H. R. Beguiristain

Two-dimensional x-ray focusing from compound lenses made of plastic

We have measured the intensity profile and transmission of x rays focused by a series of either spherical or parabolic lenses fabricated using Mylar® (C5H4O2) or Kapton® (polyimide). The use of plastics can extend the range of operation of compound refractive lenses, improving transmission and aperture size and reducing focal length. The number of unit lenses range from 193 to 600 for each compound refractive lens. Two-dimensional focusing was obtained for photon energies 8–14 keV with imaging distances of less than 1 m. For example, full-width-half-maximum linewidths down to 16 μm at a distance of only 47 cm from the lens were achieved at 9 keV. The effective apertures of the refractive lenses were measured between 250 and 364 μm with peak transmissions between 10% and 33%.

CYLINDRICAL COMPOUND REFRACTIVE X-RAY LENSES USING PLASTIC SUBSTRATES

We have measured the intensity profile of x rays focused by compound refractive lenses (CRLs) fabricated using acrylic (Lucite) and polyethylene plastics. A linear array of closely spaced holes acts as multiple cylindrical lenses. The important parameters for this type of focusing are the focal length and absorption, and, for wavelengths shorter than 3 A, low atomic number plastics are suitable. We have experimentally demonstrated that we can achieve one-dimensional focusing for photon energies between 9 and 19.5 keV with focal lengths between 20 and 100 cm. For example, using 12 keV x rays we have achieved focal full width at half maximum linewidths down to 21 μm at a distance of only 20 cm from the CRL. The x-ray source was a synchrotron emitter whose source size in the vertical dimension was 445 μm.

The Effect of Unit Lens Alignment and Surface Roughness on X-ray Compound Lens Performance

The required alignment tolerances and surface roughness for unit lens elements in a compound refractive lens (CRL) for x rays are discussed. Contrary to what one might expect and what has been stated in the patent literature, alignment tolerances are large and for typical parameter values the effect of misalignment is minor. For a parabolic lens the focusing properties of the CRL are unaltered by misalignment and there is a small increase in absorption. For a lens with spherical aberration, there is a slight change in focal length, a minor translation of the image, and a small increase in absorption. This article also shows that lens gain is not appreciably reduced if the phase shift that is introduced by the roughness is limited to ±π/4 or if the transverse period of the roughness exceeds a specified value. The CRL can benefit from a managed misalignment of the elements to reduce the phase error introduced by surface imperfections of the lens.

A simple neutron microscope using a compound refractive lens

Images obtained with a high-magnification simple neutron microscope using a compound refractive lens are presented in this letter. The short focal length of the stack of Al biconcave lenses facilitated the setup of a simple neutron microscope at the D22 small angle scattering beam line at the Institut Laue Langevin, Grenoble, France that achieved a 35× magnification and a 214 μm resolution. Higher-resolution images could be obtained using improved neutron lens systems that enhance beam delivery from neutron sources and produce high-quality images in combination with higher resolution two-dimensional neutron detectors.

X-ray focusing with compound lenses made from beryllium.

We have measured the intensity profile and transmission of x rays focused by a series of biconcave spherical unit lenses fabricated from beryllium. The use of beryllium extends the range of operation of compound refractive lenses, improving transmission, aperture size, and gain. The compound refractive lens was composed of 160 biconcave unit lenses, each with a radius of curvature of 1.9 mm. Two-dimensional focusing with a gain of 1.5 was obtained at 6.5 keV with a focal length of 93 cm. The effective aperture of the compound refractive lens was measured as 600 mum , with 9% peak transmission.

Large aperture compound lenses made of lithium

We have measured the intensity profile and transmission of x rays focused by a series of biconcave parabolic unit lenses fabricated in lithium. For specified focal length and photon energy lithium compound refractive lenses (CRL) have a larger transmission, aperture size, and gain compared to aluminum, kapton, and beryllium CRLs. The lithium compound refractive lens was composed of 335 biconcave, parabolic unit lenses each with an on-axis radius of curvature of 0.95 mm. Two-dimensional focusing was obtained at 8.0 keV with a focal length of 95 cm. The effective aperture of the CRL was measured to be 1030 μm with on-axis (peak) transmissions of 27% and an on-axis intensity gain of 18.9.

Compound refractive lenses for novel X-ray sources

Abstract We have measured the intensity profile of X-rays focused by a linear array of closely spaced spherical lenses fabricated using Mylar (C5H4O2). We have experimentally demonstrated that we can achieve two-dimensional focusing for photon energies between 7 and 9 keV with imaging distances of less than 1 m. For example, using 8-keV X-rays we have achieved full-width-at-half-maximum (FWHM) linewidths down to 27.5 μm at a distance of only 62 cm from the lens. The effective aperture of the lens was measured to be about 390 μm with 38% transmission at 9 keV. A synchrotron source having source-size dimensions of 0.44×1.7 mm2 was utilized for the experimental work. Such lenses are seen as useful for focusing and increasing the intensity of novel X-ray sources that are directional and have small source size (σ

Compound x-ray refractive lenses made of polyimide

Theoretical considerations of the parameters that enable the construction of compound refractive lenses are treated in this writing. The best performing compound refractive lenses that have been constructed to date were made by Adelphi Technology Inc. stacking individual paraboloidal lenses made of polyimide (KaptonTM). Polyimide lenses are capable of focusing photon with energies between 4 keV and 60 keV with focal lengths below 60 cm. They are not affected much by small misalignment of the individual lenses. Surface finish is less stringent than for visible light lenses. The increase in intensity in the image plane relative to the intensity that would have been obtained without a lens or gain measured at the experimental station of a bend magnet beam line was found to be 5.5 at 9 keV x-rays with transmission of 10% at that same energy. The measured values were in good agreement with the theoretical predictions at all wavelengths tested.

Development of Compound Refractive Lenses for x-rays

One-dimensional and rotationally axisymmetric two-dimensional focusing of x-rays by plastic Compound Refractive Lens (CRL) systems are demonstrated and theoretical aspects behind the design of x-ray CRLs are presented in this report. X-rays between 8 and 19.5 keV were focused by cylindrical CRLs having focal lengths between 35 and 100 cm and fabricated using acrylic (Lucite) and polyethylene. Focusing of x-rays by a spherical CRL was also demonstrated observing a focal length of 85 cm and an effective aperture of about 320 μm for 8 keV x-rays. The gain, which is the increase in intensity in the image plane relative to the intensity that would have been obtained without a lens on that plane, was 1.5 for 8 keV photons. The gain of this spherical CRL scales about three orders of magnitude higher on undulator beam lines at third generation x-ray sources from the results obtained at the bending magnet x-ray source, with dimensions 445 μm in the vertical and 1700 μm in the horizontal, used in this work.

Optics for coherent x-ray sources

Several laboratories are now in the process of designing and constructing coherent x-ray sources, and application of these beams for radiography and material studies is facilitated by having appropriate optical components to provide collimation or focusing. Control of x-rays can be achieved by employing elements that perform refraction, diffraction or reflection, as exemplified by a lens, grating or mirror, respectively. Of course, the maximum intensity of minimum image size that is obtainable from any of these elements is determined by diffraction effects. Using the parameters of the Liinac Coherent Light Source (LCLS) being studied at the Stanford Synchrotron Radiation Laboratory (SSRL), x-ray optical components can increase the beam intensity approximately eight orders of magnitude and provide submicron images. Performance comparisons are made between the zone plate, the phase zone plate, the compound refractive lens, the Fresnel compound refractive lens, and the parabolic mirror.