Research

The Webb group pursues theoretical and experimental work related to biophotonics and nanophotonics that incorporates basic research on fields and optics, communication and signal processing, and nanotechnology.

Biophotonics

Coherent and incoherent aspects of imaging for in vivo and other applications are being investigated.

The coherent optical imaging work involves speckle imaging and motion in structured illumination as a basis for super-resolution. By statistically averaging over scatterer configurations, speckle intensity correlations over object position allow us to reconstruct a hidden moving object embedded inside scattering medium that can be as thick as centimeters of biological tissue. In a remote sensing setting, a similar setup can use a scattering layer as an analyzer to enhance sensitivity and to detect changes in the incident fields, for example, to detect subwavelength lateral displacement of an object.

Using the coupled photon diffusion equations as a forward model for fluorescence, an inverse problem can be solved, allowing the calculation of fluorescence emitter locations along with optical properties of the medium. In particular, it can allow the tracking of neural activity in the brain and the reconstruction of neuronal networks. Within a localization framework, neuron-scale resolution is possible, opening the prospect of direct imaging of neuron activity throughout the brain.

Nanophotonics

The interaction of light with matter on the nanometer length scale is being studied with a view to new physical understanding and applications. This work spans super-resolution imaging, metamaterials, aperiodic structures for field control, and optomechanics.

Far subwavelength resolution of separation between dielectric scatterers is studied by accessing far-field information arising from moving the scatterers in a structured background electric field. The data obtained from numerical simulations is compared to noisy data generated from experiments and the correct separation between the scatterers is determined by minimizing a cost function. Future directions involve imaging such objects with far-subwavelength features with potential applications in semiconductor defect detection.

Aperiodic nanostructures can provide large degrees of freedom and perform functions that are not possible with periodic systems. We apply multivariate statistical analysis to investigate possible field control via aperiodic nanostructures and use it as a guideline to benefit the design process. In addition, the field statistics provide an improved understanding of the scattering properties of aperiodic nanostructures. We present a design method by which the electromagnetic pressure on a nanostructured binary material can be controlled in terms of both the enhancement and the direction. This offers new avenues for optomechanics.

We study electromagnetic wave and optical force behavior in nanostructured materials using simulations and with experiments. With an asymmetric cavity resonance, an order of magnitude larger force than the conventional limit on a perfect mirror, both pushing and pulling (in the sense of the incident light direction) has been discovered. This will benefit optomechanical applications such as all-optical switching, remote control, and laser propulsion.