HETERODYNE SHEARING INTERFEROMETRY FOR SURFACE PROFILE

WE PROPOSE TO DEVELOP AND VERIFY IN THIS PHASE I PROGRAM A TECHNIQUE THAT WILL ACCURATELY AND REPEATABLY MEASURE SURFACE PROFILES AND DISTANCES BETWEEN A TEST OBJECT AND DETECTORS USING THE SHEARING HETERODYNE INTERFEROMETRY TECHNIQUE. THE TECHNIQUE IS BASED ON SHEARING HETERODYNE INTERFEROMETRY WITH A FREQUENCY MODULATED LASER DIODE USING THE FOUR-BUCKET-INTEGRATING TECHNIQUE. IT CAN BE USED TO DETERMINE DEPTH PROFILES VARYING FROM THE SUBMICRON TO CENTIMETER RANGE WITHOUT ANY CHANGE IN THE INSTRUMENT OR ITS COMPONENTS. IN PHASE II THIS TECHNIQUE CAN BE IMPLEMENTED INTO A COMPACT INSTRUMENT THAT WILL PRIMARILY BE USED TO MEASURE DEPTH PROFILES, BUT CAN ALSO BE USED TO MEASURE THE INNER DIAMETER, THE OUT-OF-ROUND, AND THE TAPER OF A GUN BARREL. IN THE PROPOSED TECHNIQUE, THE INJECTION CURRENT OF THE LASER DIODE IS CONTINUOUSLY CHANGED TO INTRODUCE PHASE DIFFERENCES. A HIGH RESOLUTION CCD CAMERA WITH CORRECTED LINEARITY AND PIXEL-TO-PIXEL VARIATION IS USED FOR FRINGE DETECTION. THE MEASURED DATA IS STORED IN AN IBM PC WHICH WILL RUN SOFTWARE TO REDUCE NOISE AND INCREASE THE ACCURACY OF MEASUREMENTS. WE ANTICIPATED THAT THE ACCURACY AND REPEATABILITY OF THE MEASUREMENTS IN OUR LABORATORY WILL BE CLOSED TO ONE MICRON.