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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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At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1994

Improvements In Optically Stimulated Electron Emission

Optically stimulated electron emission (OSEE) used in inspection for contamination of critical bonding surfaces in solid rocket motors of Space Shuttle prior to formation of adhesive bonds on surfaces during manufacture and refurbishment. Fundamental OSEE inspection technique described in "Surface-Contamination Inspection Tool for Field Use" (MFS-25581) and "Detecting Contamination With Photoelectron Emission" (MFS-25619). OSEE measurement head easily portable, and measurement operation convenient and rapid, making it useful inspection technique in industrial environment. Reveals contamination in many situations in which other techniques do not work.

Yost, William T.↗
NASA NTRS2005

Optically Stimulated Electron Emission Contamination Monitor and Method

An apparatus and method for performing quality inspections on a test surface based on optically stimulated emission of electrons. In one embodiment, the apparatus comprises a device for producing optical radiation having a plurality of different spectrum lines, selecting at least one of the spectrum lines, and directing the selected spectrum line to the test surface, and circuitry for detecting a current of photoelectrons emitted from the test surface, generating a signal indicative of photoelectron current, and for indicating a condition of quality based on the generated signal indicative of the photoelectron current. In one embodiment, the method comprises producing optical radiation having a plurality of different spectrum lines, selecting at least one of the spectrum lines and directing the selected spectrum line to the test surface, detecting a current of photoelectrons emitted from the test surface and generating a signal indicative of photoelectron current, and indicating a condition of quality based on the generated signal indicative of the photoelectron current.

Christopher S Welch↗
NASA NTRS2006

Topside sounders as mobile ionospheric heaters

There is evidence that satellite-borne RF sounders can act as mobile ionospheric heaters in addition to performing topside sounding. The main objective of topside sounding is to use sounder-generated electromagnetic (em) waves to obtain ionospheric topside vertical electron-density (N(sub e) profiles. These profiles are obtained from mathematical inversions of the frequency vs. delay-time ionospheric reflection traces. In addition to these em reflection traces, a number of narrowband intense signals are observed starting at zero delay times after the transmitted pulses. Some of these signals, termed plasma resonances, appear at characteristic frequencies of the ambient medium such as at the electron cyclotron frequency f(sub ce), the harmonics nf(sub ce), the electron plasma frequency f(sub pe) and the upper-hybrid frequency f(sub uh), where (f(sub uh))(exp 2) = (f(sub ce))(exp 2) + (f(sub pe))(exp 2) . These signals have been attributed to the oblique echoes of sounder-generated electrostatic (es) waves. These resonances provide accurate in situ f(sub pe) and f(sub ce) values which, in turn, lead to accurate N(sub e) and [B] values where B is the ambient magnetic field. Resonances are also observed between the nf(sub ce) harmonics both above and below f(sub uh). The former, known as the Qn plasma resonances, are mainly attributed to the matching of the wave group velocity of sounder-generated (Bernstein-mode) es waves to the satellite velocity. The frequency spectrum of these waves in the magnetosphere can be used to detect non-Maxwellian electron velocity-distributions. In addition, these resonances also exhibit components that appear to be the result of plasma emissions stimulated by the sounder pulses. The plasma resonances observed between the nf(sub ce) harmonics and below f(sub uh), known as the Dn plasma resonances, are entirely attributed to such sounder-stimulated plasma emissions. There are other sounder-stimulated plasma phenomena that also fall into this category, e.g., ion affects on electron-resonant phenomena, proton-cyclotron echoes and N(sub e) field-aligned irregularities (FAI). Some of these phenomena are more pronounced when f(sub pe)/f(sub ce) approx. = n where n is an integer significantly greater than one. The observations suggest that the sounder-stimulated plasma phenomena are stimulated, or enhanced, on a time scale much less than one second. The purpose of this presentation is to review the above topics with particular emphasis on the sounder-stimulated plasma phenomena.

Benson, R. F.↗
NASA NTRS1975

Uncertainties in the far-infrared absorption of interstellar clouds

The observed absorption of far-infrared radiation by an interstellar dust cloud is a complicated function of the material properties of grains, of their column density, and of the extent of stimulated emission. At long wavelengths, neglect of stimulated emission would lead to an underestimate of the amount of absorbing material observed along a line of sight. However, if the complex index of refraction for grains is measured at the low temperatures in question, a classical analysis will be correct since the measured refractive index correctly accounts for stimulated emission. Since the grain temperatures may strongly affect the refractive index of a grain, typical interstellar grain temperature fluctuations are analyzed in a final section.

Harwit, M.↗
NASA NTRS1975

Stimulated Stokes emission with a dye laser - Intense tuneable radiation in the infrared

Tunable stimulated Stokes emission is generated at approximately 2.9 microns in barium vapor with an oscillator-amplifier dye laser. The conversion efficiency is as high as 40% and the energy output as high as 30 mJ. The emission is tuneable over about 100 wavenumbers. At high vapor pressures the tuning profile is markedly asymmetric.

Carlsten, J. L.↗
NASA NTRS1992

Optically stimulated electron emission - Current-voltage response and spectral sensitivity

A highly reproducible optically stimulated electron emission (OSEE) response steel was achieved in laboratory conditions through suppression of surface photochemistry by replacing air with argon. This permitted the characterization of the OSEE process on D6AC steel as a photodiode. With a low-pressure mercury light source, most of the OSEE current is attributed to photoelectrons released by the 185-nm mercury line with only about 5 percent of the photocurrent associated with the 254-nm line. The forward current-voltage characteristic of the OSEE diode is linear for small fields changing to a square root response at larger fields. These results are all consistent with established theories.

Welch, Christopher S.↗
NASA NTRS1995

Spectroscopic Investigation of Ce(3+) Doped Fluoride Crystals

Doping of the trivalent rare-earth cerium ion into fluoride crystals is of interest in producing turnable ultra-violet solid state lasers. These lasers are desirable for many applications in medicine, industry, and scientific research, including remote sensing. High absorption and stimulated emission cross sections of the dipole allowed 4f-5d transitions show promise in cerium as a laser ion in crystals. Several research groups have already reported the observation of stimulated emission of cerium in LiYF4, LiSrAlF6, and LiCaAlF6. However, the color center formation in the crystals due to the excited state absorption of ultra-violet pump light adds difficulty to achieving laser action. We have investigated the spectroscopic properties of cerium such as absorption and emission spectra, and lifetimes in four different fluoride crystals, including LiCaAlF6, LiSrAlF6, KyF4 and LiYF4. We have derived the polarized absorption and stimulated emission cross sections from transmission and fluorescence emission measurements for each of the host crystals. we have measured the lifetime of the lowest 5d level; moreover, investigated the temperature dependence of this lifetime and color center formation. Our results on absorption and stimulated emission cross sections for LiCaAlF6 and LiSrAlF6 are similar to the results already published.

Reinhart, Donald H.↗
NASA NTRS1988

Evaluation of materials for tunable vibronic lasers

Three techniques (peak single-pass gain, fluoresence band narrowing, and lifetime shortening) for determining the effects of stimulated emission on the spectra of solid-state vibronic laser materials have been compared. The methods were employed to determine the pump energy density and population inversion at threshold, the stimulated emission cross section, and the gain coefficient for two potential vibronic laser materials. An effective shortening of the fluorescence lifetime is predicted at high excitation levels, with a distinct threshold where stimulated emission processes become important.

Kliewer, Michael L.↗
NASA NTRS1996

A Portable Surface Contamination Monitor Based on the Principle of Optically Stimulated Electron Emission (OSEE)

Many industrial and aerospace processes involving the joining of materials, require sufficient surface cleanliness to insure proper bonding. Processes as diverse as painting, welding, or the soldering of electronic circuits will be compromised if prior inspection and removal of surface contaminants is inadequate. As process requirements become more stringent and the number of different materials and identified contaminants increases, various instruments and techniques have been developed for improved inspection. One such technique, based on the principle of Optically Stimulated Electron Emission (OSEE), has been explored for a number of years as a tool for surface contamination monitoring. Some of the benefits of OSEE are: it is non-contacting; requires little operator training; and has very high contamination sensitivity. This paper describes the development of a portable OSEE based surface contamination monitor. The instrument is suitable for both hand-held and robotic inspections with either manual or automated control of instrument operation. In addition, instrument output data is visually displayed to the operator and may be sent to an external computer for archiving or analysis.

Perey, D. F.↗
NASA NTRS2008

Using Optically Stimulated Electron Emission as an Inspection Method to Monitor Surface Contamination

During redesign of the Space Shuttle reusable solid rocket motor (RSRM), NASA amended the contract with ATK Launch Systems (then Morton Thiokol Inc.) with Change Order 966 to implement a contamination control and cleanliness verification method. The change order required: (1) A quantitative inspection method (2) A written record of actual contamination levels versus a known reject level (3) A method that is more sensitive than existing methods of visual and black light inspection. Black light inspection is only useful for inspection of contaminants that fluoresce near the 365 nm spectral line and is not useful for inspection of most silicones that will not produce strong fluorescence. Black light inspection conducted by a qualified inspector under controlled light is capable of detecting Conoco HD-2 grease in gross amounts and is very subjective due to operator sensitivity. Optically stimulated electron emission (OSEE), developed at the Materials and Process Laboratory at Marshall Space Flight Center (MSFC), was selected to satisfy Change Order 966. OSEE offers several important advantages over existing laboratory methods with similar sensitivity, e.g., spectroscopy and nonvolatile residue sampling, which provide turn around time, real time capability, and full coverage inspection capability. Laboratory methods require sample gathering and in-lab analysis, which sometimes takes several days to get results. This is not practical in a production environment. In addition, these methods do not offer full coverage inspection of the large components

Lingbloom, Mike S.↗
NASA NTRS1974

Expected far infrared polarization of H2 regions and the nuclei of galaxies

The expected polarization of far infrared sources is discussed, and it is shown that the observed degree of polarization generally depends on two factors: (1) the availability of a mechanism that can produce polarization, and (2) the gain in polarization which absorption or stimulated emission can produce within a source. It is pointed out that stimulated emission could produce sizeable gain changes in compact dust clouds such as those associated with H2 regions and possibly also in dense regions exhibiting OH and H2O masers. Whether such a gain can actually become positive (maser-like behavior) is not clear, but this would in any case depend on the chemical structure of the grain material and the spectral range of interest.

Harwit, M. O.↗
NASA NTRS1991

Theoretical studies of lasers and converters

Discussed here is Doppler broadening and its effects upon the stimulated emission cross-section connecting an upper level with a lower level in an iodine laser. The stimulated emission cross section is given. The level transitions for the iodine laser are illustrated as are the relative intensities of these transitions. Also discussed is the Voigt profile, which considers the effect of both Doppler broadening and collision broadening upon the absorption line shape. The equations describing the Voigt profile were added to the continuous flow laser model laser simulation program. The results were compared with the standard absorption profile reported in an earlier study. There seems to be no advantage to using the Voigt profile as the laser power output is relatively insensitive to changes in the absorption cross section at the pressures being considered for a space laser. One disadvantage of using the Voigt profile is the excessive numerical computations required by the additional equations.

Heinbockel, John H.↗
NASA NTRS1975

Direct nuclear pumping of a helium-xenon laser

Experiments attempting to achieve laser excitation by direct interaction of nuclear reaction products (fission fragments) with the lasing media are reported. Laser output followed reactor power surge by 50 microsec, the neutron thermalization time. The light output exhibited a threshold for onset and termination of laser action. The observed light output was shown to be caused by stimulated emission, because the signal disappeared when the totally reflecting (flat) mirror at one end of the apparatus was covered. Fission fragments were shown to be responsible for the stimulated emission, because the laser output disappeared when the U-235 liner was covered by an aluminum foil.

Helmick, H. H.↗
NASA NTRS2012

Organic materials able to detect analytes

The present invention generally relates to polymers with lasing characteristics that allow the polymers to be useful in detecting analytes. In one aspect, the polymer, upon an interaction with an analyte, may exhibit a change in a lasing characteristic that can be determined in some fashion. For example, interaction of an analyte with the polymer may affect the ability of the polymer to reach an excited state that allows stimulated emission of photons to occur, which may be determined, thereby determining the analyte. In another aspect, the polymer, upon interaction with an analyte, may exhibit a change in stimulated emission that is at least 10 times greater with respect to a change in the spontaneous emission of the polymer upon interaction with the analyte. The polymer may be a conjugated polymer in some cases. In one set of embodiments, the polymer includes one or more hydrocarbon side chains, which may be parallel to the polymer backbone in some instances. In another set of embodiments, the polymer may include one or more pendant aromatic rings. In yet another set of embodiments, the polymer may be substantially encapsulated in a hydrocarbon. In still another set of embodiments, the polymer may be substantially resistant to photobleaching. In certain aspects, the polymer may be useful in the detection of explosive agents, such as 2,4,6-trinitrotoluene (TNT) and 2,4-dinitrotoluene (DNT).

Rose, Aimee↗
NASA NTRS1972

On the stability of obliquely propagating whistlers.

By means of an energy conservation approach, this paper analyzes the growth rates of whistlers with arbitrary frequency and direction of propagation in a cold plasma permeated by a dilute energetic electron population. Numerical results are obtained for whistler frequencies and plasma characteristics prevailing at the onset of artificially stimulated emissions. It is found that the growth rates do not in general maximize for propagation along the static magnetic field, and a criterion for the existence of maximal growth at this direction is derived. An application to artificially stimulated emissions is discussed.

Brinca, A. L.↗