Template-Assisted Direct Growth of 1 Td/in(2) Bit Patterned Media.

We present a method for growing bit patterned magnetic recording media using directed growth of sputtered granular perpendicular magnetic recording media. The grain nucleation is templated using an epitaxial seed layer, which contains Pt pillars separated by amorphous metal oxide. The scheme enables the creation of both templated data and servo regions suitable for high density hard disk drive operation. We illustrate the importance of using a process that is both topographically and chemically driven to achieve high quality media.

Numerical study of multi-conjugate large area wavefront correction for deep tissue microscopy.

Wavefront distortion fundamentally limits the achievable imaging depth and quality in thick tissue. Wavefront correction can help restore the diffraction limited focus albeit with a small field of view (FOV), which limits its imaging applications. In this work, we numerically investigate whether the multi-conjugate configuration, originally developed for astronomical adaptive optics, may increase the correction FOV in random turbid media. The results show that the multi-conjugate configuration can significantly improve the correction area compared to the widely adopted pupil plane correction. Even in the simple case of single-conjugation, it still outperforms the pupil plane correction. This study provides a guideline for designing the optimal wavefront correction system in deep tissue imaging.

Postpartum cultural practices are negatively associated with depressive symptoms among Chinese and Vietnamese immigrant mothers married to Taiwanese men.

The objectives of researchers in this study were to examine acceptance and adherence to mainstream Taiwanese postpartum cultural practices and their association with postpartum depressive symptoms among Chinese and Vietnamese immigrant mothers married to Taiwanese men. While the postpartum cultural practices in China are similar to mainstream Taiwanese practices, those of Vietnam differ from Taiwanese practices. This cross-sectional survey was conducted in Taiwan from October 2007 through March 2008, and included190 immigrant mothers from China and Vietnam who had delivered a child within the past year. Immigrant mothers from China had higher levels of acceptance and adherence to mainstream Taiwanese postpartum cultural practices and a lower rate of postpartum depressive symptoms than immigrant mothers from Vietnam, but the association between adherence to "doing-the-month" practices and postpartum depressive symptoms did not vary significantly between Chinese and Vietnamese mothers. Adherence to these practices was negatively associated with postpartum depressive symptoms among immigrant mothers (OR = 0.93, 95% CI: 0.90-0.96) after adjustment for social support, duration between moving to Taiwan and delivery, and country of origin. Adherence to mainstream postpartum cultural practices was negatively associated with postpartum depressive symptoms for both Chinese and Vietnamese immigrant women married to Taiwanese men.

Phase resolved interferometric spectral modulation (PRISM) for ultrafast pulse measurement and compression.

We show through experiments and simulations that parallel phase modulation, a technique developed in the field of adaptive optics, can be employed to quickly determine the spectral phase profile of ultrafast laser pulses and to perform phase compensation as well as pulse shaping. Different from many existing ultrafast pulse measurement methods, the technique reported here requires no spectrum measurements of nonlinear signals. Instead, the power of nonlinear signals is used directly to quickly measure the spectral phase, a convenient feature for applications such as two-photon fluorescence microscopy. The method is found to work with both smooth and even completely random distortions. The experimental results are verified with MIIPS measurements.

Dynamical, bidirectional model for coherent beam combining in passive fiber laser arrays.

We generalize the recently proposed model for coherent beam combining in passive fiber laser arrays [Opt. Express 17, 19509 (2009)] to include the transient gain dynamics and the complication of counterpropagating waves, two important features characterizing actual experimental conditions. The extended model reveals that beam combining is not affected by the population relaxation process or the presence of backward propagating waves, which only serve to co-saturate the gain. The presence of nonresonant nonlinearity is found to reduce the coherent combining efficiency at high power levels. We show that the array lases at the frequencies with minimum overall losses when multiple loss mechanisms are present.

Array size scalability of passively coherently phased fiber laser arrays.

We explore, by means of experiments and simulation, the power combining efficiency and power fluctuation of coherently phased 2, 4, 6, 8, 10, 12, 14, 16-channel fiber-laser arrays using fused 50:50 single-mode couplers. The measured evolution of power combining efficiency with array size agrees with simulations based on a new propagation model. For our particular system the power fluctuations due to small wavelength-scale length variations are seen to scale with array size as N(3). Beat spectra support the notion that a lack of coherently-combined supermodes in arrays of increasing size leads to a decrease in combined-power efficiency.

Model for passive coherent beam combining in fiber laser arrays.

We present a new model for studying the beam combining mechanism, spectral and temporal dynamics, the role of nonlinearity, and the power scaling issue of discretely coupled fiber laser arrays. The model accounts for the multiple longitudinal modes of individual fiber lasers and shows directly the formation of the composite-cavity modes. Detailed output power spectra and their evolution with increasing array size and pump power are also explored for the first time. In addition, it is, to our knowledge, the only model that closely resembles the real experimental conditions in which no deliberate control of the fiber lengths (mismatch) is required while highly efficient coherent beam combining is still attained.

Bend performance of leakage channel fibers.

Bend loss of the first three modes of leakage channel fibers with various designs are studied using finite element method. It is found that very low bend loss at small bend radius can be achieved with large d/Delta. It is also found that best differential mode loss is achieved at large bend radius. It is further found that 2nd order mode loss becomes 9.1 times of fundamental mode loss at small bend radius for the bend orientation where the bending plane crosses centers of two holes and independent of d/Delta. Bend loss dependence of bend orientations are also studied. Excellent agreement between experiment and simulation is obtained.