Enhancing Optical Up-Conversion Through Electrodynamic Coupling with Ancillary Chromophores

In lanthanide-based optical materials, control over the relevant operating characteristics–for example transmission wavelength, phase and quantum efficiency–is generally achieved through the modification of parameters such as dopant/host combination, chromophore concentration and lattice structure. An alternative avenue for the control of optical response is through the introduction of secondary, codoped chromophores. Here, such secondary centers act as mediators, commonly bridging the transfer of energy between primary absorbers of externally sourced optical input and other sites of frequency-converted emission. Utilizing theoretical models based on experimentally feasible, three-dimensional crystal lattice structures; a fully quantized theoretical framework provides insights into the locally modified mechanisms that can be implemented within such systems. This leads to a discussion of how such effects might be deployed to either enhance, or potentially diminish, the efficiency of frequency up-conversion

Upconversion-induced heat generation and thermal lensing in Nd:YLF and Nd:YAG

We investigate the influence of interionic upconversion between neighboring ions in the upper laser level of Nd:YLF and Nd:YAG on population dynamics, heat generation, and thermal lensing under lasing and non-lasing conditions. It is shown that cascaded multiphonon relaxations following each upconversion process generate significant extra heat dissipation in the crystal under non-lasing compared to lasing conditions. Owing to the unfavorable temperature dependence of thermal and thermo-optical parameters, this leads, firstly, to a significant temperature increase in the rod, secondly, to strong thermal lensing with pronounced spherical aberrations and, ultimately, to rod fracture in a high-power end-pumped system. In a three-dimensional finite-element calculation, excitation densities, upconversion rates, heat generation temperature profiles, and thermal lensing are calculated. Differences in thermal lens power between non-lasing and lasing conditions up to a factor of six in Nd:YLF and up to a factor of two in Nd:YAG are experimentally observed and explained by the calculation. This results in a strong deterioration in performance when operating these systems in a Q-switched regime, as an amplifier, or on a low-gain transition. Methods to decrease the influence of interionic upconversion are discussed. It is shown that tuning of the pump wavelength can significantly alter the rod temperature

Nanocrystalline lanthanide-doped Lu3Ga5O12 garnets: interesting materials for light-emitting devices

Nanocrystalline Lu3Ga5O12, with average particle sizes of 40 nm, doped with a wide variety of luminescent trivalent lanthanide ions have been prepared using a sol\u2013gel technique. The structural and morphological properties of the powders have been investigated by x-ray powder diffraction, high resolution transmission electron microscopy and Raman spectroscopy. Structural data have been refined and are presented for Pr3+, Eu3+, Gd3+, Ho3+, Er3+ and Tm3+ dopants, while room temperature excited luminescence spectra and emission decay curves of Eu3+-, Tm3+- and Ho3+-doped Lu3Ga5O12 nanocrystals have been measured and are discussed. The Eu3+ emission spectrum shows typical bands due to 5D0 \u21927FJ (J = 0, 1, 2, 3, 4) transitions and the broadening of these emission bands with the non-exponential behaviour of the decay curves indicates the presence of structural disorder around the lanthanide ions. Lanthanide-doped nanocrystalline Lu3Ga5O12 materials show better luminescence intensities compared to Y2O3, Gd3Ga5O12 and Y3Al5O12 nanocrystalline hosts. Moreover, the upconversion emission intensity in the blue-green region for the Tm3+- and Ho3+-doped samples shows a significant increase upon 647.5 nm excitation with respect to other common oxide hosts doped with the same lanthanide ions

The Navy's Superior Supplier Incentives Program: Analysis of Supplier Proposed Benefits

The Department of Defense (DOD) launched the Superior Supplier Incentive Program in 2013 to adopt industry best practices on supply and supplier management and to explore opportunities to provide the high-performing defense contractors with benefits or reliefs that would reduce administrative burdens and streamline processes. The Department of the Navy provided an opportunity for its 2014 Superior Suppliers to submit white papers suggesting possible reliefs or benefits that would improve efficiency. This paper analyzes the 55 proposed benefits using three frameworks—Federal Acquisition Regulation (FAR) policy analysis, contract management process analysis, and risk-benefit analysis—to identify patterns or consistencies. The research reveals that FAR Part 42, Contract Management and Audit Services, and the contract management phase represent the most frustration for the Superior Suppliers. The results of the analysis can be used as a surrogate measure to identify potential improvements in the DOD’s current acquisition practices.Naval Postgraduate School Acquisition Research Progra

The Navy's superior supplier incentive program: analysis of supplier proposed benefits

MBA Professional ReportThe Department of Defense (DOD) launched the Superior Supplier Incentive Program in 2013 to adopt industry best practices on supply and supplier management and to explore opportunities to provide the high-performing defense contractors with benefits or reliefs that would reduce administrative burdens and streamline processes. The Department of the Navy provided an opportunity for its 2014 Superior Suppliers to submit white papers suggesting possible reliefs or benefits that would improve efficiency. This paper analyzes the 55 proposed benefits using three frameworks—Federal Acquisition Regulation (FAR) policy analysis, contract management process analysis, and risk-benefit analysis—to identify patterns or consistencies. The research reveals that FAR Part 42, Contract Management and Audit Services, and the contract management phase represent the most frustration for the Superior Suppliers. The results of the analysis can be used as a surrogate measure to identify potential improvements in the DOD’s current acquisition practices.http://archive.org/details/thenavyssuperior1094547806Outstanding ThesisMajor, United States ArmyLieutenant, United States NavyApproved for public release; distribution is unlimited

Energy transfer from Fe3+ to rare-earth ions in YAG and the problem of sensitization of laser emission

The static and dynamic measurements of Tm3+ spectra in YAG:Fe:Tm show that the 3H4 level is efficiently populated by transfer from Fe3+ in tetrahedral sites. The features of the transfer processes, by investigation of Tm3+ acceptor luminescence characteristics, are presented