Zugl.: Hamburg, Univ., Diss., 2008

Concentration quenching effect in ytterbium (Yb) and neodymium (Nd) doped phosphate glasses, thulium (Tm) doped germanate glass, and praseodymium (Pr) doped tellurite glass were studied. The fluorescence and lifetime of these rare-earth doped glasses with different concentrations were measured. Ion pair and clustering are included in the model to explain the quenching effect occurring in highly doped glasses. This study will help us in designing and fabricating high unit gain optical fibers.

The purpose of this investigation was to study the radiations of the 169/Tm nucleus as it de-excites after the electron capture decay of the 169/Yb. Numerous unreported gammas were present in the sample. The origins of these gamma rays were found.

Nuclear and laser spectroscopy measurements have been conducted at the Ion Guide Isotope Separator On-Line, IGISOL-IV, JYFL laboratory, Jyvaskyla. Nuclear moments have been extracted for two ground and two isomeric states of neutron deficient yttrium, 85g,mY and 86g,mY. The mean square charge radii and moments have been extracted for all states, providing, for the first time, estimates of static and dynamic quadrupole deformations in these shape transitioning nuclei. A second laser spectroscopy experiment yielded the frequency shifts between all stable isotopes of ionic ytterbium in exotic (high-lying metastable) resonance lines. Atomic field and mass shift parameters in these (high purity) transitions have been evaluated. A discussion of the impact these parameters may have on the chemical homologue, nobelium, is presented. New measurements of charge-state dependent IGISOL fission production yields (of strontium, yttrium and zirconium) are reported in this thesis. For the first time, charge state dependent effects in relative isomeric to ground state production have been detected. Possible explanations for, and exploitation of, this unexpected phenomenon is presented. A new data acquisition (DAQ) system has been built at The University of Manchester. It has been designed to fully replace the current setup used for laser spectroscopy at the JYFL laboratory. The new hardware has been extensively tested off-line and is ready to be installed at the laser-IGISOL. To work in conjunction with the new DAQ, two graphical user interfaces (GUIs) have been created, to display and sort data online, and permit efficient data extraction. Both have been shown to perform at the level required for experimental on-line use. An updated report on the status of an electrostatic ConeTrap is presented. Improved (more realistic) simulations are now seen to be capable of reproducing experimentally observed results. Further computational effort on the ion optics has shown that improved containment and transport efficiency can be readily achieved. A new trap, featuring a larger rear electrode, promises a greatly increased ion survival. The next commissioning phase will see the construction and installation of this upgraded ConeTrap.

Zugl.: Hamburg, Univ., Diss., 2009

This thesis covers the construction and characterisation of microlasers based on whispering gallery modes in ytterbium-doped microsphere resonators. The microlasers were made by drawing and fusing Yb-doped silica optical fibre into microspheres of approximately 100 μmin diameter using CO2 laser-induced melting. Access to whispering gallery modes was accomplished using a prism coupled to the evanescent field of the internal cavity modes. Microspheres with Q-factors of up to 10^7 were made using this technique. CW multimode lasing was observed at 1050 nm, with a pump threshold required for lasing estimated to be of the order of 100 μW for a 900 nm pump. Both TE and TM modes were identified in the laser emission and the ability to selectively excite each mode family (TE or TM) is shown to be directly controlled by the pump. Pulsed lasing was also observed at 975 nm and 1050 nm.

Proefschrift Universiteit van Amsterdam. / Met lit. opg. - Met samenvatting in het Nederlands.

Thesis (Ph.D.) - University of St Andrews, November 2008.

Made available in DSpace on 2014-06-11T19:25:33Z (GMT). No. of bitstreams: 0 Previous issue date: 2010-06-28Bitstream added on 2014-06-13T18:28:59Z : No. of bitstreams: 1 gordo_vo_me_ilha.pdf: 1058796 bytes, checksum: 2c8438704796726349dfe606c2595b4b (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Neste trabalho foi estudado o sistema vítreo (100-x)% (80% TeO2-20% WO3)-(x)% Yb2O3, onde x = 0; 0,1; 0,2; 0,3; 0,4 e 0,5%. As técnicas de difração de raios-X, espectroscopia no infravermelho, espectroscopia Raman e espectroscopia no UV-Vis foram usadas para caracterizar os efeitos da dopagem sobre as propriedades estruturais e ópticas dos vidros estudados. Usando os dados de espectroscopia na região espectral ultravioleta-visível foi possível observar que não houve mudança das freqüências de corte para cada composição e ainda calcular a energia de “gap” e a energia de cauda de Urbach. Usando os dados de fotoluminescência observam-se picos que indicam o desdobramento dos níveis de energia dos estados 2F7/2 e 2F5/2 dos íons de Yb3+. Para os comprimentos de onda de excitação de 514,5 a 488,0 nm, crescem as taxas de absorção do sistema vítreo TW, transferência de carga para o estado 2F5/2 do Yb3+ e da transição radiativa 2F5/2 2F7/2, aumentando, desta forma, a intensidade da fotoluminescência. Já para os comprimentos de onda de excitação 457,9 e 476,5 nm as taxas de absorção do sistema vítreo TW, a transferência de carga para o estado 2F5/2 do Yb3+ e a transição radiativa 2F5/2 2F7/2 são as mesmas e, consequentemente, a intensidade da fotoluminescência é constante. / This work presents the study on the glassy system (100-x)% (80% 20% TeO2-WO3) - (x)% Yb2O3 where x = 0, 0.1, 0.2, 0.3, 0.4 and 0 5%. The techniques of X-ray diffraction, infrared spectroscopy, Raman spectroscopy and UV-Vis were used to characterize the effects of Yb doping on the structural and optical properties of the glasses. Using data from spectroscopy ultraviolet-visible spectral region was observed that there was no change of cutting frequencies for each compound and were calculate the energy gap and Urbach tail energy. Using the data of photoluminescence peak is observed indicating the splitting of energy levels of states 2F7/2 and 2F5/2 of Yb3+ ions. The rate of electron transition probability is influenced by temperature. To the excitation wavelength of 514.5 to 488.0 nm, growing rates of absorption of the glass system TW, charge transfer to the state 2F5/2 of Yb3+ and the radiative transition 2F5/2 2F7/2, increasing thus the photoluminescence intensity. As for the excitation wavelength of 476.5 and 457.9 nm absorption rates of the TW glass system, the charge transfer state to the 2F5/2 of Yb3+ and the radiative transition 2F5/2 2F7/2 are the same and, hence the photoluminescence intensity is constant.

A ytterbium fiber laser emitting 60 watts of power at 1064 nm has been designed, fabricated, and tested. The laser has an 83% optical efficiency at this power level, ~ 10% under that predicted by the quantum defect. Typical continuous wave nonlinearities have not been detected in the laser’s output characteristics. Additionally, amplified spontaneous emission at 1030 nm has not occurred at an observable level within the laser’s spectral output. Other deleterious effects on high-power laser operation are discussed. The spectral output has precisely controlled spectral characteristics enabled by the use of fiber Bragg gratings as cavity mirrors. Additional spectral peaks are observed in the output of the resonator. The probable cause of the unexpected spectral features is parasitic lasing from Fabry Perot effects between the output facet of the fiber and the high reflectivity Fiber Bragg Grating. The future addition of an endcap will enable this system to generate greater than a kilowatt of output power while eliminating spectral abnormalities. Challenges during construction related to splicing and the results of the implemented improvements are documented. Unmanageable thermal complications with fusion splicing required the refinement of splicing, decontamination, and cleaving protocols. Standard splice functionality was ultimately regained, and assembly of the laser was continued. This laser is expected to be deployed at the Townes Institute Science and Technology Experimentation Facility (TISTEF) upon completion of the kilowatt power build. Beam shaping characterization studies will be performed upon laser delivery. Emphasis will be placed on interactions between nondiffracting beams and atmospheric turbulence.