Abstract

A simple, easy-to-implement, and robust technique is reported to offset lock two semiconductor lasers with a frequency difference easily adjustable up to a couple of tens of gigahertz (10 and 19GHz experimentally demonstrated). The proposed scheme essentially makes use of low-frequency control electronics and may be implemented with any type of single mode semiconductor laser, without any requirement for the laser linewidth. The technique is shown to be very similar to the wavelength modulation spectroscopy method commonly used for laser stabilization onto molecular absorption lines, as demonstrated by experimental results obtained using 935nm laser diodes.

© 2008 Optical Society of America

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References

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  1. H. Hori, Y. Kitayama, M. Kitano, T. Yabuzaki, and T. Ogawa, “Frequency stabilization of GaAlAs laser using a Doppler-free spectrum of the Cs-D2 line,” IEEE J. Quantum Electron. QE-19, 169-175 (1983).
  2. F. Bertinetto, P. Gambini, M. Puleo, and E. Vezzoni, “Performance and limitations of laser diodes stabilized to the sides of molecular absorption lines of ammonia,” Rev. Sci. Instrum. 64, 2128-2132 (1993).
    [CrossRef]
  3. C. M. Fitzgerald, G. J. Koch, A. M. Bullock, and A. N. Dharamsi, “Wavelength modulation spectroscopy of water vapor and line center stabilization at 1.462 μm for lidar applications,” Proc. SPIE 3945, 98-105 (2000).
  4. G. J. Koch, “Automatic laser frequency locking to gas absorption lines,” Opt. Eng. 42, 1690-1693 (2003).
  5. G. Poberaj, A. Fix, A. Assion, M. Wirth, C. Kiemle, and G. Ehret, “Airborne all-solid-state DIAL for water vapour measurements in the tropopause region: system description and assessment of accuracy,” Appl. Phys. B 75, 165-172 (2002).
  6. H.-M. Fang, S.-C. Wang, and J.-T. Shy, “Frequency stabilization of an external cavity diode laser to molecular iodine at 657.483 nm,” Appl. Opt. 45, 3173-3176 (2006).
  7. J. M. Supplee, E. A. Whittaker, and W. Lenth, “Theoretical description of frequency modulation and wavelength modulation spectroscopy,” Appl. Opt. 33, 6294-6302 (1994).
  8. S. Schilt, L. Thévenaz, and P. Robert, “Wavelength modulation spectroscopy: combined frequency and intensity laser modulation,” Appl. Opt. 42, 6728-6738 (2003).
    [CrossRef]
  9. R. Matthey, S. Schilt, D. Werner, C. Affolderbach, L. Thévenaz, and G. Mileti , “Diode laser frequency stabilisation for water-vapour differential absorption sensing,” Appl. Phys. B. 85, 477-485 (2006).
  10. G. Santarelli, A. Clairo, S. N. Lea, and G. M. Tino, “Heterodyne optical phase-locking of extended-cavity semiconductor lasers at 9 GHz,” Opt. Commun. 104, 339-344 (1994).
  11. U. Gliese, T. N. Nielsen, M. Bruun, E. L. Christensen, K. E. Stubkjaer, S. Lindgren, and B. Broberg, “A wideband heterodyne optical phase-lock loop for generation of 3-18 GHz microwave carriers,” IEEE Photon. Technol. Lett. 4, 936-938(1992).
  12. G. Ritt, G. Cennini, C. Geckeler, and M. Weitz, “Laser frequency offset locking using a side of filter technique,” Appl. Phys. B. 79, 363-365 (2004).
  13. P. Kluczynski, J. Gustafsson, A. M. Lindberg, and O. Axner, “Wavelength modulation absorption spectrometry--an extensive scrutiny of the generation of signals,” Spectrochim. Acta B 56, 1277-1354 (2001).
  14. C. Affolderbach and G. Mileti, “A compact laser head with high-frequency stability for Rb atomic clocks and optical instrumentation,” Rev. Sci. Instrum. 76, 073108 (2005).
    [CrossRef]
  15. S. Schilt and L. Thévenaz, “Experimental method based on wavelength-modulation spectroscopy for the characterization of semiconductor lasers under direct modulation,” Appl. Opt. 43, 4446-4453 (2004).
    [CrossRef]
  16. D. S. Bomse, A. C. Stanton, and J. A. Silver, “Frequency modulation and wavelength modulation spectroscopies: comparison of experimental methods using a lead-salt diode laser,” Appl. Opt. 31, 718-731 (1992).

2006 (2)

H.-M. Fang, S.-C. Wang, and J.-T. Shy, “Frequency stabilization of an external cavity diode laser to molecular iodine at 657.483 nm,” Appl. Opt. 45, 3173-3176 (2006).

R. Matthey, S. Schilt, D. Werner, C. Affolderbach, L. Thévenaz, and G. Mileti , “Diode laser frequency stabilisation for water-vapour differential absorption sensing,” Appl. Phys. B. 85, 477-485 (2006).

2005 (1)

C. Affolderbach and G. Mileti, “A compact laser head with high-frequency stability for Rb atomic clocks and optical instrumentation,” Rev. Sci. Instrum. 76, 073108 (2005).
[CrossRef]

2004 (2)

S. Schilt and L. Thévenaz, “Experimental method based on wavelength-modulation spectroscopy for the characterization of semiconductor lasers under direct modulation,” Appl. Opt. 43, 4446-4453 (2004).
[CrossRef]

G. Ritt, G. Cennini, C. Geckeler, and M. Weitz, “Laser frequency offset locking using a side of filter technique,” Appl. Phys. B. 79, 363-365 (2004).

2003 (2)

2002 (1)

G. Poberaj, A. Fix, A. Assion, M. Wirth, C. Kiemle, and G. Ehret, “Airborne all-solid-state DIAL for water vapour measurements in the tropopause region: system description and assessment of accuracy,” Appl. Phys. B 75, 165-172 (2002).

2001 (1)

P. Kluczynski, J. Gustafsson, A. M. Lindberg, and O. Axner, “Wavelength modulation absorption spectrometry--an extensive scrutiny of the generation of signals,” Spectrochim. Acta B 56, 1277-1354 (2001).

2000 (1)

C. M. Fitzgerald, G. J. Koch, A. M. Bullock, and A. N. Dharamsi, “Wavelength modulation spectroscopy of water vapor and line center stabilization at 1.462 μm for lidar applications,” Proc. SPIE 3945, 98-105 (2000).

1994 (2)

J. M. Supplee, E. A. Whittaker, and W. Lenth, “Theoretical description of frequency modulation and wavelength modulation spectroscopy,” Appl. Opt. 33, 6294-6302 (1994).

G. Santarelli, A. Clairo, S. N. Lea, and G. M. Tino, “Heterodyne optical phase-locking of extended-cavity semiconductor lasers at 9 GHz,” Opt. Commun. 104, 339-344 (1994).

1993 (1)

F. Bertinetto, P. Gambini, M. Puleo, and E. Vezzoni, “Performance and limitations of laser diodes stabilized to the sides of molecular absorption lines of ammonia,” Rev. Sci. Instrum. 64, 2128-2132 (1993).
[CrossRef]

1992 (2)

U. Gliese, T. N. Nielsen, M. Bruun, E. L. Christensen, K. E. Stubkjaer, S. Lindgren, and B. Broberg, “A wideband heterodyne optical phase-lock loop for generation of 3-18 GHz microwave carriers,” IEEE Photon. Technol. Lett. 4, 936-938(1992).

D. S. Bomse, A. C. Stanton, and J. A. Silver, “Frequency modulation and wavelength modulation spectroscopies: comparison of experimental methods using a lead-salt diode laser,” Appl. Opt. 31, 718-731 (1992).

1983 (1)

H. Hori, Y. Kitayama, M. Kitano, T. Yabuzaki, and T. Ogawa, “Frequency stabilization of GaAlAs laser using a Doppler-free spectrum of the Cs-D2 line,” IEEE J. Quantum Electron. QE-19, 169-175 (1983).

Affolderbach, C.

R. Matthey, S. Schilt, D. Werner, C. Affolderbach, L. Thévenaz, and G. Mileti , “Diode laser frequency stabilisation for water-vapour differential absorption sensing,” Appl. Phys. B. 85, 477-485 (2006).

C. Affolderbach and G. Mileti, “A compact laser head with high-frequency stability for Rb atomic clocks and optical instrumentation,” Rev. Sci. Instrum. 76, 073108 (2005).
[CrossRef]

Assion, A.

G. Poberaj, A. Fix, A. Assion, M. Wirth, C. Kiemle, and G. Ehret, “Airborne all-solid-state DIAL for water vapour measurements in the tropopause region: system description and assessment of accuracy,” Appl. Phys. B 75, 165-172 (2002).

Axner, O.

P. Kluczynski, J. Gustafsson, A. M. Lindberg, and O. Axner, “Wavelength modulation absorption spectrometry--an extensive scrutiny of the generation of signals,” Spectrochim. Acta B 56, 1277-1354 (2001).

Bertinetto, F.

F. Bertinetto, P. Gambini, M. Puleo, and E. Vezzoni, “Performance and limitations of laser diodes stabilized to the sides of molecular absorption lines of ammonia,” Rev. Sci. Instrum. 64, 2128-2132 (1993).
[CrossRef]

Bomse, D. S.

Broberg, B.

U. Gliese, T. N. Nielsen, M. Bruun, E. L. Christensen, K. E. Stubkjaer, S. Lindgren, and B. Broberg, “A wideband heterodyne optical phase-lock loop for generation of 3-18 GHz microwave carriers,” IEEE Photon. Technol. Lett. 4, 936-938(1992).

Bruun, M.

U. Gliese, T. N. Nielsen, M. Bruun, E. L. Christensen, K. E. Stubkjaer, S. Lindgren, and B. Broberg, “A wideband heterodyne optical phase-lock loop for generation of 3-18 GHz microwave carriers,” IEEE Photon. Technol. Lett. 4, 936-938(1992).

Bullock, A. M.

C. M. Fitzgerald, G. J. Koch, A. M. Bullock, and A. N. Dharamsi, “Wavelength modulation spectroscopy of water vapor and line center stabilization at 1.462 μm for lidar applications,” Proc. SPIE 3945, 98-105 (2000).

Cennini, G.

G. Ritt, G. Cennini, C. Geckeler, and M. Weitz, “Laser frequency offset locking using a side of filter technique,” Appl. Phys. B. 79, 363-365 (2004).

Christensen, E. L.

U. Gliese, T. N. Nielsen, M. Bruun, E. L. Christensen, K. E. Stubkjaer, S. Lindgren, and B. Broberg, “A wideband heterodyne optical phase-lock loop for generation of 3-18 GHz microwave carriers,” IEEE Photon. Technol. Lett. 4, 936-938(1992).

Clairo, A.

G. Santarelli, A. Clairo, S. N. Lea, and G. M. Tino, “Heterodyne optical phase-locking of extended-cavity semiconductor lasers at 9 GHz,” Opt. Commun. 104, 339-344 (1994).

Dharamsi, A. N.

C. M. Fitzgerald, G. J. Koch, A. M. Bullock, and A. N. Dharamsi, “Wavelength modulation spectroscopy of water vapor and line center stabilization at 1.462 μm for lidar applications,” Proc. SPIE 3945, 98-105 (2000).

Ehret, G.

G. Poberaj, A. Fix, A. Assion, M. Wirth, C. Kiemle, and G. Ehret, “Airborne all-solid-state DIAL for water vapour measurements in the tropopause region: system description and assessment of accuracy,” Appl. Phys. B 75, 165-172 (2002).

Fang, H.-M.

Fitzgerald, C. M.

C. M. Fitzgerald, G. J. Koch, A. M. Bullock, and A. N. Dharamsi, “Wavelength modulation spectroscopy of water vapor and line center stabilization at 1.462 μm for lidar applications,” Proc. SPIE 3945, 98-105 (2000).

Fix, A.

G. Poberaj, A. Fix, A. Assion, M. Wirth, C. Kiemle, and G. Ehret, “Airborne all-solid-state DIAL for water vapour measurements in the tropopause region: system description and assessment of accuracy,” Appl. Phys. B 75, 165-172 (2002).

Gambini, P.

F. Bertinetto, P. Gambini, M. Puleo, and E. Vezzoni, “Performance and limitations of laser diodes stabilized to the sides of molecular absorption lines of ammonia,” Rev. Sci. Instrum. 64, 2128-2132 (1993).
[CrossRef]

Geckeler, C.

G. Ritt, G. Cennini, C. Geckeler, and M. Weitz, “Laser frequency offset locking using a side of filter technique,” Appl. Phys. B. 79, 363-365 (2004).

Gliese, U.

U. Gliese, T. N. Nielsen, M. Bruun, E. L. Christensen, K. E. Stubkjaer, S. Lindgren, and B. Broberg, “A wideband heterodyne optical phase-lock loop for generation of 3-18 GHz microwave carriers,” IEEE Photon. Technol. Lett. 4, 936-938(1992).

Gustafsson, J.

P. Kluczynski, J. Gustafsson, A. M. Lindberg, and O. Axner, “Wavelength modulation absorption spectrometry--an extensive scrutiny of the generation of signals,” Spectrochim. Acta B 56, 1277-1354 (2001).

Hori, H.

H. Hori, Y. Kitayama, M. Kitano, T. Yabuzaki, and T. Ogawa, “Frequency stabilization of GaAlAs laser using a Doppler-free spectrum of the Cs-D2 line,” IEEE J. Quantum Electron. QE-19, 169-175 (1983).

Kiemle, C.

G. Poberaj, A. Fix, A. Assion, M. Wirth, C. Kiemle, and G. Ehret, “Airborne all-solid-state DIAL for water vapour measurements in the tropopause region: system description and assessment of accuracy,” Appl. Phys. B 75, 165-172 (2002).

Kitano, M.

H. Hori, Y. Kitayama, M. Kitano, T. Yabuzaki, and T. Ogawa, “Frequency stabilization of GaAlAs laser using a Doppler-free spectrum of the Cs-D2 line,” IEEE J. Quantum Electron. QE-19, 169-175 (1983).

Kitayama, Y.

H. Hori, Y. Kitayama, M. Kitano, T. Yabuzaki, and T. Ogawa, “Frequency stabilization of GaAlAs laser using a Doppler-free spectrum of the Cs-D2 line,” IEEE J. Quantum Electron. QE-19, 169-175 (1983).

Kluczynski, P.

P. Kluczynski, J. Gustafsson, A. M. Lindberg, and O. Axner, “Wavelength modulation absorption spectrometry--an extensive scrutiny of the generation of signals,” Spectrochim. Acta B 56, 1277-1354 (2001).

Koch, G. J.

G. J. Koch, “Automatic laser frequency locking to gas absorption lines,” Opt. Eng. 42, 1690-1693 (2003).

C. M. Fitzgerald, G. J. Koch, A. M. Bullock, and A. N. Dharamsi, “Wavelength modulation spectroscopy of water vapor and line center stabilization at 1.462 μm for lidar applications,” Proc. SPIE 3945, 98-105 (2000).

Lea, S. N.

G. Santarelli, A. Clairo, S. N. Lea, and G. M. Tino, “Heterodyne optical phase-locking of extended-cavity semiconductor lasers at 9 GHz,” Opt. Commun. 104, 339-344 (1994).

Lenth, W.

Lindberg, A. M.

P. Kluczynski, J. Gustafsson, A. M. Lindberg, and O. Axner, “Wavelength modulation absorption spectrometry--an extensive scrutiny of the generation of signals,” Spectrochim. Acta B 56, 1277-1354 (2001).

Lindgren, S.

U. Gliese, T. N. Nielsen, M. Bruun, E. L. Christensen, K. E. Stubkjaer, S. Lindgren, and B. Broberg, “A wideband heterodyne optical phase-lock loop for generation of 3-18 GHz microwave carriers,” IEEE Photon. Technol. Lett. 4, 936-938(1992).

Matthey, R.

R. Matthey, S. Schilt, D. Werner, C. Affolderbach, L. Thévenaz, and G. Mileti , “Diode laser frequency stabilisation for water-vapour differential absorption sensing,” Appl. Phys. B. 85, 477-485 (2006).

Mileti, G.

R. Matthey, S. Schilt, D. Werner, C. Affolderbach, L. Thévenaz, and G. Mileti , “Diode laser frequency stabilisation for water-vapour differential absorption sensing,” Appl. Phys. B. 85, 477-485 (2006).

C. Affolderbach and G. Mileti, “A compact laser head with high-frequency stability for Rb atomic clocks and optical instrumentation,” Rev. Sci. Instrum. 76, 073108 (2005).
[CrossRef]

Nielsen, T. N.

U. Gliese, T. N. Nielsen, M. Bruun, E. L. Christensen, K. E. Stubkjaer, S. Lindgren, and B. Broberg, “A wideband heterodyne optical phase-lock loop for generation of 3-18 GHz microwave carriers,” IEEE Photon. Technol. Lett. 4, 936-938(1992).

Ogawa, T.

H. Hori, Y. Kitayama, M. Kitano, T. Yabuzaki, and T. Ogawa, “Frequency stabilization of GaAlAs laser using a Doppler-free spectrum of the Cs-D2 line,” IEEE J. Quantum Electron. QE-19, 169-175 (1983).

Poberaj, G.

G. Poberaj, A. Fix, A. Assion, M. Wirth, C. Kiemle, and G. Ehret, “Airborne all-solid-state DIAL for water vapour measurements in the tropopause region: system description and assessment of accuracy,” Appl. Phys. B 75, 165-172 (2002).

Puleo, M.

F. Bertinetto, P. Gambini, M. Puleo, and E. Vezzoni, “Performance and limitations of laser diodes stabilized to the sides of molecular absorption lines of ammonia,” Rev. Sci. Instrum. 64, 2128-2132 (1993).
[CrossRef]

Ritt, G.

G. Ritt, G. Cennini, C. Geckeler, and M. Weitz, “Laser frequency offset locking using a side of filter technique,” Appl. Phys. B. 79, 363-365 (2004).

Robert, P.

Santarelli, G.

G. Santarelli, A. Clairo, S. N. Lea, and G. M. Tino, “Heterodyne optical phase-locking of extended-cavity semiconductor lasers at 9 GHz,” Opt. Commun. 104, 339-344 (1994).

Schilt, S.

Shy, J.-T.

Silver, J. A.

Stanton, A. C.

Stubkjaer, K. E.

U. Gliese, T. N. Nielsen, M. Bruun, E. L. Christensen, K. E. Stubkjaer, S. Lindgren, and B. Broberg, “A wideband heterodyne optical phase-lock loop for generation of 3-18 GHz microwave carriers,” IEEE Photon. Technol. Lett. 4, 936-938(1992).

Supplee, J. M.

Thévenaz, L.

Tino, G. M.

G. Santarelli, A. Clairo, S. N. Lea, and G. M. Tino, “Heterodyne optical phase-locking of extended-cavity semiconductor lasers at 9 GHz,” Opt. Commun. 104, 339-344 (1994).

Vezzoni, E.

F. Bertinetto, P. Gambini, M. Puleo, and E. Vezzoni, “Performance and limitations of laser diodes stabilized to the sides of molecular absorption lines of ammonia,” Rev. Sci. Instrum. 64, 2128-2132 (1993).
[CrossRef]

Wang, S.-C.

Weitz, M.

G. Ritt, G. Cennini, C. Geckeler, and M. Weitz, “Laser frequency offset locking using a side of filter technique,” Appl. Phys. B. 79, 363-365 (2004).

Werner, D.

R. Matthey, S. Schilt, D. Werner, C. Affolderbach, L. Thévenaz, and G. Mileti , “Diode laser frequency stabilisation for water-vapour differential absorption sensing,” Appl. Phys. B. 85, 477-485 (2006).

Whittaker, E. A.

Wirth, M.

G. Poberaj, A. Fix, A. Assion, M. Wirth, C. Kiemle, and G. Ehret, “Airborne all-solid-state DIAL for water vapour measurements in the tropopause region: system description and assessment of accuracy,” Appl. Phys. B 75, 165-172 (2002).

Yabuzaki, T.

H. Hori, Y. Kitayama, M. Kitano, T. Yabuzaki, and T. Ogawa, “Frequency stabilization of GaAlAs laser using a Doppler-free spectrum of the Cs-D2 line,” IEEE J. Quantum Electron. QE-19, 169-175 (1983).

Appl. Opt. (5)

Appl. Phys. B (1)

G. Poberaj, A. Fix, A. Assion, M. Wirth, C. Kiemle, and G. Ehret, “Airborne all-solid-state DIAL for water vapour measurements in the tropopause region: system description and assessment of accuracy,” Appl. Phys. B 75, 165-172 (2002).

Appl. Phys. B. (2)

G. Ritt, G. Cennini, C. Geckeler, and M. Weitz, “Laser frequency offset locking using a side of filter technique,” Appl. Phys. B. 79, 363-365 (2004).

R. Matthey, S. Schilt, D. Werner, C. Affolderbach, L. Thévenaz, and G. Mileti , “Diode laser frequency stabilisation for water-vapour differential absorption sensing,” Appl. Phys. B. 85, 477-485 (2006).

IEEE J. Quantum Electron. (1)

H. Hori, Y. Kitayama, M. Kitano, T. Yabuzaki, and T. Ogawa, “Frequency stabilization of GaAlAs laser using a Doppler-free spectrum of the Cs-D2 line,” IEEE J. Quantum Electron. QE-19, 169-175 (1983).

IEEE Photon. Technol. Lett. (1)

U. Gliese, T. N. Nielsen, M. Bruun, E. L. Christensen, K. E. Stubkjaer, S. Lindgren, and B. Broberg, “A wideband heterodyne optical phase-lock loop for generation of 3-18 GHz microwave carriers,” IEEE Photon. Technol. Lett. 4, 936-938(1992).

Opt. Commun. (1)

G. Santarelli, A. Clairo, S. N. Lea, and G. M. Tino, “Heterodyne optical phase-locking of extended-cavity semiconductor lasers at 9 GHz,” Opt. Commun. 104, 339-344 (1994).

Opt. Eng. (1)

G. J. Koch, “Automatic laser frequency locking to gas absorption lines,” Opt. Eng. 42, 1690-1693 (2003).

Proc. SPIE (1)

C. M. Fitzgerald, G. J. Koch, A. M. Bullock, and A. N. Dharamsi, “Wavelength modulation spectroscopy of water vapor and line center stabilization at 1.462 μm for lidar applications,” Proc. SPIE 3945, 98-105 (2000).

Rev. Sci. Instrum. (2)

F. Bertinetto, P. Gambini, M. Puleo, and E. Vezzoni, “Performance and limitations of laser diodes stabilized to the sides of molecular absorption lines of ammonia,” Rev. Sci. Instrum. 64, 2128-2132 (1993).
[CrossRef]

C. Affolderbach and G. Mileti, “A compact laser head with high-frequency stability for Rb atomic clocks and optical instrumentation,” Rev. Sci. Instrum. 76, 073108 (2005).
[CrossRef]

Spectrochim. Acta B (1)

P. Kluczynski, J. Gustafsson, A. M. Lindberg, and O. Axner, “Wavelength modulation absorption spectrometry--an extensive scrutiny of the generation of signals,” Spectrochim. Acta B 56, 1277-1354 (2001).

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Figures (10)

Fig. 1
Fig. 1

Scheme of the offset-locking setup: DET, high-bandwidth photodiode; DBM, double-balanced mixer. A summary of the signals experimentally measured at different stages of the system is also displayed in (a)–(e). The signals given in different gray levels in (a)–(c) refer to different master–slave frequency detunings.

Fig. 2
Fig. 2

Degeneracy obtained for (a) the beat signal, (b) the intermediate frequency signal, and (c) the laser locking point for a bandpass and a low-pass electrical filter.

Fig. 3
Fig. 3

(a) Simulation of the filter response curve and (b)–(d) of the three first harmonic signals obtained for a low-pass filter with 220 MHz cutoff frequency and for a modulation index m = 0.4 .

Fig. 4
Fig. 4

Comparison of the normalized response of the filter experimentally measured (black thin curve) and considered in the simulation model (gray thick curve).

Fig. 5
Fig. 5

(a) Normalized 1 f signals obtained experimentally (black thin curves) and from simulations (gray thick curves) for different values of the modulation index m. The normalization is made so that the maximum signal amplitude corresponds to one for both experimental and simulations curves. (b) Amplitude and width (distance between maximum and minimum) of the normalized 1 f signal as a function of the modulation index m.

Fig. 6
Fig. 6

(a) Normalized 1 f signals obtained experimentally (black thin curves) and from simulations (gray thick curves) for different values of the detection phase Φ 1 . The normalization is made so that the maximum signal amplitude corresponds to one for both experimental and simulations curves. A modulation index m = 0.44 has been considered. (b) Amplitude and offset of the normalized 1 f signal as a function of the detection phase. The offset represents the out-of-resonance 1 f signal level in Fig. 6a.

Fig. 7
Fig. 7

Error signal obtained for different optical power on the detector. (a) The power from both lasers is simultaneously varied. (b) The power from only one laser (master) is changed, whereas the power from the other laser (slave) is kept constant. (c) Amplitude of the error signal as a function of the optical power. Three series of measurements are displayed: in series 1, the power of both lasers is simultaneously varied; in series 2, the power of the master laser only is changed, whereas the power from the slave laser is kept constant. Series 3 is similar to series 2, but with a much smaller power from the slave laser. All these results have been obtained with a modulation index m = 0.14 in the slave laser.

Fig. 8
Fig. 8

(a) Scheme of the experimental setup used for the evaluation of the offset-locking technique at 10 GHz offset frequency: BS, beam splitter; M, mirror; PD, photodiode; LI, lock-in. The master laser is stabilized onto a H 2 O line at 10683.7 cm 1 using WMS with a multipass cell. The slave laser is offset locked 10 GHz away from the master using the offset-locking method. The stability of the lasers is respectively monitored using a high precision wavemeter (master) and a second H 2 O line in a linear gas cell (slave). (b) HITRAN simulation of the two H 2 O lines ( 22 mbar pure H 2 O ) used for the stabilization of the master laser (line A) and as a discriminator to monitor the stability of the slave laser (line B).

Fig. 9
Fig. 9

Evaluation of the stability of the offset-locking scheme at 10 GHz offset frequency, measured with the setup described in Fig. 8. The frequency deviation of both lasers is displayed over more than 1 day with the master laser locked onto a H 2 O line.

Fig. 10
Fig. 10

Evaluation of the stability of the offset-locking scheme at 18.79 GHz offset frequency. (a) Comparison of the error signals of the master and slave lasers, showing their parallel evolution. Large vertical hops regularly observed in both traces result from etalon fringes or other temperature-related effects in the overall optical setup. (b) Absolute stability of the offset-locked slave laser monitored with a high precision wavemeter.

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