Optical particle size measurements of hygroscopic smokes in laboratory and field environments.

Optical particle size analyzer (PSA) measurements of hygroscopic smokes are reported from experiments conducted in laboratory chambers and in field tests. Three different instruments were used: a particle sizing interferometer; a Climet (model 211); and a Particle Measurement Systems PSA (model CSASP-100-HC). Field measurements were made in relative humidity conditions ranging between 65 and 97%. The results indicate that the size distributions are at least bimodal-not log-normal-and that mean particle diameter does not appear to increase with increasing relative humidity.

Two-color two-spot laser velocimeter.

The design of a two-color two-spot laser velocimeter based on an argon laser and using backscattered light is presented. The prism assembly used in splitting the laser's output beam into 514.5- and 488.0-nm beams, also allows for the rotation of the two spots about a common center, allowing two components of a flow to be measured. The system was tested at ranges of 50, 100, and 150 m, and the results of these tests are presented.

Visibility of large spheres observed with a laser velocimeter: a simple model.

A model is developed to express the signal visibility for large refracting or reflecting spheres observed with a fringe-type laser velocimeter. The model yields a closed form solution for the visibility when scattering is observed off axis in the near forward, 90 degrees , or near backward direction. Results show that particle size range can be adjusted by aperture adjustments at the scattered light receiver. Comparison of model predictions with recently published numerical computations shows good agreement.

Sample space for particle size and velocity measuring interferometers.

An analysis is presented of some parameters that can affect the sampling characteristics of interferometers designed to measure particle size and/or velocity. In particular, it is demonstrated how particle size and electronic instrumentation affect the sampling capacity of the instrument.

Observation of large particles with a laser interferometer.

Experimental observations of large particle signals generated by the passage of a particle through the interference pattern of a laser interferometer are reported. The results show that particle size can be determined from analysis of the signal. The influence of large particle sizes in determining the velocity of the particle from the signal is discussed.

Two-component, self-aligning laser vector velocimeter.

A newly developed laser Doppler velocimeter is described. The basic optical component of the instrument is a two-dimensional ultrasonic Bragg cell. It is shown that use of this Bragg cell simplifies the optics usually required for the more conventional velocimeters, allows measurement of two-vector components of velocity, requires no adjustment of alignment mirrors, and enables both velocity component signals to be detected with a single detector. Some results from experiments using this velocimeter in an atmospheric application are described.

Determination of a third orthogonal velocity component using two rotationally displaced laser Doppler velocimeter systems.

Transformation equations are derived that may be used to determine a third orthogonal velocity component from measurements made at a common point by two rotationally displaced, two orthogonal component laser Doppler velocimeter (LDV) systems. These equations also may be used to relate velocity measurements made in a particular coordinate system to any other coordinate system. It is shown that the set of smallest angles that may be used to separate the two, two component, LDV systems is very sensitive to the relative magnitudes and directions of the individual velocity components. When the magnitudes of all velocity components are about the same, it is found that the minimum angle of separation is of the same order as the instrumental error of the LDV systems.

Measurement of particle size, number density, and velocity using a laser interferometer.

A method for determining particle size, number density, and velocity utilizing a laser interferometer is analyzed. The results show that when the fringe spacing is comparable to a particle diameter, size can be estimated; and when the fringe spacing is much greater than the average particle diameter, number density can be measured. Since the optical arrangment for the interferometer is identical to that for a number of laser velocimeters, the effects of particle size on the velocimeter signal are discussed.

Analysis of atmospheric laser Doppler velocimeters.

Fundamental relationships between backscattered power, range, wavelength, and number of scatter centers in the probe volume for the self-aligning, dual-scatter, laser doppler velocimeter are developed. It is shown that not all power scattered from the velocimeter probe volume contributes to a doppler signal. This fact leads to significant deviations in calculations involving signal-to-noise power ratios as compared to the case when only gross backscattered power is considered.

Holographic techniques for the study of dynamic particle fields.

The techniques of small particle holography are extended in an elementary way to show that multiple exposure holography can be used to study the dynamic properties of particle fields. Experimental techniques for performing such a study are then described. Finally, as a typical example, a multiple exposure hologram of an aerosol is presented with a portion of the data extracted from it. The hologram exhibits a vast amount of information including the determination of the velocity and density field, size distribution, flow structure, and diffusion rate.