Structured illumination and image enhancement of three-dimensional and moving objects at a distance via incoherent Fourier ptychography.

We experimentally apply incoherent Fourier ptychography to enhance the resolution of recorded images by projecting known, uncorrelated, random patterns at high speed onto 3D moving and distant objects. We find that the resolution enhancement factor can be greater than 2, depending on the projection and camera optics.

Separation of coherent and incoherent light using image plane vortex phase masks.

We consider the application of a modified optical vortex coronagraph as a transmissometer. We find, through theory and simulation, that the rejection of scattered light benefits from increasing the charge number of the vortex masks in the image plane, and that a combination of a vortex mask and binary pinhole can outperform the pinhole alone.

Spatial-spectral correlations of broadband speckle in around-the-corner imaging conditions.

Correlations of broadband speckle have important implications for passive, non-line-of-sight imaging. We examine the spectral and spatial correlations of broadband, around-the-corner speckle and reveal a set of equations that locate the spatial maximum of the paraxial spatial-spectral correlation function. We confirm the validity of the spatial-spectral correlation framework through experiment, theory and simulation.

Encoding information in the mutual coherence of spatially separated light beams.

Coherence has been used as a resource for optical communications since its earliest days. It is widely used for the multiplexing of data, but not for the encoding of data. Here we introduce a coding scheme, which we call mutual coherence coding, to encode information in the mutual coherence of spatially separated light beams. We describe its implementation and analyze its performance by deriving the relevant figures of merit (signal-to-noise ratio, maximum bit-rate, and spectral efficiency) with respect to the number of transmitted beams. Mutual coherence coding yields a quadratic scaling of the number of transmitted signals with the number of employed light beams, which might have benefits for cryptography and data security.

Imaging around corners in the mid-infrared using speckle correlations.

Speckle correlation imaging offers the ability to see objects through diffusive materials and around corners. Imaging self-illuminating thermal objects in non-line-of-sight scenarios is of particular interest. Here, using bispectrum and phase retrieval methods, we demonstrate speckle correlation imaging of mid-infrared objects through diffusers and around corners at resolutions near the diffraction limit. The images agree well with those recorded by conventional cameras with line-of-sight to the same objects.

Ptychographic imaging of incoherently illuminated extended objects using speckle correlations.

A scattering layer is usually considered an obstacle to imaging. However, using speckle correlation imaging techniques, the scattering layer effectively acts as a lens. To date, the speckle correlation imaging method has been limited to imaging sparse samples. Here, we demonstrate imaging of incoherently illuminated extended objects in transmission and around-the-corner geometries. We are able to image extended objects by constraining the illumination spot on the object and then scanning the object. A ptychography algorithm is used to reconstruct the extended object. This work demonstrates the applicability of ptychography to spatially incoherent light and enables a new method of imaging in spectral regions where there is limited choice in optics, such as the terahertz, extreme ultraviolet, and x-ray regions.

Cancellation of non-conservative scattering forces in optical traps by counter-propagating beams: erratum.

In a previous Letter [Opt. Lett.40, 1900 (2015)OPLEDP0146-959210.1364/OL.40.001900], we asserted that two counter-propagating beams must be polarized with opposite handedness to cancel scattering forces. A more careful calculation shows that this is not the case. The correct condition is achieved by beams with the same handedness, as derived in this Erratum.

Modulation of optical spatial coherence by surface plasmon polaritons.

The interference pattern observed in Young's double-slit experiment is intimately related to the statistical correlations of the waves emitted by the slits. As the waves in the slits become more correlated, the visibility of the interference pattern increases. Here, we experimentally modulate the statistical correlations between the optical fields emitted by a pair of slits in a metal film. The interaction between the slits is mediated by surface plasmon polaritons and can be tuned by the slit separation, which allows us to either increase or decrease the spatial coherence of the emerging fields relative to that of the incoming fields.

Cancellation of non-conservative scattering forces in optical traps by counter-propagating beams.

Non-conservative forces in optical tweezers generate undesirable behavior, such as particle loss due to radiation pressure and the preclusion of the thermodynamic equilibrium. Here, we rigorously derive criteria for the elimination of non-conservative forces, and describe how these criteria can be met by a large class of counter-propagating, focused optical beams.

Measuring coherence functions using non-parallel double slits.

We present an experimental method for the fast measurement of both the spectral (spatial) and complex degrees of coherence of an optical field using only a binary amplitude mask and a detector array. We test the method by measuring a two-dimensional spectral degree of coherence function created by a broadband thermal source. The results are compared to those expected by the van Cittert-Zernike theorem and found to agree well in both amplitude and phase.

The role of gap plasmons in light emission from tunnel junctions.

Light emission from the junction of a scanning tunneling microscope (STM) is examined in the presence of 20 nm topographical features in thin gold films. These features significantly modify the emission rates of the junction. Contributions to this modification are discriminated by examining emission rates on samples where the material is varied spatially. It is found that the variability in STM photoemission rates between a gold tip and a gold sample under ambient conditions is due to the modification of localized gap plasmon modes and not to the presence of an electroluminescent gold cluster on the STM probe apex.

Low-loss metasurface optics down to the deep ultraviolet region.

Shrinking conventional optical systems to chip-scale dimensions will benefit custom applications in imaging, displaying, sensing, spectroscopy, and metrology. Towards this goal, metasurfaces-planar arrays of subwavelength electromagnetic structures that collectively mimic the functionality of thicker conventional optical elements-have been exploited at frequencies ranging from the microwave range up to the visible range. Here, we demonstrate high-performance metasurface optical components that operate at ultraviolet wavelengths, including wavelengths down to the record-short deep ultraviolet range, and perform representative wavefront shaping functions, namely, high-numerical-aperture lensing, accelerating beam generation, and hologram projection. The constituent nanostructured elements of the metasurfaces are formed of hafnium oxide-a loss-less, high-refractive-index dielectric material deposited using low-temperature atomic layer deposition and patterned using high-aspect-ratio Damascene lithography. This study opens the way towards low-form factor, multifunctional ultraviolet nanophotonic platforms based on flat optical components, enabling diverse applications including lithography, imaging, spectroscopy, and quantum information processing.

Ultrafast optical pulse shaping using dielectric metasurfaces.

Advances in ultrafast lasers, chirped pulse amplifiers, and frequency comb technology require fundamentally new pulse-modulation strategies capable of supporting unprecedentedly large bandwidth and high peak power while maintaining high spectral resolution. We demonstrate how dielectric metasurfaces can be leveraged to shape the temporal profile of a near-infrared femtosecond pulse. Finely tailored pulse-shaping operations, including splitting, compression, chirping, and higher-order distortion, are achieved using a Fourier-transform setup embedding metasurfaces able to manipulate, simultaneously and independently, the amplitude and phase of the constituent frequency components of the pulse. Exploiting metasurfaces to manipulate the temporal characteristics of light expands their impact and opens new vistas in the field of ultrafast science and technology.