We describe a technique to optimally tune and calibrate bendable X-ray optics for submicron focusing. The focusing is divided between two elliptically cylindrical reflecting elements, a Kirkpatrick-Baez pair. Each optic is shaped by applying unequal bending couples to each end of a flat mirror. The developed technique allows optimal tuning of these systems using surface slope data obtained with a slope-measuring instrument, the long trace profiler. Because of the near linearity of the problem, the minimal set of data necessary for the tuning of each bender consists of only three slope traces measured before and after a single adjustment of each bending couple. The data are analyzed with software realizing a method of regression analysis with experimentally found characteristic functions of the benders. The resulting approximation to the functional dependence of the desired shape provides nearly final settings. Moreover, the characteristic functions of the benders found in the course of tuning can be used for retuning to a new desired shape without removal from the beamline and remeasuring. We perform a ray trace using profiler data for the finally tuned optics, predicting the performance to be expected during use of the optics on the beamline.
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.
The next generation of synchrotrons and free electron lasers require extremely high-performance x-ray optical systems
for proper focusing. The necessary optics cannot be fabricated without the use of precise optical metrology
instrumentation. In particular, the Long Trace Profiler (LTP) based on the pencil-beam interferometer is a valuable tool
for low-spatial-frequency slope measurement with x-ray optics. The limitations of such a device are set by the amount
of systematic errors and noise. A significant improvement of LTP performance was the addition of an optical reference
channel, which allowed to partially account for systematic errors associated with wiggling and wobbling of the LTP
carriage. However, the optical reference is affected by changing optical path length, non-homogenous optics, and air
turbulence. In the present work, we experimentally investigate the questions related to the use of a precision tiltmeter as
a reference channel. Dependence of the tiltmeter performance on horizontal acceleration, temperature drift, motion
regime, and kinematical scheme of the translation stage has been investigated. It is shown that at an appropriate
experimental arrangement, the tiltmeter provides a slope reference for the LTP system with accuracy on the level of
0.1 μrad (rms).
Micro-focusing is widely applied at soft and hard x-ray wavelengths. One typical method, in addition to zone plates, is to
split the focusing in the tangential and sagittal directions into two elliptically cylindrical reflecting elements, the so-called
Kirkpatrick-Baez (KB) pair. In the simplest case each optic is made by grinding and polishing a flat, and applying
unequal bending couples to each end. After briefly reviewing the nature of the bending, we show two new methods for
optimal adjustment of these mirror systems using our surface normal slope measuring instrument, the long trace profiler
(LTP). First, we adapt a method previously used to adjust mirrors on synchrotron radiation beamlines. We measure the
slope of the surface before and after a single small adjustment of each bending couple. This permits an approximation to
the functional dependence of slope on the adjustments, and allows, by applying the results of a simple matrix calculation,
direct adjustment to a nearly final setting. Typically, the near linearity of the problem determines a very fast convergence
of the adjustment procedure. Second, we subdivide the slope data from the LTP into three regions on the mirror, and fit a
circle to each sub-region by regression. This method also allows rapid iterative adjustment of both bending couples. We
show that this method is a particular case of the first one. As an overall indicator of predicted performance, we ray trace,
using profiler data, predicting the exact optical performance to be expected during use of the system.
The next generation of synchrotrons and free electron lasers requires x-ray optical systems with extremely high-performance,
generally, of diffraction limited quality. Fabrication and use of such optics requires highly accurate
metrology. In the present paper, we discuss a way to improve the performance of the Long Trace Profiler (LTP), a slope
measuring instrument widely used at synchrotron facilities to characterize x-ray optics at high-spatial-wavelengths from
approximately 2 mm to 1 m. One of the major sources of LTP systematic error is the detector. For optimal functionality,
the detector has to possess the smallest possible pixel size/spacing, a fast method of shuttering, and minimal nonuniformity
of pixel-to-pixel photoresponse. While the first two requirements are determined by choice of detector, the
non-uniformity of photoresponse of typical detectors such as CCD cameras is around 2-3%. We describe a flat-field
calibration setup specially developed for calibration of CCD camera photo-response and dark current with an accuracy
of better than 0.5%. Such accuracy is adequate for use of a camera as a detector for an LTP with performance of ~0.1
microradian (rms). We also present the design details of the calibration system and results of calibration of a DALSA
CCD camera used for upgrading our LTP-II instrument at the ALS Optical Metrology Laboratory.