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Benson, R. S.

Publications and source records attributed to Benson, R. S..

Diffraction hardware testbed and model validation

Optical systems, which operate over a wide range of Fresnel numbers, are often times performance-limited by diffraction effects. In order to characterize such effects at the 40-100 picometer level, a diffraction testbed has been built which has the capability of measuring diffraction effects at this level. Concurrently, mathematical diffraction modeling tools have been developed that propagate an input wavefront through an optical train, while retaining amplitude and phase information at a grid resolution sufficient for yielding picometer-resolution diffraction test data. This paper contains a description of this diffraction hardware testbed, the diffraction modeling approach, and a comparison of the modeled and hardware test results, which then serves as validation of the diffraction modeling methodology.

optical

Optical image of a cometary nucleus: 1980 flyby of Comet Encke

The feasibility was investigated of obtaining optical images of a cometary nucleus via a flyby of Comet Encke. A physical model of the dust cloud surrounding the nucleus was developed by using available physical data and theoretical knowledge of cometary physics. Using this model and a Mie scattering code, calculations were made of the absolute surface brightness of the dust in the line of sight of the on-board camera and the relative surface brightness of the dust compared to the nucleus. The brightness was calculated as a function of heliocentric distance and for different phase angles (sun-comet-spacecraft angle).

Wells, W. C.

Electron impact excitation rates for helium.

Electron impact excitation rates are calculated for all transitions in He I and II between individual terms for n less than or equal to 4. Rates calculated for a large number of different experimental, theoretical, and semiempirical cross sections are compared. The rates are approximated by the expression AT to the nth power exp(-alpha E sub 0/kT) over the range from 4000 to 50,000 K for He I and 10,000 to 100,000 K for He II.

Benson, R. S.