My research lies at the intersection of optics and nanotechnology, with special foci on extending the spatial resolution of optics to the nanoscale, and applications of optics in energy. In addition to gaining a deep understanding of the basic physics of the behavior of light and matter at the nanoscale, our research is driven by many exciting applications.
Absorbance modulation utilizes a thin photochromic layer that is reversibly rendered transparent by illumination at wavelength, l1 and opaque by illumination at a different wavelength, l2 (see figure). When this layer is exposed to a focused bright spot at l1 and simultaneously to a focused node at l2, the ensuing photochemical equilibrium results in a sub-wavelength transparent region in the vicinity of the node. Photons at l1 penetrate this region forming an optical nanoscale probe. The lateral size of this probe is not limited by diffraction, but by material parameters and the ratio of the intensities at the two wavelengths. In other words, optical near-fields are generated from afar.
Absorbance modulation is limited to patterning ultra-thin photoresist layers due to the evanescent nature of the optical near-field. This constraint is overcome by an alternative approach that exploits unique combinations of spectrally-selective reversible and irreversible photochemical transitions. We refer to this approach as Patterning via Optical-Saturable Transitions (POST). POST has the potential to achieve single-molecule spatial resolution with long-wavelength photons.
Light microscopes are ubiquitous, from the life sciences to the semiconductor industry. Ordinarily, diffraction limits the resolution of such microscopes to ~200nm. Electron microscopy, although capable of nanoscale resolution, is incompatible with living systems, and can even damage some inorganic materials. A significant number of fundamental questions in biology remain unanswered because of an inability to see at the nanoscale without damage. We are pursuing absorbance-modulation imaging as a technique to nanoscale microscopy or nanoscopy.
Nanotechnology will almost certainly play a leading role in solving the current energy and environmental crises. We are applyng our expertise in optics and nanofabrication to develop solar concentrators that separate and concentrate the solar spectrum to achieve overall photovoltaic energy conversion efficiencies over 50%. By selecting the optimal spectral band to illuminate a given solar cell, it is possible to overcome "hot-carrier" losses and transparency losses, both of which account for over 60% of the total energy loss.