Choice of clip levels for beam width measurements using knife-edge techniques

The scanning knife-edge technique provides a method for measuring the width of an optical beam having an arbitrary or irregular transverse profile. To implement this method, however, it is necessary to select both a clip level and a scale factor for converting the measured clip width into an effective width of the laser beam. The authors show that the preferred clip level for beam width measurements using this technique should be chosen in the range between 8.5% and about 11.6%. With a suitably matched clip level and scale factor within this range, the conversion from measured clip width to standard deviation can be made exactly accurate for TEM₀₀ Gaussian beams, and the conversion factor will become only slightly inaccurate for a wide range of other higher-order or poorer-quality beam profiles