Generalised photon sieves: fine control of complex fields with simple pinhole arrays

Spatial shaping of light beams has led to numerous new applications in fields such as imaging, optical communication, and micromanipulation. However, structured radiation is less well explored beyond visible optics, where methods for shaping fields are more limited. Binary amplitude filters are often used in these regimes and one such example is a photon sieve consisting of an arrangement of pinholes, the positioning of which can tightly focus incident radiation. Here, we describe a method to design generalized photon sieves: arrays of pinholes that generate arbitrary structured complex fields at their foci. We experimentally demonstrate this approach by the production of Airy and Bessel beams, and Laguerre–Gaussian and Hermite–Gaussian modes. We quantify the beam fidelity and photon sieve efficiency, and also demonstrate control over additional unwanted diffraction orders and the incorporation of aberration correction. The fact that these photon sieves are robust and simple to construct will be useful for the shaping of short- or long-wavelength radiation and eases the fabrication challenges set by more intricately patterned binary amplitude masks

Increasing trap stiffness with position clamping in holographic optical tweezers

We present a holographic optical tweezers system capable of position clamping multiple particles. Moving an optical trap in response to the trapped object's motion is a powerful technique for optical control and force measurement. We have now realised this experimentally using a Boulder Nonlinear Systems Spatial Light Modulator (SLM) with a refresh rate of 203Hz. We obtain a reduction of 44% in the variance of the bead's position, corresponding to an increase in effective trap stiffness of 77%. This reduction relies on the generation of holograms at high speed. We present software capable of calculating holograms in under 1ms using a graphics processor unit. © 2009 Optical Society of America

Characterization of high-dimensional entangled systems via mutually unbiased measurements

Mutually unbiased bases (MUBs) play a key role in many protocols in quantum science, such as quantum key distribution. However, defining MUBs for arbitrary high-dimensional systems is theoretically difficult, and measurements in such bases can be hard to implement. We show experimentally that efficient quantum state reconstruction of a high-dimensional multi-partite quantum system can be performed by considering only the MUBs of the individual parts. The state spaces of the individual subsystems are always smaller than the state space of the composite system. Thus, the benefit of this method is that MUBs need to be defined for the small Hilbert spaces of the subsystems rather than for the large space of the overall system. This becomes especially relevant where the definition or measurement of MUBs for the overall system is challenging. We illustrate this approach by implementing measurements for a high-dimensional system consisting of two photons entangled in the orbital angular momentum (OAM) degree of freedom, and we reconstruct the state of this system for dimensions of the individual photons from d=2 to 5.Comment: 8 page

Economic Credit in Renaissance Florence

What were the social and institutional factors that led to, and reinforced, the precocious emergence of Florentine commercial capitalism,3 especially in the domain of international merchant-banking? The dominant stream of answers, emphasized by economic historians and by economists, focuses on the invention in late-medieval and Renaissance Italy of a variety of innovative business techniques – bills of exchange, double-entry bookkeeping, partnership contracts, commercial courts. If these impressive organizational inventions are interpreted as facets of a broader rise of impersonal market rationality, then a tension emerges in Florentine, and indeed in European, historiography between economic historians and the work of social and political historians, who emphasize the deeply personalistic – mainly familial and clientelist – character of social relationships of the period. But were early-capitalist business techniques really the leading edge of a breakthrough of the market from its traditional social shackles, as the master narrative of modernization would have it? Or instead were economic relations in the market embedded in, and hence reflective of, trends in the surrounding social and political networks of the time, as anthropologically and sociologically oriented economic historians like Karl Polanyi4 have argued? Renaissance Florentine businessmen were not only businessmen, after all, they were also fathers, neighbors, politicians, friends and enemies, and patrons of the arts. But what implications, if any, did this overlap in roles have for the organization and operation of economic markets? In this article, we address these historical questions through both statistical and textual analyses of Florentine commercial credit in the early Quattrocento. Our conclusion will be that commercial credits among Florentine companies were indeed highly correlated with a wide range of non-economic, social relationships among the partners of these companies. Correlations between economic and social relations were highest in the merchant-banking pinnacle of the Florentine economy – precisely in the industries where reliance upon advanced capitalist business techniques was greatest. New capitalist business techniques thus did not displace the oligarchic social networks of the time, but rather built upon and formalized these relationships into markets. In particular, family and neighborhood provided strong ‘traditionalist’ foundations to Renaissance Florentine credit markets. But then republicanism, especially in the institutional form of its elected city council, provided the political scaffolding for personalistic social networks (and thus the economic credit networks built upon them) topologically to ‘open out’ toward expansive liquidity and growth, instead of to close inward into cliques and corruption. Three mechanisms for this institutional impact of republicanism on the emergence of credit markets are discussed: public certification of reputation (onore) through co-optative elections, and both performative and network incorporations of carefully filtered newcomers into relatively open elites5 of merchant-politicians

Synthesis of perfluorinated polyethers

A series of highly fluorinated acetylenes was prepared and their cyclization reactions were studied. A series of perfluoropolytriazines with -CF2I pendent groups were prepared. These materials can be cured thermally or photochemically to an elastomeric gum. Perfluoropolytriazines with -CN pendent groups were prepared. These materials can be crosslinked by reaction with terephthalonitrile oxide

Wide-field Infrared Survey Explorer Observations of the Evolution of Massive Star-forming Regions

We present the results of a mid-infrared survey of 11 outer Galaxy massive star-forming regions and 3 open clusters with data from the Wide-field Infrared Survey Explorer (WISE). Using a newly developed photometric scheme to identify young stellar objects and exclude extragalactic contamination, we have studied the distribution of young stars within each region. These data tend to support the hypothesis that latter generations may be triggered by the interaction of winds and radiation from the first burst of massive star formation with the molecular cloud material leftover from that earlier generation of stars. We dub this process the "fireworks hypothesis" since star formation by this mechanism would proceed rapidly and resemble a burst of fireworks. We have also analyzed small cutout WISE images of the structures around the edges of these massive star-forming regions. We observe large (1-3 pc size) pillar and trunk-like structures of diffuse emission nebulosity tracing excited polycyclic aromatic hydrocarbon molecules and small dust grains at the perimeter of the massive star-forming regions. These structures contain small clusters of emerging Class I and Class II sources, but some are forming only a single to a few new stars

Sub-shot-noise shadow sensing with quantum correlations

The quantised nature of the electromagnetic field sets the classical limit to the sensitivity of position measurements. However, techniques based on the properties of quantum states can be exploited to accurately measure the relative displacement of a physical object beyond this classical limit. In this work, we use a simple scheme based on the split-detection of quantum correlations to measure the position of a shadow at the single-photon light level, with a precision that exceeds the shot-noise limit. This result is obtained by analysing the correlated signals of bi-photon pairs, created in parametric downconversion and detected by an electron multiplying CCD (EMCCD) camera employed as a split-detector. By comparing the measured statistics of spatially anticorrelated and uncorrelated photons we were able to observe a significant noise reduction corresponding to an improvement in position sensitivity of up to 17% (0.8dB). Our straightforward approach to sub-shot-noise position measurement is compatible with conventional shadow-sensing techniques based on the split-detection of light-fields, and yields an improvement that scales favourably with the detector’s quantum efficiency

Determining the dimensionality of bipartite orbital-angular-momentum entanglement using multi-sector phase masks

The Shannon dimensionality of orbital-angular-momentum (OAM) entanglement produced in spontaneous parametric down-conversion can be probed by using multi-sector phase analysers [1]. We demonstrate a spatial light modulator-based implementation of these analysers, and use it to measure a Schmidt number of about 50