Abstract

Birefringent thin films enable the construction of polarizing elements for use with light at normal incidence. Vacuum deposition at angle θ_v on to a stationary substrate leads to the growth of a biaxial film with a columnar nanostructure tilted at angle ψ with respect to the substrate normal.1, axis-1 is in the deposition plane parallel to the columns and axis-2 is also in the deposition plane but perpendicular to the columns. Axis-3 is perpendicular to the deposition plane, and hence parallel to the surface. Typical values of the column angle and the birefringence, for zirconium oxide deposited at θ_v = 60°, are ψ ≈ 30°, n₁ − n₂ ≈ 0.31, n₁ – n₃ ≈ 0.17 and n₃ − n₂ ≈ 0.14. However, for light incident normally on such a film, the difference between the refractive indices associated with the p-polarization (parallel to the deposition plane) and the s-polarization (perpendicular to the deposition plane) is Δn = n_s − n_p ~ 0.07. Thus, only a fraction of the maximum available birefringence of a tilted-columnar film is accessed by light incident normally on the coating. Another disadvantage is that oblique deposition on to a stationary substrate leads to a film with uneven thickness.

© 1998 Optical Society of America