A new coherent soft X-ray branchline at the Advanced Light Source facility has been designed and is near completion. Using the third harmonic from the U8 undulator, this branch will operate from 200 eV to 1000 eV. This increased energy range will allow us to bring interferometric techniques previously used in the extreme ultraviolet region to the soft X-ray region.
Coherent radiation from undulator beamlines has been used to directly measure the index of refraction of several metals [1,2]. We have used this same interferometric technique to measure the indices of refraction of silicon, ruthenium, and TaSiN, materials important for EUV lithography. We now wish to use this technique to directly measure the refractive index of materials with absorption edges in the 500-800 eV range.
Also, we have begun work to use an at-wavelength phase shifting point diffraction interferometer (PS/PDI) to measure the quality of zone plates at soft X-ray wavelengths (below the oxygen K edge of 543.1 eV). The results of this experiment will aid in the evaluation of zone plates currently used in soft X-ray microscopy