Light microscopy is a widely used analytical tool because it provides nondestructive, real-time, three-dimensional imaging with chemically-specific contrast. However, diffraction effects typically blur the resolution of these microscopes to 300 nm or worse, which limits their utility for the study of nanoscale materials. In this project, research is performed to develop super-resolution techniques which retain the microscope’s ability to acquire materials and chemically specific contrast while augmenting the spatial resolution to below 100 nm. Super-resolution microscopy is made possible by altering the homogeneous illumination conditions that govern the diffraction limits. By changing the nature of the sample illumination, it is possible to encode additional spatial information, higher resolution, into the available information bandwidth of a microscope. We have developed a flexible microscope system, based on high-resolution spatial light modulators, which allow complete control over the illumination conditions. When applied to fluorescence imaging, the structured illumination can achieve a factor of 2 resolution enhancement. With the introduction of nonlinearity in the contrast mechanism, essentially arbitrary resolution enhancement can be achieved, limited only by the order and strength of the nonlinearity. Our current emphasis has been to extend the utility of super-resolution microscopy by combining it with a nonlinear vibrational spectroscopy, coherent anti-stokes Raman spectroscopy (CARS). CARS is a nonlinear optical process which mixes two laser beams together to greatly enhance the sensitivity of Raman spectroscopy and imaging, typically by a factor of 10⁴ to 10⁵. The technique provides the bond-specific, stainless contrast of vibrational spectroscopy and the two color nature of its excitation can be exploited to greatly improve the microscope’s spatial resolution through the use of spatial light modulator generated pupil phase masks. These phase masks are used to produce a narrowed, super-resolving, focal spot by delaying portions of the input beams so that they destructively interfere in some regions of the focal spot and constructively interfere elsewhere. By adjusting the position and magnitude of these interference effects, we have recently demonstrated super-resolving CARS (SR CARS) microscopy with resolution below 150 nm with 800 nm illumination (better than 4 times the diffraction limit).

We are exploring applications of super-resolution chemical imaging microscopy in the areas of health sciences and advanced materials development. We are interested in in-vitro imaging of molecular interaction pathways developed from systems biology using both structured illumination fluorescence and SR-CARS. SR-CARS is also being developed to characterize stress in nanoscale mechanical and electrical devices, and explore domain structure in self-organized nanoparticle/organic composites important to organic electronics and photovoltaic solar energy conversion.

 

key words

Confocal microscopy; Fluorescence; Molecular spectra; Nanocomposite; Nanoscale analysis; Nonlinear optics; Optical microscopy; Raman spectra; Stress; Super-resolution microscopy; Systems biology;

Citizenship:  Open to U.S. citizens

Level:  Open to Postdoctoral applicants