Gilles Cauchon

Automatic alignment of a Kirkpatrick-Baez active optic by use of a soft-x-ray Hartmann wavefront sensor.

We present what we believe to be the first automatic alignment of a synchrotron beamline by the Hartmann technique. Experiments were performed, in the soft-x-ray range (E=3 keV, lambda=0.414 nm), by using a four-actuator Kirkpatrick-Baez (KB) active optic. A system imaging the KB focal spot and a soft-x-ray Hartmann wavefront sensor were used alternatively to control the KB optic. The beam corrected with the help of the imaging system was used to calibrate the wavefront sensor. With both closed loops, we focused the beam into a 6.8 microm x 9 microm FWHM focal spot.

IMAGING OF LASER PRODUCED PLASMA AT 1.43 KEV USING FRESNEL ZONE PLATE AND BRAGG-FRESNEL LENS

X-ray imaging of plasmas with a resolution on the order of 1 μm could not be achieved with pinholes because the light flux on the detector would be too low. We tested two different types of diffractive lenses derived from the circular grating based on the Fresnel zones. Compared to pinholes, they can have an equivalent diameter of about 100 μm with a resolution of about 1 μm. The two kinds of devices tested were: (1) a transmission phase Fresnel zone lens (PFZL) associated with a multilayer mirror; (2) a reflective Bragg–Fresnel lens (BFL) which combines a multilayer mirror and the grating. The PFZL works at normal incidence by transmission; an additional mirror is used to reflect only a small bandwidth within the spectrum; the angle of reflection of the multilayer of the imaging beam on the mirror is set as to adjust the center of the useful bandwidth. The BFL works at fixed grazing incidence and we only use an off-axis part of the BFL in order to avoid the illumination of the detector by zeroth order di...

Wavefront Closed‐Loop Correction for X‐Ray Microfocusing Active Optics

Automatic alignment of a synchrotron beamline by Hartmann technique was performed, in the soft X‐ray range (E = 3 keV, λ = 0.414 nm), using a 4‐actuators Kirkpatrick‐Baez (KB) active optic. A system imaging the KB focal spot and a soft X‐ray Hartmann wave‐front sensor were used alternatively to control the KB. The beam corrected with the help of the imaging system was used to calibrate the wave‐front sensor. With both closed loops, we focused the beam into a 6.8×9 μm2 FWHM focal spot. Closed‐loop corrections are limited by the optical quality of the imaging system.

X-ray beam metrology and X-ray optic alignment by Hartmann wavefront sensing

In 2002, first experiments at the Advanced Light Source (ALS) at Berkeley, allowed us to test a first prototype of EUV Hartmann wave-front sensor. Wave-front measurements were performed over a wide wavelength range from 7 to 25 nm. Accuracy of the sensor was proved to be better than λEUV/120 rms (λEUV = 13.4 nm, about 0.1 nm accuracy) with sensitivity exceeding λEUV/600 rms, demonstrating the high metrological performances of this system. At the Swiss Light Source (SLS), we succeeded recently in the automatic alignment of a synchrotron beamline by Hartmann technique. Experiments were performed, in the hard X-ray range (E = 3 keV, λ = 0.414 nm), using a 4-actuators Kirkpatrick-Baez (KB) active optic. An imaging system of the KB focal spot and a hard X-ray Hartmann wave-front sensor were used alternatively to control the KB. The imaging system used a genetic algorithm to achieve the highest energy in the smallest spot size, while the wave-front sensor used the KB influence functions to achieve the smallest phase distortions in the incoming beam. The corrected beam achieved with help of the imaging system was used to calibrate the wave-front sensor. With both closed loops, we focused the beam into a 6.8x9 μm2 FWHM focal spot. These results are limited by the optical quality of the imaging system.

Numerical and experimental study of grating efficiency for synchrotron monochromators

The development of third-generation synchrotron sources has stimulated efforts toward high-resolution monochromators. A good knowledge of grating efficiency is needed to achieve an optimal compromise between resolution and photon flux. Because simple geometric models fail to describe correctly the gratings properties in the UVtosoft-X-ray range, we have developed a simulation software based on differential theory. A simplified R-matrix propagation algorithm assures the numerical stability of the code for deep gratings. Our numerical results are compared with previous research on deep gratings. Experimental and numerical studies have been performed on some test cases at a synchrotron source. Very good agreement between numerical prediction and measurement has been found.

The tomography beamline ANATOMIX at Synchrotron SOLEIL

ANATOMIX is a 200-m-long undulator beamline for full-field tomography techniques at photon energies from 5 to 25 keV. It is currently under construction at Synchrotron SOLEIL, the French national light source near Paris. ANATOMIX will feature experimental stations both for parallel-beam microtomography (with a beam of up to 40 mm width) and for zone-plate transmission X-ray microscopy (down to pixel sizes of 30 nm) in absorption and phase contrast. The location of ANATOMIX on a canted straight section of the SOLEIL storage ring implies specific challenges for the design and operation conditions of the beamline. In this paper we present general design aspects and the status of construction.

New optical setup for the generation of variable spot size on third generation synchrotron beamlines

In third generation synchrotron radiation beamlines, a focussed X-ray beam is often employed. However, in some cases users need to modify their spot size in order to match the broad range of samples sizes. This is the case for XPEEM microscopy beamline which need a homogeneous beam with a spot size varying from 2 to 50 μm. These specifications requires that the beamline works out of focus, and in this case the spot becomes non homogenous (as already observed experimentally on several synchrotron beamlines). In this paper, we will explain, using a geometrical approach, that this effect on the spot is produced by mirrors slope errors. We propose a new optical solution that overcomes these difficulties. Our optical solution has been validated experimentally on the second branch of the Nanospectroscopy beamline at Elettra, where we have obtained homogenous spot sizes of 10, 20 and 30 μm with the same optical design.

Technical Report: X-ray Wave-Front Measurements and X-ray Active Optics

In 2002, under a close collaboration with the Center for X-ray Optics (CXRO), we used ALS beamline 12.0 to perform the first experimental demonstration of wave-front analysis via the Hartmann technique in the EUV spectral range.

CARPEM: a computer code for predicting the diffraction efficiency of soft x-ray gratings and its application to VGD gratings optimization

We have developed a LURE a code to predict the efficiency of gratings. The code is based on differential theory and uses a simplified R-matrix propagation algorithm to obtain numerical stability on the whole range from visible to hard x-rays. Experimental and numerical studies have been performed on some test cases at a synchrotron source. A good agreement between numerical prediction and measurements has been found. The code is a rigorous application of electromagnetic theory and gives exact results as long as accurate optical constants can be attributed to grating materials. Such rigorous calculations provide an important tool for the optical engineering of modern synchrotron monochromator gratings. We give an example of application of this code to the engineering of a modern beam line and for the optimization of harmonic rejection.

New Optical Setup for the Generation of Variable Spot Size on Third Generation Synchrotron Beam lines

In third generation synchrotron radiation beamlines, a focussed X‐ray beam is often employed. However, in some cases users need to modify their spot size in order to match the broad range of samples sizes. This is the case for XPEEM microscopy beamline which need a homogeneous beam with a spot size varying from 2 to 50 μm. These specifications requires that the beamline works out of focus, and in this case the spot becomes non homogenous (as already observed experimentally on several synchrotron beamlines). In this paper, we will explain, using a geometrical approach, that this effect on the spot is produced by mirrors slope errors. We propose a new optical solution that overcomes these difficulties. Our optical solution has been validated experimentally on the second branch of the Nanospectroscopy beamline at Elettra, where we have obtained homogenous spot sizes of 10, 20 and 30 μm with the same optical design.