Engineering topics

Yu, C.

Publications and source records attributed to Yu, C..

46 records · Page 3

NASA NTRS1990

Study of mid IR fiber transmission and mode patterns under laser induced stimulated Brillouin scattering

Mid IR fiber transmission and exit radiation mode patterns at various incident CO2 laser power levels appear to be effective diagnostic tools for monitoring laser induced stimulated Brillouin scattering in various mid IR fibers. Such processes are deemed to be essential mechanisms for fiber-optic amplifiers and switches as potential replacements of current repeaters and bistable devices.

Yu, C.↗

NASA NTRS1986

Guided transmission for 10 micron tunable lasers

Performance characteristics are reported for two types of IR tunable laser guided transmission, one of which incorporates a CO2 laser, metallic piping or fiber-optics, and a detector system, while the other employs a tunable diode laser, fiber-optics, and a detector system. While existing technology furnishes low loss, rugged, near-single mode piping, fiber-optics exhibits appreciably higher loss, and its multimode fibers are fragile and chemically unstable. Studies have accordingly concentrated on such relevant fiber parameters as loss, toxicity, hygroscopicity, refractive index, flexibility, and thermal behavior at low temperature.

Yu, C.↗

NASA NTRS1985

Nucleosynthesis in the terrestrial and solar atmospheres

Variations of Delta D, delta C-13, Delta C-14 and Delta O-18 with time were measured by a lot of experiments. Many abnormalities of isotope abundances in cosmic rays were found by balloons and satellites. It is suggested that these abnormalities are related to nuclearsynthesis in the terrestrial and solar atmospheres and are closely related to solar activities.

Yu, C.↗

NASA NTRS1985

A very important process of nucleosynthesis in stars

When some nuclei are free from strong gravitational field, they are unstable and will become stable nuclei by competitions of following processes: (1) neutron-evaporation; (2) spontaneous fission; and (3) beta prime 3-decay. At the initial stage, (1) and (2) are important and (3) can be ignored. The qualitative results are as follows: (1) it seems that nuclei with A 100 come from the spontaneous fission and beta prime decay of neutron-evaporated nuclei with A similiar to 140-440, which can replace the r-process; (2) the super-heavy elements with Z=114--126 (A similiar to 330--360) can be formed. They can be observed in cosmic rage if they have the halftime T 10 to the 7th poweer years; (3) the peak in the rare-earth elements comes from the symmetric fission of super-heavy elements; (4) there are more neutron-rich nuclei in the fragments; and (5) the abundances of a 83 elements in cosmic rays are one order of magnitude higher than that in the solar system.

Yu, C.↗

NASA NTRS1983

Guidance and control of MIR TDL radiation via flexible hollow metallic rectangular pipes and fibers for possible LHS and other optical system compaction and integration

Flexible hollow metallic rectangular pipes and infrared fibers are proposed as alternate media for collection, guidance and manipulation of mid-infrared tunable diode laser (TDL) radiation. Certain features of such media are found to be useful for control of TDL far field patterns, polarization and possibly intensity fluctuations. Such improvement in dimension compatibility may eventually lead to laser heterodyne spectroscopy (LHS) and optical communication system compaction and integration. Infrared optical fiber and the compound parabolic coupling of light into a hollow pipe waveguide are discussed as well as the design of the waveguide.

Yu, C.↗

NASA NTRS1982

Integration and compaction of optical systems in the mid-infrared

Problems in the design of optical systems for use with mid-IR (MIR; 10.6-micron) lasers are reviewed. The cryogenically operated lead-chalcogenide tunable diode lasers currently used as sources emit complex far-field patterns and require sophisticated beam collection, shaping, and guide optics. Since conventional optics using large mirrors and Ge lenses are often awkward to use and sensitive to vibration, and since optical fibers for the MIR have not been perfected, current research concentrates on hollow flexible rectangular metallic pipes. These pipes are shown to provide transmission of 95 percent or better over a 1-m length, with beam shaping and polarization control. The low transmission losses and wideband IR transmission of single-crystal alkali halides suggest the feasibility of their use in MIR optical fibers and waveguides.

Yu, C.↗

NASA NTRS1978

Investigation of laser induced parametric interactions in optical waveguides and fibers

Experimental and theoretical aspects of the laser pump depletion characteristics in an optical fiber due to stimulated Raman scattering, and stimulated Brillouin scattering were studied. A review is presented of research in fiber transmission accompanied by stimulated scattering. Results of experimental work with tunable dye lasers and argon lasers are presented. The spectral profiles of the laser pump and its transmitted light through the fiber are given.

Yu, C.↗

NASA NTRS1977

The reflection coefficient in stimulated parametric backscattering

The step-function approximation of the anomalous reflection coefficient in laser-induced parametric backscattering currently used in the theory of nonlinear laser plasma interactions is improved using a simple exponential derived from elliptic functions. The validity of the single-reflection analysis is reaffirmed.

Yu, C.↗

NASA NTRS1977

Correlation between stimulated scattering processes and laser-induced damage in crystalline quartz

The results of a systematic series of experiments to uncover possible correlation between laser-induced stimulated-Brillouin-scattering (SBS) phonons and damage in quartz are presented. Such correlation is confirmed and the various thresholds are established. The anomalous transmission factor under phonon generation is found to decay exponentially as predicted with increasing incident laser power. The LF SBS phonon is also demonstrated to be a sensitive probe for precatastrophic damage.

Yu, C.↗

NASA NTRS1976

Asymptotic residual pump transmission characteristics in laser-induced stimulated Brillouin scattering

The considered asymptotic relationship is investigated and an expression is sought for the slope of the curve representing the relation between the residual fractional transmitted pump and the pump excitation in backward-traveling-wave amplification. It is found that the characteristic -2 slope of the oscillation curve is a unique property. Rapid exponential decay may very well constitute an inherent limiting factor for efficient energy conversion.

Hsu, H.↗