axis of polarization the electric field vector and the magnetic field vector are opposite to that of fig3 a thus for this configuration the ovality of the exit hole shown by oval 322 in fig3 d again being aligned with the major axis of hole ovality a polyimide film having a thickness of 50 microns was illuminated with laser light from a system as depicted in fig2 to form holes having an exit diameter of about 30 microns with a linear beam polarization the average major axis was 1 17 microns standard deviation of 0 42 for a stationary half wave plate and was only 0 15 microns standard deviation of 0 47 for a rotating half wave plate ovality as defined in fig3 5 6 and 7 is x maximum u2212 y maximum as shown in fig4 c this ovality definition is less desirable than major axis u2212 minor axis and resulted from software limitations on the automated microscope used for the empirical study however the qualitative results and magnitude of the effect is clearly demonstrated even with these less than ideal measurements fig4 a and 4b show the ovality data obtained by irradiation of a part i e a substrate with laser light that has passed through a stationary half wave plate to form 50 holes this chart is the statistical process control chart used to derive the results discussed above the average ovality difference between xmax and ymax was found to be 1 17 microns with a standard deviation of 0 42 microns it is important to note that the variation contributing to the standard deviation of 0 42 microns includes contributions from both the ablation process and the metrology tool metrology contributions are estimated to be a significant contributor to.