Publications

The cover picture shows the underlying mechanism and one of the applications of the photorefractive effect, which produces a spatial modulation of the refractive index of a material under nonuniform illumination. As illustrated on the right side, the photorefractive effect begins with light and dark fringes produced by intersecting laser beams, which, in the presence of an applied electric field E0, produce charge separation and eventually a space charge electric field. This field produces a refractive index change, that is, a hologram that can diffract light. A key feature of the effect is that it leads to asymmetric energy transfer between the two beams incident on the material. An application of this effect is image amplification, which is demonstrated on the top left side of the picture where the image of the number 5, carried by a weak beam, is amplified in the presence of a strong beam. Among the best photorefractive materials developed thus far are organic, amorphous glasses, the properties of which depend critically on the glass transition temperature (Tg) and photoconductivity, as well as polarizability anisotropy and hyperpolarizability of the molecules. The picture shows the structure of the photoconductive, nonlinear optical chromophore DCDHF-6 that forms a high-performance low-molecular weight photorefractive glass.

A fluorescence microscope image of kinesin molecules attached to a microtubule filament. Each kinesin is labeled with a fluorescent dye. The intensity of the signal (shown in pseudo colors from blue/green to red/white for low to high intensity) marks the position of kinesin on the filament. Samples such as the one shown on the cover were used in single molecule experiments to uncover a highly flexible state of kinesin when ADP is the nucleotide bound to the enzyme. [Images: H. Sosa, E. J. G. Peterman, L. S. B. Goldstein, and W. E. Moerner]

Optical images of single molecules from the Moerner Lab. Clockwise from upper left. Frequency-space: pentacene in p-terphenyl at 2 kelvin (K). Confocal: protein kinase A regulatory subunit in agarose gel, 295 K (room temperature). Total internal reflection: green fluorescent protein in polyacrylamide gel, 295 K. Far-field epifluorescence: terrylene in p-terphenyl, 2 K. Special section topics begin on p.1667.[Images: W. E. Moerner, W. P. Ambrose, S. Brasselet, J. Deich, R. M. Dickson, D. J. Norris, S. S. Taylor]