VARIABLE POLARIZATION LIDAR OPTICS SYSTEM

IT IS PROPOSED TO ADD AN INNOVATIVE VARIABLE POLARIZATION OPTICAL SYSTEM TO THE AIR FORCE ABLE (ATMOSPHERIC BACKSCATTER EXPERIMENT) LIDAR SYSTEM. THIS CAPABILITY FOR REAL-TIME, RANGE-RESOLVED POLARIZATION ANALYSIS OF ATMOSPHERIC BACKSCATTER WOULD BE UNIQUE TO THE ABLE LIDAR SYSTEM. IT WOULD ENABLE THE AIR FORCE TO ACQUIRE BOTH GROUNDBASED AND BALLOONBORNE POLARIZATION DATA OF GREATER ACCURACY THAN IS CURRENTLY ATTAINABLE. DATA OBTAINED BY EXISTING LIDAR SYSTEMS ARE BASED ON THE ASSUMPTION THAT THE POLARIZATION OF THE BACKSCATTER RADIATION IS UNCHANGED FROM THAT TRANSMITTED. THE PROPOSED SYSTEM WILL TEST THAT ASSUMPTION. IT IS PROPOSED TO STUDY THE FEASIBILITY OF IMPLEMENTING A VARIABLE POLARIZATION SYSTEM WHICH WOULD INCLUDE STATE-OF-THE-ART VARIABLE LIQUID CRYSTAL RETARDERS HAVING HIGH LASER DAMAGE THRESHOLDS. THESE RETARDERS WOULD ALTERNATELY SWITCH THE POLARIZATION OF THE THREE TRANSMITTED LIDAR WAVELENGTHS, 1064, 532, AND 355 NM. SIMILARLY AN ALTERNATELY SWITCHED POLARIZATION ANALYZER WOULD BE INCORPORATED INTO THE LIDAR RECEIVER. AN ADDITIONAL INNOVATIVE FEATURE OF THE SYSTEM WOULD BE THE USE OF A PHOTON-COUNTING AVALANCHE PHOTODIODE DETECTOR AT 1064 NM TO PROVIDE POLARIZATION DATA AT THAT ADDITIONAL WAVELENGTH.