Analysis of Nd3+:glass, solar-pumped, high-powr laser systems

The operating characteristics of Nd(3+):glass lasers energized by a solar concentrator were analyzed for the hosts YAG, silicate glass, and phosphate glass. The modeling is based on the slab zigzag laser geometry and assumes that chemical hardening methods for glass are successful in increasing glass hardness by a factor of 4. On this basis, it was found that a realistic 1-MW solar-pumped laser might be constructed from phosphate glass 4 sq m in area and 2 mm thick. If YAG were the host medium, a 1-MW solar-pumped laser need only be 0.5 sq m in area and 0.5 cm thick, which is already possible. In addition, Nd(3+) doped glass fibers were found to be excellent solar-pumped laser candidates. The small diameter of fibers eliminates thermal stress problems, and if their diameter is kept small (10 microns), they propagate a Gaussian single mode which can be expanded and transmitted long distances in space. Fiber lasers could then be used for communications in space or could be bundled and the individual beams summed or phase-matched for high-power operation

Archaeological Testing at the Selma Stagecoach Stop and Post Office (41BX1409), Bexar County, Texas

The Center for Archaeological Research (CAR) of The University of Texas at San Antonio contracted with the City of Selma, Texas—under Texas Antiquities Committee Permit No. 2395—for the purpose of conducting limited shovel testing and test excavations at the Selma Stagecoach Stop/Post Office. The building is to be restored to serve as one element of a planned historic park. Shovel testing was conducted in May 2000 on a 8,250 square foot area (766.4 m2) surrounding the stagecoach stop structure. The purpose of the shovel tests was to assess the presence of intact archaeological deposits below the surface. Thirty-nine shovel tests were excavated around the structure. The results of the shovel testing indicated that the elevated areas along the west and south elevations of the structure are relatively undisturbed. Subsequently, in October 2000, test excavations were carried out along the exterior and interior of the structure. Four units were excavated, three outside and one within the structure. These investigations resulted in the recovery of nineteenth- and twentieth-century cultural material and the documentation of architectural features. It is recommended that detailed and comprehensive archival research be conducted to compile historical and perhaps architectural details regarding the stagecoach stop/post office. In addition, it is recommended that archaeological investigations be conducted in the area of the presumed location of the north wall of the structure to pinpoint its location. Finally, it is recommended that archaeological monitoring be conducted as subsurface impacts are carried out away from the structure to identify and document any features and facilities that may have been associated with the stagecoach stop but may have been situated outside of the fenced area immediately near the structure

Periodic Quantum Tunneling and Parametric Resonance with Cigar-Shaped Bose-Einstein Condensates

We study the tunneling properties of a cigar-shaped Bose-Einstein condensate by using an effective 1D nonpolynomial nonlinear Schr\"odinger equation (NPSE). First we investigate a mechanism to generate periodic pulses of coherent matter by means of a Bose condensate confined in a potential well with an oscillating height of the energy barrier. We show that is possible to control the periodic emission of matter waves and the tunneling fraction of the Bose condensate. We find that the number of emitted particles strongly increases if the period of oscillation of the height of the energy barrier is in parametric resonance with the period of oscillation of the center of mass of the condensate inside the potential well. Then we use NPSE to analyze the periodic tunneling of a Bose-Einstein condensate in a double-well potential which has an oscillating energy barrier. We show that the dynamics of the Bose condensate critically depends on the frequency of the oscillating energy barrier. The macroscopic quantum self-trapping (MQST) of the condensate can be suppressed under the condition of parametric resonance between the frequency of the energy barrier and the frequency of oscillation through the barrier of the very small fraction of particles which remain untrapped during MQST.Comment: latex, 23 pages, 10 figures, to be published in J. Phys. B (Atom. Mol.), related papers can be found at http://www.mi.infm.it/salasnich/tdqg.htm

Two Stages in the evolution of binary alkali Bose-Einstein condensate mixtures towards phase segregation

Two stages of quantum spinodal decomposition is proposed and analyzed for this highly non-equilibrium process. Both time and spatial scales for the process are found. Qualitative agreement with existing data is found. Some cases the agreements are quantitative. Further experimental verifications are indicated.Comment: late

Compact x-ray source based on burst-mode inverse Compton scattering at 100 kHz

A design for a compact x-ray light source (CXLS) with flux and brilliance orders of magnitude beyond existing laboratory scale sources is presented. The source is based on inverse Compton scattering of a high brightness electron bunch on a picosecond laser pulse. The accelerator is a novel high-efficiency standing-wave linac and RF photoinjector powered by a single ultrastable RF transmitter at x-band RF frequency. The high efficiency permits operation at repetition rates up to 1 kHz, which is further boosted to 100 kHz by operating with trains of 100 bunches of 100 pC charge, each separated by 5 ns. The entire accelerator is approximately 1 meter long and produces hard x-rays tunable over a wide range of photon energies. The colliding laser is a Yb:YAG solid-state amplifier producing 1030 nm, 100 mJ pulses at the same 1 kHz repetition rate as the accelerator. The laser pulse is frequency-doubled and stored for many passes in a ringdown cavity to match the linac pulse structure. At a photon energy of 12.4 keV, the predicted x-ray flux is $5 \times 10^{11}$ photons/second in a 5% bandwidth and the brilliance is $2 \times 10^{12}\mathrm{photons/(sec\ mm^2\ mrad^2\ 0.1\%)}$ in pulses with RMS pulse length of 490 fs. The nominal electron beam parameters are 18 MeV kinetic energy, 10 microamp average current, 0.5 microsecond macropulse length, resulting in average electron beam power of 180 W. Optimization of the x-ray output is presented along with design of the accelerator, laser, and x-ray optic components that are specific to the particular characteristics of the Compton scattered x-ray pulses.Comment: 25 pages, 24 figures, 54 reference

Reducing vortex density in superconductors using the ratchet effect

A serious obstacle that impedes the application of low and high temperature superconductor (SC) devices is the presence of trapped flux. Flux lines or vortices are induced by fields as small as the Earth's magnetic field. Once present, vortices dissipate energy and generate internal noise, limiting the operation of numerous superconducting devices. Methods used to overcome this difficulty include the pinning of vortices by the incorporation of impurities and defects, the construction of flux dams, slots and holes and magnetic shields which block the penetration of new flux lines in the bulk of the SC or reduce the magnetic field in the immediate vicinity of the superconducting device. Naturally, the most desirable would be to remove the vortices from the bulk of the SC. There is no known phenomenon, however, that could form the basis for such a process. Here we show that the application of an ac current to a SC that is patterned with an asymmetric pinning potential can induce vortex motion whose direction is determined only by the asymmetry of the pattern. The mechanism responsible for this phenomenon is the so called ratchet effect, and its working principle applies to both low and high temperature SCs. As a first step here we demonstrate that with an appropriate choice of the pinning potential the ratchet effect can be used to remove vortices from low temperature SCs in the parameter range required for various applications.Comment: 7 pages, 4 figures, Nature (in press

Toward high brightness, multi-kilowatt solid state lasers

High average power (HAP) solid state laser output with improved beam quality has introduced new capabilities in materials processing. At the 500 W level and with a beam quality of a few'' times the diffraction limit, the General Electric NY slab is able to drill 5 cm of stainless steel in a few seconds. We expect that 2--3 kW of near infrared laser output in a low order spatial mode would enable metal working now unknown to industry. The HAP output of slab lasers is limited by the size of the available laser crystals and the pump power. Core free, six cm diameter NY boules have been grown on an experimental basis. High optical quality NG can be obtained up to 10 cm in diameter. We present the results of our modeling based on these crystals pumped by advanced arc-lamps or laser diode arrays. We project HAP laser outputs of 1.6 kW from an existing Vortek pumped NG oscillator and about 2 kW from diode pumped NY device. Several kW of laser output can be expected from two such slabs in a MOPA configuration before optical damage limits are reached. The three dimensional stress-optic code which we used to optimize our designs, was normalized to available experimental data obtained with the above NG slab at the 500 W level and a 40 W diode pumped NY test bed. Our calculations indicate the essential parameters for attainment of high beam quality. Cooling uniformity across the pumped faces of the slab is critical and the location of the transition between pumped and un-pumped regions towards the slab tips is very important. A flat pumping profile was found to be desirable and predicted one wave of distortion which should be correctable over about 75% of the aperture however, an even better wavefront was predicted over 90% of the aperture when the regions near the edges of the slab were slightly over-pumped relative to the central regions and the regions near to the ends were tapered to compensate for transition effects