Abstract

An apparatus for sizing particles, droplets, bubbles, or the like employing laser light scattering is disclosed. A laser is used for generating two beams of light having different wavelengths or polarizations. The beams with different wavelengths may be generated by an argon ion laser or by two different lasers (e.g., Helium Neon and Helium Cadmium). Two beams with orthogonal polarizations may be produced by partitioning a single linearly polarized beam and rotating the polarization of one by 90°. One of the beams is then expanded using a conventional beam expander and then redirected to be coaxial with the first beam. The beams are then focused to a common focal region. One beam is from two to four times larger in diameter than the other. An optical collection apparatus for sensing the light scattered caused by the particles, droplets, bubbles or the like passing through the focused beams has an axis extending into the focused beams. The axis of the collection apparatus may be aligned with the transmitted beams in the forward or backward direction (on-axis detection) or at some suitable angle to the beams (off-axis detection). The collection apparatus includes receiver lenses which focuses the scattered light through the beam splitter onto a first photo-detector, and light reflected from the beam splitter is directed onto a second photo-detector. The photo-detectors sense the scattered light from the beams with separate wavelengths or polarizations and produce proportionate voltage amplitudes. The peak voltages are determined from the information sensed by the light collection apparatus. A mathematical formulation is used with the known beam diameters and intensities along with the two measured signal voltage amplitudes to determine the particle trajectory through the beams and hence, particle size. The technique also allows for the determination of the sample volume cross-section and particle speed, thus allowing the determination of particle number density and volume flux.

Other References

• Heterodyne and Quasi-Heterodyne Holographic Interferometry; Dandliker & Thalmann, 24 Opt. Eng. 824, (1985)
• Heterodyne Holography Applications in Studies of Small Components, Pryputniewicz; 24 Opt. Eng. 849, (1985)
• Phase/Doppler Spray Analyzer for Simultaneous Measurements of Drop Size and Velocity Distributions; Bachalo & Hauser; 23 Opt. Eng. 583, (1984)
• Development of the Phase/Doppler Spray Analyzer for Liquid Drop Size and Velocity Characterizations; Bachalo & Houser; AIAA/SAE/ASME 20th Joint Propulsion Conf., (1984)
• MIE and Refraction Theory Comparison for Particle Sizing with the Laser Velocimeter; Pendleton; 21 App. Opt. 684, (1982)
• Method for Measuring the Size and Velocity of Spheres by Dual-Beam Light-Scatter Interferometry; Bachalo; 19 App. Opt. 363, (1980)
• Particle Sizing Using Laser Interferometry; Roberds; 16 App. Opt. 1861, (1977)
• Scattering from a Moving Spherical Particle by Two Crossed Coherent Plane Waves; Chu & Robinson; 16 App. Opt. 619, (1977)
• Laser Doppler Measurements in Two-Phase Flows; Durst & Zare; Proc. of the LDA-Symposium Copenhagen 403, (1975)
• Diffraction Analysis of Doppler Signal Characteristics for a Cross-Beam Laser Doppler Velocimeter; Robinson & Chu; 14 App. Opt. 2177, (1975)
• High Resolution Hologram Interferometry by Electronic Phase Measurement; Dandliker, Ineichen & Mottier; 9 Opt. Comm. 412, (1973)
• Interference Phase Measurement; Crane; 8 App. Opt. 538, (1969)
• Heterodyne Holographic Interferometry; Dandliker; Progress in Optics, vol. XVII, (E. Wolf ed. 1980)