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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 343 records · Page 19
All sourcesNASA NTRSDOE OSTI
NASA NTRS1988

Study of optical output couplers for submillimeter wavelength backward-wave oscillators (BWO's)

The machining of slow wave structures for high frequency backward-wave oscillators (BWO) is extremely difficult beyond 1 THz. Recently a microfabrication technique using photolithography and ion-beam assisted etching has been used to construct a prototype BWO operating at 200 to 265 GHz. The output coupler for such tubes remains a problem. Waveguides do not exist or are very lossy at the frequencies of interest (300 to 2000 GHz). This paper discusses several scaled experiments of optical output couplers for submillimeter BWOs. Various designs of planar antennas (Vivaldi horns) and lens-feed systems (Hyperhemispherical lens) were constructed and tested between 20 and 100 GHz using a spectrum analyzer. The lens system was also tested at 337 GHz using a CO2 pumped FIR laser.

Cook, Jerry D.↗
NASA NTRS1980

Submillimeter local oscillators for heterodyne spectroscopy

The major technological innovations in continuous wave (CW) submillimeter sources which are specifically suitable for application as local oscillators in heterodyne systems are reviewed. A description of the various sources is given which underscores the general principles and operating features for each type of device. Particular emphasis is placed on CW optically pumped lasers, which have had a dramatic impact as widely available sources of narrow linewidth coherent radiation. The state-of-the-art is summarized for these lasers and performance data are presented for several local oscillator packages. Optically pumped lasers are then compared and contrasted with other competing sources such as backward wave oscillators, IMPATT diodes, and Josephson junctions. By comparing their advantages and limitations for use as local oscillators, the potential applications of these different sources are projected. The prospects for increased tunability, reliability, and scalability are briefly considered, and several novel techniques for generating partially tunable radiation using Schottky diode mixers or CW Raman lasers are highlighted.

Danielewicz, E. J., Jr.↗
NASA NTRS2007

Terahertz Schottky Multiplier Sources

This viewgraph presentation reviews the multiplier source technologies and the status/Performance of THz multiplier sources. An example of a THz application is imaging radar. The presentation reviews areas of requirements for THz sources: (1) Figures of merit, (i.e., Frequency Terahertz for high resolution Bandwidth of at least 15 GHz for high range resolution Efficiency (i.e., minimize power supply requirements) (2) Output power: (i.e., Milliwatts below 800 GHz, 10s of microwatts above 1 THz, 1-2 microwatts near 2 THz (3) Mechanical--stability, compact, low mass (4) Environmental -- radiation, vibration, thermal. Several sources for 0.3 - 2 THz are reviewed: FIR lasers, quantum cascade lasers (QCL), backward-wave oscillator (BWO), and Multiplier sources. The current state of the art (SoA) is shown as Substrateless Technology. It also shows where the SoA is for devices beyond 1 THz. The presentation concludes by reviewing the options for future development, and 2 technology roadmaps

submillimeter wave↗
NASA NTRS1992

Optically pumped submillimeter laser heterodyne receivers - Astrophysical observations and recent technical developments

NASA's prospective sub-mm-wave astrophysical missions encompass the Small Explorer Submillimeter Wave Astronomy Satellite, scheduled for launch in 1995, the Submillimeter Intermediate Mission, and the Large Deployable Reflector; until these are operational, sub-mm observations will be conducted at mountain sites and aboard aircraft platforms. Attention is presently given to the technical challenges faced by terahertz-range receiver developers, and it is noted that optically pumped sub-mm lasers furnish the only practical local oscillation source for heterodyne receivers in the 600-3000 GHz range. An account is given of ground-based and airborne astrophysical applications of heterodyne receivers.

Chin, Gordon↗
NASA NTRS1992

Submillimeter heterodyne spectroscopy and remote sensing of the upper atmosphere

Submillimeter-wavelength heterodyne spectroscopy by microwave limb sounding (MLS) from orbiting satellite is a measurement technique for studying Earth's stratosphere, mesosphere and lowerr thermosphere on a global scale. Development and deployment of such tools are timely, as stratospheric ozone shileds life from solar ultraviolet radiation but is depleted by pollution from industrial activities. MLS experiments on NASA's Upper Atmosphere Research Satellite (UARS) and Earth Observing System (EOS) are now being developed and implementend for global monitoring. Atmospheric thermal-emission spectra at millimeter and submillimeter wave-lengths are measured as the instrument field of view (FOV) is scanned through the limb from above. Atmospheric profiles of molecular abundances, temperature, pressure, wind and magnetic field can be determined from the measured emission spectra. Intensity of the emission can provide abundance and temperature. Measured linewidths, and emission from temperature-insensitive O2 lines, can provide pressure. Differentitaion of measured pressure with repsect ot measured height differential (obtaiend from the instrument FOV scan encoder) can also provide temperature through atmospheric hydrostatic equilibrium (which relates temperature to pressure and height differential). Doppler shifts of spectral lines can provide wind, and Zeeman splitting of the magnetic-dipole lines of O2 can provide magnetic field.

Waters, J. W.↗