma ordem de grandeza maior que os demais RIF’s.

Un-doped, Er3+ doped (TiO2:Er3+) as well as Er3+/Yb3+ co-doped (TiO2:Er3+/Yb3+) nanocrystals with different concentrations of RE3+ (Er3+, Yb3+) were successfully synthesized using the sol-gel method. The powder X-ray diffraction (XRD) spectra revealed that all undoped and doped samples remained in anatase after annealing at 400°C. The presence of RE3+ ions in the TiO2 host lattice was confirmed by conducting elemental mapping on the samples using Scanning electron microscope (SEM) equipped with energy dispersive X-ray spectrometer (EDX), which was in agreement with X-ray photoelectron spectroscopy (XPS) results. Transmission electron microscope (TEM) images approximated particle sizes of the samples to be between 1.5 – 3.5 nm in diameter and this compares well with XRD analyses. Phonon quantification in TiO2 was achieved using Fourier transform infrared (FT-IR) spectroscopy. Optical bandgap from Ultraviolet/Visible/Near-Infrared was extrapolated from Kubelka-Munk relation and the narrowing of the bandgap for the doped samples as compared to the undoped sample was observed. The photoluminescence PL study of the samples revealed two emission peaks attributed to direct band-gap and defect-related emissions. A laser beam with 980 nm wavelength was used to irradiate the samples, and the displayed emission lines of the TiO2: Er3+ in the visible region of the electromagnetic spectrum confirmed up-conversion luminescence. Enhancement of up-conversion luminescence intensity due to Yb3+ co-doping was observed, indicating an efficient energy transfer process from the sensitizer Yb3+ to the activator Er3+. / Physics / M. Sc. (Physics)

The ultrashort chirped pulse amplification (CPA) laser technology opens the path to high intensities of 10^21 W/cm² and above in the laser focus. Such intensities allow laser-matter interaction in the relativistic intensity regime. Direct diode-pumped ultrashort solid-state lasers combine high-energy, high-power and efficient amplification together, which are the main advantages compared to flashlamp-pumped high-energy laser systems based on titanium-doped sapphire. Development within recent years in the field of laser diodes makes them more and more attractive in terms of total costs, compactness and lifetime. This work is dedicated to the Petawatt, ENergy-Efficient Laser for Optical Plasma Experiments (PENELOPE) project, a fully and directly diode-pumped laser system under development at the Helmholtz–Zentrum Dresden – Rossendorf (HZDR), aiming at 150 fs long pulses with energies of up to 150 J at repetition rates of up to 1 Hz. The focus of this thesis lies on the spectral and width manipulation of the front-end amplifiers, trivalent ytterbium-doped calcium fluoride (Yb3+:CaF2) as gain material as well as the pump source for the final two main amplifiers of the PENELOPE laser system. Here, all crucial design parameters were investigated and a further successful scaling of the laser system to its target values was shown. Gain narrowing is the dominant process for spectral bandwidth reduction during the amplification at the high-gain front-end amplifiers. Active or passive spectral gain control filter can be used to counteract this effect. A pulse duration of 121 fs was achieved by using a passive spectral attenuation inside a regenerative amplifier, which corresponds to an improvement by a factor of almost 2 compared to the start of this work. A proof-of-concept experiment showed the capability of the pre-shaping approach. A spectral bandwidth of 20nm was transferred through the first multipass amplifier at a total gain of 300. Finally, the predicted output spectrum calculated by a numerical model of the final amplifier stages was in a good agreement with the experimental results. The spectroscopic properties of Yb3+:CaF2 matches the constraints for ultrashort laser pulse amplification and direct diode pumping. Pumping close to the zero phonon line at 976nm is preferable compared to 940nm as the pump intensity saturation is significantly lower. A broad gain cross section of up to 50nm is achievable for typical inversion levels. Furthermore, moderate cryogenic temperatures (above 200K) can be used to improve the amplification performance of Yb3+:CaF2. The optical quality of the doped crystals currently available on the market is sufficient to build amplifiers in the hundred joule range. The designed pump source for the last two amplifiers is based on two side pumping in a double pass configuration. However, this concept requires the necessity of brightness conservation for the installed laser diodes. Therefore, a fully relay imaging setup (4f optical system) along the optical path from the stacks to the gain material including the global beam homogenization was developed in a novel approach. Beside these major parts the amplifier architecture and relay imaging telescopes as well as temporal intensity contrast (TIC) was investigated. An all reflective concept for the relay imaging amplifiers and telescopes was selected, which results in several advantages especially an achromatic behavior and low B-Integral. The TIC of the front-end was improved, as the pre- and postpulses due to the plane-parallel active-mirror was eliminated by wedging the gain medium.

Je présente le développement d'une expérience de production de gaz quantiques d'ytterbium. L'objectif est de réaliser des champs de jauge artificiels sur des gaz piégés dans des réseaux optiques. La combinaison de ces champs et des interactions entre atomes ouvre de nouvelles perspectives pour notre domaine comme la réalisation d'états analogues à ceux de la physique de l'effet Hall quantique fractionnaire.Tout d'abord, je présente les méthodes expérimentales développées pour produire un condensat de Bose-Einstein d'atomes (CBE) d'Yb174: un piège magnéto-optique sur la raie d'intercombinaison 1S0-3P1, son transfert dans un piège dipolaire et son transport sur une distance de 22 cm. Un condensat pur d'environ 6x10^4 est ensuite obtenu après évaporation dans un piège dipolaire croisé. Les protocoles envisagés pour réaliser des champs de jauge artificiels requièrent le couplage cohérent du niveau fondamental 1S0 et du niveau métastable 3P0 sur la transition "horloge". Nous avons construit un laser à 578nm asservi en fréquence sur une cavité de référence. En optimisant le point de fonctionnement en température de la cavité nous avons obtenu des dérives résiduelles en fréquence inférieures à 100 mHz/s. Nous avons réalisé une spectroscopie sur cette transition d'un CBE piégé ou en expansion et obtenu des largeurs de raies du l'ordre du kHz limitées par les interactions entre atomes.Enfin, je présente en détail les protocoles pour réaliser des champs de jauge artificiels dans des réseaux optiques et leur éventuelle mise en pratique et notamment un schéma pour réaliser un réseau optique bichromatique dépendant de l'état interne des atomes dans une cavité doublement résonante. / In this work I present the development of a new experiment to produce quantum degenerate gases of ytterbium. This project aims at realizing artificial gauge fields with ultracold atoms in optical lattices. Combining intense gauge fields with strong on-site interactions is expected to open a new area for ultracold quantum gases, where for instance the atomic analogs of fractional quantum Hall systems could be realized.First I describe the experimental methods for the production of a Bose-Einstein condensate (BEC) of 174Yb. This implies magneto-optical trapping on the 1S0-3P1 intercombination transition and a transport of the atomic cloud in an optical dipole trap over a distance of 22 cm. Evaporative cooling in a crossed dipole trap results in the production of pure BECs of about 6x10^4 atoms.The planned implementation of artificial gauge fields requires the coherent driving of the 1S0-3P0 clock transition of ytterbium. For this purpose an ultrastable laser system at 578 nm, frequency locked to an ultralow expansion (ULE) cavity, has been realized. A precise determination of the temperature zero-crossing point of the ULE cavity allowed us to limit laser frequency drifts below 100 mHz/s. Spectroscopic measurements of the clock transition on a trapped and free falling BEC are presented, where typical linewidths in the kHz range are observed, limited by interatomic interactions. Finally I present a detailed discussion of the methods to achieve artificial gauge fields in optical lattices and their possible experimental implementation. This includes a scheme to realize a bichromatic state-dependent optical superlattice in a doubly-resonant cavity.

This diploma thesis deals with evaluation of toxicity and bioaccumulation of photon-upconversion nanoparticles (UCNPs) in model plant maize (Zea mays). Lanthanide-doped UCNPs with different composition and size were tested in three different concentrations in this work. The exposure took place for 168 hours. Toxicity was assessed based on four macroscopic toxicological endpoints (mortality, the length of belowground part of the plants, the length of aboveground part of the plants and whole plants length). Spatial distribution of elements yttrium, ytterbium, erbium and gadolinium in model plants was determined using laser induced breakdown spectroscopy with spatial resolution of 100 m and 26 m. Distribution of UCNPs in plants was further studied with photon-upconversion microscanning with spatial resolution of 40 m. Stability of UCNPs during and after the plant exposure was also discussed in this thesis.

The ultrashort chirped pulse amplification (CPA) laser technology opens the path to high intensities of 10^21 W/cm² and above in the laser focus. Such intensities allow laser-matter interaction in the relativistic intensity regime. Direct diode-pumped ultrashort solid-state lasers combine high-energy, high-power and efficient amplification together, which are the main advantages compared to flashlamp-pumped high-energy laser systems based on titanium-doped sapphire. Development within recent years in the field of laser diodes makes them more and more attractive in terms of total costs, compactness and lifetime. This work is dedicated to the Petawatt, ENergy-Efficient Laser for Optical Plasma Experiments (PENELOPE) project, a fully and directly diode-pumped laser system under development at the Helmholtz–Zentrum Dresden – Rossendorf (HZDR), aiming at 150 fs long pulses with energies of up to 150 J at repetition rates of up to 1 Hz. The focus of this thesis lies on the spectral and width manipulation of the front-end amplifiers, trivalent ytterbium-doped calcium fluoride (Yb3+:CaF2) as gain material as well as the pump source for the final two main amplifiers of the PENELOPE laser system. Here, all crucial design parameters were investigated and a further successful scaling of the laser system to its target values was shown. Gain narrowing is the dominant process for spectral bandwidth reduction during the amplification at the high-gain front-end amplifiers. Active or passive spectral gain control filter can be used to counteract this effect. A pulse duration of 121 fs was achieved by using a passive spectral attenuation inside a regenerative amplifier, which corresponds to an improvement by a factor of almost 2 compared to the start of this work. A proof-of-concept experiment showed the capability of the pre-shaping approach. A spectral bandwidth of 20nm was transferred through the first multipass amplifier at a total gain of 300. Finally, the predicted output spectrum calculated by a numerical model of the final amplifier stages was in a good agreement with the experimental results. The spectroscopic properties of Yb3+:CaF2 matches the constraints for ultrashort laser pulse amplification and direct diode pumping. Pumping close to the zero phonon line at 976nm is preferable compared to 940nm as the pump intensity saturation is significantly lower. A broad gain cross section of up to 50nm is achievable for typical inversion levels. Furthermore, moderate cryogenic temperatures (above 200K) can be used to improve the amplification performance of Yb3+:CaF2. The optical quality of the doped crystals currently available on the market is sufficient to build amplifiers in the hundred joule range. The designed pump source for the last two amplifiers is based on two side pumping in a double pass configuration. However, this concept requires the necessity of brightness conservation for the installed laser diodes. Therefore, a fully relay imaging setup (4f optical system) along the optical path from the stacks to the gain material including the global beam homogenization was developed in a novel approach. Beside these major parts the amplifier architecture and relay imaging telescopes as well as temporal intensity contrast (TIC) was investigated. An all reflective concept for the relay imaging amplifiers and telescopes was selected, which results in several advantages especially an achromatic behavior and low B-Integral. The TIC of the front-end was improved, as the pre- and postpulses due to the plane-parallel active-mirror was eliminated by wedging the gain medium.

The use of supercontinuum light sources in different optical measurement methods, like microscopy or optical coherence tomography, has increased significantly compared to classical wideband light sources. The development of various optical measurement techniques benefits from the high brightness and bandwidth, as well as the spatial coherence of these sources. For some applications, only a portion of the broad spectral range can be used. Therefore, an increase of the spectral power density in limited spectral regions would provide a clear advantage over spectral filtering. This study describes a method to increase the spectral power density of supercontinuum sources by amplifying the excitation wavelength inside a nonlinear photonic crystal fiber (PCF). An ytterbium doped photonic crystal fiber was manufactured by a nanopowder process (drawn by the company fiberware) and used in a fiber amplifier setup as the nonlinear fiber medium. In order to characterize the fiber’s optimum operational characteristics, group-velocity dispersion (GVD) measurements were performed on the fiber during the amplification process. For this purpose, a notch-pass mirror was used to launch the radiation of a stabilized laser diode at 976 nm into the fiber sample for pumping. The performance of the fiber was compared with a conventional PCF. Finally, the system as a whole was characterized in reference to common solid state-laser-based photonic supercontinuum light sources. An improvement of the power density up to 7.2 times was observed between 1100 nm to 1380 nm wavelengths.

Supercontinuum light sources provide a high power spectral density with a high spatial coherence. Coherent octavespanning supercontinuum can be generated in photonic crystal fibers (PCFs) by launching short pulses into the fiber. In the field of optical metrology, these light sources are very interesting. For most applications, only a small part of the entire spectrum can be utilized. In biological tissue scattering, absorption and fluorescence limits the usable spectral range. Therefore, an increase of the spectral power density in limited spectral regions would provide a clear advantage over spectral filtering. This study describes a method to increase the spectral power density of supercontinuum sources by amplifying the excitation wavelength inside a nonlinear photonic crystal fiber (PCF). An all-fiber-based setup enables higher output power and power stability. An ytterbium-doped photonic crystal fiber was manufactured by a nanopowder process (drawn by the fiberware GmbH, Germany) and used in a fiber amplifier setup as the nonlinear fiber medium. In order to characterize the fiber’s optimum operational characteristics, group-velocity dispersion (GVD) measurements were performed. The performance of the fiber-based setup was compared with a free space setup. Finally, the system as a whole was characterized in reference to common solid state-laser-based supercontinuum light sources. An improvement of the power density was observed in the spectral range between 1100 nm to 1400 nm.