TRACE GAS DETECTION SYSTEM

• US 20140264031A1
• Filed: 02/12/2014
• Published: 09/18/2014
• Est. Priority Date: 03/15/2013
• Status: Abandoned Application

• Current Assignee: IMRA America Incorporated (Aisin Corp.)
• Original Assignee: IMRA America Incorporated (Aisin Corp.)
• Inventors: FERMANN, Martin E., Lee, Kevin F., Mills, Andrew A.
• Application Number:
  US14/178,985
• Publication Number:
  US 20140264031A1
• Time in Patent Office: Days
• US Class Current: 250/339.02
• CPC Class Codes: A61B 5/082 Evaluation by breath analysis, e.g. determination of the chemical composition of exhaled breath A61B5/083, A61B5/091 take precedence
• CPC Class Codes: A61B 5/097 Devices for facilitating collection of breath or for directing breath into or through measuring devices
• CPC Class Codes: G01J 3/42 Absorption spectrometry; Double beam spectrometry; Flicker spectrometry; Reflection spectrometry beam switching arrangements G01J3/08
• CPC Class Codes: G01J 3/453 by correlation of the amplitudes

Abstract

The present invention relates to a trace gas detection system. At least one embodiment includes a frequency spectrum comprising a 1st comb and an enhancement cavity characterized by having a 2^nd comb of spectral resonances. The enhancement cavity contains a sample gas for spectroscopic measurement. A dither mechanism is configured to modulate the relative spectral position between the combs at a dither frequency, f_d. The dither mechanism, in conjunction with a feedback mechanism, stabilizes the location of said 1^st comb lines with respect to the resonances of said 2^nd comb over a time scale much greater than a dither period, T_d=1/f_d. A time-averaged output from the enhancement cavity is provided to a spectroscopic measurement tool, for example a Fourier transform spectrometer. The system is capable of detecting volatile organic compounds, endogenous compounds, and may be configured for cancer detection.

Claims

1. A trace gas detection system, comprising,

An optical source producing as a primary output a frequency spectrum comprising a 1^st comb with a 1^st comb spacing within a 1^st spectral range;

an enhancement cavity containing a sample gas for spectroscopic measurement, said enhancement cavity configured to receive the primary output of said optical source and to produce a secondary output, said enhancement cavity characterized by having a 2^nd comb of approximately equidistant spectral resonances and a 2^nd comb spacing within a 2^nd spectral range,

wherein said 1^st spectral range and 2^nd spectral range overlap;

a dither mechanism configured to modulate the relative position between said 1^st comb and said 2^nd comb at a dither frequency, f_d, and to impart variations of said relative position in optical frequency space larger than an optical linewidth of said cavity resonances;

a feedback mechanism coupled to said dither mechanism to stabilize the location of said 1^st comb lines with respect to the resonances of said 2^nd comb on a time scale much greater than a dither period, T_d=1/f_d, and

a Fourier transform spectrometer configured to receive said secondary output, and to measure the spectrum of a time-averaged signal transmitted by said cavity over said time scale much longer than T_d.

2. A trace gas detection system according to claim 1, wherein said first comb is characterized by having a carrier envelope offset frequency, f_o, and allowable variations thereof of in the absence of phase locking of said carrier envelope offset frequency.

3. A trace gas detection system according to claim 1, said enhancement cavity having a comb spacing which is an integer fraction or integer multiple of said 1^st comb spacing.

4. A trace gas detection system according to claim 1, wherein said optical source comprises a mode-locked laser, an OPO, OPA, DFG system, quantum cascade laser or micro-resonator.

5. A trace gas detection system according to claim 1, further comprising a gas delivery system to insert and optionally extract a gas sample into or from said cavity.

6. A trace gas detection system according to claim 1, wherein said trace gas detection system is configured for detection of optical spectra at wavelengths>

1600 nm.

7. A trace gas detection system according to claim 1, said trace gas detection system configured for detection of optical spectra at wavelengths in the wavelength range from 3-6 μ

m.

8. A trace gas detection system according to claim 1, said trace gas detection system configured for detection of optical spectra at wavelengths in the wavelength range from 5-15 μ

m.

9. A trace gas detection system according to claim 1, wherein said dither period, T_d, is derived from the zero-crossings of an interference pattern generated by a reference laser within said Fourier transform spectrometer.

10. A trace gas detection system according to claim 9, wherein said Fourier transform spectrometer is configured to sample the signal transmitted through the cavity in synchronism with said zero-crossings of said interference pattern.

11. A trace gas detection system according to claim 1, said feedback mechanism configured for detecting the transmission peaks from said enhancement cavity and providing electronic feedback to a cavity mirror to produce an approximately uniform time spacing of said transmission peaks.

12. A trace gas detection system according to claim 1, wherein said dither mechanism is configured to modulate the position of the cavity spectral resonances of said enhancement cavity via movement of one of the cavity mirrors.

13. A trace gas detection system according to claim 1, wherein said dither mechanism is configured to modulate the comb spacing of said 1^st comb.

14. A trace gas detection system according to claim 1, wherein said dither mechanism is configured to modulate the carrier envelope offset frequency of said 1^st comb.

15. A trace gas detection system according to claim 14, wherein said optical source is diode pumped, and said carrier envelope offset frequency is modulated by dithering the diode power with a supplementary pump signal.

16. A trace gas detection system according to claim 14, wherein said carrier envelope offset frequency is modulated with a graphene modulator.

17. A trace gas detection system according to claim 1, further comprising an acousto-optic frequency shifter to modulate the carrier envelope offset frequency of said 1^st comb.

18. A trace gas detection system according to claim 1, wherein said dither period, T_d, is greater than about 100 μ

s, corresponding to a dither frequency less than about 10 kHz.

19. A trace gas detection system according to claim 1, wherein said dither period is in the range from about 1 μ

sec to about 100 μ

s, corresponding to a dither frequency in the range from about 10 kHz to 1 MHz.

20. A trace gas detection system according to claim 1, said dither mechanism configured to modulate the position of said 1^st or 2^nd frequency comb by about one free spectral range of said enhancement cavity.

21. A trace gas detection system according to claim 1, wherein said dither mechanism is configured to modulate the position of said 1^st or 2^nd frequency comb by a fraction of said free spectral range of said enhancement cavity.

22. A trace gas detection system according to claim 1, wherein said dither mechanism is configured to modulate the position of said 1^st or 2nd frequency comb by more than a free spectral range of said enhancement cavity.

23. A trace gas detection system according to claim 1, wherein said Fourier transform spectrometer is configured to sample more than two cavity transmission peaks between two zero-crossings.

24. A trace gas detection system according to claim 1, wherein said Fourier transform spectrometer is configured to sample a uniform number of cavity transmission peaks between two zero-crossings.

25. A trace gas detection system according to claim 1, said Fourier transform spectrometer configured to sample the signal transmitted through the cavity at time intervals much smaller than the time intervals between two adjacent zero crossings.

26. A trace gas detection system according to claim 1, wherein said optical source is configured as a frequency comb source with repetition rate, f_rep, and carrier envelope offset frequency, f_o, phase locked to reference signals via phase locked loops.

27. A trace gas system according to claim 26, wherein said feedback loops are arranged in said feedback mechanism.

28. A trace gas detection system according to claim 1, wherein said system is configured for breath analysis.

29. A trace gas detection system according to claim 1, wherein said system is configured for detection of volatile organic compounds.

30. A trace gas detection system according to claim 1, wherein said system is configured for detection of endogeneous compounds.

31. A trace gas detection system according to claim 1, wherein said system is configured for cancer detection via breath analysis of volatile organic and/or endogenous compounds.

32. A trace gas detection system, comprising,

An optical source producing as a primary output a frequency spectrum comprising a 1^st comb with a 1^st comb spacing within a 1^st spectral range, said first spectral range comprising wavelengths>

1600 nm;

an enhancement cavity containing a sample gas for spectroscopic measurement, said enhancement cavity configured to receive the primary output of said optical source and to produce a secondary output, said enhancement cavity characterized by having a 2^nd comb of approximately equidistant spectral resonances and a 2^nd comb spacing within a 2^nd spectral range,

wherein said 1^st spectral range and 2^nd spectral range overlap;

a dither mechanism configured to modulate the relative position between said 1^st comb and said 2^nd comb at a dither frequency, f_d, and to impart variations of said relative position in optical frequency space larger than an optical linewidth of said cavity resonances;

a feedback mechanism coupled to said dither mechanism to stabilize the location of said 1^st comb lines with respect to the resonances of said 2^nd comb on a time scale much greater than a dither period, T_d=1/f_d, and

a spectroscopic measurement tool comprising an optical detection system, said tool configured for frequency resolved detection of a time-averaged signal transmitted through the enhancement cavity.

33. A trace gas detection system according to claim 32, wherein said optical detection system comprises a one dimensional detector array or a two dimensional detector array.

34. A trace gas system, comprising:

an optical source producing as a primary output a frequency spectrum comprising a 1^st comb with a 1^st comb spacing within a 1^st spectral range;

an enhancement cavity containing a sample gas for spectroscopic measurement, said enhancement cavity configured to receive the primary output of said optical source and to produce a secondary output, said enhancement cavity characterized by having a 2^nd comb of approximately equidistant spectral resonances and a 2^nd comb spacing within a 2^nd spectral range,

wherein said 1^st spectral range and 2^nd spectral range overlap;

a dither mechanism configured to modulate the relative position between said 1^st comb and said 2^nd comb at a dither frequency, f_d, and to impart variations of said relative position in optical frequency space larger than an optical linewidth of said cavity resonances; and

a spectroscopic measurement tool configured to receive said secondary output, and to measure the spectrum of a time-averaged signal transmitted by said cavity over said time scale much longer than T_d=1/f_d,

wherein the spectroscopic tool is configured to provide a signal for synchronization of dithering with spectroscopic data acquisition.

35. A trace gas system according to claim 34, wherein said spectroscopic tool comprises a Fourier transform spectrometer (FTS) having a reference laser from which an interference signal is generated, and said FTS is configured to sample a signal transmitted through said enhancement cavity in synchronism with zero crossings of said interference signal.

36. A trace gas system according to claim 35, further comprising a feedback mechanism coupled to said dither mechanism, wherein a dither period, T_d, is derived from zero crossings of said interference signal and used to control said dither mechanism via said feedback mechanism.