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Hunter, W. R.

Publications and source records attributed to Hunter, W. R..

At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1980

Effect of UV irradiation on evaporated ZnS films

Evaporated ZnS films used as a component in reflectance enhancing or decreasing multilayer coatings for mirrors, transparent optical materials, and vacuum UV reflecting optics, are investigated with reference to the reflectance loss under UV irradiation and the formation of ZnO as a result of the decomposition of ZnS in the presence of oxygen. Reflectance measurements over a broad wavelength range reveal that the UV induced reflectance losses are generally restricted to wavelengths shorter than 4000 A and are most severe in the vacuum UV region. After 134 hr of UV exposure initially polycrystalline film of 150-200 A thick is completely converted to amorphous ZnO. The results demonstrate that caution should be exercised in employing ZnS as the outer layer in an optical coating system designed for use in the UV and vacuum UV regions.

Hass, G.↗
NASA NTRS1978

On the use of classical and conical diffraction mountings for XUV gratings

A description is given of the properties of plane diffraction gratings used in conical diffraction. Formulas are given for computing the direction of the diffracted orders. Experiments were performed to investigate the behavior of gratings used on conical diffraction mountings. Comparisons made with classical diffraction mountings show a significant increase in the efficiency of the -1 order. An empirical formula to predict the efficiencies of gratings used in conical diffraction mountings has been verified by the measurements.

Neviere, M.↗
NASA NTRS1978

Design criteria for reflection polarizers and analyzers in the vacuum ultraviolet

Reflection polarizers and analyzers for the extreme UV spectral region are discussed. The conditions for optimum polarization are presented, and the polarization characteristics of a number of metal coatings, including gold and some of the platinum metals, are given. The performance of three- and four-mirror polarizers, using these metal coatings, is discussed. The properties required of a polarization analyzer are presented, and the performance of single and three- and four-reflection analyzers are discussed in terms of the optical properties of coating materials that might be useful for analyzers.

Hunter, W. R.↗
NASA NTRS1978

Reflection polarizers for the vacuum ultraviolet using Al + MgF2 mirrors and an MgF2 plate

Consideration is given to the design and operation of a three-mirror reflecting polarizer where one of the reflecting surfaces is an MgF2 plate, the other surfaces are Al + MgF2 coatings, and one reflection occurs at or near the true Brewster angle. It is found that the polarizer is most efficient in the 1200-2000 A wavelength region, and that by optimum selection of the angle of incidence on the MgF2 plate, polarization values of 100 and over are yielded from 900 to 3000 A. The polarizer may be used at wavelengths as short as 500 A, although it is observed that at such wavelengths the polarization value decreases to about 10. It is noted that all reflecting polarizers operating in the vacuum ultraviolet wavelength may manifest changing characteristics as their mirrors become contaminated, and that polarization must therefore be occasionally remeasured.

Hass, G.↗
NASA NTRS1977

Measuring concave diffraction grating efficiencies at grazing incidence

The efficiency of a concave diffraction grating in a given order is obtained by measuring the intensities of the diffracted and incident beams and taking their ratio. A valid measurement requires that both the incident and diffracted beams be collected by the detector. At grazing incidence, however, the diffracted beam may spread beyond the detector due to aberrations. In addition, the diffracted beams of consecutive orders may overlap so that unambiguous efficiency measurements cannot be made. The effect of aberrations on efficiency measurements has been studied, using ray tracing, for the geometry of the measuring instrument in use at the Naval Research Laboratory. This instrument is attached to a VUV monochromator which furnishes a diverging beam. The main effect of aberrations for this instrument is a spread of the diffracted beam in the direction of dispersion. The width of the diffracted beam is wavelength dependent and is minimal at the horizontal focus, spreading to longer and shorter wavelengths. Reducing the divergence of the incident beam reduces the spread but, for small radius gratings, not always sufficiently so that the entire diffracted beam can be collected by the detector. The distance from the detector to the grating can also be adjusted to aid in collecting all the diffracted beam.

Hunter, W. R.↗
NASA NTRS1977

Thin aluminum filters for use on the Apollo Telescope Mount XUV spectrographs

Thin, unbacked, aluminum film filters were used on two extreme ultraviolet (XUV) instruments flown on the Apollo Telescope Mount of Skylab by the Naval Research Laboratory to transmit the XUV radiation while blocking the longer wavelength radiation that would saturate the detector. The requirements placed on these filters - large size, resistance to degradation by high acoustic and vibration fields, and low pinhole transmittances - were far more severe than those placed on any filters previously flown. Special techniques were developed for vacuum evaporation of the aluminum, removal of the films from the substrates, supporting the films and mounting them to obtain finished filters, and storing them so that no degradation took place. A description of these techniques will be given.

Schumacher, R. J.↗
NASA NTRS1977

Optical contamination - Its prevention in the XUV spectrographs flown by the U.S. Naval Research Laboratory in the Apollo Telescope Mount

During construction and testing of the XUV spectrographs flown in the ATM by the Naval Research Laboratory, many problems associated with optical contamination were encountered. Solving these problems required setting up a contamination prevention program to select the materials used in constructing the instruments and to delineate procedures in assembling, testing, and storing the instruments. A brief description is given of methods of assessing the effects of contamination and of the procedures used to prevent contamination.

Hunter, W. R.↗
NASA NTRS1974

Optical grating evaluator - A device for detailed measurement of diffraction grating efficiencies in the vacuum ultraviolet

A device for detailed measurement of diffraction grating efficiencies and over-all performance in the VUV has been designed and constructed at the Naval Research Laboratory. The system employs semiautomated mechanisms to scan the face of the grating with a narrow monochromatic beam, and an efficiency map of the grating surface is produced on a strip chart recorder. Grating efficiency in the various diffracted orders and intensity of light scattered between orders may also be measured. A unique feature is the ability to determine the angle and effectiveness of grating blaze and variations in blaze under different conditions of illumination.

Michels, D. J.↗
NASA NTRS1973

Increase in transmittance of unbacked aluminum filters exposed to RF or dc discharges in oxygen

Results of an experimental study of the effect of discharges in oxygen on the oxide thickness and transmittance of aluminum filters. The studies were performed by exposing the filters to RF discharges and dc glow discharges in oxygen. In all experiments except one in which an aluminum ring was used as the cathode an increase in the transmittance of the filters is noted. It is thus demonstrated that the transmittance of aluminum filters increases on exposure to electrical discharges in oxygen, although it is not certain whether this phenomenon is caused by atomic oxygen.

Hunter, W. R.↗
NASA NTRS1972

Cleaning of contaminated channel electron multiplier arrays.

Polymerized organic materials found in vacuum systems frequently contaminate the individual channels (which can be as small as 15 microns) of an oil-pumped channel electron multiplier array used as a vacuum UV- to visible-radiation conversion device. It is shown that exposure to an oxygen plasma is an effective means of decontaminating the channels, thereby restoring the sensitivity of the device.

Harlow, F. E.↗
NASA NTRS1972

Reflectance of evaporated rhenium and tungsten films in the vacuum ultraviolet from 300 to 2000 A.

Discussion of the dependence of the reflectance of Re and W on the substrate temperature during deposition, film thickness, and aging during exposure to air. Re and W of 99.99% purity were evaporated with a 6-kW fine-focused electron gun and deposited on glass and fused quartz plates of various temperatures ranging from 40 to 500 C. With Re, films of highest reflectance were obtained by evaporation onto unheated substrates, whereas with W, heating of the substrate greatly increased the reflectance of the deposited films. For both metals, the reflectance losses during extended exposure to air remained rather small, indicating that the oxide films formed on both film materials at room temperature were very thin.

Cox, J. T.↗