The Vector Vortex Coronagraph: Laboratory Results and First Light at Palomar Observatory

High-contrast coronagraphy will be needed to image and characterize faint extra-solar planetary systems. Coronagraphy is a rapidly evolving field, and many enhanced alternatives to the classical Lyot coronagraph have been proposed in the past ten years. Here, we discuss the operation of the vector vortex coronagraph, which is one of the most efficient possible coronagraphs. We first present recent laboratory results, and then first light observations at the Palomar observatory. Our near-infrared H-band (centered at ~ 1.65 microns) and K-band (centered at ~ 2.2 microns) vector vortex devices demonstrated excellent contrast results in the lab, down to ~ 1e-6 at an angular separation of 3 lb/d. On sky, we detected a brown dwarf companion 3000 times fainter than its host star (HR 7672) in the Ks band (centered at ~2.15 microns), at an angular separation of ~ 2.5 lb/d. Current and next-generation high-contrast instruments can directly benefit from the demonstrated capabilities of such a vector vortex: simplicity, small inner working angle, high optical throughput (>90%), and maximal off-axis discovery space

Optical Vectorial Vortex Coronagraphs using Liquid Crystal Polymers: theory, manufacturing and laboratory demonstration

In this paper, after briefly reviewing the theory of vectorial vortices, we describe our technological approach to generating the necessary phase helix, and report results obtained with the first optical vectorial vortex coronagraph (OVVC) in the laboratory. To implement the geometrical phase ramp, we make use of Liquid Crystal Polymers (LCP), which we believe to be the most efficient technological path to quickly synthesize optical vectorial vortices of virtually any topological charge. With the first prototype device of topological charge 2, a maximum peak-to-peak attenuation of 1.4×10^(-2) and a residual light level of 3×10^(-5) at an angular separation of 3.5 λ/d (at which point our current noise floor is reached) have been obtained at a wavelength of 1.55 μm. These results demonstrate the validity of using space-variant birefringence distributions to generate a new family of coronagraphs usable in natural unpolarized light, opening a path to high performance coronagraphs that are achromatic and have low-sensitivity to low-order wavefront aberrations

Inter-State, Intra-State, and Extra-State Wars: A Comprehensive Look at Their Distribution over Time, 1816–1997

Students of world politics disagree about the approaching outlook for war. Are we in the midst of an era of peace with a declining prospect of war, or are we facing a future characterized by increasing “ethnic” conflicts? This puzzle has led scholars to call for a more comprehensive examination of the phenomenon of war. A discussion concerning this need for a new look at war had also arisen within the Correlates of War Project. For more than three decades the Correlates of War Project's database has served the research needs of most of the quantitative world politics community, especially in identifying and trying to account for several classes of war (inter-state, extra-systemic, and civil) throughout the international system since 1816. However, a number of the disagreements in the literature concerning the prospects of war derive from the tendency of many researchers to rely on only one of our data sets (e.g., inter-state war). Here we wish to stimulate a broader view of war by examining the interplay among the three major types of war. Historical developments of the past half-century, and especially since the end of the Cold War, have rendered the original COW war typology increasingly incomplete. Consequently, we developed a modified typology of war and attempted to format the descriptive variables in ways that would facilitate a more comparative and comprehensive analysis of warfare. While the reader should be reassured that Inter-state Wars remain as previously defined, we introduce the term “Intra-state War” in place of our original Civil War category, and the term “Extra-state War” in place of our initial Extra-systemic War category, allowing us to reclassify several such wars. This revised typology coupled with an update of the data allows us to take a fresh look at the question whether, from the perspective of the past two centuries, war is in fact becoming less common. The article concludes with a series of analyses that describe the patterns and trends of all types of war––reflecting the new typology––since the Congress of Vienna. These analyses reflect a disquieting constancy in warfare and hint at patterns of interchangeability or substitutability among the types of war.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/71639/1/1468-2478.4701003.pd