Biomedical subjects

J Hrdý

Publications and source records attributed to J Hrdý.

12 recordsLinked to original sources

PubMed2006

Diffractive-refractive optics in the Laue case: first experiment.

The possibility of sagittally focusing synchrotron radiation using an asymmetric Laue crystal with profiled surfaces has been experimentally demonstrated for the first time. The sample was a Si single crystal with two parallel cylindrical holes of diameter 8 mm. The axes of the holes formed an angle of 7.95 degrees with the (111) diffracting planes and were arranged vertically with respect to the diffracting planes. 15.35 keV synchrotron radiation was diffracted in the space between the holes. The minimum thickness of this Laue crystal was 0.5 mm. The diffracted beam formed an angle of 0.55 degrees with the exit surface. The experiment was performed at beamline BM05 at the ESRF. The length of the beamline was not sufficiently long to detect the focus, but the experiment clearly showed that the diffracted beam was sagittally convergent.

Crystallization↗

PubMed2003

Diffractive refractive optics: the possibility of sagittal focusing in Laue-case diffraction.

The sagittal deviation of a Laue-diffracted X-ray beam caused by the inclination of an exit crystal surface with respect to an entrance crystal surface has been studied both theoretically and experimentally. The use of this effect for sagittal focusing of X-ray synchrotron radiation diffracted by a Laue crystal is suggested. The focusing is based on the refraction effect due to the parabolic profile of an exit or/and entrance surface. The crystal is not bent. In order to achieve a reasonable focusing distance, the crystal should be cut asymmetrically. The experiment was performed at beamline BM5 at the ESRF.

Journal Article↗

PubMed2001

Sagittal focusing of synchrotron radiation diffracted on the walls of a longitudinal hole drilled into a single-crystal monochromator.

A very simple method of sagittal focusing of X-ray synchrotron radiation is presented. A special ray-tracing program which utilizes the diffraction-refraction effect is developed. It is demonstrated both by ray-tracing simulations and by an experiment whereby a reasonably good sagittal concentration of 8 keV synchrotron radiation may be achieved by diffraction on the walls of a cylindrical hole drilled into an Si crystal. The holes were drilled parallel to the (111) planes and their diameter, 1 mm, was chosen so that the focusing distance fits the geometrical arrangement of beamline BM5 at the ESRF. Two such crystals have been used in a dispersive and non-dispersive arrangement. The better result was achieved using the dispersive arrangement. The intensity at the centre of the focus is increased by five times with respect to unfocused radiation. Excellent agreement exists between the ray-tracing simulations and experimental results.

Journal Article↗

PubMed2001

Refraction in general asymmetric X-ray Bragg diffraction.

When the surface of a single-crystal monochromator is not parallel to the diffracting crystallographic planes, the diffracted beam is generally deviated from the plane of diffraction and the angle between the diffracted beam and the diffracting planes is different from the angle between the incident beam and the diffracting planes. The angular diffraction regions for the incident and diffracted beams are also different. This is the manifestation of the refraction occurring during Bragg diffraction. Very simple formulae are presented which describe this situation in a general case (e.g. for a rotated-inclined X-ray monochromator). These formulae allow sagittally focusing monochromators for synchrotron radiation to be easily designed, based on X-ray diffraction-refraction phenomena. Some important properties of such types of monochromators are deduced.

Journal Article↗

PubMed2001

First observation of meridional focusing of an X-ray beam using diffraction by a crystal with a transverse groove.

The possibility of concentrating a synchrotron X-ray beam using diffraction by a single crystal with a properly designed transverse groove on its surface, suggested earlier, has been studied experimentally. Here, the first experimental demonstration of this effect is reported, performed on beamline BM5 at the ESRF. The experimental result confirms the theoretical model.

Journal Article↗

PubMed2000

X-ray diffraction on Si single crystal with a W-shaped longitudinal groove.

The measurement of the sagittal deviation of an X-ray beam diffracted on the inclined surface of an Si(111) single crystal was performed on beamline BM5 at the ESRF, with lambda = 0.1 nm and an inclination angle, beta, of 70 degrees . The measured value agrees with the theory developed in previous papers. The topographic picture of the longitudinal edge shows a structure that can be explained in terms of the properties of inclined diffraction.

Journal Article↗

PubMed2000

Meridional focusing of X-rays diffracted onto a single crystal with a transversal groove (Bragg-diffraction asymmetric lens).

It is shown that a properly designed transversal groove machined into the surface of a single-crystal monochromator may concentrate (focus) the diffracted radiation meridionally. From this result and from previous papers on the Bragg-diffraction inclined lens it follows that a properly designed depression fabricated into the surface of a single-crystal monochromator should provide two-dimensional focusing of a diffracted synchrotron radiation beam.

Journal Article↗

PubMed1998

X-ray inclined lens.

As defined here, the term ;inclined lens' means a longitudinal parabolic groove fabricated into a crystal monochromator. If properly designed, it should provide the horizontal (sagittal) focusing of an X-ray beam. The focusing is based on the sagittal deviation of the beam diffracted on the wall of the groove. This effect follows from the dynamical theory of inclined diffraction. The focusing efficiency is limited compared with other methods. On the other hand, the simplicity is the main advantage of this device. The exact shape of the groove is calculated and several methods of keeping the vertical dimension of the beam small are proposed.

Journal Article↗

PubMed1998

Rotated-inclined double-crystal monochromator for synchrotron radiation: aberration and its compensation.

A rotated-inclined double-crystal X-ray monochromator was designed for high-power undulator beamlines for SPring-8 to reduce the impinging radiation power density. Recently, it has been shown that an inclined double-crystal monochromator suffers from a certain type of geometrical aberration that may be relatively easily compensated. In this paper, it is shown that a similar aberration exists also in the case of rotated-inclined monochromators and that as in the inclined case the aberration may also be compensated.

Journal Article↗

PubMed1998

Finite-element study of a toothed-crystal monochromator.

A toothed-crystal monochromator, proposed in previous papers, is a modification of an inclined monochromator, which reduces the impinging radiation power density on the surface of a crystal for broad synchrotron radiation beams. The surface of the monochromator has a triangular toothed structure oriented in such a way that it represents an inclined monochromator. Finite-element analysis of thermally induced deformation was performed for a particular shape of toothed crystal and for a flat crystal of the same average thickness. It was estimated that the toothed-crystal monochromator may provide 70% higher radiation power than the flat-crystal monochromator.

Journal Article↗

PubMed1998

Observation of horizontal focusing of X-rays using a toothed-crystal monochromator.

The behaviour of a toothed-crystal monochromator for synchrotron radiation was studied for the first time on the GILDA CRG beamline at the ESRF. A new kind of horizontal focusing was observed which may be attributed to the properties of inclined diffraction. We have also observed a vertical focusing of the beam, the nature of which remains unexplained.

Journal Article↗

PubMed1995

Compensation of Aberration of Inclined X-ray Monochromators.

Inclined double-crystal monochromator for synchrotron radiation suffer from aberration that is connected with the horizontal divergence of the synchrotron radiation beam. Two different methods are proposed to compensate for this aberration. The first method introduces slightly different angles of inclination for the first and the second monochromator crystals. The condition for the difference of the angles of inclination is Bragg angle dependent and also depends on the projection of the distance of both crystals onto the direction of the normal to the diffracting planes. The second method uses an additional inclined double-crystal monochromator cut such that the aberration introduced by the first pair of crystals is nearly completely compensated by the second pair of crystals. This method is independent of wavelength. Both methods are illustrated by ray tracing.

Journal Article↗