Laser cooling by over 7†K in Yb-doped ZBLAN fibers with high-power pumping at atmospheric pressure.

Anti-Stokes fluorescence (ASF) cooling has been demonstrated to be a viable method for balancing the waste heat produced in gain materials. In addition, radiation-balanced fiber lasers and amplifiers at atmospheric pressure have recently been developed. Here, we evaluate the cooling characteristics in a long section of a Yb-doped ZBLAN fiber with high pump power. The fiber has a 200-µm-diameter core and is doped with 3 wt. % Yb3+. As indicated by a thermal camera, cooling by over 7 K below ambient temperature was achieved by core pumping at 1030 nm. The temperature drop distribution at multiple measurement points in the fiber was evaluated with a maximum pump power of tens of watts. The results demonstrate the excellent ASF cooling performance of Yb-doped ZBLAN fibers. This study has great significance for the development of high-power radiation-balanced fiber lasers.

Fast time-evolving random polarization beam smoothing for laser-driven inertial confinement fusion.

We propose a random polarization smoothing method for low-coherence laser to obtain focal spot with random polarization that evolves rapidly in sub-picosecond timescales. Random polarization smoothing is realized by a half-aperture wave plate with sufficient thickness. The degree of polarization and polarization evolution of the focal spot are studied theoretically. The calculation results show that random polarization smoothing can make the polarization of focal spot evolve rapidly and randomly in time and space. Experimentally, the polarization of the focal spot of low-coherence laser with random polarization smoothing is measured by a single-shot polarimeter. The measurement results show that the degree of polarization of the focal spot is reduced to 0.22 on average, which proves the effectiveness of random polarization smoothing. The random polarization smoothing technique on low-coherence laser is expected to reduce the laser plasmas instability through its multi-dimensional random evolution properties.

Full-aperture random polarization smoothing for a low-coherence laser facility.

Two new random polarization smoothing methods using full-aperture elements are proposed on low-coherence lasers, one using birefringent wedge and one using flat birefringent plate. By designing the crystal axis direction and wedge angle of the birefringent plates, the methods can selectively introduce time delay and spatial displacement, so as to obtain fast random evolution of transient polarization by utilizing low spatiotemporal coherence of the laser focal field. Both methods avoid the near field discontinuity and can be used under high fluence. The method using birefringent wedge can slightly improve focal spot uniformity, and the method using flat birefringent plate can obtain non-polarization with DOP lower than 2%. Theoretical studies show that the resulting focal polarization evolves rapidly on sub-picosecond timescales and rapidly covers the entire Poincaré sphere. The method using birefringent wedge is achieved in experiment. The results show that the degree of polarization of the focal spot is reduced from 1 to 0.27, which proves the effectiveness of the full-aperture random polarization smoothing. The full-aperture random polarization smoothing can generate a focal field very close to unpolarized thermal light, which is expected to suppress the laser plasmas instability.

Scanning high-power continuous wave laser-generated bulk acoustic waves.

The ultrasonic bulk waves generated by a high-power continuous laser scanning along the surface of aluminum material were theoretically investigated. Although the temperature rise generated by this scanning laser irradiation was small, it provided a large temperature gradient, which was able to generate measurable ultrasonic waves. Detailed discussions were given to the influence of scanning speed on the generation propagation direction and the amplitude of the wavefront. The longitudinal and transverse waves would be generated in the material only when the scanning speeds reached a certain range. What's more, the amplitude of the wavefronts were significantly enhanced if the wavefront angle controlled by the scanning speed matched with the propagation direction of the ultrasound. In summary, it expounded a method to obtain the ultrasonic signal of direction, controlled from the perspective of numerical simulation, as long as the scanning speed met the requirements.

Imaging gigahertz zero-group-velocity Lamb waves.

Zero-group-velocity (ZGV) waves have the peculiarity of being stationary, and thus locally confining energy. Although they are particularly useful in evaluation applications, they have not yet been tracked in two dimensions. Here we image gigahertz zero-group-velocity Lamb waves in the time domain by means of an ultrafast optical technique, revealing their stationary nature and their acoustic energy localization. The acoustic field is imaged to micron resolution on a nanoscale bilayer consisting of a silicon-nitride plate coated with a titanium film. Temporal and spatiotemporal Fourier transforms combined with a technique involving the intensity modulation of the optical pump and probe beams gives access to arbitrary acoustic frequencies, allowing ZGV modes to be isolated. The dispersion curves of the bilayer system are extracted together with the quality factor Q and lifetime of the first ZGV mode. Applications include the testing of bonded nanostructures.

Diagnostic Value of Urine Cytology in Bladder Cancer. A Meta-Analysis.

OBJECTIVE: To evaluate the diagnostic value of urine cytology in detecting bladder cancer using meta-analysis. STUDY DESIGN: Public databases, including PubMed, Embase, Springer, Elsevier Science Direct, Cochrane Library, and Google Scholar, were searched before February 2015. Sensitivity, specificity, positive likelihood ratio (LR), negative LR, and diagnostic odds ratio (DOR) of urine cytology in individual studies were calculated using random effects model or fixed effect model. The summary receiver operating characteristic (SROC) curve was applied for performance of urine cytology. Publication bias of the included studies was evaluated by Egger's test. RESULTS: A total of 17 separate studies consisting of 5,908 patients with bladder cancer were included in the meta-analysis. Significant heterogeneity between the studies (I2 = 98.6%, p < 0.01) and effect sizes were pooled using random effects model. Overall sensitivity, specificity, positive LR, negative LR, and DOR of urine cytology were 0.37 (95% CI 0.35-0.39), 0.95 (95% CI 0.94-0.95), 7.39 (95% CI 4.97-10.98), 0.56 (95% CI 0.47-0.68), and 15.76 (95% CI 9.03-27.50), respectively. The area under the curve (AUC) and Q* index were 0.80 and 0.74, respectively. No publication bias was observed (p = 0.12). CONCLUSION: Our data indicate that urine cytology might be more suitable as an assistant method in bladder cancer detection by combining with other diagnostic methods with high sensitivity.