A pulsed ruby laser holographic interferometer was used to detect density gradients in the airflow around an airfoil at subsonic speeds in a low speed wind tunnel. These experiments proved that vibration of the optical components or object between exposures of the interferometric hologram does not destroy the detection of density gradients but actually can aid in the flow visualization. The density gradients determined from the fringe pattern analysis are consistent with the anticipated flow pattern.
Electroluminescent phosphors are used as the display portion of infrared image converters, operated at liquid-nitrogen temperature. These phosphors lose considerable brightness upon cooling, giving a dim display. This report demonstrates the sources of this brightness loss during cooling as (1) due to spectral shift to wavelengths less visible to the eye and (2) changes in dielectric constant of the binder during cooling, causing a decrease in effective electric field applied to the phosphor particles. Some improvement in brightness can be demonstrated by using very thin phosphor layers, thereby increasing the effective applied field.
The photoelectric emission from barium oxide has been investigated by measuring the total photoelectric yield and the distributions in kinetic energy of the emitted electrons using an improved magnetic velocityanalyzer tube. The energy distribution measurements revealed four "fast peaks" which are interpreted as being associated with direct transitions from energy levels located approximately 1.0, 1.4, 2.0, and 2.6 eV below the vacuum level. Confirmation of these transitions was obtained from plots of the spectral distribution of the total photoelectric yield. A "slow peak" was observed in the energy distributions at about 0.5 eV which is attributed to exciton-induced photoelectric emission. Evidence is presented indicating that this is a true peak and not the truncated tail of a distribution which peaks at still lower energies. Possible identifications of the energy levels involved in the direct transitions and the energy loss mechanism involved in the exciton-induced transitions are discussed.
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