Engineering topics

Coulter, Daniel R.

Publications and source records attributed to Coulter, Daniel R..

25 records · Page 2

NASA NTRS1989

Materials development for precision segmented reflector applications

The requirements developed to guide the selection of current and future materials for precision segmented reflectors are presented along with a list of desirable properties. Some potential candidate materials including modified fiber reinforced organic matrix composites as well as carbon/carbon composites, graphite/glass composites, and metal matrix composites are identified. It is noted that in the near term, it is likely that modified fiber reinforced organic matrix composites have good applicability. In the longer term, materials such as carbon/carbon composites, graphite/glass composites and metal matrix composites may provide the best mix of properties.

Coulter, Daniel R.↗

NASA NTRS1989

Optical limiting in solutions of metallo-phthalocyanines and naphthalocyanines

Optical limiting measurements have been made on solutions of several metal containing phthalocyanines and naphthalocyanines. Measurements at 532nm using nanosecond pulses from a Q-switched Nd:YAG laser show limiting throughputs of 1-10 millijoules with mild focussing in alcohol solutions with nominal transmissions of 30-70 percent. Measurements on chloro-aluminum-phthalocyanine solutions utilizing individual 30 psec pulses or trains (spanning about 100nsec) of modelocked pulses have shown even lower limiting throughputs. Thus, the dynamic range of the limiting behavior has been shown to cover at least three orders of magnitude. Prompt limiting is attributed to strong singlet-singlet (S1-Sn) absorption, whereas the longer time limiting behavior is postulated to result from strong triplet-triplet (T1-Tn) absorption. In addition to these studies, efforts have been underway to identify materials with reduced limiting throughput and improved optical transmission characteristics.

Coulter, Daniel R.↗

NASA NTRS1988

Second and third order nonlinear optical properties of conjugated molecules and polymers

Second- and third-order nonlinear optical properties of some newly synthesized organic molecules and polymers are reported. Powder second-harmonic-generation efficiencies of up to 200 times urea have been realized for asymmetric donor-acceptor acetylenes. Third harmonic generation chi(3)s have been determined for a series of small conjugated molecules in solution. THG chi(3)s have also been determined for a series of soluble conjugated copolymers prepared using ring-opening metathesis polymerization. The results are discussed in terms of relevant molecular and/or macroscopic structural features of these conjugated organic materials.

Perry, Joseph W.↗

NASA NTRS1987

O-atom degradation mechanisms of materials

The low Earth orbit environment is described and the critical issues relating to oxygen atom degradation are discussed. Some analytic techniques for studying the problem and preliminary results on the underlying degradation mechanisms are presented.

Coulter, Daniel R.↗

NASA NTRS1987

Production of pulsed atomic oxygen beams via laser vaporization methods

Energetic pulsed atomic oxygen beams were generated by laser-driven evaporation of cryogenically frozen ozone/oxygen films and thin films of indium-tin oxide (ITO). Mass and energy characterization of beams from the ozone/oxygen films were carried out by mass spectrometry. The peak flux, found to occur at 10 eV, is estimated from this data to be 3 x 10(20) m(-2) s(-1). Analysis of the time-of-flight data indicates a number of processes contribute to the formation of the atomic oxygen beam. The absence of metastable states such as the 2p(3) 3s(1) (5S) level of atomic oxygen blown off from ITO films is supported by the failure to observe emission at 777.3 nm from the 2p(3) 3p(1) (5P sub J) levels. Reactive scattering experiments with polymer film targets for atomic oxygen bombardment are planned using a universal crossed molecular beam apparatus.

Brinza, David E.↗

NASA NTRS1986

Gated photochemical hole burning in photoadducts of polyacenes

A photoadduct of anthracene and tetracene (A-T) in a polymer matrix at 1.5 K generates an absorption spectrum which exhibits two-color, photon-gated photochemical hole burning (PHB) when irradiated with narrowband exciting light into the 0-0 band of the S1-S0 absorption. The efficiency of this PHB process is found to be enhanced by simultaneous irradiation near the maximum of the Tn-T1 absorption of A-T; hole widths of less than 0.07/cm have been observed for this photochemical cleavage of A-T.

Iannone, Mark↗

NASA NTRS1986

Production of pulsed atomic oxygen beams via laser vaporization methods

The generation of energetic pulsed atomic oxygen beams by laser-driven evaporation of cryogenically frozen ozone/oxygen films and thin indium-tin oxide (ITO) films is reported. Mass spectroscopy is used in the mass and energy characterization of beams from the ozone/oxygen films, and a peak flux of 3 x 10 to the 20th/sq m per sec at 10 eV is found. Analysis of the time-of-flight data suggests that several processes contribute to the formation of the oxygen beam. Results show the absence of metastable states such as the 2p(3)3s(1)(5S) level of atomic oxygen blown-off from the ITO films. The present process has application to the study of the oxygen degradation problem of LEO materials.

Brinza, David E.↗