RESUMEN
A fast ellipsometry system with a resolution of only a few nanoseconds that can simultaneously measure all four Stokes parameters was developed for use in dynamic experiments. Due to its fine temporal resolution, the system is useful for a wide variety of dynamic setups, two of which are presented, fast foil heating and shock compression. As a test case the optical properties of nickel were measured in a fast foil heating setup. The complex index of refraction and emissivity at 532 nm and in the range of 1000-1900 K are presented. It was found that the emissivity monotonously increases below and above the melting point while an abrupt increase of about 2% was observed at the phase transition. These results are in accordance with the literature. Shock compression experiments included sample-free surface measurements. Samples of 1020 steel were shocked up to 25 GPa on the Hugoniot curve. The measured optical properties under these conditions showed a significant change; the value of the emissivity was doubled.
RESUMEN
The influence of aperture averaging on the two-wavelength intensity covariance function was experimentally determined for visible (0.63 microm) and infrared (1.06 microm) collinear, approximately spherical beams which propagated through the earth's turbulent atmosphere. Range varied from 1300 to 3250 m, and due to the prevailing atmospheric conditions, most measurements were made in the strong turbulence regimes. Results show that (1) the covariance function monotonically decreases as the receiver aperture size increases; (2) the correlation coefficient attains high values > or = 0.7) even for a relatively small aperture size of 5 mm; (3) while the single wavelength probability distribution of the intensity is approximately lognormal, the experimental two-wavelength conditional probabilities are higher than those predicted by the lognormal model.
RESUMEN
A device for the measurement of concentration fluctuations in flowing gases which can be used to establish and control the degree of mixing is described. The design is based on an improved laser-schlieren technique combined with photometric detection. The device operates on-line and has high sensitivity and fast response. A quantitative sensitivity evaluation is made and checked experimentally. The device is used to characterize the performance of some simple mixing configurations. The detection limits for various gas mixtures are given.