Real-time, continuous-wave terahertz imaging using a microbolometer focal-plane array

• US 20080156991A1
• Filed: 03/20/2006
• Published: 07/03/2008
• Est. Priority Date: 03/21/2005
• Status: Active Grant

• Current Assignee: Massachusetts Institute of Technology
• Original Assignee: Massachusetts Institute of Technology
• Inventors: Hu, Qing, Min Lee, Alan W.
• Granted Patent: US 7,692,147 B2
• Time in Patent Office: Days
• US Class Current: 250/341.1
• CPC Class Codes: G01N 21/3151 using two sources of radiation of different wavelengths G01N21/33 - G01N21/39 take precedence
• CPC Class Codes: G01N 21/3563 for analysing solids; Preparation of samples therefor
• CPC Class Codes: G01N 21/3581 using far infrared light; using Terahertz radiation

Abstract

The present invention generally provides a terahertz (THz) imaging system that includes a source for generating radiation (e.g., a quantum cascade laser) having one or more frequencies in a range of about 0.1 THz to about 10 THz, and a two-dimensional detector array comprising a plurality of radiation detecting elements that are capable of detecting radiation in that frequency range. An optical system directs radiation from the source to an object to be imaged. The detector array detects at least a portion of the radiation transmitted through the object (or reflected by the object) so as to form a THz image of that object.

Claims

1. A terahertz imaging system, comprising

a source for generating radiation having one or more frequencies in a range of about 0.1 THz to about 10 THz,

a bolometer detector suitable for detecting radiation generated by said source, and

an optical system disposed between said source and said detector for directing the radiation generated by said source onto said detector.

2. The imaging system of claim 1, wherein said bolometer detector comprises an array of uncooled bolometer detecting elements.

3. The imaging system of claim 1, wherein said radiation source generates radiation having a power in a range of about 1 mW to about 100 mW.

4. The imaging system of claim 1, wherein said radiation source generates radiation having a power in a range of about 5 mW to about 100 mW.

5. The imaging system of claim 1, wherein said imaging system comprises an image plane at which an object to be imaged can be disposed.

6. The imaging system of claim 5, wherein said optical system comprises one or more elements for directing the source radiation onto said object for illumination thereof and one or more elements for directing at least a portion of radiation transmitted through or reflected from said object onto said bolometer array elements so as to generate an image of said object.

7. The imaging system of claim 6, wherein said system is capable of acquiring images of said object at a rate of at least about 20 frames per second.

8. The imaging system of claim 7, wherein said system is capable of acquiring images of said object at a rate of about 60 frames per second.

9. The imaging system of claim 1, wherein said bolometer detector comprises a vanadium oxide film as a radiation sensing element.

10. The imaging system of claim 1, wherein said bolometer detector comprises a film of a semi-metal as a radiation sensing element.

11. The imaging system of claim 10, wherein said semi-metal comprises bismuth.

12. The imaging system of claim 1, wherein said source comprises a quantum cascade laser (QCL).

13. The imaging system of claim 12, wherein said quantum cascade laser generates continuous wave (CW) radiation in a range of about 1 THz to about 10 THz.

14. The imaging system of claim 12, wherein said quantum cascade laser generates CW radiation having at least one frequency component in a range of about 2 THz to about 5 THz.

15. The imaging system of claim 13, wherein said quantum cascade laser generates said terahertz radiation at a power greater than about 1 mW.

16. The imaging system of claim 15, wherein said quantum cascade laser generates said terahertz radiation at a power level in a range of about 1 mW to about 10 mW.

17. A terahertz imaging system, comprising

a source of terahertz radiation generating radiation pulses having one or more frequency components in a range of about 0.1 THz to about 10 THz,

an optical system for directing said radiation pulses to an object to be imaged,

an array of detecting elements for detecting at least a portion of the THz radiation transmitted through the object or reflected by the object to generate detection signals, said elements being further adapted to generate reference signals corresponding to detection of ambient infrared radiation in absence of said THz radiation,

a processor in communication with said detector array,

wherein said processor generates a THz image of the object based on a difference of said detection and reference signals.

18. The terahertz imaging system of claim 17, wherein said array of detecting elements generate said detection and reference signals during at least two different temporal periods.

19. The terahertz imaging system of claim 17, wherein said source is configured to generate a radiation pulse during the temporal period in which said detection signals are generated.

20. The terahertz imaging system of claim 19, wherein said radiation pulse has a duration less than that of the temporal period in which the detection signals are generated.

21. The terahertz imaging system of claim 17, wherein said radiation source comprises a quantum cascade laser.

22. The terahertz imaging system of claim 17, wherein said imaging system generates images of the object at a rate of in a range of about 20 to 60 images per second.

23. The terahertz imaging system of claim 17, wherein said detecting elements comprise bolometer detecting elements.

24. The terahertz imaging system of claim 17, wherein said detecting elements comprise uncooled bolometer detecting elements.

25. A terahertz imaging system, comprising:

a plurality of terahertz radiation sources generating radiation at different frequencies in a range of about 0.1 THz to about 10 THz,

an optical system for directing radiation from said sources to an object to be imaged,

a controller in communication with said sources for selectively activating the source to illuminate the object at different frequencies,

an array of radiation detecting elements disposed to detect at least a portion of radiation transmitted through said object or reflected by the object to generate at least two images of the object corresponding to two of said frequencies.

26. The terahertz imaging system of claim 25, wherein said radiation sources comprise quantum cascade lasers.

27. The terahertz imaging system of claim 25, wherein said radiation detecting elements comprise bolometer detection elements.

28. A terahertz imaging system, comprising

a source for generating radiation having one or more frequency components in a range of about 0.1 THz to about 10 THz,

an optical system for directing said radiation to an object to be imaged,

a two-dimensional array of radiation detecting elements disposed relative to said object to detect at least a portion of the radiation transmitted through the object or reflected by the object so as to form an terahertz image of said object.

29. The terahertz imaging system of claim 28, wherein said radiation source comprises a QCL.

30. The terahertz imaging system of claim 28, wherein said detector array comprises an array of microbolometer elements.

31. A method of terahertz imaging, comprising

acquiring two or more terahertz images of a material disposed within a visibly opaque container,

identifying said material by comparing said images with known terahertz spectral signatures of said material.