Method And System For Sensing And Identifying Foreign Particles In A Gaseous Environment

• US 20080079938A1
• Filed: 09/28/2006
• Published: 04/03/2008
• Est. Priority Date: 09/28/2006
• Status: Active Grant

• Current Assignee: The United States Of America As Represented By The National Aeronautics And Space Administration
• Original Assignee: Space Administration, The Government of The US As Represented By The Secretary of The Navy
• Inventors: Park, Yeonjoon, Choi, Sang H.
• Granted Patent: US 7,375,808 B2
• Time in Patent Office: Days
• US Class Current: 356/318
• CPC Class Codes: G01J 3/02 Details
• CPC Class Codes: G01J 3/0229 using masks, aperture plates, spatial light modulators or spatial filters, e.g. reflective filters
• CPC Class Codes: G01J 3/4406 Fluorescence spectrometry
• CPC Class Codes: G01N 21/6402 Atomic fluorescence; Laser induced fluorescence
• CPC Class Codes: G01N 21/6456 Spatial resolved fluorescence measurements; Imaging

Abstract

An optical method and system sense and identify a foreign particle in a gaseous environment. A light source generates light. An electrically-conductive sheet has an array of holes formed through the sheet. Each hole has a diameter that is less than one quarter of the light'"'"'s wavelength. The sheet is positioned relative to the light source such that the light is incident on one face of the sheet. An optical detector is positioned adjacent the sheet'"'"'s opposing face and is spaced apart therefrom such that a gaseous environment is adapted to be disposed therebetween. Alterations in the light pattern detected by the optical detector indicate the presence of a foreign particle in the holes or on the sheet, while a laser induced fluorescence (LIF) signature associated with the foreign particle indicates the identity of the foreign particle.

Claims

1. An optical system for use in sensing and identifying a foreign particle in a gaseous environment, comprising:

a light source for generating light having a known wavelength;

an electrically-conductive opaque sheet having first and second faces opposing one another with an array of holes formed through said sheet and extending between said first and second faces, each of said holes having a diameter that is less than one quarter of said known wavelength, said sheet positioned relative to said light source such that said light is incident on said first face; and

optical detection means positioned adjacent said second face and spaced apart therefrom such that a gaseous environment is adapted to be disposed therebetween, said optical detection means detecting a light pattern at said second face when said light is incident on said first face, wherein alterations in said light pattern are indicative of the presence of a foreign particle between said first face and said optical detection means.

2. An optical system as in claim 1 wherein said light source comprises a laser, and wherein a laser induced fluorescence (LIF) signature associated with the foreign particle is indicative of the identity of the foreign particle.

3. An optical system as in claim 1 further comprising a light transmissive substrate coupled to said sheet.

4. An optical system as in claim 3 wherein said light transmissive substrate comprises quartz glass.

5. An optical system as in claim 1 wherein said optical detection means comprises:

a charge coupled device (CCD) array for detecting said light pattern; and

a spectrometer for measuring said LIF signature.

6. An optical system for sensing and identifying a foreign particle in a gaseous environment, comprising:

a light source for generating light having a known wavelength;

an electrically-conductive opaque sheet having first and second faces opposing one another with an array of holes formed through said sheet and extending between said first and second faces, each of said holes having a diameter that is less than one quarter of said known wavelength, said sheet positioned relative to said light source such that said light is incident on said first face;

optical detection means positioned adjacent said second face and spaced apart therefrom such that a gaseous environment is adapted to be disposed therebetween, said optical detection means detecting a light pattern at said second face when said light is incident on said first face, wherein alterations in said light pattern are indicative of the presence of a foreign particle between said first face and said optical detection means.

7. A optical system as in claim 6 wherein:

said light source comprises a laser,

said optical detection means further measures a laser induced fluorescence (LIF) signature associated with the foreign particle; and

said optical system further comprises processing means coupled to said optical detection means for identifying the foreign particle using said LIF signature.

8. An optical system as in claim 6 further comprising a light transmissive substrate coupled to said sheet.

9. An optical system as in claim 8 wherein said light transmissive substrate comprises quartz glass.

10. An optical system as in claim 6 wherein said optical detection means comprises:

a charge coupled device (CCD) array for detecting said light pattern; and

a spectrometer for measuring said LIF signature.

11. An optical system as in claim 6 wherein said processing means includes a database of known LIF signatures with which said LIF signature of the foreign particle is compared.

12. An optical system for sensing and identifying a foreign particle in a gaseous environment, comprising:

a laser for generating laser light having a known wavelength;

a substrate that is transmissive with respect to said laser light;

a metallic thin-film having first and second faces opposing one another with said first face being coupled to said substrate, said metallic thin-film having an array of identically-sized holes formed therethrough land extending between said first and second faces thereof, each of said holes having a diameter that is less than one quarter of said known wavelength, said metallic thin-film positioned relative to said laser such that said laser light is incident on said first face after passing through said substrate;

optical detection means positioned adjacent said second face and spaced apart therefrom such that a gaseous environment is adapted to be disposed therebetween, said optical detection means detecting a light pattern at said second face when said light is incident on said first face, wherein alterations in said light pattern are indicative of the presence of a foreign particle between said first face and said optical detection means, said optical detection means further measuring a laser induced fluorescence (LIF) signature associated with the foreign particle; and

processing means coupled to said optical detection means for identifying the foreign particle using said LIF signature.

13. An optical system as in claim 12 wherein said substrate comprises quartz glass.

14. An optical system as in claim 12 wherein said optical detection means comprises:

a charge coupled device (CCD) array for detecting said light pattern; and

a spectrometer for measuring said LIF signature.

15. An optical system as in claim 12 wherein said processing means includes a database of known LIF signatures with which said LIF signature of the foreign particle is compared.

16. A method of sensing and identifying a foreign particle in a gaseous environment, comprising:

generating light having a known wavelength;

providing an electrically-conductive opaque sheet having first and second faces opposing one another with an array of holes formed through said sheet and extending between said first and second faces, each of said holes having a diameter that is less than one quarter of said known wavelength, said sheet positioned such that said light is incident on said first face;

detecting a light pattern at said second face when said light is incident on said first face, wherein alterations in said light pattern are indicative of the presence of a foreign particle between said first face and said optical detection means.

17. A method according to claim 16 wherein said light is laser light, and said method further comprises detecting a laser induced fluorescence (LIF) signature associated with the foreign particle wherein said LIF signature is indicative of the identity of the foreign particle.

18. A method of sensing and identifying a foreign particle in a gaseous environment, comprising:

providing a metallic thin-film having a quantum aperture array formed therethrough;

generating light having a known wavelength;

positioning the thin-film in the light such that a surface plasmon polariton (SPP) is generated at a face of the thin-film;

monitoring an emission pattern of the SPP wherein a disturbance in the emission pattern is indicative of the presence of a foreign particle.

19. A method according to claim 18 wherein said light is laser light, and said method further comprises measuring a laser induced fluorescence (LIF) signature associated with the foreign particle wherein said LIF signature is indicative of the identity of the foreign particle.