Measurement system for measuring transverse displacements of engineering structures and geodetic datum line determination

The system includes a laser beam transmitter, a CCD array connected to a signal processing and analysing device, and a diffractive element with a variable focal length situated in the optical axis of the system between the transmitter and the CCD array. The diffractive element is composed of a pair of identical and parallel zone plates (P) rotationally mounted in respect to each other in the optical axis of the system. Each zone plate (P) has equally arranged elliptical zones situated around the plate centre, forming a wavefront focusing in the shape of a focal cross falling onto the CCD array. Another system comprises a spatial light modulator (SLM) situated on the laser beam path forming a diffractive element with a variable focal length in the form of a hyperbolic zone plate forming a wavefront focusing in the shape of a focal cross falling onto the CCD array.