From Event: SPIE Optical Engineering + Applications, 2017
As resolving power targets have increased with each generation of beamlines commissioned in synchrotron radiation facilities worldwide, diffraction gratings are quickly becoming crucial optical components for meeting performance targets. However, the metrology of variable-line-spacing (VLS) gratings for high resolution beamlines is not widespread; in particular, no metrology facility at any US DOE facility is currently equipped to fully characterize such gratings. To begin to address this issue, the Optics Group at the Advanced Photon Source at Argonne, in collaboration with SOLEIL and with support from Brookhaven National Laboratory (BNL), has developed an alternative beam path addition to the Long Trace Profiler (LTP) at Argonne’s Advanced Photon Source. This significantly expands the functionality of the LTP not only to measure mirrors surface slope profile at normal incidence, but also to characterize the groove density of VLS diffraction gratings in the Littrow incidence up to 79°, which covers virtually all diffraction gratings used at synchrotrons in the first order. The LTP light source is a 20mW HeNe laser, which yields enough signal for diffraction measurements to be performed on low angle blazed gratings optimized for soft X-ray wavelengths. We will present the design of the beam path, technical requirements for the optomechanics, and our data analysis procedure. Finally, we discuss challenges still to be overcome and potential limitations with use of the LTP to perform metrology on diffraction gratings.
Janet Sheung, Jun Qian, Joseph Sullivan, Muriel Thomasset, Jonathan Manton, Sunil Bean, Peter Takacs, Joseph Dvorak, and Lahsen Assoufid, "Metrology of variable-line-spacing x-ray gratings using the APS Long Trace Profiler," Proc. SPIE 10385, Advances in Metrology for X-Ray and EUV Optics VII, 1038508 (Presented at SPIE Optical Engineering + Applications: August 06, 2017; Published: 7 September 2017); https://doi.org/10.1117/12.2279053.
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