Mango wiggler as a novel insertion device providing a large and symmetrical imaging field of view.

A novel insertion device is introduced, designated as the Mango wiggler, designed for synchrotron radiation (SR) imaging that provides a large field of view. This innovative device is constructed from two orthogonal planar wigglers with a small difference in their period lengths, eliciting the phase difference of the magnetic fields to incrementally transitions from 0 to π/2. Such a configuration enlarges the vertical divergence of the light source, as with the horizontal divergence. The appellation `Mango wiggler' derives from the distinctive mango-shaped contour of its radiation field. A comprehensive suite of theoretical analyses and simulations has been executed to elucidate the radiation properties of the Mango wiggler, employing SPECTRA and Mathematica as calculation tools. In conjunction with the ongoing construction of the High Energy Photon Source in Beijing a practical Mango wiggler device has been fabricated for utilization in SR imaging applications. Theoretical analyses were applied to this particular Mango wiggler to yield several theoretical conclusions, and several simulations were performed according to the measured magnetic field results.

Spatial-frequency-oriented measurement strategy in two-dimensional slope deflectometry systems.

A single-point-probe-based slope profiler is a common measurement scheme for the measurement of freeform optical surfaces, which has been a challenging research direction. Efficiency is a key issue in two-dimensional scanning-based measurement. This study establishes a measurement system simulation model and reveals that the height reconstruction accuracy of different reconstruction algorithms is primarily correlated with the sampling density. The spatial resolution calibrated of the slope measurement device is also identified to be an essential part of the strategy. Based on a kind of slope profiler, this paper applies variable sampling intervals for different spatial frequency characteristics of the surface under test (SUT). The result shows that the reconstruction accuracy can be controlled by selecting sampling parameters and calibrating the slope measurement device. For objects with different spatial characteristics, targeted optimization of the measurement scheme can be achieved. This strategy also has a certain universality for general scanning slope measurement and height reconstruction, providing a reference for device selection and sampling settings for different spatial frequency measurement requirements.

A magnetically controlled chemical-mechanical polishing (MC-CMP) approach for fabricating channel-cut silicon crystal optics for the High Energy Photon Source.

Crystal monochromators are indispensable optical components for the majority of beamlines at synchrotron radiation facilities. Channel-cut monochromators are sometimes chosen to filter monochromatic X-ray beams by virtue of their ultrahigh angular stability. Nevertheless, high-accuracy polishing on the inner diffracting surfaces remains challenging, thus hampering their performance in preserving the coherence or wavefront of the photon beam. Herein, a magnetically controlled chemical-mechanical polishing (MC-CMP) approach has been successfully developed for fine polishing of the inner surfaces of channel-cut crystals. This MC-CMP process relieves the constraints of narrow working space dictated by small offset requirements and achieves near-perfect polishing on the surface of the crystals. Using this method, a high-quality surface with roughness of 0.614 nm (root mean square, r.m.s.) is obtained in a channel-cut crystal with 7 mm gap designed for beamlines at the High Energy Photon Source, a fourth-generation synchrotron radiation source under construction. On-line X-ray topography and rocking-curve measurements indicate that the stress residual layer on the crystal surface was removed. Firstly, the measured rocking-curve width is in good agreement with the theoretical value. Secondly, the peak reflectivity is very close to theoretical values. Thirdly, topographic images of the optics after polishing were uniform without any speckle or scratches. Only a nearly 2.5 nm-thick SiO2 layer was observed on the perfect crystalline matrix from high-resolution transmission electron microscopy photographs, indicating that the structure of the bulk material is defect- and dislocation-free. Future development of MC-CMP is promising for fabricating wavefront-preserving and ultra-stable channel-cut monochromators, which are crucial to exploit the merits of fourth-generation synchrotron radiation sources or hard X-ray free-electron lasers.

Enhanced-spatial-resolution optical surface profiler based on focusing deflectometry.

Deflectometric slope profiler is an essential technique for accessing the surface metrology of mirrors used in synchrotron radiation beamlines. To increase the upper spatial frequency bandwidth limits of deflectometric slope profiler, reducing the beam spot size on the mirrors is necessary. In this paper, we introduce a profiler system: the focusing long trace profiler (FLTP). It contains a newly developed optical head capable of raising upper spatial frequency bandwidth limits by using a focused beam instead of a collimated beam to scan the sample. This feature has been proven in a numerical simulation experiment, where a spatial resolution of up to around 0.05 mm was reached when the sample is set at focus plane. The system is implemented and characterized in several experiments; calibration of the focusing optical head shows that it can achieve a high angular accuracy of sub-50 nrad root-mean-square (rms) and defocusing of sample under test (SUT) has no effect on the measurement results; the measurement tests also demonstrate the system's advantage in highly curved mirror profile metrology.

A novel coating to avoid corrosion effect between eutectic gallium-indium alloy and heat sink metal for X-ray optics cooling.

Owing to the parasitic vibration effect of the cooling medium and pipes of X-ray optics, the vibration decoupling cooling method based on eutectic gallium-indium (EGaIn) alloy has become very crucial for fourth generation synchrotron radiation advanced light sources. However, there is an issue that the corrosion of the EGaIn alloy to the heat sink metal [e.g., copper (Cu) plate] results in the solidification and the failure of eliminating the parasitic vibration effect. To deal with the problem, a novel anti-corrosion coating based on tungsten (W) is presented in this paper. It possesses better corrosion resistance performance compared with the traditional coating of nickel (Ni). The experimental investigation was carried out, in which the EGaIn alloy was exposed to several typical metal materials in conditions of various time durations and various temperatures, which were considered as controls. Furthermore, the corrosion effects are analyzed and evaluated in two aspects of micromorphology and the chemical composition by using an optical microscope and a scanning electron microscope as well as x-ray diffraction. The results show that non obvious corrosion occurred for W, 0.33 mm and 48 µm thick transition micro-area, respectively, for Cu and Ni. In addition, new substances CuGa2 and Ni3Ga7 occurred, respectively, for Cu and Ni for 36 hours at 250 °C. The EGaIn alloy will freeze after corroding 18 µm substrate for Ni or 30 µm for Cu. Furthermore, the W coating that was prepared by magnetron sputtering has been implemented for feasibility validation.

Highly efficient thermal deformation optimization method for smart-cut mirrors over the entire photon energy range.

A method to optimize the notches of water-cooled white-beam mirrors over the entire photon energy range is proposed. A theoretical method is used to quantitatively evaluate the influence of the thermal load on the thermal deformation of a mirror. The result of theoretical calculations and finite-element analysis are consistent, which proves the feasibility of the method. The root mean square of the curvatures of the thermal deformation of the white-beam mirror over the entire photon energy range can be minimized. This method greatly simplifies the design work of water-cooled white-beam mirrors.

Numerical iteration method to reduce the surface shape error of a bendable mirror in synchrotron radiation.

X-ray mirrors with high focusing performance are extensively used in the synchrotron radiation field. Especially for vertical reflecting bendable mirrors, many elements such as gravity, extended parts used for the bending mechanism, etc., usually affect the surface shape precision. There are no effective methods to remove all these errors at this point. However, an iteration method can be adopted to solve this problem. In this paper, a novel, to the best of our knowledge, iteration method on decreasing the error between the practice surface shape and the desired one is proposed. Not only can the precision of the surface shape be realized by this method, but also computational efficiency. Errors induced by gravity can be compensated for by an analytical method, while errors caused by the extended parts should be eliminated by a numerical method. Therefore, two main kinds of errors-gravity and parts of clamping-can be removed by iteration. Some examples are presented to illustrate the advantages of this method by comparison with the regular one.

An improved differential-grating plane-mirror heterodyne interferometer for small roll angle measurement of a linear motion.

In the previous studies on roll angle (ROLL) measurements which are based on the concept of the combination of a diffraction grating displacement technique and a laser heterodyne interferometry, there is always a lack of ideally functional retro-reflectors and corresponding optical configurations resulting in misalignment and unconfident monitoring. To overcome this problem, a differential-grating plane-mirror heterodyne interferometer is proposed in this paper, in which the grating displacement sensing method is utilized to promote angular interferometry as a reliable ROLL measurement. The working mechanism is thoroughly demonstrated through the theoretical derivation and performance analysis. In particular, the exploited configuration here including a differential grating with excellent robustness and a plane mirror with doubled resolution enables improved performance compared with the existing methods. Furthermore, a corresponding prototype is also developed to validate the proposed method successfully. So, it features merits such as an ultra-high resolution up to 1 nrad, a high sampling rate of kHz and easy practicability, which is significant for high-accuracy and real-time ROLL monitoring and compensation for advanced manufacturing and scientific instruments.

A novel method for measuring the focal point of a sagittal-focusing Laue crystal monochromator.

In order to overcome space limitations, a novel method is introduced to measure the focal point size of a sagittally bent Laue crystal monochromator by using a multi-hole array. Combined with ray-tracing measurements, the focal length and focused beam size were determined. Theoretical simulations and experiments were performed to demonstrate the feasibility of this method. The experimental results show that this method can provide a fast way of measuring the focusing characteristics of a sagittally bent Laue crystal monochromator.

Large-aperture prism-array lens for high-energy X-ray focusing.

A new prism-array lens for high-energy X-ray focusing has been constructed using an array of different prisms obtained from different parabolic structures by removal of passive parts of material leading to a multiple of 2π phase variation. Under the thin-lens approximation the phase changes caused by this lens for a plane wave are exactly the same as those caused by a parabolic lens without any additional corrections when they have the same focal length, which will provide good focusing; at the same time, the total transmission and effective aperture of this lens are both larger than those of a compound kinoform lens with the same focal length, geometrical aperture and feature size. This geometry can have a large aperture that is not limited by the feature size of the lens. Prototype nickel lenses with an aperture of 1.77 mm and focal length of 3 m were fabricated by LIGA technology, and were tested using CCD camera and knife-edge scan method at the X-ray Imaging and Biomedical Application Beamline BL13W1 at Shanghai Synchrotron Radiation Facility, and provided a focal width of 7.7 µm and a photon flux gain of 14 at an X-ray energy of 50 keV.

Laser-heating-based active optics for synchrotron radiation applications.

Active optics has attracted considerable interest from researchers in synchrotron radiation facilities because of its capacity for x-ray wavefront correction. Here, we report a novel and efficient technique for correcting or modulating a mirror surface profile based on laser-heating-induced thermal expansion. An experimental study of the characteristics of the surface thermal deformation response indicates that the power of a milliwatt laser yields a bump height as low as the subnanometer scale and that the variation of the spot size modulates the response function width effectively. In addition, the capacity of the laser-heating technique for free-form surface modulation is demonstrated via a one-dimensional surface correction experiment. The developed method is a promising new approach toward effective x-ray active optics coupled with at-wavelength metrology techniques.

Sub-500 nm hard x ray focusing by compound long kinoform lenses.

The focusing performance of polymethyl methacrylate compound long kinoform lenses with 70 µm aperture and 19.5 mm focal length was characterized with 8 keV x rays using the knife-edge scan method at the 4W1A transmission x-ray microscope beamline of Beijing Synchrotron Radiation Facility. The experiment result shows a best FWHM focus size of 440 nm with 31% diffraction efficiency.

Wavefront aberrations of x-ray dynamical diffraction beams.

The effects of dynamical diffraction in x-ray diffractive optics with large numerical aperture render the wavefront aberrations difficult to describe using the aberration polynomials, yet knowledge of them plays an important role in a vast variety of scientific problems ranging from optical testing to adaptive optics. Although the diffraction theory of optical aberrations was established decades ago, its application in the area of x-ray dynamical diffraction theory (DDT) is still lacking. Here, we conduct a theoretical study on the aberration properties of x-ray dynamical diffraction beams. By treating the modulus of the complex envelope as the amplitude weight function in the orthogonalization procedure, we generalize the nonrecursive matrix method for the determination of orthonormal aberration polynomials, wherein Zernike DDT and Legendre DDT polynomials are proposed. As an example, we investigate the aberration evolution inside a tilted multilayer Laue lens. The corresponding Legendre DDT polynomials are obtained numerically, which represent balanced aberrations yielding minimum variance of the classical aberrations of an anamorphic optical system. The balancing of classical aberrations and their standard deviations are discussed. We also present the Strehl ratio of the primary and secondary balanced aberrations.