Compact laser diode monitor using defined laser momentum vectors to cause emission of a coherent photon in a selected direction

• US 5,617,206 A
• Filed: 12/04/1995
• Issued: 04/01/1997
• Est. Priority Date: 12/04/1995
• Status: Expired due to Term

• Current Assignee: Chromx Optics, Llc
• Original Assignee: Applied Physical Science International
• Inventors: Fay, Theodore D.
• Primary Examiner(s): Hantis, K.
• Application Number:
  US08/566,965
• Time in Patent Office: 484 Days
• Field of Search: 356/311, 356/301, 356/39, 356/320, 128/633, 250/574
• US Class Current: 356/320
• CPC Class Codes: G01N 2021/653 Coherent methods [CARS]
• CPC Class Codes: G01N 21/65 Raman scattering

Abstract

A compact laser diode monitor for measuring concentrations of individual atomic and molecular species in both gaseous and semitransparent fluids, includes a first diode laser having an output for resonantly exciting a first selected electronic transition of a specific atomic or molecular species of a sample, and a second diode laser having an output for resonantly exciting a second selected electronic transition of said specific atomic or molecular species of said sample. A difference between said first and second frequency outputs is equal to a vibrational energy level difference of the specific atomic or molecular species. Further said first and second frequency outputs are simultaneously directed into said sample, with selected momentum vectors in order to cause the selected atomic or molecular species to emit a coherent photon signal in a selected direction having a frequency equal to twice the first frequency output minus the second frequency output. A detector is provided for receiving the emitted coherent photon signal and spectrally analyzing the emitted coherent photon signal.

Claims

1. A compact laser diode monitor for measuring concentrations of individual atomic and molecular species in both gaseous and semitransparent fluids, the monitor comprising:

first diode laser means for exciting a first selected electronic transition of a specific atomic or molecular species of a sample, said first laser means having a first frequency output resonant with the first selected electronic transition;

second diode laser means for exciting a second selected electronic transition of said specific atomic or molecular species of said sample, said second laser means having a second frequency output resonant with the second selected electronics transition, a difference between said first and second frequency outputs being equal to a vibrational energy level difference of the specific atomic or molecular species;

means for simultaneously directing said first and second frequency outputs into said sample, with selected momentum vectors in order to cause the selected atomic or molecular species to emit a coherent photon signal in a selected direction having a frequency equal to twice the first frequency output minus the second frequency output; and

means for detecting the emitted coherent photon signal and spectrally analyzing the emitted coherent photon signal.

2. The monitor according to claim 1 wherein the means for directing said first and second frequency outputs into said sample comprises lens means for causing said first and second frequency outputs to converge onto said sample.

3. The monitor according to claim 2 wherein the means for directing said first and second frequency outputs into said sample further comprising mirror means for causing first and second frequency outputs passing through the sample to reenter the sample a selected number of times.

4. The monitor according to claim 3 wherein the selected number of times is at least 50.

5. The monitor according to claim 4 wherein said lens means and mirror means are spaced apart from one another no more than 2 centimeters.

6. The monitor according to claim 2 further comprising optical means, disposed between said sample and the means for detecting, for reducing fluorescent signal, generated by said sample, entering said means for detecting the emitted coherent photon signal.

7. The monitor according to claim 6 wherein said means for detecting the emitted coherent photon signal comprises a tunable wavelength filter.

8. The monitor according to claim 7 wherein the tunable wavelength filter is tunable by application of heat thereto.

9. The monitor according to claim 8 wherein said tunable wavelength filter comprises a Fabry Perot device having two spaced apart flat parallel plates with an inorganic chemical disposed between the plates, said organic chemical having an index of refraction change rate with temperature.

10. The monitor according to claim 9 wherein said inorganic chemical has an index of refraction decreasing with increasing temperature.

11. The monitor according to claim 8 wherein said tunable wavelength filter comprises a Fabry Perot device having two spaced apart flat parallel plates, comprising a solid inorganic material, said solid inorganic material having an index of refraction change rate with temperature.

12. The monitor according to claim 9, 10 or 11 further comprising thermoelectric heater means for tuning the Fabry Perot device.

13. The monitor according to claim 9 wherein said means for detecting the emitted coherent photon signal comprises detector array means for receiving the selected Fabry Perot fringe, and producing an electrical signal corresponding thereto.

14. The monitor according to claim 13 wherein said means for detecting the emitted coherent photon signal comprises detector array means for receiving the selected Fabry Perot fringe and producing an electrical signal corresponding thereto.

15. The monitor according to claim 13 wherein said means for detecting the emitted coherent photon signal comprises detector array means for receiving one of the Fabry Perot fringes and the selected fringe and producing electrical signals corresponding thereto.

16. The monitor according to claim 9 wherein said means for detecting the emitted coherent photon signal comprises broadband filter means for isolating a single order of fringe output of the Fabry Perot device.

17. The monitor according to claim 16 wherein said broadband filter means comprises an acousto-optic tunable filter.

18. A compact laser diode monitor for comparing concentrations of individual atomic and molecular species in both gaseous and semitransparent fluids, the monitor comprising:

first diode laser means for exciting a first selected electronic transition of a specific atomic or molecular species of a sample and a standard, said first laser means having a first frequency output resonant with the first selected electronic transition;

second diode laser means for exciting a second selected electronic transition of said specific atomic or molecular species of said sample and the standard, said second laser means having a second frequency output resonant with the second selected electronics transition, a difference between said first and second frequency outputs being equal to a vibrational energy level difference of the specific atomic molecular species;

means for simultaneously directing said first and second frequency outputs into said sample and standard with selected momentum vectors in order to cause the selected atomic or molecular species in the sample and standard to emit coherent photon signals in selected directions having a frequency equal to twice the first frequency output minus the second frequency output; and

means for detecting the emitted coherent signals and comparing same.

19. The monitor according to claim 18 wherein the means for directing said first and second frequency outputs into said sample comprises lens means for causing said first and second frequency outputs to converge onto said sample and standard.

20. The monitor according to claim 19 wherein the means for directing said first and second frequency outputs into said sample further comprising mirror means for causing first and second frequency outputs passing through the sample to reenter the sample and standard a selected number of times.

21. The monitor according to claim 20 wherein the selected number of times is at least 50.

22. The monitor according to claim 21 wherein said lens means and mirror means are spaced apart from one another no more than 2 centimeters.

23. The monitor according to claim 19 further comprising optical means, disposed between said sample and standard and the means for detecting, for reducing fluorescent signal, generated by said sample, entering said means for detecting the emitted coherent photon signals.

24. The monitor according to claim 23 wherein said means for detecting the emitted coherent photon signal comprises a tunable wavelength filter.

25. The monitor according to claim 24 wherein the tunable wavelength filter is tunable by application of heat thereto.

26. The monitor according to claim 25 wherein said tunable wavelength filter comprises a Fabry Perot device having two spaced apart flat parallel plates with an organic chemical disposed between the plates, said organic chemical having an index of refraction change rate with temperature.

27. The monitor according to claim 26 wherein said organic chemical has an index of refraction decreasing with increasing temperature.

28. The monitor according to claim 25 wherein said tunable wavelength filter comprises a Fabry Perot device having two spaced apart flat parallel plates, comprising a solid inorganic material, said solid inorganic material having an index of refraction change rate with temperature.

29. The monitor according to claim 26, 27 or 28 further comprising thermoelectric heater means for tuning the Fabry Perot device.

30. The monitor according to claim 26 wherein said means for detecting the emitted coherent photon signal comprises dispersive means, disposed for receiver output from the tunable wavelength filter, for selecting Fabry Perot fringes in the output for viewing.

31. The monitor according to claim 30 wherein said means for detecting the emitted coherent photon signals comprises detector array means for receiving the selected Fabry Perot fringes and producing electrical signals corresponding thereto.

32. The monitor according to claim 30 wherein said means for detecting the emitted coherent photon signals comprises detector array means for receiving one of the Fabry Perot fringes and the selected fringe and producing electrical signals corresponding thereto.

33. The monitor according to claim 26 wherein said means for detecting the emitted coherent signals comprises broadband filter means for isolating a single order of fringe output of the Fabry Perot device.

34. The monitor according to claim 33 wherein said broadband filter means comprises an acousto-optic tunable filter.

35. A method for monitoring concentrations of individual atomic and molecular species in both gases and semitransparent fluids, said method comprising the steps of:

directing a first laser having a frequency resonant with a first selected electronic transition of a specific atomic or molecular species into a sample comprising the specific atomic or molecular species;

simultaneously directing a second laser into said sample in order to cause the selected atomic or molecular species to emit a coherent photon signal in a selected direction, said second laser having a frequency resonant with a second selected electronic transition of the specific atomic or molecular species, a difference between said first and second laser resonant frequencies being equal to a vibrational energy level difference of the specific atomic or molecular species; and

detecting the emitted coherent photon signal.

36. The method according to claim 35 further comprising the step of directing the first and second lasers into the sample with vector momentums causing the selected atomic or molecular species to emit the coherent photon signal in the selected direction.