Research Effect of Four-Quadrant Detector Detection Spot in Atmospheric Turbulence

Abstract

Movement frequency of atmospheric turbulence is varied between a few Hz to hundreds Hz. when laser is transmitted in atmospheric some characteristic will be changed by turbulence modulation. The energy distribution form and shape of spot will be varied with movement frequency of turbulence. When spot is detected by four-quadrant detector output of detector will be effect. In order to test effect of turbulence to detector and ensure output signal can be amplified and processing effectively a kind of spot detection circuit was designed in turbulent environment. Two bands amplification was used in system. The noise suppression was completed in first band and variable gain amplifier was used in second to meet require of light intensity. Testing system was set up which can research characteristic of quadrant detector in turbulence. Experiment of spot detection in field was done. Distance from transmitting to receiving is 800m and 12.5km. Conclusions have been obtained by experimental when Distance is 800m subdivision can be up to 7 in photosensitive surface. At the same time we can see that impact of turbulence on laser transmission is a combination result with modulation of high and low frequency. And ability to spot detection has been invalid in 12.5 kilometers distances because of photosensitive surface occupied by noise from impact of turbulence, which show subdivision of quadrant detector has been broken in long distance.