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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
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Bevealed tip gives optimum coupling efficiency. Abrasive tape used to grind tip of optical fiber. Grinding force depends on stiffness of optical fiber. "Roof" shape on end of optical glass fiber increases efficiency which couples laser light. End surface angle of 65 degrees with perpendicular required for optimum coupling. Since fiber and tape are light in weight and compliant, ridge defect-free, and chipping on fiber edge totally eliminated.
Numerically controlled milling machine modified to make head reciprocate. Modification accomplished by removal of original milling head from machine and by mounting vertical slide in its place. Vertical slide driven up and down by connecting rod bolted off-center to drive pulley. Pulley driven by belt from variable-speed electric motor. Milling-machine head then attached to vertical slide. Mechanism allowed independent control of reciprocating surface speed through variation of speed of electric motor.
The elements of a Wolter type II telescope have been fabricated using a small area tool in a computer controlled facility. The absolute radius of the mirrors can be established to 0.812 micron, and relative heights on the surfaces can be determined to 0.016 micron. The primary has a 0.041-micron rms surface error, and the secondary has a 0.054-micron surface error.
The surface finishing of X ray grazing incidence optics is a most demanding area of optical processing, both in terms of metrology and application of optical finishing techniques. An existing optical mirror was processed using a new removal technique that uses a jet of finely dispersed and extremely small particles that impact a surface, which under the correct conditions, produces an ultrasmooth surface, especially on aspheric curvatures. The surfaces of the SO56 mirror are tapered conical shapes that have a continuously changing radius with the primary mirror having a parabolic shape and the secondary mirror a hyperbolic shape. An optical ray trace that was conducted of a telescope used the measured parameters from the existing substrates to set up the prescription for the optical layout. The optimization indicated a wavefront performance of 0.10 A at 0.633 micron.
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Future x-ray telescopes will likely require lightweight mirrors to attain the large collecting areas needed to accomplish the science objectives. Understanding and demonstrating processes now is critical to achieving sub-arcsecond performance in the future. Consequently, designs not only of the mirrors but of fixtures for supporting them during fabrication, metrology, handling, assembly, and testing must be adequately modeled and verified. To this end, MSFC is using finite-element modeling to study the effects of mounting on thin, full-shell grazing-incidence mirrors, during all processes leading to a flight.
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Wafer reuse techniques help offset the cost of III-V growth substrates by using a single wafer for multiple growths, but costly re-polishing after device removal limits the end benefit. In this work, we present planarization growth by hydride vapor-phase epitaxy (HVPE), a potentially low-cost growth technique, as a method of smoothing rough substrates for subsequent high-quality device growth without the need for polishing. First, we show there is a threshold for allowable substrate roughness without device degradation by comparing devices grown by organometallic vapor-phase epitaxy (OMVPE) on epi-ready polished and pre-polished substrates that did not have the final epi-ready polish. We then demonstrate successful smoothing with HVPE growth on substrates with different surface morphologies, with features ranging from general roughness to large facets. Initial devices grown by HVPE on a pre-polished substate showed no degradation compared to a control wafer, indicating that planarizing rough substrates through HVPE growth is a promising path toward being able to use rough substrates directly for growth, without costly polishing steps.