Effect of oxide layer thickness on polarization mitigation

We analyze the influence of oxide layer thickness on polarization cancellation using crossed fold mirrors. We measure the linear retardance of three individual aluminum coated mirrors over the visible to near infra-red region by employing a spectroscopic Mueller matrix polarimeter. By fitting the measured linear retardance data with the theoretical model described by Fresnel's law, the native oxide layer thickness of three mirrors are determined as 4.40 nm, 5.75 nm, and 4.10 nm respectively. We perform polarization cancellation by using crossed fold mirrors. The oxide layer thickness difference of 1.35 nm between the first two mirrors limits the polarization cancellation to 0.65° of retardance at 650 nm. We show that the first and last fold mirrors having nearly same amount of oxide layer thickness reduces the residual quantity to 0.15° at 650 nm.