Fourier magnitude of the field incident on a random scattering medium from spatial speckle intensity correlations.

Spatial speckle intensity correlations are used to determine the spatial Fourier magnitude of a field incident on a random scattering medium. The patterned beam is scanned across the scattering medium, and the speckle pattern on the opposite side is imaged at each beam position. A theory based on a Green's function representation is used to reconstruct the spatial Fourier magnitude of the patterned incident field.

Demonstration of terahertz frequency-dependent field transformation in an irregular waveguide structure with direct measurement of the internal electric fields.

We demonstrate irregular scattering structure frequency-dependent field control at terahertz frequencies by means of a TM(10) to TM(30) mode converter designed for operation near 300 GHz and fabricated out of lithium niobate. Imaging of the electric fields in the sample, with a Fourier analysis of the time domain signal, yielded the performance as a function of frequency.

Interferometry from a scattering medium.

A two-beam random interferometer is demonstrated where coupling is facilitated by a scattering medium. A modulation observed in the normalized second-order intensity frequency correlation of the transmitted light is attributed to the relative temporal delay of the two beams and is insensitive to beam alignment and spacing.

Subwavelength imaging with a multilayer silver film structure.

A Ag/SiO2 multilayer imaging structure is shown to have subwavelength performance. Loss is the major limitation, and selection of low-loss materials and suitable operating wavelengths has a significant impact on performance. The influence of the variables is presented, and vortices are shown to exist.

Demonstration of mode conversion in an irregular waveguide.

Communications wavelength waveguide mode conversion is demonstrated in an irregular metal-walled structure that was designed by using multiresolution optimization. Strong scatter and a large number of degrees of freedom allowed high-efficiency conversion in a device having a length of just a few wavelengths. The fabrication approach draws on standard semiconductor processing. Mode-selective reflectors, splitters, phase shifters, and other elements can be achieved by using this principle.

Metrics for negative-refractive-index materials.

The importance of loss in the field solution for left-handed media, and in particular, the impact on what would otherwise be a purely evanescent field, is addressed. Using an equivalent electric current source, field solutions are constructed in semi-infinite and finite thickness left-handed media. In the slab case, field growth and power dissipation metrics with uniform amplitude and uniform power excitation, respectively, provide a means to evaluate the potential of a left-handed material lens. Power dissipation suggests that field growth will be adversely impacted.

Spectral and temporal speckle field measurements of a random medium.

The zero-mean circular complex Gaussian field statistics of a random medium are experimentally demonstrated in the optical domain, thus verifying this key assumption of statistical optics. Using a frequency-tunable laser source in a fixed-path-length interferometer, we obtain optical field fluctuations in the time and frequency domains that clearly show that the ensemble-averaged temporal intensity converges to the photon transit time distribution, which for the samples used is in excellent agreement with a diffusion model.

Temporal response of a random medium from third-order laser speckle frequency correlations.

We demonstrate for the first time that the temporal response of a random medium can be obtained from optical intensity fluctuations. Our method uses third-order intensity correlations of measured speckle patterns from a multiple scattering random medium as a function of optical frequency. In particular, our experimental results for the temporal response extracted from third-order intensity correlations are in good agreement with the predictions of a diffusion model. Our results are valid for waves in random media where the scattered field is described by circular complex Gaussian statistics.

Facile synthesis of a fluorescent deoxycytidine analogue suitable for probing the RecA nucleoprotein filament.

We report the synthesis of the fluorescent 2'-deoxycytidine analogue 5-methylpyrimidin-2-one nucleoside, its incorporation at three specified sites in a single 60-nucleotide DNA molecule, and the use of its total and polarized intrinsic fluorescence to characterize RecA-DNA complexes. [reaction: see text]

Expression studies of superoxide dismutases in nodules and leaves of transgenic alfalfa reveal abundance of iron-containing isozymes, posttranslational regulation, and compensation of isozyme activities.

The composition of antioxidant enzymes, especially superoxide dismutase (SOD), was studied in one nontransgenic and three transgenic lines of nodulated alfalfa plants. Transgenic lines overproduced MnSOD in the mitochondria of nodules and leaves (line 1-10), MnSOD in the chloroplasts (line 4-6), and FeSOD in the chloroplasts (line 10-7). In nodules of line 10-7, the absence of transgene-encoded FeSOD activity was due to a lack of mRNA, whereas in nodules of line 4-6 the absence of transgene-encoded MnSOD activity was due to enzyme inactivation or degradation. Transgenic alfalfa showed a novel compensatory effect in the activities of MnSOD (mitochondrial) and FeSOD (plastidic) in the leaves, which was not caused by changes in the mRNA levels. These findings imply that SOD activity in plant tissues and organelles is regulated, at least partially, at the posttranslational level. All four lines had low CuZnSOD activities and an abundant FeSOD isozyme, especially in nodules, indicating that FeSOD performs important antioxidant functions other than the scavenging of superoxide radicals generated in photosynthesis. This was confirmed by the detection of FeSOD cDNAs and proteins in nodules of other legumes such as cowpea, pea, and soybean. The cDNA encoding alfalfa nodule FeSOD was characterized and the deduced protein found to contain a plastid transit peptide. A comparison of sequences and other properties reveals that there are two types of FeSODs in nodules.