Engineering Papers⌕ Search

Engineering topics

Forbes, F. F.

Publications and source records attributed to Forbes, F. F..

At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1980

A polarizer for vacuum ultraviolet

An MgF2 double Rochon prism, useful as a polarizer or analyzer in wavelengths longer than 1300A is described. Measurements of MgF2 transmission and of polarizer angular beam deviation from 1150 to 2900A are presented. The prism is comprised of 2.25 mm, MgF2 depolarizers, optically contacted. At normal incidence, a 4% transmission gain was measured from 6000 to 2200A, compared with air spaced elements. One depolarizer was vibrated to 40 g from 20 to 3500 Hz without deterioration in optical contact. Transmissions below 1400A are not good. In thin samples, surface loss is twice absorption loss in the range 1150 to 1500A. Refraction indices and a computer ray trace were used in processing photographic beam divergence data. If care is taken to remedy scattering effects, the prism is an efficient on-axis polarizer in the 1300 to 3000A range.

Steinmetz, D. L.↗
NASA NTRS1980

Second generation detector for low order global solar oscillations

The first observations of long period low order global solar oscillations grew out of diameter measurements made over an extended period of time. As a result of these investigations, a detailed understanding of the surface properties of the oscillations evolved, allowing development of a second generation detector. This new detector, currently under development directly utilizes various surface properties of the oscillations and does not, therefore, directly involve diameter measurements. The specifications of the detector, its supporting telescope and the observing program are reviewed.

Forbes, F. F.↗
NASA NTRS1974

Astronomical Fourier spectropolarimetry

Spectra of the Stokes polarization parameters of Venus (resolution 0.5 per cm) are presented. They were obtained at the Cassegrain focus of the 154-cm telescope of the National Mexican Observatory, Baja California, Mexico, July 12 and 13, 1972, with the Fourier Interferometer Polarimeter (FIP). A preliminary, limited analysis of four spectral features and of the CO2 rotational band structures at 6080 and 6200 per cm has demonstrated that spectral polarization is indeed present. These experimental results, confirmed by two series of observations, provide substantiation for this theoretically predicted phenomenon. They also tend to show that the FIP represents a novel astronomical tool for variable spectral resolution studies of both the intensity and the state of polarization of astronomical light sources.

Forbes, F. F.↗
NASA NTRS1973

A high-resolution Fourier-transform infrared spectrometer.

We have developed a Fourier-transform infrared spectrometer having a resolution of 0.5/cm over the range of wavelength from 1 to 5.5 microns. It has been used to observe the sun over this wavelength range from a Lear Jet flying at an altitude of 14 km, and to observe a number of stars from the ground, using the 229-cm telescope of the Steward Observatory and the 152-cm aluminum-mirror telescope at the Observatorio Astronomico Nacional in the Sierra de San Pedro Martir, Baja California, Mexico. The solar spectrum is given here, while the ground-based spectra are being published separately.

Johnson, H. L.↗