University of Kiel

About: University of Kiel is a education organization based out in Kiel, Germany. It is known for research contribution in the topics: Population & Transplantation. The organization has 27816 authors who have published 57114 publications receiving 2061802 citations. The organization is also known as: Christian Albrechts University & Christian-Albrechts-Universität zu Kiel.

Adaptive subwavelength control of nano-optical fields.

Abstract: The size of mechanical tools limits their spatial resolution. In the case of a drill, for instance, its diameter determines the size of the smallest hole that it can make, with 1-mm holes from 10-mm drills an obvious impossibility. But in the world of optics, the 'impossible' can happen. Aeschlimann et al. demonstrate a light-based tool that not only 'drills holes' smaller than its own size (its wavelength), but does so in selectable positions that can be changed at the speed of light. The experiment combines adaptive control with nano-optics, to control interactions between light and matter with sub-wavelength resolution and femtosecond timing. Adaptive shaping of the phase and amplitude of femtosecond laser pulses has been developed into an efficient tool for the directed manipulation of interference phenomena, thus providing coherent control over various quantum-mechanical systems1,2,3,4,5,6,7,8,9,10. Temporal resolution in the femtosecond or even attosecond range has been demonstrated, but spatial resolution is limited by diffraction to approximately half the wavelength of the light field (that is, several hundred nanometres). Theory has indicated11,12 that the spatial limitation to coherent control can be overcome with the illumination of nanostructures: the spatial near-field distribution was shown to depend on the linear chirp of an irradiating laser pulse. An extension of this idea to adaptive control, combining multiparameter pulse shaping with a learning algorithm, demonstrated the generation of user-specified optical near-field distributions in an optimal and flexible fashion13. Shaping of the polarization of the laser pulse14,15 provides a particularly efficient and versatile nano-optical manipulation method16,17. Here we demonstrate the feasibility of this concept experimentally, by tailoring the optical near field in the vicinity of silver nanostructures through adaptive polarization shaping of femtosecond laser pulses14,15 and then probing the lateral field distribution by two-photon photoemission electron microscopy18. In this combination of adaptive control1,2,3,4,5,6,7,8,9,10 and nano-optics19, we achieve subwavelength dynamic localization of electromagnetic intensity on the nanometre scale and thus overcome the spatial restrictions of conventional optics. This experimental realization of theoretical suggestions11,12,13,16,17,20 opens a number of perspectives in coherent control, nano-optics, nonlinear spectroscopy, and other research fields in which optical investigations are carried out with spatial or temporal resolution.

Constraints on the magnitude and patterns of ocean cooling at the Last Glacial Maximum

Abstract: Observation-based reconstructions of sea surface temperature from relatively stable periods in the past, such as the Last Glacial Maximum, represent an important means of constraining climate sensitivity and evaluating model simulations1. The first quantitative global reconstruction of sea surface temperatures during the Last Glacial Maximum was developed by the Climate Long-Range Investigation, Mapping and Prediction (CLIMAP) project in the 1970s and 1980s (refs 2, 3). Since that time, several shortcomings of that earlier effort have become apparent4. Here we present an updated synthesis of sea surface temperatures during the Last Glacial Maximum, rigorously defined as the period between 23 and 19 thousand years before present, from the Multiproxy Approach for the Reconstruction of the Glacial Ocean Surface (MARGO) project5. We integrate microfossil and geochemical reconstructions of surface temperatures and include assessments of the reliability of individual records. Our reconstruction reveals the presence of large longitudinal gradients in sea surface temperature in all of the ocean basins, in contrast to the simulations of the Last Glacial Maximum climate available at present6, 7.