4,689 research outputs found
Direct solar-pumped iodine laser amplifier
This semiannual progress report covers the period from March 1, 1987 to September 30, 1987 under NASA grant NAG1-441 entitled 'Direct solar-pumped iodine laser amplifier'. During this period Nd:YAG and Nd:Cr:GSGG crystals have been tested for the solar-simulator pumped cw laser, and loss mechanisms of the laser output power in a flashlamp-pumped iodine laser also have been identified theoretically. It was observed that the threshold pump-beam intensities for both Nd:YAG and Nd:Cr:GSGG crystals were about 1000 solar constants, and the cw laser operation of the Nd:Cr:GSGG crystal was more difficult than that of the Nd:YAG crystal under the solar-simulator pumping. The possibility of the Nd:Cr:GSGG laser operation with a fast continuously chopped pumping was also observed. In addition, good agreement between the theoretical calculations and the experimental data on the loss mechanisms of a flashlamp-pumped iodine laser at various fill pressures and various lasants was achieved
XeCl laser pumped iodine laser using t-C4F9I
An iodine photodissociation laser using t-C4F9I as the active material was pumped by an XeCl laser. An iodine laser output energy of 3 mJ with pulse duration of 25 ns was obtained when the pumping pulse energy was 80 mJ, the iodide pressure was 70 torr, and the reflectance of the output mirror was 85 percent. The high pumping efficiency and low threshold pump power achieved in this experiment are attributable to the high absorption cross section at the pump laser wavelength (308 nm) of the iodide used
Direct solar-pumped iodine laser amplifier
The optimum conditions of a solar pumped iodine laser are found in this research for the case of a continuous wave operation and a pulsed operation. The optimum product of the pressure(p) inside the laser tube and the tube diameter(d) was pd=40 approx. 50 torr-cm on the contrary to the case of a high intensity flashlamp pumped iodine laser where the optimum value of the product is known to be pd=150 torr-cm. The pressure-diameter product is less than 1/3 of that of the high power iodine laser. During the research period, various laser materials were also studied for solar pumping. Among the laser materials, Nd:YAG is found to have the lowest laser threshold pumping intensity of about 200 solar constant. The Rhodamine 6G was also tested as the solar pumped laser material. The threshold pumping power was measured to be about 20,000 solar constant. The amplification experiment for a continuously pumped iodine laser amplifier was performed using Vortek solar simulator and the amplification factors were measured for single pass amplification and triple pass amplification of the 15 cm long amplifier tube. The amplification of 5 was obtained for the triple pass amplification
Signatures of the neutrino mass hierarchy in supernova neutrinos
The undetermined neutrino mass hierarchy may leave an observable imprint on
the neutrino fluxes from a core-collapse supernova (SN). The interpretation of
the observables, however, is subject to the uncertain SN models and the flavor
conversion mechanism of neutrinos in a SN. We attempt to propose a qualitative
interpretation of the expected neutrino events at terrestrial detectors,
focusing on the accretion phase of the neutrino burst. The flavor conversions
due to neutrino self-interaction, the MSW effect, and the Earth regeneration
effect are incorporated in the calculation. It leads to several distinct
scenarios that are identified by the neutrino mass hierarchies and the
collective flavor transitions. Consequences resulting from the variation of
incident angles and SN models are also discussed.Comment: 15 pages, 9 figure
Critical Behavior in the Rotating D-branes
The low energy excitation of the rotating D3-branes is thermodynamically
stable up to a critical angular momentum density. This indicates that there is
a corresponding phase transition of the =4 large super Yang-Mills
theory at finite temperature. On the side of supergravity, we investigate the
phase transition in the grand canonical ensemble and canonical ensemble. Some
critical exponents of thermodynamic quantities are calculated. They obey the
static scaling laws. Using the scaling laws related to the correlation length,
we get the critical exponents of the correlation function of gauge field. The
thermodynamic stability of low energy excitations of the rotating M5-branes and
rotating M2-branes is also studied and similar critical behavior is observed.
We find that the critical point is shifted in the different ensembles and there
is no critical point in the canonical ensemble for the rotating M2-branes. We
also discuss the Hawking-Page transition for these rotating branes. In the
grand canonical ensemble, the Hawking-Page transition does not occur. In the
canonical ensemble, however, the Hawking-Page transition may appear for the
rotating D3- and M5-branes, but not for the rotating M2-branes.Comment: Revtex, 17 pages, minor changes, the discussion on the Hawking-Page
transition and references adde
Transient conduction and radiation in a semi-transparent phase change medium in an annulus
The effect of thermal radiation on the solidification of an absorbing, emitting, isotropically scattering infinite and finite, semi-transparent gray medium bounded between two concentric cylinders is investigated. The conservation of energy principle employing enthalpy and temperature as dependent variables is coupled with a set of moment equations which are derived from the radiative transfer equations and Marshak type boundary conditions by applying P-1 differential approximations.
The transient temperature distribution, interface location of a semi-transparent phase change medium, and the local radiative radial and axial heat flux has been obtained by using a Gauss-Seidel iterative numerical scheme for some typical geometric dimensions and parameters. The numerical results for the one-dimensional axisymmetric case of pure conduction are verified by comparison with an analytical approximation where the change in the internal energy in the solid phase is neglected.
The results for an optically thick cylindrical medium are obtained, analyzed, and displayed in graphs
Computational Analysis for Time Dependent Two Dimensional Flow of Incompressible Homogeneous Newtonian Fluid (Spin Up Problem)
A digital computer method and a program which employs optimized successive overrelaxation were developed to solve certain problems involving time-dependent two-dimensional flow of an incompressible homogeneous Newtonian fluid.
Bubble sort techniques were used in a boundary field and a vectorization of the inner-most Do-loops of the program was carried out using a CRAY-1 computer. A polygon region was selected for analysis purposes.
As a test program, "Spin-up problem" for a circular region with rotating solid boundary conditions was analyzed. The results of computations using a fine mesh were in good agreement with analytical results.
Finally, a flow contained in an infinite cylinder with part-moving boundarie-s is examined. It is to be applied to an analysis of a flow in a circular cavity
Direct solar-pumped iodine laser amplifier
In order to evaluate the feasibility of the solar pumped dye laser, the parametric study of a dye laser amplifier pumped by a solar simulator and flashlamp was carried out, and the amplifier gains were measured at various pump beam irradiances on the dye cell. Rhodamine 6G was considered as a candidate for the solar pumped laser because of its good utilization of the solar spectrum and high quantum efficiency. The measurement shows that a solar concentration of 20,000 is required to reach the threshold of the dye. The work to construct a kinetic model algorithm which predicts the output parameter of laser was progressed. The kinetic model was improved such that there is good agreement between the theoretical model and experimental data for the systems defined previously as flashlamp pumped laser oscillator, and the long path length solar pumped laser
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