### Abstract

An acoustic method for the measurement of the effective temperature and
refractive index of air for precision length interferometry is
described. The method can be used to improve the accuracy of
interferometric length measurements outside the best laboratory
conditions and also in industrial conditions. The method is based on the
measurement of speed of 50-kHz ultrasound over the same distance
measured with a laser interferometer. The measured speed of ultrasound
is used to define the effective temperature or the refractive index of
air along the laser beam path using the equations presented. The
measured speed of sound, Cramer equation, dispersion correction, and
Edlén equations are used in the fitting of new equations for the
effective air temperature and refractive index of air as a function of
speed of 50-kHz ultrasound. The standard uncertainties of the effective
temperature and the refractive index of air equations are 15 mK and
1.7×10

^{–8}, respectively. The uncertainties of the effective temperature and refractive index of air measured with the test setup for distances of about 5 m are 25 mK and 2.6×10^{–8}, respectively.Original language | English |
---|---|

Pages (from-to) | 2400-2409 |

Number of pages | 10 |

Journal | Optical Engineering |

Volume | 43 |

Issue number | 10 |

DOIs | |

Publication status | Published - 2004 |

MoE publication type | A1 Journal article-refereed |