Polarization-ratio reflectance for determining optical constants using laser high-order harmonics

We describe a method for deriving optical constants in the extreme ultraviolet from the measured ratio of p- to s-polarized reflectance curves (as a function of angle). These measurements use laser-generated high-order harmonics, which have the advantage of easily rotatable linear polarization. We show that this ratio technique markedly reduces sensitivity to possible systematic brightness and alignment drifts of the harmonic signal during measurement. We also demonstrate that optical constants can be extracted from ratio reflectance measurements as well as they can from absolute reflectance measurements.