The invention relates to a device for remote measurement of the properties of the atmosphere, more particularly a device used to detect atmospheric turbulence. The device operates on the lidar principle, using the backscattering of a laser beam by the air. The device comprises a laser emission source (1), optical means (5) for collecting a backscattered beam (3) that is backscattered by targets illuminated by the emission source (1), the backscattered beam (3) being substantially centerd about the wavelength of the emission source (1), and means (9) for generating interference fringes (24) resulting from the backscattered beam (3). The device also includes a spatial filter (11) allowing only a central spot of the interference fringes to be seen and, at the center of the spatial filter (11), a mask for blocking off the center of the central spot and more particularly the Mie line of the backscattered beam.
The present invention relates to a frequency shifter in an optical path containing a continuous laser source, and it comprises at least two frequency shift modules placed in parallel and each containing an optical propagation medium, the optical path length of which is modified according to the desired frequency shift, each of these modules being controlled separately, this shifter comprising a switch (14) which is connected to the outputs of these modules and is controlled so as to choose, at each instant, the module providing the desired frequency shift, the switch delivering, at its output, a continuous optical beam whose frequency is adjusted by contiguous sections.
