Realizing the experimental potential of high-brightness, next generation synchrotron and free-electron laser light sources
requires the development of reflecting x-ray optics capable of wavefront preservation and high-resolution nano-focusing.
At the Advanced Light Source (ALS) beamline 5.3.1, we are developing broadly applicable, high-accuracy, in situ, at-wavelength
wavefront measurement techniques to surpass 100-nrad slope measurement accuracy for diffraction-limited
Kirkpatrick-Baez (KB) mirrors.
The at-wavelength methodology we are developing relies on a series of wavefront-sensing tests with increasing accuracy
and sensitivity, including scanning-slit Hartmann tests, grating-based lateral shearing interferometry, and quantitative
knife-edge testing. We describe the original experimental techniques and alignment methodology that have enabled us to
optimally set a bendable KB mirror to achieve a focused, FWHM spot size of 150 nm, with 1 nm (1.24 keV) photons at
3.7 mrad numerical aperture. The predictions of wavefront measurement are confirmed by the knife-edge testing.
The side-profiled elliptically bent mirror used in these one-dimensional focusing experiments was originally designed
for a much different glancing angle and conjugate distances. Visible-light long-trace profilometry was used to pre-align
the mirror before installation at the beamline. This work demonstrates that high-accuracy, at-wavelength wavefront-slope
feedback can be used to optimize the pitch, roll, and mirror-bending forces in situ, using procedures that are
deterministic and repeatable.