We report on the development of a polarimeter for characterizing reflective surfaces throughout the extreme ultraviolet (EUV). The instrument relies on laser high-order harmonics generated in helium, neon, or argon gas. The 800 nm laser generates a discrete comb of odd harmonics up to order 100 (wavelengths from 8-62 nm). The flux of EUV light is a couple orders of magnitude less than a synchrotron source but 30,000 times greater than a plasma source currently in operation at BYU. The polarimeter determines the reflectance from surfaces as a function of incident angle, linear light polarization orientation, and wavelength. The instrument uses a wave plate in the laser beam to control the orientation of the harmonic polarization (linear, same as laser). After reflecting from the sample, the harmonic beams are dispersed by a grating and focused onto a micro-channel plate coupled to a phosphor screen. We have demonstrated the feasibility of this project with a simple prototype instrument, which measured the reflectance of samples from 30 nm to 62 nm. The prototype demonstrated that sensitivity is sufficient for measuring reflectances as low as 0.5% for both s- and p-polarized light. The full instrument employs extensive scanning mobility as opposed to the fixed angle and fixed wavelength range of our earlier prototype. An advantage of employing harmonics as a source for EUV polarimetry is that a wide range of wavelengths can be measured simultaneously. This project represents an authentic 'work-horse' application for high-order harmonics, as opposed to merely demonstrating proof of concept.
