Photon Factory Activity Report 2004 #22 Part B (2005)
Instrumentation and Technique

8C, 15B, 15C /2004G261

Development of X-ray Depolarizer
Yoshinori UEJI*1, Yuki BISAIJI1, Touru KURIYAMA1, Kouhei OKITSU2, Yoshiyuki AMEMIYA1
1
Department of Advanced Material Science, The University of Tokyo, Kashiwanoha, Kashiwa, Chiba
277-8561, Japan
2
Engineering Research Institute, The University of Tokyo, Yayoi, Bunkyo, Tokyo 113-8656, Japan
Introduction
Polarization property of synchrotron radiation has
been utilized widely owing to the recent development ofX-ray polarizer and phase retarder. However, it can be anuisance too in some cases. In general, most of samples
of interest are more or less sensitive to X-ray polarization,and hence, it is necessary to characterize the polarization
state of X-ray beam incident to a sample even when thepolarization property is not utilized in the experiments.
But, it is not easy to characterize the polarization
states ofX-rays. Therefore, it would be useful if
unpolarized X-rays could be obtained in stead of notwell-defined polarized X-rays for experiments in which
the use of polarized X-rays is not intended and/or
complicates the data analysis. As an example, MAD
method which is widely used in protein structure analysis
assumes no polarization dependence of anomalous
scattering factors, and the accuracy of the data analysis
would be improved if unpolarized X-rays would beavailable.
Here, we propose an idea to generate unpolarized
X-rays from polarized synchrotron X-ray radiation byusing a transmission-type X-ray phase retarder as adepolarizer. An X-ray phase retarder is an opticalcomponent to utilize double refraction which takes placein the vicinity of Bragg condition in a perfect crystal. The
phase shift is approximately proportional to the inverse ofdeviation angle from Bragg condition. If the crystal is set
just at Bragg condition, it should yield the random phaseshift of the X-ray beam on average, resulting in
generating pseudo unpolarized states of X-rays. The
performance of the depolarizer will be reported.
Experimental & Results
The phase retarder used as a depolarizer was a(100)-oriented diamond (300 & 800 µm thickness) crystal
giving a 111 reflection in an asymmetric Laue geometry.
The energy of the incident X-ray was set at the cobalt K
absorption edge (7709 eV). The energy spread was about
1 eV, and the horizontal beam divergence was 20 arcsec.
The phase retarder used as a depolarizer wasevaluated by using an X-ray ellipsometer, which consistedof the analyser and the quarter plate. Fig.1(a) shows thatthe output beam is highly depolarized. The degrees ofpolarization (Pl) were 0.043 and 0.042, for 300 and 800µm thick depolarizers, respectively. It means that thedependence of a depolarizer's performance on thickness is264Users' Reportnegligible unlike a phase retarder. The losses of the X-ray
intensity with 300 and 800 µm thick depolarizers were50% and 85%, respectively.

Figure 1 Evaluation by an X-ray ellipsometer

For comparison, the phase retarder was evaluatedalso when it was used as a quarter plate (QP) and it wasconfirmed that a high-degree ( 0.94 and 0.98, for 300 and
800 µm thick QPs, respectively) of vertical polarized Xrays were generated (Fig.1(b)).
These experiments have shown that the X-ray phaseretarder works reasonably as an X-ray depolarizer.
* ueji@k.u-tokyo.ac.jp