Real-time wavelength corrected heterodyne laser interferometry

Abstract We describe the combined methods of displacement heterodyne laser interferometry with wavelength tracking based on a Fabry–Perot cavity to correct the instantaneous wavelength in air. The optical frequency of the interferometry source was locked to the resonance peak of an open cavity, directly linking the refractive index changes to frequency changes. Using this method, refractive index changes are compensated by an appropriate change in the laser frequency in real time, eliminating the limitations with environmental parameter measurement bandwidth uncertainties associated with equation-based corrections. In this paper, the principles of the system are explained and experimental results showed a difference of 2 nm compared with traditional equation-based techniques. The measurement uncertainty and practical considerations for implementation are also discussed.

[1]  Masato Aketagawa,et al.  Measurement of air-refractive-index fluctuation from frequency change using a phase modulation homodyne interferometer and an external cavity laser diode , 2008, International Symposium on Laser Metrology.

[2]  L. Howard,et al.  Real-time displacement measurements with a Fabry-Perot cavity and a diode laser , 2001 .

[3]  S. Topcu,et al.  Heterodyne refractometer and air wavelength reference at 633 nm , 2003 .

[4]  H Han Haitjema,et al.  Calibration of displacement sensors up to 300 µm with nanometre accuracy and direct traceability to a primary standard of length , 2000 .

[5]  J. L. Hall,et al.  Real-time precision refractometry: new approaches. , 1997, Applied optics.

[6]  Akira Ishida,et al.  Two-Wavelength Displacement-Measuring Interferometer Using Second-Harmonic Light to Eliminate Air-Turbulence-Induced Errors , 1989 .

[7]  K. Meiners-Hagen,et al.  Refractive index determination in length measurement by two-colour interferometry , 2008 .

[8]  K. P. Birch,et al.  An Updated Edln Equation for the Refractive Index of Air , 1993 .

[9]  P. Ciddor.  Refractive index of air: new equations for the visible and near infrared. , 1996, Applied optics.

[10]  Masato Aketagawa,et al.  Measurement of air-refractive-index fluctuation from laser frequency shift with uncertainty of order 10−9 , 2009 .

[11]  V. Korpelainen,et al.  Acoustic method for determination of the effective temperature and refractive index of air in accurate length interferometry , 2004 .

[12]  John L. Hall,et al.  Laser phase and frequency stabilization using an optical resonator , 1983 .

[13]  K. P. Birch,et al.  LETTER TO THE EDITOR: Correction to the Updated Edln Equation for the Refractive Index of Air , 1994 .

[14]  Nathan R Newbury,et al.  Wavelength references for interferometry in air. , 2005, Applied optics.

[15]  B. Edĺen.  The Refractive Index of Air , 1966 .

[16]  N. Bobroff.  Recent advances in displacement measuring interferometry , 1993 .