Abstract

We have demonstrated microwave optical double resonance spectroscopy of the ν1 + ν3 and ν1 + 2ν4 bands of ammonia in a hollow-core photonic bandgap fiber. Signal strength and lineshapes are analyzed. Spectroscopic assignments of previously assigned lines and previously proposed assignments have been confirmed and new assignments have been made. Several microwave transitions in the excited vibrational states have been measured for the first time.

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References

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  1. H. Jones, “Infrared-Microwave Double Resonance Techniques,” in Modern Aspects of Microwave Spectroscopy, G. W. Chantry, ed., (Academic Press, N.Y., 1979).
  2. C. Ishibashi, R. Saneto, and H. Sasada, “Infrared radio-frequency double resonance spectroscopy of molecular vibrational-overtone bands using a Fabry-Perot cavity-absorption cell,” J. Opt. Soc. Am. B 18(7), 1019–1029 (2001).
    [CrossRef]
  3. A. Czajkowski, A. J. Alcock, J. E. Bernard, A. A. Madej, M. Corrigan, and S. Chepurov, “Studies of saturated absorption and measurements of optical frequency for lines in the ν1 + ν3 and ν1 + 2ν4 bands of ammonia at 1.5 microm,” Opt. Express 17(11), 9258–9269 (2009).
    [CrossRef] [PubMed]
  4. U. Merker, H. K. Srivastava, A. Callagari, K. K. Lehmann, and G. Scoles, “Eigenstate resolved infrared and millimeter-wave-infrared double resonance spectroscopy of methylamine in the N-H stretch first overtone region,” Phys. Chem. Chem. Phys. 1(10), 2427–2433 (1999).
    [CrossRef]
  5. S. L. Coy and K. K. Lehmann, “Modeling the rotational and vibrational structure of the i.r. and optical spectrum of NH3,” Spectrochim. Acta 45A, 47–56 (1989).
  6. F. Benabid, F. Couny, J. C. Knight, T. A. Birks, and P. St. J. Russell, “Compact, stable and efficient all-fibre gas cells using hollow-core photonic crystal fibres,” Nature 434(7032), 488–491 (2005).
    [CrossRef] [PubMed]
  7. S. Ghosh, J. E. Sharping, D. G. Ouzounov, and A. L. Gaeta, “Resonant optical interactions with molecules confined in photonic band-gap fibers,” Phys. Rev. Lett. 94(9), 093902 (2005).
    [CrossRef] [PubMed]
  8. J. Henningsen, J. Hald, and J. C. Petersen, “Saturated absorption in acetylene and hydrogen cyanide in hollow-core photonic bandgap fibers,” Opt. Express 13(26), 10475–10482 (2005).
    [CrossRef] [PubMed]
  9. R. Thapa, K. Knabe, M. Faheem, A. Naweed, O. L. Weaver, and K. L. Corwin, “Saturated absorption spectroscopy of acetylene gas inside large-core photonic bandgap fiber,” Opt. Express 31, 2489–2491 (2006).
  10. J. Hald, J. C. Petersen, and J. Henningsen, “Saturated optical absorption by slow molecules in hollow-core photonic band-gap fibers,” Phys. Rev. Lett. 98(21), 213902 (2007).
    [CrossRef] [PubMed]
  11. K. Knabe, S. Wu, J. Lim, K. A. Tillman, P. S. Light, F. Couny, N. Wheeler, R. Thapa, A. M. Jones, J. W. Nicholson, B. R. Washburn, F. Benabid, and K. L. Corwin, “10 kHz accuracy of an optical frequency reference based on (12)C2H2-filled large-core kagome photonic crystal fibers,” Opt. Express 17(18), 16017–16026 (2009).
    [CrossRef] [PubMed]
  12. P. Londero, V. Venkataraman, A. R. Bhagwat, A. D. Slepkov, and A. L. Gaeta, “Ultralow-power four-wave mixing with Rb in a hollow-core photonic band-gap fiber,” Phys. Rev. Lett. 103(4), 043602 (2009).
    [CrossRef] [PubMed]
  13. A. M. Cubillas, J. Hald, and J. C. Petersen, “High resolution spectroscopy of ammonia in a hollow-core fiber,” Opt. Express 16(6), 3976–3985 (2008).
    [CrossRef] [PubMed]
  14. A. R. Bhagwat and A. L. Gaeta, “Nonlinear optics in hollow-core photonic bandgap fibers,” Opt. Express 16(7), 5035–5047 (2008).
    [CrossRef] [PubMed]
  15. J. Henningsen and J. C. Petersen, “Infrared-microwave double resonance in methanol: coherent effects and molecular parameters,” J. Opt. Soc. Am. B 5(9), 1848–1857 (1988).
    [CrossRef]
  16. J. Henningsen and J. Hald, “Dynamics of gas flow in hollow core photonic bandgap fibers,” Appl. Opt. 47(15), 2790–2797 (2008).
    [CrossRef] [PubMed]
  17. C. H. Townes, and A. L. Schawlow, Microwave Spectroscopy (McGraw-Hill, N.Y., 1955).
  18. L. Lundsberg Nielsen, F. Hegelund, and F. M. Nicolaisen, “Analysis of the high-resolution spectrum of ammonia (14NH3) in the near-infrared region, 6400-6900 cm−1,” J. Mol. Spectrosc. 162(1), 230–245 (1993).
    [CrossRef]
  19. L.-H. Xu, Z. Liu, I. Yakovlev, M. Yu. Tretyakov, and R. M. Lees, “External cavity tunable diode laser NH3 spectra in the 1.5 μm region,” Infrared Phys. Technol. 45(1), 31–45 (2004).
    [CrossRef]
  20. L. Li, R. M. Lees, and L.-H. Xu, “External cavity tunable diode laser spectra of the ν1+2ν4 stretch-band combination bands of 14NH3 and 15NH3,” J. Mol. Spectrosc. 243(2), 219–226 (2007).
    [CrossRef]
  21. R. M. Lees, L. Li, and L.-H. Xu, “New VISTA on ammonia in the 1.5 μm region: Assignments for the ν3+2ν4 bands of 14NH3 and 15NH3 by isotopic shift labeling,” J. Mol. Spectrosc. 251(1-2), 241–251 (2008).
    [CrossRef]

2009

2008

2007

L. Li, R. M. Lees, and L.-H. Xu, “External cavity tunable diode laser spectra of the ν1+2ν4 stretch-band combination bands of 14NH3 and 15NH3,” J. Mol. Spectrosc. 243(2), 219–226 (2007).
[CrossRef]

J. Hald, J. C. Petersen, and J. Henningsen, “Saturated optical absorption by slow molecules in hollow-core photonic band-gap fibers,” Phys. Rev. Lett. 98(21), 213902 (2007).
[CrossRef] [PubMed]

2006

R. Thapa, K. Knabe, M. Faheem, A. Naweed, O. L. Weaver, and K. L. Corwin, “Saturated absorption spectroscopy of acetylene gas inside large-core photonic bandgap fiber,” Opt. Express 31, 2489–2491 (2006).

2005

F. Benabid, F. Couny, J. C. Knight, T. A. Birks, and P. St. J. Russell, “Compact, stable and efficient all-fibre gas cells using hollow-core photonic crystal fibres,” Nature 434(7032), 488–491 (2005).
[CrossRef] [PubMed]

S. Ghosh, J. E. Sharping, D. G. Ouzounov, and A. L. Gaeta, “Resonant optical interactions with molecules confined in photonic band-gap fibers,” Phys. Rev. Lett. 94(9), 093902 (2005).
[CrossRef] [PubMed]

J. Henningsen, J. Hald, and J. C. Petersen, “Saturated absorption in acetylene and hydrogen cyanide in hollow-core photonic bandgap fibers,” Opt. Express 13(26), 10475–10482 (2005).
[CrossRef] [PubMed]

2004

L.-H. Xu, Z. Liu, I. Yakovlev, M. Yu. Tretyakov, and R. M. Lees, “External cavity tunable diode laser NH3 spectra in the 1.5 μm region,” Infrared Phys. Technol. 45(1), 31–45 (2004).
[CrossRef]

2001

1999

U. Merker, H. K. Srivastava, A. Callagari, K. K. Lehmann, and G. Scoles, “Eigenstate resolved infrared and millimeter-wave-infrared double resonance spectroscopy of methylamine in the N-H stretch first overtone region,” Phys. Chem. Chem. Phys. 1(10), 2427–2433 (1999).
[CrossRef]

1993

L. Lundsberg Nielsen, F. Hegelund, and F. M. Nicolaisen, “Analysis of the high-resolution spectrum of ammonia (14NH3) in the near-infrared region, 6400-6900 cm−1,” J. Mol. Spectrosc. 162(1), 230–245 (1993).
[CrossRef]

1989

S. L. Coy and K. K. Lehmann, “Modeling the rotational and vibrational structure of the i.r. and optical spectrum of NH3,” Spectrochim. Acta 45A, 47–56 (1989).

1988

Alcock, A. J.

Benabid, F.

Bernard, J. E.

Bhagwat, A. R.

P. Londero, V. Venkataraman, A. R. Bhagwat, A. D. Slepkov, and A. L. Gaeta, “Ultralow-power four-wave mixing with Rb in a hollow-core photonic band-gap fiber,” Phys. Rev. Lett. 103(4), 043602 (2009).
[CrossRef] [PubMed]

A. R. Bhagwat and A. L. Gaeta, “Nonlinear optics in hollow-core photonic bandgap fibers,” Opt. Express 16(7), 5035–5047 (2008).
[CrossRef] [PubMed]

Birks, T. A.

F. Benabid, F. Couny, J. C. Knight, T. A. Birks, and P. St. J. Russell, “Compact, stable and efficient all-fibre gas cells using hollow-core photonic crystal fibres,” Nature 434(7032), 488–491 (2005).
[CrossRef] [PubMed]

Callagari, A.

U. Merker, H. K. Srivastava, A. Callagari, K. K. Lehmann, and G. Scoles, “Eigenstate resolved infrared and millimeter-wave-infrared double resonance spectroscopy of methylamine in the N-H stretch first overtone region,” Phys. Chem. Chem. Phys. 1(10), 2427–2433 (1999).
[CrossRef]

Chepurov, S.

Corrigan, M.

Corwin, K. L.

Couny, F.

Coy, S. L.

S. L. Coy and K. K. Lehmann, “Modeling the rotational and vibrational structure of the i.r. and optical spectrum of NH3,” Spectrochim. Acta 45A, 47–56 (1989).

Cubillas, A. M.

Czajkowski, A.

Faheem, M.

R. Thapa, K. Knabe, M. Faheem, A. Naweed, O. L. Weaver, and K. L. Corwin, “Saturated absorption spectroscopy of acetylene gas inside large-core photonic bandgap fiber,” Opt. Express 31, 2489–2491 (2006).

Gaeta, A. L.

P. Londero, V. Venkataraman, A. R. Bhagwat, A. D. Slepkov, and A. L. Gaeta, “Ultralow-power four-wave mixing with Rb in a hollow-core photonic band-gap fiber,” Phys. Rev. Lett. 103(4), 043602 (2009).
[CrossRef] [PubMed]

A. R. Bhagwat and A. L. Gaeta, “Nonlinear optics in hollow-core photonic bandgap fibers,” Opt. Express 16(7), 5035–5047 (2008).
[CrossRef] [PubMed]

S. Ghosh, J. E. Sharping, D. G. Ouzounov, and A. L. Gaeta, “Resonant optical interactions with molecules confined in photonic band-gap fibers,” Phys. Rev. Lett. 94(9), 093902 (2005).
[CrossRef] [PubMed]

Ghosh, S.

S. Ghosh, J. E. Sharping, D. G. Ouzounov, and A. L. Gaeta, “Resonant optical interactions with molecules confined in photonic band-gap fibers,” Phys. Rev. Lett. 94(9), 093902 (2005).
[CrossRef] [PubMed]

Hald, J.

Hegelund, F.

L. Lundsberg Nielsen, F. Hegelund, and F. M. Nicolaisen, “Analysis of the high-resolution spectrum of ammonia (14NH3) in the near-infrared region, 6400-6900 cm−1,” J. Mol. Spectrosc. 162(1), 230–245 (1993).
[CrossRef]

Henningsen, J.

Ishibashi, C.

Jones, A. M.

Knabe, K.

Knight, J. C.

F. Benabid, F. Couny, J. C. Knight, T. A. Birks, and P. St. J. Russell, “Compact, stable and efficient all-fibre gas cells using hollow-core photonic crystal fibres,” Nature 434(7032), 488–491 (2005).
[CrossRef] [PubMed]

Lees, R. M.

R. M. Lees, L. Li, and L.-H. Xu, “New VISTA on ammonia in the 1.5 μm region: Assignments for the ν3+2ν4 bands of 14NH3 and 15NH3 by isotopic shift labeling,” J. Mol. Spectrosc. 251(1-2), 241–251 (2008).
[CrossRef]

L. Li, R. M. Lees, and L.-H. Xu, “External cavity tunable diode laser spectra of the ν1+2ν4 stretch-band combination bands of 14NH3 and 15NH3,” J. Mol. Spectrosc. 243(2), 219–226 (2007).
[CrossRef]

L.-H. Xu, Z. Liu, I. Yakovlev, M. Yu. Tretyakov, and R. M. Lees, “External cavity tunable diode laser NH3 spectra in the 1.5 μm region,” Infrared Phys. Technol. 45(1), 31–45 (2004).
[CrossRef]

Lehmann, K. K.

U. Merker, H. K. Srivastava, A. Callagari, K. K. Lehmann, and G. Scoles, “Eigenstate resolved infrared and millimeter-wave-infrared double resonance spectroscopy of methylamine in the N-H stretch first overtone region,” Phys. Chem. Chem. Phys. 1(10), 2427–2433 (1999).
[CrossRef]

S. L. Coy and K. K. Lehmann, “Modeling the rotational and vibrational structure of the i.r. and optical spectrum of NH3,” Spectrochim. Acta 45A, 47–56 (1989).

Li, L.

R. M. Lees, L. Li, and L.-H. Xu, “New VISTA on ammonia in the 1.5 μm region: Assignments for the ν3+2ν4 bands of 14NH3 and 15NH3 by isotopic shift labeling,” J. Mol. Spectrosc. 251(1-2), 241–251 (2008).
[CrossRef]

L. Li, R. M. Lees, and L.-H. Xu, “External cavity tunable diode laser spectra of the ν1+2ν4 stretch-band combination bands of 14NH3 and 15NH3,” J. Mol. Spectrosc. 243(2), 219–226 (2007).
[CrossRef]

Light, P. S.

Lim, J.

Liu, Z.

L.-H. Xu, Z. Liu, I. Yakovlev, M. Yu. Tretyakov, and R. M. Lees, “External cavity tunable diode laser NH3 spectra in the 1.5 μm region,” Infrared Phys. Technol. 45(1), 31–45 (2004).
[CrossRef]

Londero, P.

P. Londero, V. Venkataraman, A. R. Bhagwat, A. D. Slepkov, and A. L. Gaeta, “Ultralow-power four-wave mixing with Rb in a hollow-core photonic band-gap fiber,” Phys. Rev. Lett. 103(4), 043602 (2009).
[CrossRef] [PubMed]

Lundsberg Nielsen, L.

L. Lundsberg Nielsen, F. Hegelund, and F. M. Nicolaisen, “Analysis of the high-resolution spectrum of ammonia (14NH3) in the near-infrared region, 6400-6900 cm−1,” J. Mol. Spectrosc. 162(1), 230–245 (1993).
[CrossRef]

Madej, A. A.

Merker, U.

U. Merker, H. K. Srivastava, A. Callagari, K. K. Lehmann, and G. Scoles, “Eigenstate resolved infrared and millimeter-wave-infrared double resonance spectroscopy of methylamine in the N-H stretch first overtone region,” Phys. Chem. Chem. Phys. 1(10), 2427–2433 (1999).
[CrossRef]

Naweed, A.

R. Thapa, K. Knabe, M. Faheem, A. Naweed, O. L. Weaver, and K. L. Corwin, “Saturated absorption spectroscopy of acetylene gas inside large-core photonic bandgap fiber,” Opt. Express 31, 2489–2491 (2006).

Nicholson, J. W.

Nicolaisen, F. M.

L. Lundsberg Nielsen, F. Hegelund, and F. M. Nicolaisen, “Analysis of the high-resolution spectrum of ammonia (14NH3) in the near-infrared region, 6400-6900 cm−1,” J. Mol. Spectrosc. 162(1), 230–245 (1993).
[CrossRef]

Ouzounov, D. G.

S. Ghosh, J. E. Sharping, D. G. Ouzounov, and A. L. Gaeta, “Resonant optical interactions with molecules confined in photonic band-gap fibers,” Phys. Rev. Lett. 94(9), 093902 (2005).
[CrossRef] [PubMed]

Petersen, J. C.

Russell, P. St. J.

F. Benabid, F. Couny, J. C. Knight, T. A. Birks, and P. St. J. Russell, “Compact, stable and efficient all-fibre gas cells using hollow-core photonic crystal fibres,” Nature 434(7032), 488–491 (2005).
[CrossRef] [PubMed]

Saneto, R.

Sasada, H.

Scoles, G.

U. Merker, H. K. Srivastava, A. Callagari, K. K. Lehmann, and G. Scoles, “Eigenstate resolved infrared and millimeter-wave-infrared double resonance spectroscopy of methylamine in the N-H stretch first overtone region,” Phys. Chem. Chem. Phys. 1(10), 2427–2433 (1999).
[CrossRef]

Sharping, J. E.

S. Ghosh, J. E. Sharping, D. G. Ouzounov, and A. L. Gaeta, “Resonant optical interactions with molecules confined in photonic band-gap fibers,” Phys. Rev. Lett. 94(9), 093902 (2005).
[CrossRef] [PubMed]

Slepkov, A. D.

P. Londero, V. Venkataraman, A. R. Bhagwat, A. D. Slepkov, and A. L. Gaeta, “Ultralow-power four-wave mixing with Rb in a hollow-core photonic band-gap fiber,” Phys. Rev. Lett. 103(4), 043602 (2009).
[CrossRef] [PubMed]

Srivastava, H. K.

U. Merker, H. K. Srivastava, A. Callagari, K. K. Lehmann, and G. Scoles, “Eigenstate resolved infrared and millimeter-wave-infrared double resonance spectroscopy of methylamine in the N-H stretch first overtone region,” Phys. Chem. Chem. Phys. 1(10), 2427–2433 (1999).
[CrossRef]

Thapa, R.

Tillman, K. A.

Tretyakov, M. Yu.

L.-H. Xu, Z. Liu, I. Yakovlev, M. Yu. Tretyakov, and R. M. Lees, “External cavity tunable diode laser NH3 spectra in the 1.5 μm region,” Infrared Phys. Technol. 45(1), 31–45 (2004).
[CrossRef]

Venkataraman, V.

P. Londero, V. Venkataraman, A. R. Bhagwat, A. D. Slepkov, and A. L. Gaeta, “Ultralow-power four-wave mixing with Rb in a hollow-core photonic band-gap fiber,” Phys. Rev. Lett. 103(4), 043602 (2009).
[CrossRef] [PubMed]

Washburn, B. R.

Weaver, O. L.

R. Thapa, K. Knabe, M. Faheem, A. Naweed, O. L. Weaver, and K. L. Corwin, “Saturated absorption spectroscopy of acetylene gas inside large-core photonic bandgap fiber,” Opt. Express 31, 2489–2491 (2006).

Wheeler, N.

Wu, S.

Xu, L.-H.

R. M. Lees, L. Li, and L.-H. Xu, “New VISTA on ammonia in the 1.5 μm region: Assignments for the ν3+2ν4 bands of 14NH3 and 15NH3 by isotopic shift labeling,” J. Mol. Spectrosc. 251(1-2), 241–251 (2008).
[CrossRef]

L. Li, R. M. Lees, and L.-H. Xu, “External cavity tunable diode laser spectra of the ν1+2ν4 stretch-band combination bands of 14NH3 and 15NH3,” J. Mol. Spectrosc. 243(2), 219–226 (2007).
[CrossRef]

L.-H. Xu, Z. Liu, I. Yakovlev, M. Yu. Tretyakov, and R. M. Lees, “External cavity tunable diode laser NH3 spectra in the 1.5 μm region,” Infrared Phys. Technol. 45(1), 31–45 (2004).
[CrossRef]

Yakovlev, I.

L.-H. Xu, Z. Liu, I. Yakovlev, M. Yu. Tretyakov, and R. M. Lees, “External cavity tunable diode laser NH3 spectra in the 1.5 μm region,” Infrared Phys. Technol. 45(1), 31–45 (2004).
[CrossRef]

Appl. Opt.

Infrared Phys. Technol.

L.-H. Xu, Z. Liu, I. Yakovlev, M. Yu. Tretyakov, and R. M. Lees, “External cavity tunable diode laser NH3 spectra in the 1.5 μm region,” Infrared Phys. Technol. 45(1), 31–45 (2004).
[CrossRef]

J. Mol. Spectrosc.

L. Li, R. M. Lees, and L.-H. Xu, “External cavity tunable diode laser spectra of the ν1+2ν4 stretch-band combination bands of 14NH3 and 15NH3,” J. Mol. Spectrosc. 243(2), 219–226 (2007).
[CrossRef]

R. M. Lees, L. Li, and L.-H. Xu, “New VISTA on ammonia in the 1.5 μm region: Assignments for the ν3+2ν4 bands of 14NH3 and 15NH3 by isotopic shift labeling,” J. Mol. Spectrosc. 251(1-2), 241–251 (2008).
[CrossRef]

L. Lundsberg Nielsen, F. Hegelund, and F. M. Nicolaisen, “Analysis of the high-resolution spectrum of ammonia (14NH3) in the near-infrared region, 6400-6900 cm−1,” J. Mol. Spectrosc. 162(1), 230–245 (1993).
[CrossRef]

J. Opt. Soc. Am. B

Nature

F. Benabid, F. Couny, J. C. Knight, T. A. Birks, and P. St. J. Russell, “Compact, stable and efficient all-fibre gas cells using hollow-core photonic crystal fibres,” Nature 434(7032), 488–491 (2005).
[CrossRef] [PubMed]

Opt. Express

Phys. Chem. Chem. Phys.

U. Merker, H. K. Srivastava, A. Callagari, K. K. Lehmann, and G. Scoles, “Eigenstate resolved infrared and millimeter-wave-infrared double resonance spectroscopy of methylamine in the N-H stretch first overtone region,” Phys. Chem. Chem. Phys. 1(10), 2427–2433 (1999).
[CrossRef]

Phys. Rev. Lett.

J. Hald, J. C. Petersen, and J. Henningsen, “Saturated optical absorption by slow molecules in hollow-core photonic band-gap fibers,” Phys. Rev. Lett. 98(21), 213902 (2007).
[CrossRef] [PubMed]

S. Ghosh, J. E. Sharping, D. G. Ouzounov, and A. L. Gaeta, “Resonant optical interactions with molecules confined in photonic band-gap fibers,” Phys. Rev. Lett. 94(9), 093902 (2005).
[CrossRef] [PubMed]

P. Londero, V. Venkataraman, A. R. Bhagwat, A. D. Slepkov, and A. L. Gaeta, “Ultralow-power four-wave mixing with Rb in a hollow-core photonic band-gap fiber,” Phys. Rev. Lett. 103(4), 043602 (2009).
[CrossRef] [PubMed]

Spectrochim. Acta

S. L. Coy and K. K. Lehmann, “Modeling the rotational and vibrational structure of the i.r. and optical spectrum of NH3,” Spectrochim. Acta 45A, 47–56 (1989).

Other

H. Jones, “Infrared-Microwave Double Resonance Techniques,” in Modern Aspects of Microwave Spectroscopy, G. W. Chantry, ed., (Academic Press, N.Y., 1979).

C. H. Townes, and A. L. Schawlow, Microwave Spectroscopy (McGraw-Hill, N.Y., 1955).

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Figures (6)

Fig. 1
Fig. 1

Typical energy level scheme and transitions for MODR spectroscopy of ammonia.

Fig. 2
Fig. 2

Experimental setup for MODR spectroscopy in a HC–PBF. ECL is the extended cavity diode laser. EDFA is the optical amplifier. L1, L2 and L3 are lenses used for coupling light in and out of fibers. PD is the photodetector.

Fig. 3
Fig. 3

Measurements performed with an ammonia pressure of 25 Pa, RF power of 95 mW, and off-resonant optical power after the HC-PBF of 50 mW. a) Photo detector DC voltage divided by 0.04 V (for clarity) as a function of optical detuning in MHz. b) Relative MODR signal multiplied by 106 as a function of optical detuning in MHz. RF detuning fixed at 0 MHz. Lock-in time constant: 10 ms. Scan rate: 460 MHz/s. c) Residual from a Gaussian fit to curve b, displaced vertically for clarity. d) Relative MODR signal multiplied by 106 as a function of microwave detuning in units of 0.1 MHz (i.e. expanded horizontal scale). Optical detuning fixed at 0 MHz. Lock-in time constant: 10 ms. Scan rate: 22 MHz/s. e) Residual from a Lorentzian fit to curve d, displaced vertically. f) Similar to b, except pressure at 190 Pa.

Fig. 4
Fig. 4

(a) Measured Naperian absorbance at resonance as a function of gas pressure in the vacuum box. (b) Measured amplitude of MODR signal as a function of gas pressure. Optical power: 50 mW. RF power: 95 mW. The solid line is a smooth curve through the measured data.

Fig. 5
Fig. 5

Measurements at a pressure of 25 Pa and at zero detunings. Squares: Relative MODR signal amplitude as a function of optical power at the photodetector position. RF power fixed at 95 mW. Filled circles: Relative MODR signal amplitude as a function of average RF power at waveguide output. Optical power fixed at 50 mW. Open circles: Calculated amplitude as a function of RF power assuming constant modulation amplitude. The solid lines are smooth curves through the measured data.

Fig. 6
Fig. 6

Energy level diagram showing the infrared and microwave transition associated with observed MODR signals connected to the (J,K) = (6,3) ground state levels. Microwave transitions shown in parenthesis are calculated from combination differences. Two of the excited state microwave transitions are outside the range of the equipment available.

Tables (1)

Tables Icon

Table 1 Microwave optical double resonance transitions in ammonia (ν1 + ν3 band)

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