X-ray Compound Refractive Lenses Research Articles

Liquid compound refractive X-ray lens.

We introduce the concept of a liquid compound refractive X-ray zoom lens. The lens is generated by pumping a suitable liquid lens material like water, alcohol or heated lithium through a line of nozzles each forming a jet with the cross section of lens elements. The system is housed, so there is a liquid-circulation. This lens can be used in white beam at high brilliance synchrotron sources, as radiation damages are cured by the continuous reformation of the lens. The focal length can be varied by closing nozzles, thus reducing the number of lens elements in the beam.

CRL-based ultra-compact transfocator for X-ray focusing and microscopy.

A new ultra-compact transfocator (UCTF) based on X-ray compound refractive lenses (CRLs) is presented. The device can be used to change the number of one- and two-dimensional focusing CRLs by moving the individual parabolic lenses one-by-one independently, thus providing permanent energy and focal-length tunability for scanning and full-field X-ray microscopy applications. The small overall size and light weight of the device allow it to be integrated in any synchrotron beamline, while even simplifying the experimental layout. The UCTF was tested at the Excillium MetalJet microfocus X-ray source and at theP14 EMBL (PETRA-III) beamline, demonstrating high mechanical stability and lens positioning repeatability.

Ptychographic characterisation of polymer compound refractive lenses manufactured by additive technology.

The recent success in the development of high-precision printing techniques allows one to manufacture free-standing polymer structures of high quality. Two-photon polymerization lithography is a mask-less technique with down to 100 nm resolution that provides full geometric freedom. It has recently been applied to the nanofabrication of X-ray compound refractive lenses (CRLs). In this article we report on the characterization of two sets of CRLs of different design produced by two-photon polymerization-induced lithography.

Investigation of `glitches' in the energy spectrum induced by single-crystal diamond compound X-ray refractive lenses.

Single-crystal diamond stands out among all the candidate materials that could be exploited to fabricate compound refractive lenses (CRLs) owing to its extremely stable properties. Among all related experimental features, beam divergence, χ-angles relative to the incoming beam in Eulerian geometry and different positions of the X-ray beam relative to the lens geometry may influence the transmission energy spectrum of CRLs. In addition, the orientation of the single-crystal diamond sample may also affect the glitches significantly. To verify these initial assumptions, two experiments, an energy scan and an ω-scan, were set up by employing a polished diamond plate consisting of five biconcave lenses. The results show that beam divergence does not affect the spectrum, nor do χ-angles when ω is set to zero. Nevertheless, different incident positions have an appreciable effect on the transmission spectrum, in particular the `strengths' of the glitches. This is attributed to absorption. The ω-scan setup is capable of determining the so-called orientation matrix, which may be used to predict both `energy positions' and `strengths' of the glitches.

Computer simulations of X-ray spherical wave dynamical diffraction in one and two crystals in the Laue case.

This article reports computer simulations of X-ray spherical wave dynamical diffraction in one and two single crystals in the Laue case. An X-ray compound refractive lens (CRL) as a secondary radiation source of spherical waves was considered for the first time and in contrast to previous simulations with the assumption of the use of a slit. The main properties of the CRL as a secondary source are discussed and two focusing phenomena are analysed. The first one is the diffraction focusing effect for one single crystal in the reflected beam and in the case of a large source-to-detector distance. The second one is the same but for two single crystals and for the twice-reflected beam in the case of a short distance between the source and detector. The first effect is well pronounced in the case of strong absorption. However, it may also be used as an element of an energy spectrometer in the medium and even weak absorption case. The second effect will appear in the case of weak absorption. It is shown that it is not effective to use it in an energy spectrometer. In the case of weak absorption the transverse size of the diffraction focused beam will oscillate together with the reflected beam integral intensity. The oscillation period is close to the extinction length.

Rocking curve and spatial coherence properties ofalong X-ray compound refractive lens.

Semi-analytical theory of a long set of X-ray compound refractive lenses (CRLs) based on recurrence relations is developed further. The geometrical aperture, angular divergence of incident radiation and source size were accurately taken into account. Using this theory it is possible to calculate the width of the rocking curve of a long (40.7 cm) Be CRL which coincides with experimental data obtained earlier. By this approach the transverse coherence length for the X-ray beam after passing a set of CRLs of arbitrary complexity has been estimated. It is shown that at the focus this coherence length is equal to a diffraction-limited beam size (beam size in the case of a point source) and has minimal difference with the real beam size.

Simultaneous 8.2 keV phase-contrast imaging and 24.6 keV X-ray diffraction from shock-compressed matter at the LCLS

In this work, we demonstrate simultaneous phase-contrast imaging (PCI) and X-ray diffraction from shock compressed matter at the Matter in Extreme Conditions endstation, at the Linac Coherent Light Source (LCLS). We utilize the chromaticity from compound refractive X-ray lenses to focus the 24.6 keV 3rd order undulator harmonic of the LCLS to a spot size of 5 μm on target to perform X-ray diffraction. Simultaneous PCI from the 8.2 keV fundamental X-ray beam is used to visualize and measure the transient properties of the shock wave over a 500 μm field of view. Furthermore, we demonstrate the ability to extend the reciprocal space measurements by 5 Å−1, relative to the fundamental X-ray energy, by utilizing X-ray diffraction from the 3rd harmonic of the LCLS.

A Shack-Hartmann Sensor for Single-Shot Multi-Contrast Imaging with Hard X-rays

An array of compound refractive X-ray lenses (CRL) with 20 × 20 lenslets, a focal distance of 20cm and a visibility of 0.93 is presented. It can be used as a Shack-Hartmann sensor for hard X-rays (SHARX) for wavefront sensing and permits for true single-shot multi-contrast imaging the dynamics of materials with a spatial resolution in the micrometer range, sensitivity on nanosized structures and temporal resolution on the microsecond scale. The object’s absorption and its induced wavefront shift can be assessed simultaneously together with information from diffraction channels. In contrast to the established Hartmann sensors the SHARX has an increased flux efficiency through focusing of the beam rather than blocking parts of it. We investigated the spatiotemporal behavior of a cavitation bubble induced by laser pulses. Furthermore, we validated the SHARX by measuring refraction angles of a single diamond CRL, where we obtained an angular resolution better than 4 μ rad.

Generalized pupil function of a compound X-ray refractive lens.

Quality of a refractive compound X-ray lens can be limited by imperfections in surfaces of unit lenses and stacking precision. In general case both the lens transmission and optical aberrations define properties of a beam in the lens exit plane; together they can be expressed in terms of the generalized pupil function. In this work we measure this function for a diamond single crystal compound refractive lens. Consequently, we apply the pupil function to evaluate the performance of the examined compound refractive X-ray lens. A number of practically important conclusions can be drawn from such analysis.

Planar PMMA X-ray compound refractive lenses with cascaded parabolic microstructures

X-ray compound refractive lenses (CRLs) have been successfully integrated into third- and fourth-generation synchrotron radiation sources. We have developed a new planar CRL architecture using cascaded parabolic microstructures constructed with polymethylmethacrylate. Two sets of CRL elements with different parabolic profile parameter values, radius of curvature R, and geometric aperture R0 were integrated. One half of the set had a large geometric aperture (R1=100μm and R01=141μm), while the other half of the set had a small radius of curvature (R2=50μm and R02=70μm). The cascaded parabolic CRLs (CP-CRLs) were tested for hard X-ray microfocusing in the BL15U1 beamline at the Shanghai Synchrotron Radiation Facility. Experimental results showed that the developed CP-CRLs achieved two-dimensional focusing of the incident X-ray beams. The measured focal length was 0.341 m, and the transmission was 10.12%. The measured horizontal and vertical full width half maxima of the focused X-ray spot were 9.78μm and 9.70μm, respectively. Thus, the experimental results obtained in this work confirmed the theoretical calculations of CP-CRL microfocusing performance.

Polymer X-ray refractive nano-lenses fabricated by additive technology.

The present work demonstrates the potential applicability of additive manufacturing to X-Ray refractive nano-lenses. A compound refractive lens with a radius of 5 µm was produced by the two-photon polymerization induced lithography. It was successfully tested at the X-ray microfocus laboratory source and a focal spot of 5 μm was measured. An amorphous nature of polymer material combined with the potential of additive technologies may result in a significantly enhanced focusing performance compared to the best examples of modern X-ray compound refractive lenses.

Effective aperture of X-ray compound refractive lenses.

A new definition of the effective aperture of the X-ray compound refractive lens (CRL) is proposed. Both linear (one-dimensional) and circular (two-dimensional) CRLs are considered. It is shown that for a strongly absorbing CRL the real aperture does not influence the focusing properties and the effective aperture is determined by absorption. However, there are three ways to determine the effective aperture in terms of transparent CRLs. In the papers by Kohn [(2002). JETP Lett. 76, 600-603; (2003). J. Exp. Theor. Phys. 97, 204-215; (2009). J. Surface Investig. 3, 358-364; (2012). J. Synchrotron Rad. 19, 84-92; Kohn et al. (2003). Opt. Commun. 216, 247-260; (2003). J. Phys. IV Fr, 104, 217-220], the FWHM of the X-ray beam intensity just behind the CRL was used. In the papers by Lengeler et al. [(1999). J. Synchrotron Rad. 6, 1153-1167; (1998). J.Appl. Phys. 84, 5855-5861], the maximum intensity value at the focus was used. Numerically, these two definitions differ by 50%. The new definition is based on the integral intensity of the beam behind the CRL over the real aperture. The integral intensity is the most physical value and is independent of distance. The new definition gives a value that is greater than that of the Kohn definition by 6% and less than that of the Lengeler definition by 41%. A new approximation for the aperture function of a two-dimensional CRL is proposed which allows one to calculate the two-dimensional CRL through the one-dimensional CRL and to obtain an analytical solution for a complex system of many CRLs.

Optical performance of materials for X-ray refractive optics in the energy range 8-100 keV.

A quantitative analysis of the crucial characteristics of currently used and promising materials for X-ray refractive optics is performed in the extended energy range 8-100 keV. According to the examined parameters, beryllium is the material of choice for X-ray compound refractive lenses (CRLs) in the energy range 8-25 keV. At higher energies the use of CRLs made of diamond and the cubic phase of boron nitride (c-BN) is beneficial. It was demonstrated that the presence of the elements of the fourth (or higher) period has a fatal effect on the functional X-ray properties even if low-Z elements dominate in the compound, like in YB66. Macroscopic properties are discussed: much higher melting points and thermal conductivities of C and c-BN enable them to be used at the new generation of synchrotron radiation sources and X-ray free-electron lasers. The role of crystal and internal structure is discussed: materials with high density are preferable for refractive applications while less dense phases are suitable for X-ray windows. Single-crystal or amorphous glass-like materials based on Li, Be, B or C that are free of diffuse scattering from grain boundaries, voids and inclusions are the best candidates for applications of highly coherent X-ray beams.

Hard-X-ray imaging of laser plasma using axisymmetric refractive lenses

An experimental scheme for studying laser-produced plasmas under extremal conditions with the aid of a compound refractive X-ray lens has been implemented. Laser-produced plasma bunches have been imaged in hard X-rays upon intense laser irradiation of a copper foil target.

High-resolution X-ray diffraction based on 1D and 2D refractive lenses

The results of studying a silicon-germanium (Si-Ge) nanoheterostructure using refractive X-ray optics are described. The diffraction patterns near the silicon Bragg-diffraction peak 400 in the focal plane of refractive lenses are recorded and analyzed. The experiments are carried out in two different geometries: using 1D and 2D X-ray compound refractive lenses.

On the use of a ZrO x -SiO2 multilayer structure as a test sample for high-resolution X-ray microscopy

An image of a ZrOx-SiO2 multilayer structure with a magnification factor of 46, recorded in the mode of high-resolution transmission electron microscopy, and the absorption profile of the multilayer structure, recorded by scanning X-ray microscopy, are obtained using X-ray compound refractive lenses (CRL). Based on these results, a conclusion can be drawn regarding the possibility of using the multilayer structure as a universal test object for high-resolution X-ray microscopy.

Recent Micro X-ray Focusing Optics and High-Pressure Applications at SPring-8

We have developed unique x-ray focusing optics by using compound x-ray refractive lens (CRL) designated for the high-pressure XRD beamline BL10XU [1] of SPring-8. The CRL is a set of planar cross-lenses with a quasi-parabolic profile for focusing in two directions, and are fabricated from the SU-8 polymer by deep x-ray lithography at the IMT in Germany [2]. The focusing optics consisted by two sets of CRL and a pinhole in tandem. The set of the upstream CRL and the pinhole as a virtual source are used for generation of homogeneously divergent beam. The downstream CRL, which is placed between a pinhole and a focal point (sample position), is utilized for focusing the x-ray towards the micron size. The focused beam size is defined by the relationship between a pinhole diameter and the ratio of source-lens versus lens-focal point distances. We have succeeded in focusing the x-ray beam down to 2.4 microns in vertical and 2.1 microns in horizontal, as we had designed, under the following conditions: 30 keV x-ray, 10 micron pinhole in diameter and 11:1 ratio of source-lens:lens-sample distances. The beam flux, which was converted to flux density as about 1015 cps/mm2, was enough strong to obtain XRD profiles in sub-second exposure, even at the sample condition under few hundred GPa. Using this system, we have obtained clearly districted XRD profiles from sub-structures of microns size in DAC, such as electrodes for electrical resistance measurement, micro-anvils settled in the sample chamber, and so on. Micro-beam technique will bring us new applications for high-pressure experiments, and become more important in order to enhance precise analysis, such as grains/elements distribution, partial melting, solution and/or chemical reactions in a sample chamber of DAC, as well as in order to collect high-quality XRD under above 500 GPa. Furtehrmore, the sub-micron beam focusing is now achievable and will be a key-technique for a probe of a scanning XRD microscope.

Design and fabrication of cascaded X-ray planar parabolic compound refractive lens

Due to its attractive features such as compact size, simple to align and wide working range of photon energy, the X-ray compound refractive lens (CRL) has gradually become one of the standard accessories to focus the X-ray beams from the synchrotron radiation light source. In this paper, a cascaded planar parabolic CRL is designed and fabricated. The novel CRL is composed of type Ⅰ and type Ⅱ refractive elements in order to achieve a small spot size while maintaining the transmission. In type I refractive element, the parabolic geometry aperture (R0) is large, while, in type Ⅱ refractive element, the radius of curvature (R) at the parabolic vertex is small. So N1 numbers of type I and N2 numbers of type Ⅱ refractive elements are cascaded to form a single-chip CRL. A cascaded X-ray planar parabolic CRL is constructed using PMMA material by means of LIGA techniques. The main structural parameters of type Ⅰ refractive elements are: N1=15, R1=200 μm, 2R01=564 μm. The main structural parameters of type Ⅱ refractive elements are: N2=20, R2=50 μm, 2R02=140 μm. The cascaded planar parabolic CRL is tested on the beam line whose original incident X-ray spot is 200 μm×100 μm at Shanghai synchrotron radiation facility. The measured lateral focusing spot size is 24.9 μm@8 keV, the transmission rate is 2.19% and the focal length is 1.052 m.

Beamline BL-07 at Indus-2: a facility for microfabrication research

The X-ray lithography beamline on Indus-2 is now operational, with two modes of operation. With a pair of X-ray mirrors it is possible to tune the energy spectrum between 1 and 20 keV with a controlled spectral bandwidth. In its 'no optics' mode, hard X-rays up to 40 keV are available. Features and performance of the beamline are presented along with some example structures. Structures fabricated include honeycomb structures in PMMA using a stainless steel stencil mask and a compound refractive X-ray lens using a polyimide-gold mask in SU-8.

At-wavelength metrology using the X-ray speckle tracking technique: case study of a X-ray compound refractive lens

The X-ray speckle tracking technique has been established on the Test beamline B16 at Diamond and is being used as a valuable tool for at-wavelength metrology. We show here the possibilities and the achievable performances of the X-ray Speckle Tracking technique for optics characterization: the description is illustrated with the case study of the characterization of a compound refractive lens. This optical element was characterized online using the speckle tracking method with nanoradian accuracy and micrometer spatial resolution. For discussion purpose, the results are compared to the ones obtained under similar conditions using a grating interferometer.