Quantum cascade laser frequency stabilization at the sub-Hz level

Journal name:
Nature Photonics
Volume:
9,
Pages:
456–460
Year published:
DOI:
doi:10.1038/nphoton.2015.93
Received
Accepted
Published online

Abstract

High-precision measurements with molecules may refine our knowledge of various fields of physics, from atmospheric and interstellar physics to the standard model or physics beyond it. Most of them can be cast as absorption frequency measurements, particularly in the mid-infrared ‘molecular fingerprint’ region, creating the need for narrow-linewidth lasers of well-controlled frequency. Quantum cascade lasers provide a wide spectral coverage anywhere in the mid-infrared, but show substantial free-running frequency fluctuations. Here, we demonstrate that the excellent stability and accuracy of an ultra-stable near-infrared laser, transferred from a metrological institute through a fibre link, can be copied to a quantum cascade laser using an optical frequency comb. The obtained relative stability and accuracy of 2 × 10−15 and 10−14 exceed those demonstrated so far with quantum cascade lasers by almost two orders of magnitude. This set-up enables us to measure molecular absorption frequencies with state-of-the-art uncertainties, confirming its potential for ultra-high-precision spectroscopy.

At a glance

Figures

  1.  Experimental set-up.
    Figure 1:  Experimental set-up.

    The NIR frequency reference, νref, generated at LNE-SYRTE with ultra-stable (US) laser #1 is transferred to LPL through a 43-km-long optical-fibre link. Its absolute frequency is measured against primary frequency standards by the use of an OFC (SYRTE-OFC). Its stability is provided by an ultra-stable cavity (see Methods) whose frequency drift is removed by an acousto-optic modulator (AOM). At LPL, the comb repetition rate, frep, of an OFC is phase-locked onto this reference. The QCL is then phase-locked onto a harmonic of frep by performing sum-frequency generation in an AgGaSe2 crystal (see Methods). The beat note of frequency Δ1 is processed to generate the error signal for the QCL phase-lock loop (PLL). The signal of frequency Δ1′ on photodiode PD1 corresponds to the beat note between the MIR reference and a multiple of frep and the signal of frequency Δ2 on photodiode PD2 corresponds to the beat note between the MIR reference and the QCL. The stabilities and frequency noise PSDs are evaluated by using a counter and a fast Fourier transform (FFT) analyser. Arrows indicate movable optics and the padlocks symbolize the OFCs' phase-lock loops. Ultra-stable laser #2 is used to evaluate the spectral purity of the LPL comb.

  2. Assessment of the QCL frequency stability.
    Figure 2: Assessment of the QCL frequency stability.

    Fractional frequency stability of the beat note between the QCL phase-locked onto the NIR reference (QCL/OFC) and the MIR reference (curve a, red squares), the beat note between the MIR reference and the OFC (curve b, blue circles), the OFC (curve c, green triangles) and the beat note between the QCL and the CO2 laser, both stabilized onto the OFC (curve d, black stars). Overlapping Allan deviations are processed from data measured using a Λ-type counter with 1 s gate time. For curve d, a dead-time free counter was used.

  3. Characterization of frequency noises.
    Figure 3: Characterization of frequency noises.

    Frequency noise PSD of the beat note between the QCL phase-locked onto the NIR reference (QCL/OFC) and the MIR reference (curve a, red), the beat note between the MIR reference and the OFC (curve b, blue), the OFC (curve c, green), the noise-compensated 43 km optical-fibre link (curve d, brown) and the free-running QCL (curve e, black). All these PSDs are relative to a carrier frequency of 29.1 THz (10.3 µm wavelength).

  4.  QCL line shape and beat note with the MIR reference.
    Figure 4:  QCL line shape and beat note with the MIR reference.

    a, Calculated QCL line shape showing a 0.2 Hz FWHM (10 mHz resolution bandwidth). This estimation is based on the temporal data used to derive the OFC relative stability (curve c of Fig. 2) and the OFC frequency noise PSD (curve c of Fig. 3). b, Beat note between the QCL phase-locked onto the NIR reference and the MIR reference, recorded with a FFT analyser (125 mHz resolution, average of 10 sweeps of 8 s). The beat note is offset to zero by subtracting ∼50 kHz. The red line is a Lorentzian fit of the data with a linewidth (FWHM) of 10 Hz.

  5.  OsO4 spectrum, in the vicinity of the R(14) emission line of CO2.
    Figure 5:  OsO4 spectrum, in the vicinity of the R(14) emission line of CO2.

    Two lines are recorded over a span of 5 MHz in steps of 5 kHz, using third harmonic detection. The x axis is offset by νOsO4/R(14) = 29,137,747,033,333 Hz, corresponding to the reported absolute frequency of the OsO4 reference line (left-hand line)39. The right-hand line has not yet been reported in the literature. Inset: spectrum of the reference line recorded over 200 kHz in steps of 1 kHz. These data are fitted to the sum of a third and fifth derivative of a Lorentzian.

References

  1. Carr, L. D., DeMille, D., Krems, R. V. & Ye, J. Cold and ultracold molecules: science, technology and applications. New J. Phys. 11, 055049 (2009).
  2. Barry, J. F., McCarron, D. J., Norrgard, E. B., Steinecker, M. H. & DeMille, D. Magneto-optical trapping of a diatomic molecule. Nature 512, 286289 (2014).
  3. Tokunaga, S. K. et al. Probing weak force-induced parity violation by high-resolution mid-infrared molecular spectroscopy. Mol. Phys. 111, 23632373 (2013).
  4. Baron, J. et al. Order of magnitude smaller limit on the electric dipole moment of the electron. Science 343, 269272 (2014).
  5. De Angelis, M., Gagliardi, G., Gianfrani, L. & Tino, G. M. Test of the symmetrization postulate for spin-0 particles. Phys. Rev. Lett. 76, 28402843 (1996).
  6. Koelemeij, J. C. J., Roth, B., Wicht, A., Ernsting, I. & Schiller, S. Vibrational spectroscopy of HD+ with 2-ppb accuracy. Phys. Rev. Lett. 98, 173002 (2007).
  7. Daussy, C. et al. First direct determination of the Boltzmann constant by an optical method: towards a new definition of the kelvin. Phys. Rev. Lett. 98, 250801 (2007).
  8. Moretti, L. et al. Determination of the Boltzmann constant by means of precision measurements of H2O line shapes at 1.39 µm. Phys. Rev. Lett. 111, 060803 (2013).
  9. Shelkovnikov, A., Butcher, R. J., Chardonnet, C. & Amy-Klein, A. Stability of the proton-to-electron mass ratio. Phys. Rev. Lett. 100, 150801 (2008).
  10. Hudson, E. R., Lewandowski, H. J., Sawyer, B. C. & Ye, J. Cold molecule spectroscopy for constraining the evolution of the fine structure constant. Phys. Rev. Lett. 96, 143004 (2006).
  11. Jansen, P., Bethlem, H. L. & Ubachs, W. Perspective: tipping the scales: search for drifting constants from molecular spectra. J. Chem. Phys. 140, 010901 (2014).
  12. Hugi, A., Villares, G., Blaser, S., Liu, H. C. & Faist, J. Mid-infrared frequency comb based on a quantum cascade laser. Nature 492, 229233 (2012).
  13. Schliesser, A., Picqué, N. & Hänsch, T. W. Mid-infrared frequency combs. Nature Photon. 6, 440449 (2012).
  14. Faist, J. et al. Quantum cascade laser. Science 264, 553556 (1994).
  15. Yao, Y., Hoffman, A. J. & Gmachl, C. F. Mid-infrared quantum cascade lasers. Nature Photon. 6, 432439 (2012).
  16. Bielsa, F. et al. HCOOH high resolution spectroscopy in the 9.18 µm region. J. Mol. Spec. 247, 4146 (2008).
  17. Bartalini, S. et al. Frequency-comb-referenced quantum-cascade laser at 4.4 μm. Opt. Lett. 32, 988990 (2007).
  18. Bressel, U., Ernsting, I. & Schiller, S. 5 µm laser source for frequency metrology based on difference frequency generation. Opt. Lett. 37, 918 (2012).
  19. Borri, S. et al. Direct link of a mid-infrared QCL to a frequency comb by optical injection. Opt. Lett. 37, 10111013 (2012).
  20. Cappelli, F. et al. Subkilohertz linewidth room-temperature mid-infrared quantum cascade laser using a molecular sub-Doppler reference. Opt. Lett. 37, 48114813 (2012).
  21. Mills, A. A. et al. Coherent phase lock of a 9 µm quantum cascade laser to a 2 µm thulium optical frequency comb. Opt. Lett. 37, 40834085 (2012).
  22. Galli, I. et al. Comb-assisted subkilohertz linewidth quantum cascade laser for high-precision mid-infrared spectroscopy. Appl. Phys. Lett. 102, 121117 (2013).
  23. Hansen, M. G. et al. Robust, frequency-stable and accurate mid-IR laser spectrometer based on frequency comb metrology of quantum cascade lasers up-converted in orientation-patterned GaAs. Opt. Express 21, 2704327056 (2013).
  24. Sow, P. L. T. et al. A widely tunable 10-μm quantum cascade laser phase-locked to a state-of-the-art mid-infrared reference for precision molecular spectroscopy. Appl. Phys. Lett. 104, 264101 (2014).
  25. Tombez, L., Schilt, S., Hofstetter, D. & Südmeyer, T. Active linewidth-narrowing of a mid-infrared quantum cascade laser without optical reference. Opt. Lett. 38, 50795082 (2013).
  26. Acef, O. Metrological properties of CO2/OsO4 optical frequency standard. Opt. Commun. 134, 479486 (1997).
  27. Bernard, V. et al. Spectral purity and long-term stability of CO2 lasers at the hertz level. IEEE J. Quantum Electron. QE-31, 19131918 (1995).
  28. Fasci, E. et al. Narrow-linewidth quantum cascade laser at 8.6 µm. Opt. Lett. 39, 49464949 (2014).
  29. Hagemann, C. et al. Ultrastable laser with average fractional frequency drift rate below 5 × 10−19/s. Opt. Lett. 39, 51025105 (2014).
  30. Guéna, J. et al. Progress in atomic fountains at LNE-SYRTE. IEEE Trans. Ultrason. Ferroelec. Freq. Control 59, 391410 (2012).
  31. Amy-Klein, A. et al. Absolute frequency measurement of a SF6 two-photon line by use of a femtosecond optical comb and sum-frequency generation. Opt. Lett. 30, 33203322 (2005).
  32. Chanteau, B. et al. Mid-infrared laser phase-locking to a remote near-infrared frequency reference for high-precision molecular spectroscopy. New J. Phys. 15, 073003 (2013).
  33. Vainio, M., Merimaa, M. & Halonen, L. Frequency-comb-referenced molecular spectroscopy in the mid-infrared region. Opt. Lett. 36, 41224124 (2011).
  34. Jiang, H. et al. Long-distance frequency transfer over an urban fiber link using optical phase stabilization. J. Opt. Soc. Am. B 25, 20292035 (2008).
  35. Predehl, K. et al. A 920-kilometer optical fiber link for frequency metrology at the 19th decimal place. Science 336, 441444 (2012).
  36. Bernard, V. et al. CO2 laser stabilization to 0.1-Hz level using external electrooptic modulation. IEEE J. Quantum Electron. 33, 12821287 (1997).
  37. Ducos, F., Hadjar, Y., Rovera, G. D., Zondy, J. J. & Acef, O. Progress toward absolute frequency measurements of the 127I2-stabilized Nd:YAG laser at 563.2 THz/532 nm. IEEE Trans. Instrum. Meas. 50, 539542 (2001).
  38. Elliott, D. S., Roy, R. & Smith, S. J. Extracavity laser band-shape and bandwidth modification. Phys. Rev. A 26, 1218 (1982).
  39. Acef, O., Michaud, F. & Rovera, G. D. Accurate determination of OsO4 absolute frequency grid at 28/29 THz. IEEE Trans. Instrum. Meas. 48, 567570 (1999).
  40. Chardonnet, C. & Borde, C. J. Hyperfine interactions in the ν3 band of osmium tetroxide: accurate determination of the spin-rotation constant by crossover resonance spectroscopy. J. Mol. Spectrosc. 167, 7198 (1994).
  41. Chardonnet, C. Spectroscopie de saturation de hautes précision et sensibilité en champ laser fort. Applications aux molécules OsO4, SF6 et CO2 et à la métrologie des fréquences. Thèse de doctorat d’état, Université Paris 13 (1989).
  42. Daussy, C. et al. Long-distance frequency dissemination with a resolution of 10−17. Phys. Rev. Lett. 94, 203904 (2005).
  43. Salumbides, E. J. et al. Bounds on fifth forces from precision measurements on molecules. Phys. Rev. D 87, 112008 (2013).
  44. Karr, J. P. et al. High-accuracy calculations in the H2+ molecular ion: towards a measurement of mp/me Can. J. Phys. 85, 497507 (2007).
  45. Guinet, M., Mondelain, D., Janssen, C. & Camy-Peyret, C. Laser spectroscopic study of ozone in the 100←000 band for the SWIFT instrument. J. Quant. Spectr. Rad. Transfer 111, 961972 (2010).
  46. Schneider, M. & Hase, F. Improving spectroscopic line parameters by means of atmospheric spectra: theory and example for water vapor and solar absorption spectra. J. Quant. Spectr. Rad. Transfer 110, 18251839 (2009).
  47. Telle, H. R., Lipphardt, B. & Stenger, J. Kerr-lens, mode-locked lasers as transfer oscillators for optical frequency measurements. Appl. Phys. B 74, 16 (2002).
  48. Nicolodi, D. et al. Spectral purity transfer between optical wavelengths at the 10−18 level. Nature Photon. 8, 219223 (2014).
  49. Zhang, W. et al. Characterizing a fiber-based frequency comb with electro-optic modulator. IEEE Trans. Ultrason. Ferroelec. Freq. Control 59, 432438 (2012).
  50. Rohart, F. et al. Absorption line shape recovery beyond the detection bandwidth limit: application to the precision spectroscopic measurement of the Boltzmann constant. Phys. Rev. A 90, 042506 (2014).

Download references

Author information

Affiliations

  1. Laboratoire de Physique des Lasers, Université Paris 13, Sorbonne Paris Cité, CNRS, 99 Avenue Jean-Baptiste Clément, Villetaneuse 93430, France

    • Bérengère Argence,
    • Bruno Chanteau,
    • Olivier Lopez,
    • Christian Chardonnet,
    • Christophe Daussy,
    • Benoît Darquié &
    • Anne Amy-Klein
  2. LNE-SYRTE, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Universités, UPMC Univ. Paris 06, 61 Avenue de l'Observatoire, Paris 75014, France

    • Daniele Nicolodi,
    • Michel Abgrall &
    • Yann Le Coq

Contributions

B.A., B.C., O.L., Y.L.C. and A.A.K. conceived and designed the experiment. B.A., B.C., D.N., B.D. and A.A.K. performed the experiment. B.A., O.L., D.N., M.A., C.D., B.D., Y.L.C. and A.A.K. analysed the data. B.A., M.A., B.D., Y.L.C. and A.A.K. contributed materials/analysis tools. All authors discussed the results. B.A., O.L., D.N., M.A., C.C., C.D., B.D., Y.L.C. and A.A.K. wrote the paper.

Competing financial interests

The authors declare no competing financial interests.

Corresponding authors

Correspondence to:

Author details

Additional data