Search

International audience; This paper presents the development, the operating principle, and the experimental results of an innovative technique for the measurement of acoustic pressures in the range of 40 mHz up to 5 Hz. This new measurement technique is based on the use of a Fabry Perot refractometer in which the air density variations related to an acoustic wave can be tracked and determined by measuring the optical frequency variations of a laser locked on a longitudinal mode of the Fabry Perot cavity. This approach covers a wider range in the low and infrasonic frequencies compared to conventional sensors.

We present our first results in the realization of an absolute distance meter that will bring well-defined and metrologically traceable measurements for distances of several kilometers. The purpose is to achieve an accuracy of 1 mm up to 5 km and beyond. To this end, the developed prototype operates at two different wavelengths, 780 nm and 1560 nm. For each of these wavelengths, the measured distance is determined from the phase accumulated by a radio-frequency carrier propagated in air by a laser beam modulated in intensity. Thus, using the dispersion relation between these two measurements, a compensation of the refractive index of air can be applied, i.e. no measurement of temperature, pressure and CO2 content of the air is required. In this paper, the principle of the two-wavelength absolute distance meter is explained, and preliminary results are presented, for each wavelength and with air refractive index compensation.