Applied Physics B

, Volume 101, Issue 3, pp 497–509

Highly sensitive dispersion spectroscopy by probing the free spectral range of an optical cavity using dual-frequency modulation


DOI: 10.1007/s00340-010-4120-9

Cite this article as:
Schmidt, F.M., Ma, W., Foltynowicz, A. et al. Appl. Phys. B (2010) 101: 497. doi:10.1007/s00340-010-4120-9


Dual-frequency modulation (DFM) has been used to continuously track the frequency shifts of optical cavity modes in the vicinity of an optical transition of a gas inside the cavity for assessment of the gas concentration. A theoretical description of the size and lineshape of the DFM dispersion spectroscopy (DFM-DS) signal is given. Since the signal is measured in terms of a radio frequency the technique is insensitive to laser intensity fluctuations. The signal strength, which can accurately be obtained by curve fitting, only depends on fundamental parameters (including the line strength), thus enabling quantitative detection without calibration procedure. In a first demonstration, using a compact setup based on a narrowband fiber laser, the change in free spectral range around a value of 379.9 MHz due to an acetylene transition near 1531 nm was measured with a resolution of 6 Hz (i.e. with an accuracy of 1.5 parts in 108) in 12.5 s acquisition time, which corresponds to a minimum detectable integrated absorption (SNR=3) of 3×10−9 cm−1.

Copyright information

© Springer-Verlag 2010

Authors and Affiliations

  • F. M. Schmidt
    • 1
  • W. Ma
    • 1
  • A. Foltynowicz
    • 1
  • O. Axner
    • 1
  1. 1.Department of PhysicsUmeå UniversityUmeåSweden
  2. 2.Laboratory of Physical Chemistry, Department of ChemistryUniversity of HelsinkiHelsinkiFinland
  3. 3.College of Physics and Electronics EngineeringShanxi UniversityTaiyuanP.R. China
  4. 4.JILA, National Institute of Standards and Technology and University of Colorado, Department of PhysicsUniversity of ColoradoBoulderUSA