Tito E. Huber

FAR-INFRARED PROPAGATION IN METAL WIRE MICROSTRUCTURES

Densely packed arrays (76% volume fraction) of 10 μm diameter parallel indium wires exhibit an enhanced transmission, of ∼103, relative to an indium foil of equal thickness for far-infrared (k<80u2009cm−1) propagating along the wire length. The absorption increases as k0.45±0.07 and is explained by the dynamic Maxwell–Garnett model, which includes eddy current dissipation. The effective surface conductivity is depressed fiftyfold with respect to the bulk. The implications for plasmons in metal wire microstructures and for developing simultaneously transmissive and conductive composites are discussed.

Microwave and far-infrared propagation in conductive microstructured composites

Abstract In a recent publication [T.E. Huber, L. Luo, Appl. Phys. Lett. 70 (1997) 2502.] we discussed a structural enhancement of the electromagnetic transmission in composites. We showed that densely packed arrays (76% volume fraction) of 10 μm diameter parallel indium wires exhibit an enhanced transmission, of ∼ 10 3 , relative to an indium foil of equal thickness for far-infrared (10 cm −1 k cm −1 ) propagating along the wire length. The absorption increases as k 0.45 ± 0.07 and is explained by the dynamic Maxwell-Gannett model, which includes eddy current dissipation. It is of considerable practical interest to extend the range of application of these composite properties to the microwave domain. Here we will discuss recent measurements of the transmission of microwaves in wire array composites in the 8–12 GHz frequency range.

Dielectric Properties of Glass Capillary Arrays

Glass Capillary Arrays (GCA) are low density columnar monolithic structures made of soda-lime glass. This structure, in which 76% of volume between the columns, the channels, is void, also has a greatly reduced dielectric constant in comparison with bulk glass. We have measured the index of refraction and absorption of samples of GCAs in the X-band, 8 × 10 9 Hz to 1.2×10 10 Hz, for various orientations of the channels with respect to the polarization. For channels perpendicular to the polarization direction we have measured an index of refraction of 1.15. In comparison the index of refraction of (bulk) soda-lime glass is 2.6. We also examined the absorption in the far-infrared (FIR) frequency range between 6×10 11 Hz and 6×10 12 Hz. In this frequency range we obtain a k 2 dependence due to losses in the glass matrix at higher frequencies. The results of the X-band and FIR results are interpreted in terms of an effective medium theory of the real and imaginary part of the dielectric constant of the composite.

Optical properties of metal wire array composites

According to effective medium theories, electrically conducting composites consisting of parallel metal wires embedded in a transparent dielectric can propagate light in the direction of the wire length. The authors have prepared densely packed arrays (76% volume fraction) of 10-{micro}m diameter indium wires by high pressure injection of glass microchannel plates. For wavelengths longer than 100 {micro}m (k < 100 cm{sup {minus}1}) the absorption of the wire array is almost three orders of magnitude smaller than that of an indium foil of equal thickness. The measured absorption increases as K{sup 0.45{+-}0.07} and can be accounted for by including magnetic dipole effects.

Hybridization of the rotational state of HD adsorbed on porous materials: Porous Vycor glass and MgO.

Abstract We present measurements of the infrared absorption corresponding to the roto-vibrational transitions of HD adsorbed in Porous Vycor Glass and MgO pills. For glass the absorption line bandwidths at low coverages of HD are more than two times larger than those of adsorbed H2 and D2. Also, we observe the transitions corresponding to δJ=3 and δJ=5, whereas only the allowed δJ=0, ±2 are observed for the pure isotopes. HD is a molecule possessing spherical symmetry whose center-of-mass is asymmetrically located. Our observations strongly suggest hindrance of the rotational states of HD which may be attributed to the hybridization of rotations and adsorbed HD phonons resulting from the molecule mass-asymmetry. Results for HD on MgO are simmilarly analyzed and will be discussed also.

Free expansion of hydrogen in helium at low temperatures.

Abstract In order to understand the formation of clusters of molecular hydrogen in helium we evaluated isentropic-expansion paths on the pressure-temperature phase diagrams. The optimal initial conditions are derived. The prospect of detecting the resulting clusters using infrared absorption spectroscopy and light scattering optical is discussed, the ultimate goal being that of observing supercooled liquid hydrogen. Preliminary results will be discussed.