Measurement of X-ray Beam Coherence along Multiple Directions Using 2-D Checkerboard Phase Grating

Summary

The measurement protocol and data analysis procedure are given for obtaining transverse coherence of a synchrotron radiation X-ray source along four directions simultaneously using a single 2-D checkerboard phase grating. This simple technique can be applied for complete transverse coherence characterization of X-ray sources and X-ray optics.

Abstract

A procedure for a technique to measure the transverse coherence of synchrotron radiation X-ray sources using a single phase grating interferometer is reported. The measurements were demonstrated at the 1-BM bending magnet beamline of the Advanced Photon Source (APS) at Argonne National Laboratory (ANL). By using a 2-D checkerboard π/2 phase-shift grating, transverse coherence lengths were obtained along the vertical and horizontal directions as well as along the 45° and 135° directions to the horizontal direction. Following the technical details specified in this paper, interferograms were measured at different positions downstream of the phase grating along the beam propagation direction. Visibility values of each interferogram were extracted from analyzing harmonic peaks in its Fourier Transformed image. Consequently, the coherence length along each direction can be extracted from the evolution of visibility as a function of the grating-to-detector distance. The simultaneous measurement of coherence lengths in four directions helped identify the elliptical shape of the coherence area of the Gaussian-shaped X-ray source. The reported technique for multiple-direction coherence characterization is important for selecting the appropriate sample size and orientation as well as for correcting the partial coherence effects in coherence scattering experiments. This technique can also be applied for assessing coherence preserving capabilities of X-ray optics.

Introduction

The third-generation hard X-ray synchrotron radiation sources, such as the APS at ANL, Lemont, IL, USA (http://www.aps.anl.gov), have had tremendous impacts on the development of X-ray sciences. A synchrotron radiation source generates a spectrum of electromagnetic radiations, from infrared to X-ray wavelengths, when charged particles, such as electrons, are made to move near the speed of light in a circular orbit. These sources have very unique properties such as high brightness, pulsed and pico-second timing structure, and large spatial and temporal coherence. X-ray beam spatial coherence is an important parameter of the third and fourth generation synchrotron sourc....

Protocol

1. Planning of the Experiment

1. Identify the synchrotron beamline. Contact beamline scientist to find the appropriateness of the experiment at that beamline.
   NOTE: Experiments reported in this manuscript were performed at the 1-BM-B beamline, which is dedicated to optics and detectors testing, under XSD of APS.
2. Submit a user proposal and beam time request.
3. Work out the details of the experiment with the beamline scientist and specify the required instruments including motorized stages for the grating and detector alignment, 2-dimensional detector (CCD or CMOS), long translation stage covering the least and farthest distances needed b....

Results

While detailed experimental and simulation results could be found elsewhere⁸, this section only shows selected results to illustrate the above measurement and data analysis procedures. Figure 1 represents the experiment setup at the APS 1-BM-B beamline. The beam size is defined by a 1×1 mm² slit placed upstream of the Double Crystal Monochromator (DCM) and 25 m from the bending magnet source. The DCM is tuned to output photon energy of 18 keV. The X-ray beam passes through several B.......

Discussion

Figure 5 shows the estimated transverse coherence length along all four directions. Clearly, the 90° direction has higher ξ_θ compared to 0° direction. Since the beamline optics has negligible effect on the beam coherence at the grating relative location, the measured coherence area is inversely proportional to the source size area. The presented X-ray beam coherence measurement technique maps this accurately which can be shown as an ellipse with its major axis alon.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
1-BM-B bending magnet X-ray source	Advanced photon Source/ Argonne National Lab		http://www.aps.anl.gov/Xray_Science_Division/Optics/Beamline/
LYSO Scintillator	Proteus Inc		http://www.apace-science.com/proteus/lyso.htm#top
Coolsnap HQ2 CCD detector	Photometrics		http://www.photometrics.com/products/ccdcams/coolsnap_hq2.php
ATC 2000 UHV sputtering deposition system	AJA International Inc		http://www.ajaint.com/systems_atc.htm
MICROPOSIT S1800 photoresist	Dow
MICROPOSIT 351 developer	Dow
MA/BA6 lithography system	SUSS MicroTec		http://www.suss.com/en/products-solutions/products/mask-aligner/maba6/overview.html
Spin coater WS-400-6NPPB	Laurell Technologies Corporation		http://www.laurell.com/spin-coater/?model=WS-400-6NPP-LITE
JBX-9300FS electron beam lithography system	JEOL		http://www.jeolusa.com/PRODUCTS/PhotomaskDirectWriteLithography/ElectronBeamLithography/JBX-9500FS/tabid/245/Default.aspx
CS-1701 RIE system	Nordson March		http://www.nordson.com/EN-US/DIVISIONS/MARCH/PRODUCTS/LEGACY/Pages/CS-1701-Anisotropic-RIE-Plasma-System.aspx
Techni Gold 25E	Technic		http://www.technic.com/eu/applications/industrial/industrial-chemistry/plating-chemistry
Dektak-8 surface profiler	Bruker		http://brukersupport.com/ProductDetail/1136
MICROPOSIT 1165 remover	Dow