Sub-wavelength imaging at infrared frequencies using an array of metallic nanorods

We demonstrate that an array of metallic nanorods enables sub-wavelength (near-field) imaging at infrared frequencies. Using an homogenization approach, it is theoretically proved that under certain conditions the incoming radiation can be transmitted by the array of nanorods over a significant distance with fairly low attenuation. The propagation mechanism does not involve a resonance of material parameters and thus the resolution is not strongly affected by material losses and has wide bandwidth. The sub-wavelength imaging with $\lambda/10$ resolution by silver rods at 30 THz is demonstrated numerically using full-wave electromagnetic simulator.Comment: 12 pages, 16 figures, submitted to PR

Wide-angle perfect absorber/thermal emitter in the THz regime

We show that a perfect absorber/thermal emitter exhibiting an absorption peak of 99.9% can be achieved in metallic nanostructures that can be easily fabricated. The very high absorption is maintained for large angles with a minimal shift in the center frequency and can be tuned throughout the visible and near-infrared regime by scaling the nanostructure dimensions. The stability of the spectral features at high temperatures is tested by simulations using a range of material parameters.Comment: Submitted to Phys. Rev. Let

GENETIC CONTROL OF THE IMMUNE RESPONSE : THE EFFECT OF GRAFT-VERSUS-HOST REACTION ON THE ANTIBODY RESPONSE TO POLY-L(TYR,GLU)-POLY-D,L-ALA--POLY-L-LYS IN NONRESPONDER MICE

The transfer of parental (H-2k/k) nonresponder lymphoid cells into heterozygous (H-2k/q) nonresponder recipients at the time of primary challenge with aqueous poly-L(Tyr,Glu)-poly-D,L-Ala-poly-L-Lys [(T,G)-A--L] elicited the production of both IgM and IgG anti-(T,G)-A--L antibody. Normally, the production of IgG anti-(T,G)-A--L antibody is restricted to strains possessing the responder Ir-1 allele. The timing and intensity of the graft-versus-host (GVH) reaction required for this effect were found to be critical. Injection of H-2k/k cells into H-2k/q recipients 1 wk before antigen challenge did not elicit IgG anti-(T,G)-A--L antibody production, and markedly suppressed IgM anti-(T,G)-A--L antibody production. The transfer of alloimmune (H-2q-primed) H-2k/k cells at the time of antigen challenge was also associated with no IgG and little IgM anti-(T,G)-A--L antibody production. These data are consistent with the model that nonresponder thymus-derived lymphocytes (T cells) activated in a GVH reaction can substitute for (T,G)-A--L-reactive T cells to induce a shift from IgM to IgG anti-(T,G)-A--L antibody production

Dust in the Photospheric Environment II. Effect on the Near Infrared Spectra of L and T Dwarfs

We report an attempt to interpret the spectra of L and T dwarfs with the use of the Unified Cloudy Model (UCM). For this purpose, we extend the grid of the UCMs to the cases of log g = 4.5 and 5.5. The dust column density relative to the gas column density in the observable photosphere is larger at the higher gravities, and molecular line intensity is generally smaller at the higher gravities. The overall spectral energy distributions (SEDs) are f_{J} < f_{H} < f_{K} in middle and late L dwarfs, f_{J} f_{K} in early T dwarfs (L/T transition objects), and finally f_{J} > f_{H} > f_{K} in middle and late T dwarfs, where f_{J}, f_{H}, and f_{K} are the peak fluxes at J, H, and K bands, respectively, in f_{nu} unit. This tendency is the opposite to what is expected for the temperature effect, but can be accounted for as the effect of thin dust clouds formed deep in the photosphere together with the effect of the gaseous opacities including H_2 (CIA), H_2O, CH_4, and K I. Although the UCMs are semi-empirical models based on a simple assumption that thin dust clouds form in the region of T_{cr} < T < T_{cond} (T_{cr} = 1800K is an only empirical parameter while T_{cond} about 2000K is fixed by the thermodynamical data), the major observations including the overall SEDs as well as the strengths of the major spectral features are consistently accounted for throughout L and T dwarfs. In view of the formidable complexities of the cloud formation, we hope that our UCM can be of some use as a guide for future modelings of the ultracool dwarfs as well as for interpretation of observed data of L and T dwarfs.Comment: 43 pages, 13 figures, to appear in Astrophys. J. (May 20, 2004) Some minor corrections including the address of our web site, which is now read

Electrically injected cavity polaritons

We have realised a semiconductor quantum structure that produces electroluminescence while operating in the light-matter strong coupling regime. The mid-infrared light emitting device is composed of a quantum cascade structure embedded in a planar microcavity, based on the GaAs/AlGaAs material system. At zero bias, the structure is characterised using reflectivity measurements which show, up to room temperature, a wide polariton anticrossing between an intersubband transition and the resonant cavity photon mode. Under electrical injection the spectral features of the emitted light change drastically, as electrons are resonantly injected in a reduced part of the polariton branches. Our experiment demonstrates that electrons can be selectively injected into polariton states up to room temperature.Comment: 10 pages, 4 figure

Low Temperature Opacities

Previous computations of low temperature Rosseland and Planck mean opacities from Alexander & Ferguson (1994) are updated and expanded. The new computations include a more complete equation of state with more grain species and updated optical constants. Grains are now explicitly included in thermal equilibrium in the equation of state calculation, which allows for a much wider range of grain compositions to be accurately included than was previously the case. The inclusion of high temperature condensates such as Al$_2$O$_3$ and CaTiO$_3$ significantly affects the total opacity over a narrow range of temperatures before the appearance of the first silicate grains. The new opacity tables are tabulated for temperatures ranging from 30000 K to 500 K with gas densities from 10$^{-4}$ g cm$^{-3}$ to 10$^{-19}$ g cm$^{-3}$. Comparisons with previous Rosseland mean opacity calculations are discussed. At high temperatures, the agreement with OPAL and Opacity Project is quite good. Comparisons at lower temperatures are more divergent as a result of differences in molecular and grain physics included in different calculations. The computation of Planck mean opacities performed with the opacity sampling method are shown to require a very large number of opacity sampling wavelength points; previously published results obtained with fewer wavelength points are shown to be significantly in error. Methods for requesting or obtaining the new tables are provided.Comment: 39 pages with 12 figures. To be published in ApJ, April 200