28 September 2011 An experimental apparatus for diffraction-limited soft x-ray nano-focusing
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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.
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Daniel J. Merthe, Daniel J. Merthe, Kenneth A. Goldberg, Kenneth A. Goldberg, Valeriy V. Yashchuk, Valeriy V. Yashchuk, Sheng Yuan, Sheng Yuan, Wayne R. McKinney, Wayne R. McKinney, Richard Celestre, Richard Celestre, Iacopo Mochi, Iacopo Mochi, James Macdougall, James Macdougall, Gregory Y. Morrison, Gregory Y. Morrison, Senajith B. Rakawa, Senajith B. Rakawa, Erik Anderson, Erik Anderson, Brian V. Smith, Brian V. Smith, Edward E. Domning, Edward E. Domning, Tony Warwick, Tony Warwick, Howard Padmore, Howard Padmore, } "An experimental apparatus for diffraction-limited soft x-ray nano-focusing", Proc. SPIE 8139, Advances in X-Ray/EUV Optics and Components VI, 813907 (28 September 2011); doi: 10.1117/12.894116; https://doi.org/10.1117/12.894116

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