A model of the cornea's lamellar structure is proposed that is capable of explaining experimental results obtained for the transmission of normal-incidence polarized light through rabbit and bovine cornea. The model consists of a large number of planar lamellae, each approximated as a uniaxial birefringent layer, stacked one upon another with various angular orientations. Polarized light transmission through the composite system is modeled theoretically by use of the Jones matrix formalism. The light transmission is calculated numerically for a large number of model lamellae arrangements, each generated from a statistical description, and histograms are constructed of various properties of the light transmission, including the minimum and maximum cross-polarized output intensities. It is demonstrated that various structural and optical parameters of the lamellae arrangements of actual corneas may be estimated by comparison of the calculations with detailed experimental data. Certain characteristics of the histograms are identified that permit a clear distinction between random and partially ordered systems. Comparisons with previously published experimental data provide strong evidence that the lamellae orientations are not entirely random, but rather a significant fraction are oriented in a fixed, preferred direction.
Pulsed-photoacoustic spectroscopy (PPAS) in the near-infrared portion of the optical spectrum was used as a local technique for quantitative monitoring of tissue hemoglobin concentration and its oxygenation state. A pulsed, tunable optical source coupled to a 1mm-diameter optical fiber cable was used to deliver optical energy to the tissue under study. The fiber was placed either on the exterior surface or inserted into the tissue. An ultrasonic signal was produced in the tissue as a result of the absorbed light pulse energy. Since the rate of conversion of laser light energy to heat was rapid and the laser pulse was much shorter than the tissue thermal-diffusion length, the ultrasonic signal amplitude was proportional to the energy absorbed. Spectra of absorbing compounds were obtained by measuring the variation in the acoustic signal with source wavelength. In contrast with near-infrared spectroscopic techniques that measure diffuse light transmission and assume knowledge of the pathlength of light traveling through tissues in order to determine the absorption coefficient, the photoacoustic response is produced directly by light absorption. Light scattering merely modifies the spatial distribution of the absorbed energy. Our studies demonstrate that photoacoustic spectra obtained both in-vitro and in-vivo allow determination of relative changes in the concentration of oxy-and de-oxyhemoglobin.
Abstract. In this paper we present ultraviolet to near infrared spectrographic observations of high-speed artificial plasma jet interactions with the ionosphere. The plasma .jets were injected quasi-parallel to the magnetic field at an altitude of 140 km during the Fluxus -1 and-2 experiments. The jets contained aluminum ions and were generated using a shaped-charge device known as an Explosive Type Generator (ETG). Satellite-based spectrographic observations of the plasma jet show typical auroral emission features associated with electron impact excitation. The auroral features include emission at 135.6 nm (eI) and 557.7 nm (eI). The 135.6 nm emission was prompt while the 557.7 nm was observed for 5 seconds. The most likely source of these auroral emissions are ionospheric and magnetospheric electrons that neutralize the plasma jet.
Abstract. The purpose of the Fluxus-1 and-2 active experiments is to study plasma jets injected parallel to the magnetic field and to study the interaction of these jets with the magnetic field. The experiments were conducted using a shaped-charge device, known as an explosive type generator (ETG), that produced an artificial aluminum plasma jet. In Fluxus -1 and-2 the jet was injected nearly parallel to the geomagnetic field at an altitude of 140 km toward an instrumented diagnostic payload located about 100 m away from the ETG. A -•50% reduction in the magnetic field was observed as the plasma jet passed by the diagnostic payload. Comparisons of 3-dimensional simulation results with the observed magnetic field perturbations suggest that the Fluxus-1 plasma jet was -•30 ø from the magnetic field direction while the Fluxus-2 plasma jet was directed nearly parallel to the magnetic field.
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