In situ small particle diagnostics

• US 4,679,939 A
• Filed: 12/23/1985
• Issued: 07/14/1987
• Est. Priority Date: 12/23/1985
• Status: Expired due to Fees

• Current Assignee: The United States of America As Represented By The Secretary of Agriculture
• Original Assignee: The United States of America As Represented By The Secretary of Agriculture
• Inventors: Jones, John H., Seiber, Brian L., Price, Lynwood L., Kiech, Earl L., Curry, Bill P., Powell, Homer M.
• Primary Examiner(s): Willis, Davis L.
• Assistant Examiner(s): Koren, Matthew W.
• Application Number:
  US06/812,206
• Time in Patent Office: 568 Days
• Field of Search: 356/336, 356/338, 356/339, 250/564, 250/574
• US Class Current: 356/336
• CPC Class Codes: G01N 15/0205 by optical means
• CPC Class Codes: G01N 15/0227 using imaging; using holography
• CPC Class Codes: G01N 2021/178 Methods for obtaining spatial resolution of the property being measured
• CPC Class Codes: G01N 2021/4721 using a PSD
• CPC Class Codes: G01N 21/21 Polarisation-affecting properties G01N21/19 takes precedence
• CPC Class Codes: G01N 21/53 within a flowing fluid, e.g. smoke

Abstract

Small particle diagnostic apparatus employing illumination by coherent light of high polarization ratio, polarized separation of the reflected particle scatter optical signals and the ability to consider particles in plural locations of a diagnostic aperture aided by use of a vidicon or other position-sensitive transducer device and an optional image intensifier device. Digital storage and analysis of the particle scatter data and computer control of the optical and analysis sequences are contemplated.

Claims

1. Particle stream diagnostic apparatus comprising:

means for illuminating a cross-section of said particle stream with polarized coherent light directed along a lateral axis traversing said stream and cross-section;

means for generating a first electrical signal representing light flux from said illuminating means transmitted across said cross-section through said particle stream;

means located at a predetermined scattering angle with respect to the plane of said cross-section lateral axis and said stream for collecting particle scattered light originating in multiple locations of said illuminated cross-section as first light signals;

means for segregating said first light signals into component second and third signals of dissimilar polarization angles;

means for segregating said second and third light signals over an image plane, each said image plane light signal including geometrically identifiable signal areas originating respectively in light form said cross-section multiple locations;

means for transducing said signal areas in said second and third light signals on said image plane into second and third electrical signal pairs; and

means for analyzing a plurality of said first, second and third electrical signals.

2. The diagnostic apparatus of claim 1 wherein said means for illuminating includes a laser.

3. The diagnostic apparatus of claim 2 wherein said laser is a pulsed laser.

4. The diagnostic apparatus of claim 3 wherein said laser is a pulsed excimer laser.

5. The diagnostic apparatus of claim 3 wherein said laser is a frequency doubled ruby laser.

6. The diagnositc apparatus of claim 3 wherein said laser is a frequency quadrupled YAG laser.

7. The diagnostic apparatus of claim 2 wherein said laser has a major output spectrum selected in response to the upper and lower limits of particle size in said particle stream.

8. The diagnostic apparatus of claim 2 wherein said laser has a major output spectrum in the range of two hundred seventy-five to three hundred thirty nanometers.

9. The diagnostic apparatus of claim 2 wherein said laser has a vertically polarized majority output.

10. The diagnostic apparatus of claim 9 wherein said laser has a vertical polarization amplitude to horizontal polarization amplitude ratio of at least thirty-five to one.

11. The diagnostic apparatus of claim 2 further including polarization means located in the light output path of said laser intermediate to said laser and said particle stream for increasing the vertical to horizontal polarization ratio, in a plane parallel to the plane of said particle scattered light, of the illumination received at said particle stream.

12. The diagnostic apparatus of claim 11 wherein said polarization means includes an external polarizing element.

13. The diagnostic apparatus of claim 12 wherein said polarization means includes a plurality of quartz windows mounted at Brewster'"'"'s angle rotational positions.

14. The diagnostic apparatus of claim 2 wherein said laser is tunable over spectral regions adjacent a nominal output wavelength.

15. The diagnostic apparatus of claim 2 wherein said means for illuminating includes a focusing lens located intermediate said laser and said particle stream.

16. The diagnostic apparatus of claim 15 wherein said scattering angle is in the range of eighty-five to ninety-five degrees.

17. The diagnostic apparatus of claim 1 wherein said scattering angle is in the range of eighty-nine to ninety-one degrees.

18. The diagnostic apparatus of claim 17 wherein said scattering angle is ninety degrees.

19. The diagnostic apparatus of claim 1 wherein said multiple locations are greater than ten in number.

20. The apparatus of claim 1 wherein said means for segregating said first light signals ihto component signals includes an optical beam splitter.

21. The apparatus of claim 20 wherein said means for dispersing includes a mirror member located in at least one output path of said optical beam splitter.

22. The apparatus of claim 1 wherein said image plane is a portion of a light intensifier apparatus.

23. The apparatus of claim 1 wherein said image plane is the photosensitive surface of an optical-to-electrical transducer element.

24. The apparatus of claim 23 further including refrigeration means for cooling said optical-to-electrical transducer element to temperatures below ambient,

whereby thermal noise components in the output signal of said transducer element are reduced in magnitude.

25. The apparatus of claim 1 wherein said means for transducing includes a vidicon tube.

26. The apparatus of claim 1 wherein said means for transducing includes a solid state optical-to-electrical transducer element.

27. The apparatus of claim 26 wherein said transducer element is a charge coupled device transducer.

28. The apparatus of claim 1 wherein said means for analyzing includes a digital computer connected and programmed to collect and store successive values of said first, second and third electrical signals in organized arrangement.

29. The apparatus of claim 1 wherein said means for analyzing includes means for comparing the relative magnitude of said second and third light signals.

30. A method for particle stream scattering diagnosis comprising the steps of:

illuminating a cross-section of said particle stream with polarized coherent light directed along a lateral axis transversing said stream and cross-section;

generating a first electrical signal representing light transmitted across said cross-section through said particle stream;

collecting particle scattered light originating in multiple locations within said cross-section and directed at a predetermined scattering angle with respect to the plane of said cross-section lateral axis and said stream into first light signals;

segregating said first light signals into component second and third signals of dissimilar polarization;

mapping said second and third light signals onto an image plane, each said image plane light signal including geometrically identifiable signal areas originating respectively in light from said cross-section and multiple locations;

transducing said signal areas in said second and third light signals on said image plane into second and third electrical signals; and

analyzing a plurality of said first, second and third electrical signals for particle population related variations.

31. The method of claim 30 further including the step of tuning the wavelength of said polarized coherent light to an optimum wavelength with respect to the size of said scattered particles.

32. The method of claim 30 wherein said step of transducing includes scanning said image plane.

33. The method of claim 30 wherein said analyzing step includes performing a Mie scattering theory based analysis.

34. Particle stream diagnostic signal generating apparatus comprising:

laser means for illuminating a cross-section of said particle stream with coherent polarized light directed along an axis transverse of said cross section;

means located at a predetermined angle with respect to said cross section axis and said stream for collecting the particle scattered light originating in plural locations of said illuminated cross section into first optical signals;

means for segregating said first light signals into a second and third signal pair of component optical signals of orthogonal polarization vectors;

means for projecting said second and third component optical signals over a common image plane, said image plane receiving a second and third optical signal pair for each said cross-section location first optical signal; and

means for transducing said second and third optical signal pairs into electrical signal pairs.

35. The apparatus of claim 34 wherein said projected second and third component optical signals are side by side physically disposed on said image plane.