Nanofocused x rays are indispensable because they can provide high spatial resolution and high sensitivity for x-ray nanoscopy/spectroscopy. A focusing system using total reflection mirrors is one of the most promising methods for producing nanofocused x rays due to its high efficiency and energy-tunable focusing. The authors have developed a fabrication system for hard x-ray mirrors by developing elastic emission machining, microstitching interferometry, and relative angle determinable stitching interferometry. By using an ultraprecisely figured mirror, they realized hard x-ray line focusing with a beam width of 25nm at 15keV. The focusing test was performed at the 1-km-long beamline of SPring-8.

Efficient focusing of hard x rays to 25 nm by a total reflection mirror

A differential coating method is described for fabricating high-performance x-ray microfocusing mirrors. With this method, the figure of ultrasmooth spherical mirrors can be modified to produce elliptical surfaces with low roughness and low figure errors. Submicron focusing is demonstrated with prototype mirrors. The differential deposition method creates stiff monolithic mirrors which are compact, robust, and easy to cool and align. Prototype mirrors have demonstrated gains of more than 104 in beam intensity while maintaining submilliradian divergence on the sample. This method of producing elliptical mirrors is well matched to the requirements of an x-ray microdiffraction Kirkpatrick–Baez focusing system.

Elliptical x-ray microprobe mirrors by differential deposition

Metrology plays an important role in surface figuring with subnanometer accuracy. We have developed relative angle determinable stitching interferometry for the surface figuring of elliptical mirrors, in order to realize hard x-ray nanofocusing. In a stitching system, stitching angles are determined not by the general method using a common area between neighboring shots, but by the new method using the mirror’s tilt angles measured at times when profile data are acquired. The high measurement accuracy of approximately 4nm (peak-to-valley) was achieved in the measurement of a cylindrical surface having the same curvature as the elliptically designed shape to enable hard x-ray nanofocusing.

Relative angle determinable stitching interferometry for hard x-ray reflective optics

The next generation of synchrotrons and free electron laser facilities requires x-ray optical systems with extremely high performance, generally of diffraction limited quality. Fabrication and use of such optics requires adequate, highly accurate metrology and dedicated instrumentation. Previously, we suggested ways to improve the performance of the Long Trace Profiler (LTP), a slope measuring instrument widely used to characterize x-ray optics at long spatial wavelengths. The main way is use of a CCD detector and corresponding technique for calibration of photo-response non-uniformity [J. L. Kirschman, et al., Proceedings of SPIE 6704, 67040J (2007)]. The present work focuses on the performance and characteristics of the upgraded LTP-II at the ALS Optical Metrology Laboratory. This includes a review of the overall aspects of the design, control system, the movement and measurement regimes for the stage, and analysis of the performance by a slope measurement of a highly curved super-quality substrate with less than 0.3 microradian (rms) slope variation.

/pdf/performance-of-the-upgraded-ltp-ii-at-the-als-optical-uzs93xsgqz.pdf

Performance of the upgraded LTP-II at the ALS Optical Metrology Laboratory

The development of third generation light sources like theAdvanced Light Source (ALS) or BESSY II brought to a focus the need forhigh performance synchrotron optics with unprecedented tolerances forslope error and micro roughness. Proposed beam lines at Free ElectronLasers (FEL) require optical elements up to a length of one meter,characterized by a residual slope error in the range of 0.1murad (rms),and rms values of 0.1 nm for micro roughness. These optical elements mustbe inspected by highly accurate measuring instruments, providing ameasurement uncertainty lower than the specified accuracy of the surfaceunder test. It is essential that metrology devices in use at synchrotronlaboratories be precisely characterized and calibrated to achieve thistarget. In this paper we discuss a proposal for a Universal Test Mirror(UTM) as a realization of a high performance calibration instrument. Theinstrument would provide an ideal calibration surface to replicate aredundant surface under test of redundant figure. The application of asophisticated calibration instrument will allow the elimination of themajority of the systematic error from the error budget of an individualmeasurement of a particular optical element. We present the limitationsof existing methods, initial UTM design considerations, possiblecalibration algorithms, and an estimation of the expectedaccuracy.

/pdf/proposal-for-a-universal-test-mirror-for-characterization-of-1j04z306ib.pdf

Proposal for a Universal Test Mirror for Characterization of Slope Measuring Instruments

Modifications of the long trace profiler at the Advanced Photon
Source at Argonne National Laboratory have significantly improved its
accuracy and repeatability for measuring the figure of large flat and
long-radius mirrors. Use of a Dove prism in the reference beam path
corrects phasing problems between mechanical errors and thermally
induced system errors. A single reference correction now completely
removes both of these error signals from the measured surface
profile. The addition of a precision air conditioner keeps the
temperature in the metrology enclosure constant to within ±0.1 °C
over a 24-h period and has significantly improved the stability and the
repeatability of the measurements. Long-radius surface curvatures
can now be measured absolutely with a high degree of
confidence. These improved capabilities are illustrated with a
series of measurements of a 500-mm-long mirror with a 5-km radius of
curvature. The standard deviation in the average of ten slope
profile scans is 0.3 µrad, and the corresponding standard
deviation in the height error is 4.6 nm.

Cynthia J. Bresloff

Papers

Improvements in the accuracy and the repeatability of long trace profiler measurements.