Laboratory studies of alkali metal filter deposition, ultraviolet transmission, and visible blocking.

Far-ultraviolet alkali metal or Wood's filters have been produced and tested supporting the production of a flight filter for the Wide Field Planetary Camera 2 on the Hubble Space Telescope. Sodium layers 0.5-1-microm thick transmit up to 40% in the ultraviolet while efficiently blocking visible wavelengths. The prevention of visible pinholes is assisted by a clean, sleek-free surface and a cooled substrate during deposition. The coatings are stabilized efficiently by a bismuth overcoating whose transmission spectrum is presented. We also report for the first time, to our knowledge, the first demonstrated long-wavelength cutoff from a lithium filter, with a shorter cutoff wavelength than sodium and potentially higher stability for astronomical imaging.

Response of the Io plasma torus to comet Shoemaker-Levy 9.

Spectroscopic and imaging observations of the Io plasma torus were made in June and July 1994 in conjunction with the encounter of periodic comet Shoemaker-Levy 9 with Jupiter. Characteristic emissions from sulfur and oxygen ions showed a decline of about 30 percent in the extreme ultraviolet and an increase of about 40 percent in the far ultraviolet relative to preimpact observations. Changes in the extreme ultraviolet may be indicative of small changes in the torus electron temperature as a result of quenching of electrons by dust associated with the comet passage. However, no new emission features indicative of fragment dust within the torus were detected. The characteristic torus morphology seen in ground-based imaging was typical of that observed in the past.

Molecular Origin of Io's Fast Sodium.

Neutral sodium emissions encircling Jupiter exhibit an intricate and variable structure that is well matched by a simple loss process from Io's atmosphere. These observations imply that fast neutral sodium is created locally in the Io plasma torus, both near Io and as much as 8 hours downstream. Sodium-bearing molecules may be present in Io's upper atmosphere, where they are ionized by the plasma torus and swept downstream. The molecular ions dissociate and dissociatively recombine on a short time scale, releasing neutral fragments into escape trajectories from Jupiter. This theory explains a diverse set of sodium observations, and it implies that molecular reactions (particularly electron impact ionization and dissociation) are important at the top of Io's atmosphere.

The jovian nebula: a post-voyager perspective.

Voyager 1 carried a diverse collection of magnetospheric probes through the inner Jovian magnetosphere in March 1979. The ensuing data analysis and theoretical investigation provided a comprehensive description of the Jovian nebula, a luminous torus populated with newly released heavy ions drawn from Io's surface. Recent refinements in Earth-based imaging instrumentation are used to extend the Voyager in situ picture in temporal and spatial coverage. An analysis of [SIII] and [SII] optical emissions observed during the Jovian apparitions of 1981 through 1983 reveals three distinct torus components. Regularities have been identified in the ion partitioning and ion densities in the hot outer and inner tori, sharply defined radial structure is found in the plasma near Io, and the relative permanence of the cool inner torus is inferred. An extended cloud of neutral material is required as a source of fresh ions in the nebula.

High spectral resolution lidar to measure optical scattering properties of atmospheric aerosols. 1: theory and instrumentation.

A high spectral resolution lidar technique to measure optical scattering properties of atmospheric aerosols is described. Light backscattered by the atmosphere from a narrowband optically pumped oscillator-amplifier dye laser is separated into its Doppler broadened molecular and elastically scattered aerosol components by a two-channel Fabry-Perot polyetalon interferometer. Aerosol optical properties, such as the backscatter ratio, optical depth, extinction cross section, scattering cross section, and the backscatter phase function, are derived from the two-channel measurements.

Broadband dielectric mirror coatings for Fabry-Perot spectroscopy.

A general approach to the design of broadband dielectric multilayer coatings for Fabry-Perot spectroscopy is described, with specific application to the design of coatings for the PEPSIOS spectrometer. Designs are presented for reflectivities of 91.5 +/- 1.0% over spectral ranges (lambda(max)/lambda(min)) from 1.3 to 2.0.

Fabry-perot spectrometer adjustment for the compensation of Doppler shift from rapidly rotating and rapidly flowing sources.

The Doppler shift of light from a rapidly rotating or rapidly flowing source limits the spectroscopic resolution with which it can be studied using Fabry-Perot spectrometers that have the usual axial fringe adjustment. Because of the angular dependence of the wavenumber transmitted by the Fabry-Perot, the entrance aperture can be positioned off-axis at an angle chosen such that the wavenumber shift across the entrance aperture matches the shift presented by the source, thereby compensating for the Doppler effect. The principle can be extended to the Michelson interferometer for Fourier transform spectroscopy when the Michelson is used without field compensation. High resolution spectra obtained with a PEPSIOS spectrometer using the entire disk of Jupiter, a rapidly rotating planet, are presented as an example.