METHOD OF ANALYZING A REMOTELY-LOCATED OBJECT UTILIZING AN OPTICAL TECHNIQUE TO DETECT TERAHERTZ RADIATION

Abstract

A method of analyzing a remotely-located object includes the steps of inducing a volume of an ionized ambient gas to emit pulsed terahertz radiation directed toward a targeted object by focusing an optical pump beam in the volume and ionizing another volume of the ambient gas to produce a sensor plasma by focusing an optical probe beam in the other volume of ambient gas. The interaction, in the sensor plasma, of the focused optical probe beam and an incident terahertz wave, which is produced by the targeted object reflecting, scattering, or transmitting the pulsed terahertz radiation, produces a resultant radiation. Detecting an optical component of the resultant radiation emitted by the sensor plasma facilitates detection of a signature of the targeted object imposed onto the incident terahertz radiation.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A illustrates one embodiment of a system for remotely analyzing an object in an exemplary environment in which the system may be used, wherein terahertz waves reflected by an object are detected.

FIG. 1B illustrates one embodiment of a system for remotely analyzing an object in an exemplary environment in which the system may be used, wherein terahertz waves scattered by an object are detected.

FIG. 2 illustrates another embodiment of a system for remotely analyzing an object in accordance with an aspect of the present invention.

FIGS. 3A, 3B, and 3C illustrate techniques to generate terahertz radiation in an ambient gas by using optical beams, in accordance with an aspect of the present invention.

FIG. 4 illustrates one embodiment of a technique to detect terahertz radiation using a gas plasma as a sensor, in accordance with an aspect of the present invention.

FIG. 5 illustrates one embodiment of a system for detecting terahertz radiation using an ionized gas as a sensor, in accordance with an aspect of the present invention.

FIGS. 6A and 6B illustrate an embodiment of a system for analyzing a remotely-located object, in accordance with an aspect of the present invention.

FIGS. 6C and 6D illustrate another embodiment of a system for analyzing a remotely-located object, in accordance with an aspect of the present invention.

FIG. 6E illustrates an embodiment of a system for analyzing a remotely-located object wherein the same plasma is used as an emitter and sensor of terahertz radiation, in accordance with an aspect of the present invention.

FIG. 7A illustrates an embodiment of a system that utilizes optically-induced ionized gas to emit and detect terahertz radiation to analyze objects, in accordance with an aspect of the present invention, wherein a terahertz wave transmitted through a targeted object is detected.

FIG. 7B illustrates an embodiment of a system that utilizes optically-induced ionized gas to emit and detect terahertz radiation to analyze objects, in accordance with an aspect of the present invention, wherein a terahertz wave reflected by a targeted object is detected.

FIG. 7C illustrates another embodiment of a system that utilizes optically-induced ionized gas to emit and detect terahertz radiation to analyze objects, in accordance with an aspect of the present invention, wherein a terahertz wave transmitted through a targeted object is detected.

FIG. 8A illustrates a plot of the measured absorption coefficient of tryptonphan obtained using the embodiment of FIG. 7C, in accordance with the present invention.

FIG. 8B illustrates a plot of the measured attenuation of water vapor at 30 percent relative humidity and at a room temperature as a function of frequency obtained using the embodiment of FIG. 7C, in accordance with the present invention.

FIG. 9A illustrates an embodiment of a system for analyzing a remotely-located object that provides spectroscopy analysis, in accordance with an aspect of the present invention.

FIG. 9B illustrates an embodiment of a system for analyzing a remotely-located object that provides spectroscopic imaging, in accordance with an aspect of the present invention.

Claims

1. A method of detecting terahertz radiation comprising: ionizing a volume of an ambient gas to produce a sensor plasma by focusing an optical probe beam in the volume; anddetecting an optical component of resultant radiation produced from an interaction of the focused optical probe beam and an incident terahertz wave in the sensor plasma.

2. The method of claim 1 further comprising focusing the terahertz wave in the sensor plasma.

3. The method of claim 1 wherein the detecting comprises focusing at least the optical component of the resultant radiation with means for optical focusing located a distance from the sensor plasma.

4. The method of claim 1 wherein the detecting further comprises attenuating a component of the resultant radiation, the component comprising a frequency of the optical probe beam.

5. The method of claim 1 wherein the optical probe beam comprises an optical radiation component having a fundamental frequency and a harmonic optical radiation component having a frequency that is harmonically related to the fundamental frequency.

6. A method of analyzing a remotely-located object comprising: inducing a volume of ionized ambient gas to emit pulsed terahertz radiation directed toward a targeted object by focusing an optical pump beam in the volume;ionizing another volume of an ambient gas to produce a sensor plasma by focusing an optical probe beam in the another volume; anddetecting an optical component of resultant radiation produced from an interaction of the focused optical probe beam and an incident terahertz wave in the sensor plasma, the incident terahertz wave being produced by an interaction of the pulsed terahertz radiation with the targeted object.

7. The method of claim 6 further comprising focusing the incident terahertz wave in the sensor plasma.

8. The method of claim 6 wherein the detecting comprises focusing the optical component of the resultant radiation with means for optical focusing located a distance from the sensor plasma.

9. The method of claim 6 wherein the optical component of the resultant radiation comprises a harmonic of a fundamental frequency of the optical probe beam.

10. The method of claim 6 wherein the optical probe beam comprises at least one pulse of optical radiation.

11. The method of claim 6 wherein the targeted object comprises an explosive material or a biological agent or a chemical agent that is harmful to humans.

12. The method of claim 6 wherein the optical probe beam comprises an optical radiation component having a fundamental frequency and a harmonic optical radiation component having a frequency that is harmonically related to the fundamental frequency.

13. The method of claim 6 wherein the volume of ionized ambient gas is located more than thirty meters away from a source of the optical pump beam.

14. The method of claim 6 wherein the sensor plasma is located more than thirty meters away from a site where the optical component is detected.

15. The method of claim 6 wherein the detecting is performed more than thirty meters from the targeted object.

16. A system for detecting terahertz radiation comprising: a source of an optical probe beam;means for focusing the optical probe beam to produce a focused optical probe beam that ionizes a volume of an ambient gas to produce a sensor plasma; andan optical detector for detecting an optical component of resultant radiation emitted from the sensor plasma as a result of an interaction, in the sensor plasma, of the focused optical probe beam and an incident terahertz wave.

17. The system of claim 16 further comprising a means for focusing the terahertz wave in the sensor plasma.

18. The system of claim 16 wherein the optical detector comprises means for focusing the optical component of the resultant radiation, the means for focusing the optical component being located a distance from the sensor plasma.

19. The system of claim 16 wherein the optical component of the resultant radiation comprises a harmonic of a fundamental frequency of the optical probe beam, and the optical detector further comprises an optical filter for attenuating a component of the resultant radiation comprising the fundamental frequency of the optical probe beam.

20. The system of claim 16 wherein the optical probe beam comprises at least one pulse of optical radiation.

21. The system of claim 16 wherein the terahertz wave comprises at least one pulse of terahertz radiation.

22. The system of claim 16 wherein the optical probe beam comprises an optical radiation component having a fundamental frequency and a harmonic optical radiation component having a frequency that is harmonically related to the fundamental frequency, and the system further comprises means for shifting a relative phase of the optical radiation component and the harmonic optical radiation component.

23. The system of claim 16 wherein the optical detector comprises a photomultiplier tube or a photodiode.

24. A system for analyzing a remotely-located object comprising: a source of an optical pump beam;means for focusing the optical pump beam to produce a focused optical pump beam that ionizes a volume of an ambient gas to produce an emitter plasma and induces an emission, from the emitter plasma, of pulsed terahertz radiation directed toward a targeted object;a source of an optical probe beam;another means for focusing the optical probe beam to produce a focused optical probe beam that ionizes another volume of the ambient gas to produce a sensor plasma; andan optical detector for detecting an optical component of resultant radiation emitted from the sensor plasma as a result of an interaction, in the sensor plasma, of the focused optical probe beam and a resultant terahertz wave, the resultant terahertz wave comprising terahertz radiation reflected, scattered, or transmitted by the targeted object in response to an incidence of the pulsed terahertz radiation at the targeted object.

25. The system of claim 24 further comprising means for focusing the resultant terahertz wave in the sensor plasma.

26. The system of claim 24 wherein the optical detector comprises means for focusing at least the optical component of the resultant radiation, the means for focusing at least the optical component being located a distance from the sensor plasma.

27. The system of claim 24 wherein the optical component of the resultant radiation comprises a harmonic of a fundamental frequency of the optical probe beam, and the optical detector further comprises an optical filter for attenuating a component of the resultant radiation comprising the fundamental frequency of the optical probe beam.

28. The system of claim 24 wherein the optical probe beam comprises at least one pulse of optical radiation.

29. The system of claim 24 wherein the optical probe beam comprises an optical radiation component having a fundamental frequency and a harmonic optical radiation component having a frequency that is harmonically related to the fundamental frequency.

30. The system of claim 24 wherein the optical detector comprises a photomultiplier tube or a photodiode.

31. The system of claim 24 wherein the emitter plasma is located more than thirty meters away from the source of the optical pump beam.

32. The system of claim 24 wherein the sensor plasma is located more than thirty meters away from the optical detector.

33. The system of claim 24 wherein the optical detector is located more than thirty meters from the targeted object.

34. The system of claim 24 wherein the targeted object comprises an explosive material or a biological agent or a chemical agent that is harmful to humans.

35. A method of analyzing a remotely-located object comprising: inducing a volume of an ionized ambient gas to emit pulsed terahertz radiation directed toward a targeted object by focusing an optical pump beam in the volume;focusing an optical probe beam in the volume of the ionized ambient gas; anddetecting an optical component of resultant radiation produced from an interaction of the focused optical probe beam and an incident terahertz wave in the volume of the ionized ambient gas, the incident terahertz wave being produced by an interaction of the pulsed terahertz radiation with the targeted object.

36. The method of claim 6 wherein the volume and the another volume overlap.

37. The system of claim 24 wherein the volume and the another volume overlap.

38. The method of claim 6 further comprising processing the optical component of resultant radiation detected by the detecting to produce spectroscopy analysis information.

39. The method of claim 38 further comprising producing a spectroscopy image from the spectroscopy analysis information.

40. The system of claim 24 further comprising a spectroscopy signal processing unit for analyzing the optical component of resultant radiation detected by the optical detector.

41. The system of claim 40 further comprising an imaging signal processing unit for producing a spectroscopy image from spectroscopy analysis information provided by the spectroscopy signal processing unit.