Subcentimeter radiation detection and frequency domain spectroscopy

• US 7,291,839 B1
• Filed: 05/03/2005
• Issued: 11/06/2007
• Est. Priority Date: 05/03/2004
• Status: Expired due to Fees

• Current Assignee: Joseph R. Demers
• Original Assignee: Emcore Corporation
• Inventors: Logan, Ronald T. Jr., Demers, Joseph R
• Primary Examiner(s): Porta; David
• Assistant Examiner(s): Rosenberger; Frederick F
• Application Number:
  US11/121,350
• Time in Patent Office: 917 Days
• Field of Search: None
• US Class Current: 250/341.1
• CPC Class Codes: G01J 3/42 Absorption spectrometry; Double beam spectrometry; Flicker spectrometry; Reflection spectrometry beam switching arrangements G01J3/08
• CPC Class Codes: G01N 21/3504 for analysing gases, e.g. multi-gas analysis
• CPC Class Codes: G01N 21/3581 using far infrared light; using Terahertz radiation

Abstract

A system, method and detection arrangement for investigation of a sample are described. A laser illumination arrangement generates (i) a source laser energy that is incident on a source to cause emission of subcentimeter radiation, at least a portion of which interacts with the sample to serve as a sample influenced radiation incident on a detector and (ii) a detector laser energy that is incident on the detector to produce an optical component of the detector laser energy offset with respect to a corresponding optical component of the source laser energy so that the collective energy at the detector generates an electrical output signal responsive to the sample influenced radiation. In another aspect, a detection arrangement is used with at least two continuous wave lasers for causing the detector body to respond in a way which produces a frequency down-converted signal from an incident electromagnetic radiation.

Claims

1. A system for investigation of a sample, said system comprising:

a source arrangement having a source frequency response;

a detector arrangement in a positional relationship with said source arrangement such that said sample is located in relation to the source arrangement and the detector arrangement, and said detector arrangement having a detector frequency response; and

a laser illumination arrangement for generating

(i) a source laser energy that is produced by at least two lasers that are offset phase locked with respect to one another and which source laser energy is incident on said source arrangement, based on the source frequency response, in a way which causes the source arrangement to emit subcentimeter radiation, at least a portion of which subcentimeter radiation interacts with said sample and the source laser energy interacts to produce a frequency sweep in the subcentimeter radiation and, thereafter, at least some of said portion of the subcentimeter radiation serves as a sample influenced radiation that is incident on the detector arrangement, based on said positional relationship, and

(ii) a detector laser energy that is incident on said detector arrangement and offset phase locked with the source laser energy in a way which produces at least one optical component of the detector laser energy that is offset with respect to a corresponding optical component of the source laser energy so that the detector laser energy and the sample influenced radiation interact, based on said detector frequency response, in a way which at least generates an electrical output signal across the detector arrangement such that the electrical output signal is responsive to the sample influenced radiation including said frequency sweep.

2. The system of claim 1 wherein said optical component of the detector laser energy is offset by a phase shift with respect to the corresponding optical component of the source laser energy.

3. The system of claim 1 wherein said optical component of the detector laser energy is offset by a frequency shift with respect to the corresponding optical component of the source laser energy.

4. The system of claim 1 including an arrangement for recovering said electrical output signal.

5. The system of claim 4 including a processing arrangement for using said electrical output signal in a way which serves to identify said sample.

6. The system of claim 5 wherein said processing arrangement is configured for responding to at least one of a phase shift and an amplitude change that is present in said electrical output signal and induced responsive to said subcentimeter radiation passing through said sample.

7. The system of claim 1 wherein said source arrangement is a photoconductive switch.

8. The system of claim 7 wherein said source arrangement includes a source body formed using LTG ErAs/GaAs.

9. The system of claim 1 wherein said detector arrangement is a photoconductive switch.

10. The system of claim 9 wherein said detector arrangement includes a detector body of the detector photoconductive switch that is formed using LTG ErAs/GaAs.

11. The system of claim 1 wherein said source laser energy and said detector laser energy are each characterized by a phase fluctuation characteristic and said illumination arrangement is configured for correlating the phase fluctuation characteristic between the source laser energy and the detector laser energy to cause the detector laser energy to cooperate with the subcentimeter radiation in a way which produces a modified phase fluctuation characteristic of said electrical output signal that is less than the phase fluctuation characteristic of the source laser energy and the detector laser energy.

12. The system of claim 1 wherein said laser illumination arrangement produces said source laser energy as a first laser energy having a first wavelength that is incident on said source arrangement and having said frequency sweep and a second laser energy having a second wavelength, different from said first wavelength, that is also incident on said source arrangement so that the source arrangement mixes the first laser energy and the second laser energy to produce said subcentimeter radiation with said frequency sweep, and said laser illumination arrangement produces said detector laser energy in a first light path that is configured for using said first laser energy with said frequency sweep to illuminate the detector arrangement with a first light path laser energy and in a second light path that is configured for using said second laser energy to illuminate the detector arrangement with a second light path laser energy such that at least one of the first light path laser energy and the second light path laser energy is offset with respect to a respective one of the first laser energy and the second laser energy to cause mixing of the (i) first light path laser energy, (ii) the second light path laser energy and (iii) the subcentimeter radiation at the detector arrangement to produce at least said electrical output signal responsive to the subcentimeter radiation and said frequency sweep, as influenced by said sample.

13. The system of claim 12 wherein said first light path includes a first light path modulator for using the first laser energy to produce said first light path laser energy.

14. The system of claim 13 wherein said first light path modulator is a phase modulator.

15. The system of claim 13 wherein said second light path includes a second light path modulator for using the second laser energy to produce said second light path laser energy.

16. The system of claim 15 wherein said first light path modulator and said second light path modulator cooperate to form an overall differential modulator.

17. The system of claim 16 wherein said overall differential modulator is configured to use a selected one of phase modulation and frequency modulation.

18. The system of claim 12 wherein said electrical output signal is produced only when said subcentimeter radiation is incident on the detector arrangement along with the detector laser energy.

19. The system of claim 12 wherein said laser illumination arrangement includes a mode locked laser for producing an output frequency comb and said laser illumination arrangement further includes a first laser and a second laser for producing a first laser energy and a second laser energy, respectively, and for producing a modified laser energy using the third laser energy, and a phase locking arrangement for offset phase locking the first laser, the second laser, the third laser energy and, thereby, the modified laser energy to the frequency comb such that a phase fluctuation characteristic is correlated between the first laser energy, the second laser energy and the modified laser energy and said laser illumination arrangement is configured for using said modified laser energy, which also includes said phase fluctuation characteristic, correlated with the phase fluctuation characteristic of the first and second lasers to produce the detector laser energy as a combination of the modified laser energy and the second laser energy, and said detector arrangement uses said detector laser energy and said subcentimeter radiation in a way which produces a modified phase fluctuation characteristic, in said electrical output signal that is less than the correlated phase fluctuation characteristic of the first laser energy, second laser energy and third laser energy.

20. The system of claim 19 wherein said detector arrangement uses the second laser energy, modified laser energy and subcentimeter radiation such that the phase fluctuation characteristic, correlated therebetween, cancels at least to a limited extent in producing the modified phase fluctuation characteristic.

21. The system of claim 19 wherein said first, second and third lasers are semiconductor laser diodes.

22. The system of claim 21 wherein at least one of said semiconductor diodes is a distributed feedback laser.

23. The system of claim 12 wherein said illumination arrangement includes a first laser and a second laser for generating said first laser energy and said second laser energy, respectively, such that the first laser energy and the second laser energy are incident on the source arrangement as said source laser energy and said first light path offsets the first laser to produce the first light path laser energy such that the first light path laser energy is incident on said detection arrangement, as one part of said detector laser energy, and a second light path from the second laser to the detection arrangement such that the second laser energy is incident on the detector arrangement, as said second light path energy and thereby forming another part of said detector laser energy.

24. The system of claim 23 wherein said first light path includes a selected one of a phase modulator and a frequency shifter for producing the offset of said first light path laser energy from the first laser energy at an offset frequency.

25. The system of claim 23 wherein said first laser energy, said second laser energy and said first light path laser energy each include a phase fluctuation characteristic that is correlated with one another and said detector arrangement uses said detector laser energy and said subcentimeter radiation in a way which causes said phase noise to cancel, at least to a limited extent, with respect to said electrical output signal.

26. The system of claim 25 wherein said laser illumination arrangement includes a mode locked laser for producing an output frequency comb and an arrangement for locking said first and second lasers to the frequency comb of the mode locked laser such that said phase fluctuation characteristic is correlated between the first laser energy, the second laser energy and the first light path laser energy.

27. The system of claim 12 wherein said laser illumination arrangement includes (i) a first laser for use in producing said first laser energy, (ii) a sweep oscillator for producing a given frequency sweep, and (iii) a first offset phase locked loop for controlling the first laser using said given frequency sweep such that the first laser contributes the given frequency sweep to said first laser energy.

28. The system of claim 27 including a mode locked laser for producing a frequency comb that exhibits a plurality of modes and a second laser for cooperating with the first laser to produce the first laser energy and the second laser energy, and a second offset phase locked loop where the first laser is phase locked to a given mode of the mode locked laser by the first offset phase locked loop and the second laser is phase locked to a different mode of the mode locked laser and the first laser is swept relative to the given mode of the mode locked laser by the first offset phase locked loop.

29. The system of claim 27 wherein the second offset phase locked loop is configured to cooperate with the mode locked laser to provide an overall frequency sweep that is greater than the given frequency sweep.

30. The system of claim 29 wherein said mode locked laser includes a comb spacing at a comb spacing frequency and said illumination arrangement is configured for cooperatively adjusting the sweep oscillator and the second offset phase locked loop during the frequency sweep, to avoid a region of ambiguity at one-half of said comb spacing.

31. The system of claim 29 wherein the first offset phase locked loop is further configured to cooperate with the mode locked laser to sequentially use one or more other modes of the mode locked laser to further increase said overall frequency sweep.

32. The system of claim 1 wherein said laser illumination arrangement is configured for causing said sample influenced radiation, in the predetermined arrangement, to reflect from the sample.

33. The system of claim 1 wherein said laser illumination arrangement is configured for causing said sample influenced radiation, in the predetermined arrangement, to pass through said sample with the detector arrangement in a spaced apart relationship from the source arrangement.

34. The system of claim 1 wherein said detector frequency response of the detector arrangement is customized by using a detector body with an integrally formed antenna.

35. The system of claim 34 wherein said first light path includes a selected one of a phase modulator and a frequency shifter for producing the offset of the corresponding optical component of the detector laser energy at an offset frequency and said antenna is configured for generating the offset frequency as an electrical bias voltage that is present across the detector body.

36. A method for investigation of a sample, said method comprising:

providing a source arrangement having a source frequency response;

placing a detector arrangement in a positional relationship with said source arrangement such that said sample is located in relation to the source arrangement and the detector arrangement, and said detector arrangement having a detector frequency response; and

configuring a laser illumination arrangement for generating

(i) a source laser energy that is produced by at least two lasers that are offset phase locked with respect to one another and which source laser energy is incident on said source arrangement, based on the source frequency response, in a way which causes the source arrangement to emit subcentimeter radiation, at least a portion of which subcentimeter radiation interacts with said sample and the source laser energy interacts to produce a frequency sweep in the subcentimeter radiation and, thereafter, at least some of said portion of the subcentimeter radiation serves as a sample influenced radiation that is incident on the detector arrangement, based on said positional relationship, and

(ii) a detector laser energy that is incident on said detector arrangement and offset phase locked with the source laser energy in a way which produces at least one optical component of the detector laser energy that is offset with respect to a corresponding optical component of the source laser energy so that the detector laser energy and the sample influenced radiation interact, based on said detector frequency response, in a way which at least generates an electrical output signal across the detector arrangement such that the electrical output signal is responsive to the sample influenced radiation including said frequency sweep.

37. An apparatus for detecting a subcentimeter radiation, said apparatus comprising:

a detector having a detector arrangement with a detector frequency response having said subcentimeter radiation incident on the detector arrangement; and

an illumination arrangement for continuously illuminating the detector arrangement with laser radiation that is produced by at least two continuous wave lasers that are offset phase locked with respect to one another and at least one of which lasers provides a light output that includes a frequency sweep for causing the detector arrangement to respond, based on said detector frequency response and said frequency sweep, in a way which causes the laser radiation to interact with the subcentimeter radiation to produce a frequency down-converted signal from the subcentimeter radiation.

38. A system for investigation of a sample, said system comprising:

a source arrangement having a source with a source frequency response;

the apparatus of claim 37 having said detector arrangement in a positional relationship with said source arrangement such that said sample is located in relation thereto and said illumination arrangement is configured for producing said laser radiation including

(i) a source laser energy that is produced by at least two lasers that are offset phase locked with respect to one another and which source laser energy is incident on the source arrangement, based on the source frequency response, in a way which causes the source arrangement to emit said subcentimeter radiation, at least a portion of which subcentimeter radiation interacts with said sample and the source laser energy interacts to produce a frequency sweep in the subcentimeter radiation and, thereafter, at least some of said portion of the subcentimeter radiation serves as a sample influenced radiation that is incident on the detector arrangement, based on said positional relationship, and

(ii) a detector laser energy that is incident on said detector arrangement and offset phase locked with the source laser energy in a way which produces at least one optical component of the detector laser energy that is offset with respect to a corresponding optical component of the source laser energy so that the detector laser energy and the sample influenced radiation interact, based on said detector frequency response, in a way which at least generates an electrical output signal across the detector arrangement such that the electrical output signal is responsive to the sample influenced radiation including said frequency sweep.

39. The apparatus of claim 37 including using a photoconductive switch as said detector arrangement.

40. The apparatus of claim 39 wherein said photoconductive switch includes LTG ErAs/GaAs.

41. A method for detecting a subcentimeter radiation, said method comprising:

providing a detector with a detector frequency response having said subcentimeter radiation incident on the detector; and

configuring an illumination arrangement for continuously illuminating the detector arrangement with laser radiation that is produced by at least two continuous wave lasers that are offset phase locked with respect to one another and at least one of which lasers provides a light output that includes a frequency sweep for causing the detector arrangement to respond, based on said given frequency response and said frequency sweep, in a way which causes the laser radiation to interact with the subcentimeter radiation to produce a frequency down-converted signal from the subcentimeter radiation.