Sparsity driven ultrasound imaging

An image formation framework for ultrasound imaging from synthetic transducer arrays based on sparsity-driven regularization functionals using single-frequency Fourier domain data is proposed. The framework involves the use of a physics-based forward model of the ultrasound observation process, the formulation of image formation as the solution of an associated optimization problem, and the solution of that problem through efficient numerical algorithms. The sparsity-driven, model-based approach estimates a complex-valued reflectivity field and preserves physical features in the scene while suppressing spurious artifacts. It also provides robust reconstructions in the case of sparse and reduced observation apertures. The effectiveness of the proposed imaging strategy is demonstrated using experimental data

Single-frequency master-oscillator photonic crystal fiber amplifier with 148 W output power

We report on a high-power ytterbium doped photonic crystal fiber amplifier using a single-frequency Nd:YAG non-planar ring oscillator seed source. With a large-mode-area photonic crystal fiber, operation below the threshold of stimulated Brillouin scattering is demonstrated with up to 148 W of continuous-wave output power and a slope efficiency of 75%. At maximum output power the amplified spontaneous emission was suppressed by more than 40 dB and the polarization extinction ratio was better than 22 dB. In order to investigate the overlap of the photonic crystal fiber transverse-mode with a Gaussian fundamental mode, sensitive beam quality measurements with a Fabry-Perot ring-cavity are presented

Stabilized High Power Laser for Advanced Gravitational Wave Detectors

Second generation gravitational wave detectors require high power lasers with several 100W of output power and with very low temporal and spatial fluctuations. In this paper we discuss possible setups to achieve high laser power and describe a 200W prestabilized laser system (PSL). The PSL noise requirements for advanced gravitational wave detectors will be discussed in general and the stabilization scheme proposed for the Advanced LIGO PSL will be described. Special emphasis will be given to the most demanding power stabilization requiremets and new results (RIN ≤ 4×10-9/surdHz) will be presented

Determination of the laser-induced damage threshold of polymer optical fibers

Investigating the properties of manufactured polymer optical fibers is essential to determine proper areas of application. Using pulsed laser radiation, especially with respect to laser activity in optical fibers, the maximum acceptable transmittable energy without inducing damage is of particular interest. Therefore, this work is related to laser-induced damage in polymer optical fibers at a wavelength of 532 nm and a pulse duration of 7.3 ns. In particular, the influence of the coupling condition on the transmittable pulse energy and the damage behavior applying an R-on-1 test procedure are analyzed in this study. The obtained results give information about the long-Term behavior and will be used to optimize the manufacturing process. © COPYRIGHT SPI