Parabolic Compound Refractive Lenses Research Articles

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.

Parabolic single-crystal diamond lenses for coherent x-ray imaging

We demonstrate parabolic single-crystal diamond compound refractive lenses designed for coherent x-ray imaging resilient to extreme thermal and radiation loading expected from next generation light sources. To ensure the preservation of coherence and resilience, the lenses are manufactured from the highest-quality single-crystalline synthetic diamond material grown by a high-pressure high-temperature technique. Picosecond laser milling is applied to machine lenses to parabolic shapes with a ≃1 μm precision and surface roughness. A compound refractive lens comprised of six lenses with a radius of curvature R=200 μm at the vertex of the parabola and a geometrical aperture A=900 μm focuses 10 keV x-ray photons from an undulator source at the Advanced Photon Source facility to a focal spot size of ≃20×90 μm2 with a gain factor of ≃50−100.

Measurement of coherence length and incoherent source size of hard x-ray undulator beamline at Pohang Light Source-II.

We measured the spatial coherence length and incoherent source size of a hard x-ray undulator beamline at Pohang Light Source-II, the stored electron energy of which has been increased from 2.5 GeV to 3 GeV. The coherence length was determined by single-slit measurement of the visibility of the Fresnel diffraction pattern. The correlated incoherent source size was cross-checked for three different optics: the single slit, beryllium parabolic compound refractive lenses, and the Fresnel zone plate. We concluded that the undulator beamline has an effective incoherent source size (FWHM) of 540 μm (horizontal) × 50 μm (vertical).

Development of high aspect ratio X-ray parabolic compound refractive lens at Indus-2 using X-ray lithography

A synchrotron beamline dedicated to soft and deep X-ray lithography is operational on Indus-2 synchrotron source and is being used for high aspect ratio microfabrication. This X-ray lithography facility provides the access to X-ray mask fabrication, X-ray exposures and development of micro-nano structures. We report the development of planar parabolic refractive X-ray lenses in SU-8 for energy range 8---20 keV using this facility. The focussing properties of X-ray lenses were studied with synchrotron radiation in the X-ray energy range 8---20 keV on the moderate emittance machine Indus-2. A focal spot of 11 μm at 15.9 keV is obtained with a gain of 18.

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.

The role of single element errors in planar parabolic compound refractive lenses

The propagation of X-rays through a compound refractive lens (CRL) with imperfect CRL elements is investigated. The trajectories of random rays within the geometrical optics regime are calculated in one plane using Monte Carlo methods. Three different lenses were simulated: Be, Al and Ni lenses designed for photon energies of 20 keV, 60 keV and 175 keV, respectively. The results show that while transverse displacements of single elements in a CRL do not influence imaging resolution, rotational errors can be important. Systematic calculations of aberrations owing to the deviation of the element's surface from a perfect parabolic shape are also presented.

High resolution x-ray microscope

The authors present x-ray images of grid meshes and biological material obtained using a microspot x-ray tube with a multilayer optic and a 92-element parabolic compound refractive lens (CRL) made of a plastic containing only hydrogen and carbon. Images obtained using this apparatus are compared with those using an area source with a spherical lens and a spherical lens with multilayer condenser. The authors found the best image quality using the multilayer condenser with a parabolic lens, compared to images with a spherical lens and without the multilayer optics. The resolution was measured using a 155-element parabolic CRL and a multilayer condenser with the microspot tube. The experiment demonstrates about 1.1μm resolution.

Ray-tracing simulation of parabolic compound refractive lenses

X-ray compound refractive lenses (CRL) are becoming a widespread tool for the generation of microfocus spot sizes at synchrotron beamlines. The calculation of their performance by means of ray-tracing is useful for a rapid estimation of flux, resolution and focusing properties achievable in a beamline, when other optics are present, or simply to study the lens acceptance and focusing in the presence of a particular bending magnet, wiggler or undulator X-ray source. The ray-tracing method presented in this paper has been used to calculate the efficiency of beryllium CRL's using, for the instrument layout, realistic source size and divergence, and usual optics like perfect crystal monochromators. It is shown that the intensity transmitted by the lens, the effective aperture and the gain are in good agreement with analytical formulas. Additional information provided when running the program are the precise shape of beam at the focus, and at any position along the optical axis. For instance the intensity distribution at the CRL entrance and exit planes allows a comparison between the effective and the geometrical apertures. Finally, the method provides a precise value for the lens focal distance, which depends on the CRL length.

Small-angle options of the upgraded ultrasmall-angle x-ray scattering beamline BW4 at HASYLAB

We present the upgrade and present status of the ultrasmall-angle x-ray scattering (USAXS) beamline BW4 at the Hamburg Synchrotronstrahlungslabor. In order to extend the accessible scattering vector range, new small-angle setups have been established, making use of the high flux and small divergence of BW4. In standard transmission geometry using a beam size of B=400×400μm2 (horizontal×vertical), typical small-angle resolution ranges from dmax=90to650nm, depending on sample-to-detector distance. Additionally a new microfocus option has been established. This microfocus option allows reducing the sample size by one order of magnitude. Using parabolic beryllium compound refractive lenses, a new standard beam size of B=65×35μm2 (horizontal×vertical) can be provided. The μ-SAXS resolution is as high as dmax=150nm. Using μ-SAXS in combination with grazing incidence (μ-GISAXS) on a standard noble metal gradient multilayer, we prove the feasibility of μ-GISAXS experiments at a second generation source.

X-ray parabolic lenses made from glassy carbon by means of laser

Parabolic planar compound refractive lenses (CRLs) made from glassy carbon by means of laser ablation are presented. They have radii of curvatures of 5 and 200μm and geometric apertures of 40 and 900μm, respectively. The numbers of biconcave elements in the CRLs were 4, 7, and 200. The planar lenses allow formation of a linear focus of length comparable with the depths of their profiles. Usage of two CRLs in a crossed geometry provides formation of two-dimensional focus. The lenses were tested at the European Synchrotron Radiation Facility at the bending magnet beam line BM-5. The minimum experimental size of the focus has been achieved as 1.4μm.

Planar parabolic X-ray refractive lens made of glassy carbon

Experimental results of synchrotron radiation focusing by parabolic planar compound refractive lenses, made of glassy carbon, are presented. The lenses with the curvature radius of 5 and 200 μm, and with the geometric aperture of 40 and 900 μm were developed. The number of bi-concave elements in the compound lenses was from 4 to 200. The experiments were performed at the ESRF at the bending magnet beamline BM-5. The minimum size of the focus was observed as 1.4 μm.

Multi-prism x-ray lens

Refractive x-ray lenses with a triangular surface profile have been used to focus a synchrotron beam to sub-μm line width. These lenses are free from spherical aberration and work in analogy with one-dimensional focusing parabolic compound refractive lenses. However, the focal length can be easily varied by changing the gap between the two jaws. Silicon lenses were fabricated by wet anisotropic etching, and epoxy replicas were molded from the silicon masters. The lenses provided intensity gains up to a factor of 32 and the smallest focal line width was 0.87 μm. The simplified geometry and associated fabrication technique open possibilities for low-Z materials such as beryllium, which should greatly enhance the performance of refractive x-ray optics.

High resolution imaging and lithography with hard x rays using parabolic compound refractive lenses

Parabolic compound refractive lenses are high quality optical components for hard x rays. They are particularly suited for full field imaging, with applications in microscopy and x-ray lithography. Taking advantage of the large penetration depth of hard x rays, the interior of opaque samples can be imaged with submicrometer resolution. To obtain the three-dimensional structure of a sample, microscopy is combined with tomographic techniques. In a first hard x-ray lithography experiment, parabolic compound refractive lenses have been used to project the reduced image of a lithography mask onto a resist. Future developments are discussed.

Hard X-ray full field microscopy and magnifying microtomography using compound refractive lenses

For hard X-rays, parabolic compound refractive lenses (PCRLs) are genuine imaging devices like glass lenses for visible light. Based on these new lenses, a hard X-ray full field microscope has been constructed that is ideally suited to image the interior of opaque samples with a minimum of sample preparation. As a result of a large depth of field, CRL micrographs are sharp projection images of most samples. To obtain 3D information about a sample, tomographic techniques are combined with magnified imaging.

Refractive lenses as a beam diagnostics tool for high-energy synchrotron radiation

Parabolic compound refractive lenses (CRLs) for hard X rays have been used to image the electron beam at undulator and bending-magnet beamlines at the ESRF. The measurements yield the shape and size of the synchrotron radiation source, and show that CRLs with paraboloid surface shape can be used as a beam diagnostics tool at high-energy electron storage rings. The optical resolution of the imaging setup can be as small as 4 μm . This is smaller than typical values of the electron beam size in third-generation synchrotron sources. We report measurements at two ESRF beamlines and resolution calculations taking into account the properties of synchrotron radiation and the transmission characteristics of the CRLs used.

A microscope for hard x rays based on parabolic compound refractive lenses

We describe refractive x-ray lenses with a parabolic profile that are genuine imaging devices, similar to glass lenses for visible light. They open considerable possibilities in x-ray microscopy, tomography, microanalysis, and coherent scattering. Based on these lenses a microscope for hard x rays is described, that can operate in the range from 2 to 50 keV, allowing for magnifications up to 50. At present, it is possible to image an area of about 300 μm in diameter with a resolving power of 0.3 μm that can be increased to 0.1 μm. This microscope is especially suited for opaque samples, up to 1 cm in thickness, which do not tolerate sample preparation, like many biological and soil specimens.