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The problem of phase reconstruction from intensity is considered in the paraxial geometrical optics regime. The data consist of intensity measurements on two planes orthogonal to the direction of propagation. A new variational principle is used to find the ray mapping between the planes. The mapping is found by minimizing an appropriate function. The minimization process involves a nonlinear partial differential equation. A numerical algorithm for solving this equation is described. The phase is then integrated from the ray mapping. Finally, the method and code are examined by applying them to simulated data.

This article examines the current state of the national security debate in South Korea in the context of rapid democratization, a growing desire on the part of South Korea to pursue a more balanced and independent foreign policy posture even as it retains its core alliance with the United States, and the confluence of political and strategic forces that have combined to create unprecedented change in South Korea's security perceptions. While the missile defense issue continues to remain as a relatively minor facet of South Korea's overall national security debate, it illustrates the extent to which South Korean views have shifted since the end of the Cold War but particularly since the advent of the Kim Dae Jung government (1998–2003) and continuing well into the administration of Roh Moo Hyun. Specifically, the article traces the changing contours of South Korea's national security paradigm, Seoul's “New Thinking” on key foreign policy and national security issues, the missile threat and missile defense,...

In sharp contrast to land-dominant forces with only limited technological capabilities, key armed forces such as the PRC's People's Liberation Army (PLA), Japan's Self Defense Forces (SDF), and the South and North Korean militaries have built up significant power projection capabilities since the 1980s. North Korea's weapons of mass destruction (WMD) programs and assets (including a potential nuclear weapons capability) have surfaced as key security concerns since the early 1990s and for its part, China has begun to implement its own revolution in military affairs (RMA) strategies that may enable the PRC to have very robust power projection capabilities by 2020 or 2030. If one includes Indian and Pakistani nuclear weapons programs into the broader strategic equation, Asia may well face an increasingly volatile arms race over the next 20–30 years. Seen within this context, the role of air power is likely to assume growing importance in East Asia's projected force modernization programs, given the ...

The future of European and Asian security can no longer be separated owing to pervasive globalization, the rise of East Asia as a new geopolitical hub, and the increasing web of interests that binds the United States, the European Union (EU), and East Asia together. Of the three key relationships‐the transatlantic, the transpacific, and the Eurasian‐the latter remains the weakest owing to a combination of historical, political, and economic reasons. Improving this relationship from the strategic, economic, and conceptual dimensions will bring significant dividends to the two regions. Operationalizing this challenge, however, is going to be cumbersome and time consuming given the historical lack of strategic interaction between East Asia and Europe.

An iterative phase-shifting algorithm based on the least-squares principle is developed to overcome the random piston and tilt wavefront errors generated from the phase shifter. The algorithm iteratively calculates the phase distribution and the phase-shifting map to minimize the sum of squared errors in the interferograms. The performance of the algorithm is evaluated via computer simulations and validated by the Fizeau interferometer measurements. The results show that the proposed algorithm has a fast convergence rate and satisfactory phase-estimation accuracy, improving the measurement precision of the phase-shifting interferometers with significant phase-shifter errors.

A subaperture stitching algorithm was developed for testing aspheric surfaces. The full aperture was divided into one central circular region plus several partially-overlapping annuli. Each annulus was composed of partially-overlapping circular subapertures. The phase map in each subaperture was obtained through the phase-shifting interferometry and retrieved by an iterative tilt-immune phase-shifting algorithm and a Zernike-polynomial-based phase-unwrapping process. All subapertures in one annulus were stitched simultaneously in least-squares sense. By eliminating the relative piston and tilt between adjacent subapertures, the sum of squared errors in the overlapped regions was minimized. The phase stitching between annuli also utilized the least-squares method in the overlapped region. Simulation results on a test wavefront with 30-wave spherical aberrations demonstrated the effectiveness of the proposed algorithm. The rms phase residue after the phase-shifting, phase-unwrapping and phase-stitching processes was 0.006 waves, which met the precision requirement of common interferometers. This algorithm should be applicable to general surfaces in subaperture stitching interferometry.

An iterative least-squares-based phase-shifting algorithm was developed to cope with random pistons and tilts from the phase shifter. The allowable tilt amount was 0.5 waves over the pupil. The achieved rms accuracy was 0.0024 radians.

We studied the in-and the out-coupling efficiencies of photons with a thin InGaAs slab covered by periodic gold nano-slit arrays, by measuring transmission and photoluminescence (PL) spectra. While the maximum in-coupled photons into the InGaAs slab waveguide were found at dip positions in transmission spectra, the mostly out-coupled photons were observed as peaks in PL spectra. For different periods of slit arrays and incident angles we discussed spectral positions of transmission dips and efficiency of the in-coupling influenced by the absorption coefficient of InGaAs. In PL spectra we measured overall enhanced PL intensities from the InGaAs slab covered by slit arrays compared to that of a bare InGaAs, where the peak positions are determined by the period of slit arrays as well. Our findings are important for designing semiconductors both as an optically passive waveguide and active light emitter. (C) 2012 Optical Society of America

Purpose : To evaluate the geometry of carotid artery by assessing the images of contrast-enhanced MR angiography (CE-MRA) and interrelationships between the geometry of carotid artery and clinical factors. Materials and Methods : 216 consecutive patients who performed supraaortic CE-MRA with fast spoiled gradient-echo imaging were included. Their medical records were reviewed for variable information including risk factors predictive of generalized atherosclerotic disease (age, hypertension (HTN), diabetes mellitus, hyperlipidema, and smoking), sex, body weight, height, and body mass index (BMI). We reviewed the CE-MRA with carotid origin (3 types), carotid artery tortuosity, angle of internal carotid artery bifurcation, the type of aortic arch branching, and the presence of the coiling of carotid artery. Results : Multinomial logistic regression analysis showed that significantly contributed clinical backgrounds for carotid origin were the age and the BMI. With an increase of age at 1, the probability that the type of carotid origin become from type 1 to type 2 was 0.9 times (p=0.004) in right carotid artery (RCA), 0.9 times (p = 0.031) in left carotid artery (LCA), 0.9 times that are likely to be type3 from type 2 (pand , respectively. Conclusion : The BMI, age, sex and presence of HTN affects the geometry of carotid arteries, the site of origin and tortuosity of carotid artery specifically.