Particle image velocimetry system having an improved hollow-waveguide-based laser illumination system
An illumination system for a particle image velocimetry system has an illumination source, a hollow tapered optical funnel arranged to receive illumination light from the illumination source, a hollow optical waveguide optically coupled to an output end of the hollow tapered optical funnel, and a beam shaping optical system optically coupled to an output end of the hollow optical waveguide. The illumination system is constructed to provide a light sheet to illuminate particles within a fluid under observation. A particle image velocimetry system has such an illumination system.
1. An illumination system for a particle image velocimetry system comprising:
an illumination source;
a hollow tapered optical funnel arranged to receive illumination light from said illumination source;
a hollow optical waveguide optically coupled to an output end of said hollow tapered optical funnel; and
a beam shaping optical system optically coupled to an output end of said hollow optical waveguide, wherein said illumination system is constructed to provide a light sheet to illuminate particles within a fluid under observation.
2. The illumination system for a particle image velocimetry system according to claim 1 , wherein said hollow tapered optical funnel has a cone angle that is smaller than 1° so that illumination light from said illumination source is at a grazing incidence within about 1° of a 90° angle of incidence.
3. The illumination system for a particle image velocimetry system according to claim 1 , wherein said hollow tapered optical funnel is an uncoated material having a refractive index at an operating wavelength that is greater than 1.0.
4. The illumination system for a particle image velocimetry system according to claim 3 , wherein said uncoated material is a glass material.
5. The illumination system for a particle image velocimetry system according to claim 4 , wherein said glass material is PYREX glass.
6. The illumination system for a particle image velocimetry system according to claim 1 , wherein said hollow optical waveguide is a hollow optical fiber having a coating of a material selected to reduce transmission losses for the wavelength of the illumination source.
7. The illumination system for a particle image velocimetry system according to claim 6 , wherein said coating of said optical fiber is a cyclic olefin polymer coating.
8. The illumination system for a particle image velocimetry system according to claim 1 , wherein said illumination source comprises a laser having a 532 nm output wavelength.
9. The illumination system for a particle image velocimetry system according to claim 1 , wherein said illumination source comprises a pulsed laser.
10. The illumination system for a particle image velocimetry system according to claim 1 , wherein said illumination source comprises a continuous wave laser.
11. The illumination system for a particle image velocimetry system according to claim 9 , wherein said pulsed laser is a Nd:YAG pulsed laser having a 532 nm output wavelength.
12. The illumination system for a particle image velocimetry system according to claim 1 , wherein said beam shaping optical system comprises an objective lens arranged to receive at least a portion of light that emerges from said output end of said hollow optical waveguide to provide a collimated output beam.
13. The illumination system for a particle image velocimetry system according to claim 12 , wherein said beam shaping optical system further comprises a Powell lens arranged to receive said collimated output beam from said objective lens to form a sheet of illumination light.
14. The illumination system for a particle image velocimetry system according to claim 13 , wherein said sheet of illumination light has a thickness in a range from about 0.5 mm to about 1.0 mm.
15. The illumination system for a particle image velocimetry system according to claim 13 , wherein said sheet of illumination light has a width in a detection region of at least about 10 mm.
16. The illumination system for a particle image velocimetry system according to claim 1 , wherein said illumination system is able to provide a peak power density of at least 1 GW/cm 2 .
17. A particle image velocimetry system, comprising:
an illumination system arranged to illuminate particles within a fluid flow;
a detection system arranged to detect light from particles illuminated by said illumination system and to output a signal to be processed; and
a signal processing system constructed to be in communication with said detection system to receive said signal to be processed,
wherein said illumination system comprises:
an illumination source;
a hollow tapered optical funnel arranged to receive illumination light from said illumination source;
a hollow optical waveguide optically coupled to an output end of said hollow tapered optical funnel; and
a beam shaping optical system optically coupled to an output end of said hollow optical waveguide, wherein said illumination system is constructed to provide a light sheet to illuminate particles within a fluid under observation.
18. The particle image velocimetry system according to claim 17 , wherein said hollow tapered optical funnel has a cone angle that is smaller than 1° so that illumination light from said illumination source is at a grazing incidence within about 1° of a 90° angle of incidence.
19. The particle image velocimetry system according to claim 17 , wherein said hollow tapered optical funnel is an uncoated material having a refractive index at an operating wavelength that is greater than 1.0.
20. The particle image velocimetry system according to claim 19 , wherein said uncoated material is a glass material.
21. The particle image velocimetry system according to claim 20 , wherein said glass material is PYREX glass.
22. The particle image velocimetry system according to claim 17 , wherein said hollow optical waveguide is a hollow optical fiber having a coating of a material selected to reduce transmission losses for the wavelength of the illumination source.
23. The particle image velocimetry system according to claim 22 , wherein said coating of said optical fiber is a cyclic olefin polymer coating.
24. The particle image velocimetry system according to claim 17 , wherein said illumination source comprises a laser having a 532 nm output wavelength.
25. The particle image velocimetry system according to claim 17 , wherein said illumination source comprises a pulsed laser.
26. The particle image velocimetry system according to claim 17 , wherein said illumination source comprises a continuous wave laser.
27. The particle image velocimetry system according to claim 25 , wherein said pulsed laser is a Nd:YAG pulsed laser having a 532 nm output wavelength.
28. The particle image velocimetry system according to claim 17 , wherein said beam shaping optical system comprises an objective lens arranged to receive at least a portion of light that emerges from said output end of said hollow optical waveguide to provide a collimated output beam.
29. The particle image velocimetry system according to claim 28 , wherein said beam shaping optical system further comprises a Powell lens arranged to receive said collimated output beam from said objective lens to form a sheet of illumination light.
30. The particle image velocimetry system according to claim 29 , wherein said sheet of illumination light has a thickness in a range from about 0.5 mm to about 1.0 mm.
31. The particle image velocimetry system according to claim 29 , wherein said sheet of illumination light has a width in a detection region of at least 10 mm.
32. The particle image velocimetry system according to claim 17 , wherein said illumination system is able to provide a peak power density of at least 1 GW/cm 2 .