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We describe the Dragonfly Telephoto Array, a robotic imaging system optimized for the detection of extended ultra-low surface brightness structures. The array consists of eight Canon 400 mm f/2.8 L IS II USM telephoto lenses coupled to eight science-grade commercial CCD cameras. The lenses are mounted on a common framework and are coaligned to simultaneously image the same position on the sky. The system provides an imaging capability equivalent to a 0.4 m aperture f/1.0 refractor with a 2.6° × 1.9° field of view. The system is driven by custom software for instrument control and robotic operation. Data is collected with noncommon optical paths through each lens, and with careful tracking of sky variations in order to minimize systematic errors that limit the accuracy of background estimation and flat-fielding. The system has no obstructions in the light path, optimized baffling, and internal optical surfaces coated with a new generation of antireflection coatings based on subwavelength nanostructures. As a result, the array's point-spread function has a factor of ∼10 less scattered light at large radii than well-baffled reflecting telescopes. The Dragonfly Telephoto Array is capable of imaging extended structures to surface brightness levels below μB = 30 mag arcsec-2 in ∼10 h integrations (without binning or foreground star removal). This is considerably deeper than the surface brightness limit of any existing wide-field telescope. At present, no systematic errors limiting the usefulness of much longer integration times have been identified. With longer integrations (50-100 h), foreground star removal, and modest binning, the Dragonfly Telephoto Array is capable of probing structures with surface brightnesses below μB = 32 mag arcsec-2. The detection of structures at these surface brightness levels may hold the key to solving the \"missing substructure\" and \"missing satellite\" problems of conventional hierarchical galaxy formation models. The Dragonfly Telephoto Array is therefore executing a fully automated multiyear imaging survey of a complete sample of nearby galaxies in order to undertake the first census of ultrafaint substructures in the nearby universe.

Gradient metasurfaces are two-dimensional optical elements capable of manipulating light by imparting local, space-variant phase changes on an incident electromagnetic wave. These surfaces have thus far been constructed from nanometallic optical antennas, and high diffraction efficiencies have been limited to operation in reflection mode. We describe the experimental realization and operation of dielectric gradient metasurface optical elements capable of also achieving high efficiencies in transmission mode in the visible spectrum. Ultrathin gratings, lenses, and axicons have been realized by patterning a 100-nanometer-thick Si layer into a dense arrangement of Si nanobeam antennas. The use of semiconductors can broaden the general applicability of gradient metasurfaces, as they offer facile integration with electronics and can be realized by mature semiconductor fabrication technologies.

Gravitational lensing is a powerful astrophysical and cosmological probe and is particularly valuable at submillimeter wavelengths for the study of the statistical and individual properties of dusty star-forming galaxies. However, the identification of gravitational lenses is often time-intensive, involving the sifting of large volumes of imaging or spectroscopic data to find few candidates. We used early data from the Herschel Astrophysical Terahertz Large Area Survey to demonstrate that wide-area submillimeter surveys can simply and easily detect strong gravitational lensing events, with close to 100% efficiency.

A plasmonic antenna array is used to control the propagation of a light beam across an interface. The precise manipulation of a propagating wave using phase control is a fundamental building block of optical systems. The wavefront of a light beam propagating across an interface can be modified arbitrarily by introducing abrupt phase changes. We experimentally demonstrated unparalleled wavefront control in a broadband optical wavelength range from 1.0 to 1.9 micrometers. This is accomplished by using an extremely thin plasmonic layer (~λ/50) consisting of an optical nanoantenna array that provides subwavelength phase manipulation on light propagating across the interface. Anomalous light-bending phenomena, including negative angles of refraction and reflection, are observed in the operational wavelength range.

Cataract is a visible opacity in the lens substance, which, when located on the visual axis, leads to visual loss. Age-related cataract is a cause of blindness on a global scale involving genetic and environmental influences. With ageing, lens proteins undergo non-enzymatic, post-translational modification and the accumulation of fluorescent chromophores, increasing susceptibility to oxidation and cross-linking and increased light-scatter. Because the human lens grows throughout life, the lens core is exposed for a longer period to such influences and the risk of oxidative damage increases in the fourth decade when a barrier to the transport of glutathione forms around the lens nucleus. Consequently, as the lens ages, its transparency falls and the nucleus becomes more rigid, resisting the change in shape necessary for accommodation. This is the basis of presbyopia. In some individuals, the steady accumulation of chromophores and complex, insoluble crystallin aggregates in the lens nucleus leads to the formation of a brown nuclear cataract. The process is homogeneous and the affected lens fibres retain their gross morphology. Cortical opacities are due to changes in membrane permeability and enzyme function and shear-stress damage to lens fibres with continued accommodative effort. Unlike nuclear cataract, progression is intermittent, stepwise and non-uniform.

We demonstrate a magnifying superlens that can be integrated into a conventional far-field optical microscope. Our design is based on a multilayer photonic metamaterial consisting of alternating layers of positive and negative refractive index, as originally proposed by Narimanov and Engheta. We achieved a resolution on the order of 70 nanometers. The use of such a magnifying superlens should find numerous applications in imaging.

Imaging systems that exploit arrays of photodetectors in curvilinear layouts are attractive due to their ability to match the strongly nonplanar image surfaces (i.e., Petzval surfaces) that form with simple lenses, thereby creating new design options. Recent work has yielded significant progress in the realization of such \"eyeball\" cameras, including examples of fully functional silicon devices capable of collecting realistic images. Although these systems provide advantages compared to those with conventional, planar designs, their fixed detector curvature renders them incompatible with changes in the Petzval surface that accompany variable zoom achieved with simple lenses. This paper describes a class of digital imaging device that overcomes this limitation, through the use of photodetector arrays on thin elastomeric membranes, capable of reversible deformation into hemispherical shapes with radii of curvature that can be adjusted dynamically, via hydraulics. Combining this type of detector with a similarly tunable, fluidic plano-convex lens yields a hemispherical camera with variable zoom and excellent imaging characteristics. Systematic experimental and theoretical studies of the mechanics and optics reveal all underlying principles of operation. This type of technology could be useful for night-vision surveillance, endoscopic imaging, and other areas that require compact cameras with simple zoom optics and wide-angle fields of view.

We describe the design, manufacture, commissioning, and performance of PMAS, the Potsdam Multi‐Aperture Spectrophotometer. PMAS is a dedicated integral field spectrophotometer optimized to cover the optical wavelength regime of 0.35–1 μm. It is based on the lens array–fiber bundle principle of operation. The instrument employs an all‐refractive fiber spectrograph, built with CaF2optics, to provide good transmission and high image quality over the entire nominal wavelength range. A set of user‐selectable reflective gratings provides low to medium spectral resolution of approximately 1.5, 3.2, and 7 Å in first order, depending on the groove density (1200, 600, 300 grooves mm−1). 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Other special features include a cryogenic CCD camera for field acquisition and guiding, a nod‐shuffle mode for beam switching and improved sky background subtraction, and a scanning Fabry‐Pérot etalon in combination with the standard IFU (PYTHEAS mode). PMAS was initially designed and built as an experimental traveling instrument with optical interfaces to various telescopes (Calar Alto 3.5 m, ESO VLT, LBT). It is offered as a common‐user instrument at Calar Alto under contract to MPIA Heidelberg since 2002.

In 1873, Ernst Abbe discovered what was to become a well-known paradigm: the inability of a lens-based optical microscope to discern details that are closer together than half of the wavelength of light. However, for its most popular imaging mode, fluorescence microscopy, the diffraction barrier is crumbling. Here, I discuss the physical concepts that have pushed fluorescence microscopy to the nanoscale, once the prerogative of electron and scanning probe microscopes. Initial applications indicate that emergent far-field optical nanoscopy will have a strong impact in the life sciences and in other areas benefiting from nanoscale visualization.

The synergy of complex materials and complex light is expected to add a new dimension to the science of light and its applications. Metamaterials and singular optics are two fascinating branches of modern optics that until recently were rapidly developing in parallel yet independently. The former considers “simple” linearly or circularly polarized light or Gaussian beam propagation in “complex” materials with properties not found in nature. However, light can be a more complex phenomenon; in addition to conventional polarization states (spin), light beams can be radially or azimuthally polarized and carry orbital angular momentum (OAM). Structured light beams, containing phase or polarization singularities, enable properties and applications such as diffraction-free and self-healing propagation, single-molecule spectroscopy, nanoscale focusing, and even particle acceleration. A fascinating example of a beam carrying OAM is the optical vortex—a donut-shaped beam with a helical phase front (see the figure, panel A) ( 1 – 3 ).