Advanced X-ray Optics Metrology for Nanofocusing and Coherence Preservation - eScholarship

SRN Article from the workshop: “Advanced X-Ray Optics Metrology for Nano-focusing and Coherence Preservation” Kenneth Goldberg and Valeriy Yashchuk, Lawrence Berkeley National Laboratory published in Synchrotron Radiation News, Vol. 21, No. 2, 2008, pp. 11–12 What is the point of developing new high-brightness light sources if beamline optics won’t be available to realize the goals of nano-focusing and coherence preservation? That was one of the central questions raised during a workshop at the 2007 Advanced Light Source Users’ Meeting. Titled, “Advanced X-Ray Optics Metrology for Nano-focusing and Coherence Preservation,” the workshop was organized by Kenneth Goldberg and Valeriy Yashchuk (both of Lawrence Berkeley National Laboratory, LBNL), and it brought together industry representatives and researchers from Japan, Europe, and the US to discuss the state of the art and to outline the optics requirements of new light sources. Many of the presentations are viewable on the workshop website http://goldberg.lbl.gov/MetrologyWorkshop07/ . Many speakers shared the same view of one of the most significant challenges facing the development of new high-brightness third and fourth generation x-ray, soft x-ray, and EUV light sources: these sources place extremely high demands on the surface quality of beamline optics. In many cases, the 1–2-nm surface error specs that define the outer bounds of “diffraction-limited” quality are beyond the reach of leading facilities and optics vendors. To focus light to 50-nm focal spots, or smaller, from reflective optics and to preserve the high coherent flux that new sources make possible, the optical surface quality and alignment tolerances must be measured in nano-meters and nano-radians. Without a significant, well-supported research effort, including the development of new metrology techniques for use both on and off the beamline, these goals will likely not be met. The scant attention this issue has garnered is evident in the stretched budgets and limited manpower currently dedicated to metrology. With many of the world’s leading groups represented at the workshop, it became clear that Japan and Europe are several steps ahead of the US in this critical area. But the situation isn’t all dire: several leading groups are blazing a trail forward, and the recognition of this issue is increasing. The workshop featured eleven invited talks whose presenters came from Japan, Europe, and the US. Showing how to build support for this research, Howard Padmore (LBNL) presented a strategy based on recent successful efforts to establish a new program in advanced detectors within the US Department of Energy (DOE). The gap between the current state of the art and new beamline optics requirements was one of the main issues raised by Peter Takacs (BNL). Along with several other speakers, Takacs showed that for x-ray wavelengths, a mirror figure error of 0.5-nm RMS decreases the Strehl ratio noticeably, a 1.0-nm error reduces it to half, and a 2.0-nm error can destroy focusing entirely. Takacs then placed this field in context with a very interesting historical overview, going back to the seminal work of Mori in Japan (1965),