Joseph Geddes

I am a postdoc at the Beckman Institute at the University of Illinois at Urbana-Champaign. My research interests center on novel optical materials applied to fundamental problems in optical devices and energy supply. One theme in the work is the optical properties of complex materials---i.e. materials in which many symmetries are broken on length scales comparable to optical wavelengths.

More information is available at my web site.

Research

One project aims to analyze the propagation of light through nanostructured materials. These include holographically fabricated photonic crystals and sculptured thin films, two materials that can be used to better match the impedance between semiconductors and air to make solar cells and light emitting diodes more efficient. Whole system optical design can help optimize the overall device efficiency. For example, I have analyzed the optics of photovoltaic systems that combine lens arrays with solar cells on flexible substrates [1]. The flexibility of the substrates allows for the possibility of folding up the module to make a cheap one-axis tracker. Such lens and module designs could reduce the range of incidence angles over which the impedance must be matched.

A second project concerns the design of optical materials with desirable characteristics. A metamaterial is a composite whose properties---i.e., strength, electrical conductivity, piezoelectric coefficients, etc.---are either qualitatively different or quantitatively surpass those of its components. These composites, which have been extant for some time, do not obey the simple volume mixing rules that lie at the heart of much theory on composite materials [2, 3]. As such, they exhibit a form of emergent behavior. My calculations indicate that the intrinsically large nonlinearities of metals could be accessed and increased by fabrication of composites comprising alternating metal and dielectric layers of subwavelength thickness [4]. The effective third-order nonlinear susceptibilities could be orders of magnitude larger than those intrinsic to the metallic component due to a resonance effect, though the enhancement is limited to the direction perpendicular to the layer interfaces.

Another effort is directed at a more fundamental understanding of how to control electrons and phonons in condensed matter. This area has been identified by the Department of Energy as a grand challenge in basic science that must be solved to underpin future energy technology [5]. I helped develop an optical pulse shaping algorithm to coherently excite the vibrational normal modes of a chemical species of interest [6, 7]. This algorithm was originally developed for biological imaging, but I intend to extend its range of applicability to more general problems of coherent control of complex matter. The ultimate goal is to eventually use the knowledge gained to help design such technologies as optical nanoantenna rectifiers or photocatalysts.

Sustainability

Like the notion of complexity itself, the definitions people use for sustainability vary with context. How can the sustainability of global human and ecological systems be measured? To start, it might help to examine ideas from physics and engineering that may shed some light on the larger issue of global sustainability: equilibria (static and dynamic), stability, and self organized criticality. What are necessary and sufficient conditions for a complex physical system to be sustainable, and can any of those conditions be extended to apply in a global context? In particular, how much of an unsustainable system's behavior can be explained by either its inability to react quickly enough (i.e. slow feedback) or by inappropriate reactions (i.e. insufficient or wrong responses)?

Although my primary interest in sustainability concerns energy supply and climate change, I would like to learn about and discuss some other global systems: water, biodiversity, the nitrogen cycle, etc. It would be interesting to identify commonalities and interactions between those systems and those of energy and climate.

At the summer school, I would like to learn how to better place my own materials and optics research into a larger context of technology development. Several recent papers on the dynamics of energy technology development by Santa Fe Institute researchers (e.g. [8]) piqued my interest in this topic. How do the dynamics of change in energy technologies compare to those for other technologies that affect sustainability?

References

[1] J. Yoon, A. J. Baca, S.-I. Park, P. Elvikis, J. B. Geddes III, L. Li, R. H. Kim, J. Xiao, S. Wang, T-H. Kim, M. J. Motala, B. Y. Ahn, E. B. Duoss, J. A. Lewis, R. G. Nuzzo, P. M. Ferreira, Y. Huang, A. Rockett, and J. A. Rogers, "Ultrathin silicon solar microcells for semitransparent, mechanically flexible and microconcentrator module designs," Nature Mater. 7: 907-915 (2008).

[2] A. Lakhtakia, ed., "Selected Papers on Linear Optical Composite Materials," SPIE, Bellingham, WA, USA (1996).

[3] R. M. Walser, Metamaterials: An introduction, in W. Weiglhofer and A. Lakhtakia, eds., "Introduction to Complex Mediums for Optics and Electromagnetics," SPIE, Bellingham, WA, USA (2003).

[4] J. B. Geddes III, E. C. Nelson, and P. V. Braun, "Design of uniaxial metallodielectric metamaterials having large optical nonlinearities," APS March Meeting, New Orleans, LA, USA (10-14 Mar. 2008).

[5] Basic Energy Sciences Advisory Committee, "Directing matter and energy: Five challenges for science and the imagination," U. S. Department of Energy (2007).

[6] D. L. Marks, J. B. Geddes III, and S. A. Boppart, "Molecular identification by generating coherence between molecular normal modes using stimulated Raman scattering," Opt. Lett. 34: 1756-1758 (2009).

[7] J. B. Geddes III, D. L. Marks, and S. A. Boppart, "Optical pulse shaping for selective excitation of coherent molecular vibrations by stimulated Raman scattering," Proc. SPIE 7183: 718311 (2009).

[8] J. D. Farmer and J. Trancik, "Dynamics of technological development in the energy sector," The London Accord: 1-24 (2007).