Displacement sensing resolution of position-sensitive detectors in atmospheric turbulence using retroreflected beam

The position sensing resolution of a lateral-effect photodiode (LEP) and a four-quadrant (4Q) photodetector used as the position sensitive detector (PSD) in a sensor which measures the lateral displacement of a corner cube reflector (CCR) by illuminating it and detecting the position of the reflected light spot with the PSD is studied. An LEP is much noisier than a 4Q detector, but in an outdoor environment the sensitivity of the 4Q detector to atmospheric turbulence due to defocusing makes its resolution worse than that of an LEP. Submillimeter resolutions at the target distances of several hundreds of meters are electrically achievable with an LEP. Outdoors, however, its resolution is also bounded by the atmospheric turbulence. In turbulent measurement conditions, standard deviations of better than 1 cm were typically achievable up to the distance of 300 m and about 10 cm up to half a kilometer.